SEPARATION PROCESSES LABORATORY II · Web viewThis laboratory manual is prepared by the Department of Chemical Engineering, Faculty of Chemical Engineering for the Separation Processes

SEPARATION PROCESSES II LABORATORY

DEPARTMENT OF CHEMICAL ENGINEERINGFACULTY OF CHEMICAL ENGINEERINGUNIVERSITI TEKNOLOGI MALAYSIA (UTM)

Faculty of Chemical Engineering (FChE)

SEPARATION PROCESSES LABORATORY II

JOHOR BAHRU CAMPUS


PREFACE

This laboratory manual is prepared by the Department of Chemical Engineering, Faculty of Chemical Engineering for the Separation Processes Laboratory II (SKF 3741). The purpose of this lab manual is to serve as guidelines to students, technical staff and lab instructors to assist in performing and understanding the experiments in Unit Operation.

Separation Processes Laboratory II syllabus consists of a total of seven experiments; Sieving, Fluidized Beds, Vacuum Filtration, Tray Dryer, Spray Dryer, Evaporation and Vapour-Liquid Equilibrium (VLE). The topics covered in this course are essentially particulate solid separation processes, drying and evaporation experiments. All the equipments are prepared to instill a clear understanding of the concepts and principles learnt in Unit Operation I and Unit Operation II classes. The theories lie in the subjects will be fully utilized in this laboratory.

In this course, chemical engineering students will be introduced to the application of the semi-industry scale equipments as a preparation before entering the actual workplaces. This course will give a ‘hands on’ experience to the students on how to handle the equipments and to interpret the data taken from the experiments, which provides practical and informative exposure about operational mechanisms of separation systems that can be used in the chemical/bio-process industries.

This course is not only focused on conducting experimental works but it also emphasizes on the development of team working skills. Maximal efficient use of teamwork skills is required to complete each experiment on time and produce a quality work product. By providing conducive laboratory environment, it enables promotion of positive interaction and communication among students and lab personnel, which then can train them to be a responsible and discipline person in any given situation. With these proactive attitudes, the aim of creating professionalism at work can be achieved. In order to be a successful process engineer, a student should have a clear vision and make the best use of this subject to gain as much knowledge and experience as possible.


CONTENTS

1. Preface2. Table of Contents3. Introduction and Basics4. Guidelines for Preparing Lab Report5. List of Experiments6. Experiment 1: Sieving7. Experiment 2: Fluidized Beds8. Experiment 3: Vacuum Filtration9. Experiment 4: Tray Dryer10 Experiment 5: Spray Dryer11. Experiment 6: Evaporation Column12. Experiment 7: Vapour-Liquid Equilibrium (VLE)


INTRODUCTION AND BASICS

Student Learning Outcomes

At the completion of this course, students should be able to:

Operate the equipment properly in order to obtain the significant data. Calculate drying time for constant- rate and falling-rate period in drying process. Study the characterization of solid particles and to calculate the average size and

size distribution of the particles using Tyler standard screen analysis in particle technology.

Determine which equipment is suitable to separate any given type of particulate solids.

Explain how the data is being generated and analyze data for each equipment involved.

Function effectively as a member of a team and prepare a meaningful laboratory report.

Safety in the Laboratory

Ensuring the safety of personnel and protection of facilities are paramount in any laboratory experience.

General safety rules

1. Every student must wear lab coat and shoes (slippers or sandals are totally prohibited) and student must always be in a good manner.

2. Practice good housekeeping. Make sure all tables and experimental surroundings are in a clean and organized condition and all tools should be placed in order before leaving the laboratory.

3. All the specific safety precautions in the laboratory must be obeyed.4. Students should be responsible on the equipments. Do not leave the lab while

apparatus is on.5. Every student is prohibited from smoking, drinking or eating in the laboratory. 6. Pay attention and be careful when running the experiment to govern the accuracy

of the results and to avoid accidents. 7. Students are not allowed to run experiment after the scheduled time except for

cases where it is ordered by the supervisor and the student is monitored by lecturer and laboratory technicians.

8. All litters and wastes from the experiment must be thrown away in a dust bin or a special designated area. Do not throw litters and wastes in wash bin or urinal.

9. Do not make noise in the laboratory.10. Students must familiarize themselves with the location of emergency aids e.g. fire

extinguisher, emergency shower etc.11. Any accident must be reported immediately and verbally to lecturer and/or

laboratory technicians.

12. Experimental data must be endorsed by lecturer or laboratory technicians after completing the experiment.


Safety attire

1. Every student must wear proper safety equipments at all times when running an experiment. Most of the experiments involve chemicals, high temperature and pressure. Therefore, safety glasses must be put on to protect the eyes.

2. Safety helmet must be used if students need to climb; e.g. distillation column to collect data and record the observation.

Laboratory equipments

1. Students are prohibited from using the experimental equipments before receiving a comprehensive explanation from lecturer/laboratory assistants. This is not only dangerous to the students and other lab personnel in the laboratory, but can also damage the equipments.

2. Before using the equipments, make sure of the appropriate and correct power source and plug for the equipments.

3. Sensitive equipments cannot be moved. Use the equipments in the designated area.

4. Any damage to the equipment while using it must be reported immediately to the responsible laboratory technician. Do not try to repair it yourself.

5. Students are forbidden from using damaged equipments.

Disposal of laboratory’s wastes

1. Students are held responsible for cleaning the table area, equipments that they used as well as the laboratory surroundings to avoid hazards to other users.

2. Wastes must be properly labeled and disposed in a designated area.

Electricity, gas and others

1. All sources of gas, fuel and gas flow valve must be turned off tightly before leaving the laboratory and when they are not in use. The cover of a fume chamber must be lowered to the lowest level.

2. Make sure the right power source is used with the equipment to be engaged. Equipments which are not in use must be switched off.

3. If students intend to leave an operating equipment, make sure the equipment can operate safely. Students also need to inform their absence to the laboratory technicians.

Attendance and Participation

The nature of laboratory studies is not only the limited time, activity intensive but also limited in resources. Therefore, attendance at the regularly scheduled class sessions is


vital to successfully produce the required deliverables. Team members depend on the availability of the entire team to maximize the value of the team’s products. In addition to that, the following rules must be complied:

1. Students are mandatory to participate in all the outlined experiments. Students is considered FAIL if they do not attend even one experiment. Students are also required to sign an attendance record.

2. Students must come to the laboratory 10 minutes earlier before the experiments starts, well prepared and organized. To ensure the experiment goes smoothly, students are required to read and understand the work procedures and experimental theory before the lab hour.

3. Each experiment will take around 3 hours. Students will be divided into several groups. A supervisor will conduct the class and will be assisted by lab technicians The time allocation for the experiment is as follows:

Time allocation Activity

The first 15 min Students briefly read the experimental procedure and theory as well as identifying the equipments and apparatus needed.

The next 1.5 hrs Students run the experiment

The next 1 hr Students must complete the lab report

The last 15 min Students clean up the working area and the equipments used.

Grading

The final grade of this course is determined from all graded objects with weighting and grading as follows.

Summative assessment

No. Graded objects Number % each Weightage

1 Lab works 6 experiments 100% 80%

2 Test 1 20% 20%Overall Total 100

The date, time and venue of the test will be announced once after all the experiments are completed.

Assessment of each experiment will be based on the following;

Overall team assessment for each experiment


No. Activity Submission % total

1 System Identification* System identification sheet 5%2 Lab Preparation

Report** Experimental sheet 5%

3 Q&A on lab preparation report explanation and justification*

(based on Lab Preparation Report) 5%

4 Final Report** Group report 80%5 Professionalism* Observation checklist 5%

Overall Total 100%

*individual assessment**team assessment

**Team-based Lab work will be multiplied with a grade adjustment factor from peer rating to assess students’ team-working ability. Students have to submit the peer rating form after each experiment. Otherwise they will get a factor of zero.

Individual assessment for professionalism will be based on the following attributes:

Accountability Participation Clothing Ethics Safety

The lab reports will be assessed by proportionally weighting performance in the following categories.

No. Assessment % each

1 Technical Aspects 5%2 Abstract 10%


3 Introduction 10%4 Literature Review/Theory 10%5 Methodology 10%6 Results 10%7 Discussion 30%8 Conclusion 10%9 References 5%

Overall Total 100%

Lab reports should be submitted not later than 1 week after the experimental work. Students are responsible to submit all lab report on time. Failure to do that will be penalised 10% per day.

GUIDELINES FOR PREPARING LAB REPORT

Basically, your Lab Report should tell what you did, why you did it, what you learned and the significance of your results. The report does not have to be extremely long. In fact, the key to writing an excellent report lies in presenting concisely your response to the objectives of the project and justifying that response with appropriate documentation. The Lab Report should consist of the following sections:


1. Title page

This page should include the title of the experiment, experiment date, submission date, name of the supervisor, section no, group no, name of the group members.

2. Abstract

The abstract is the report in miniature. It summarizes the whole report in one, concise paragraph of about 100-200 words. As distinguished from the introduction, the abstract tells the reader what will be done and lays the groundwork. Also, the abstract summarizes the report itself, not the actual experiment. Hence, you cannot write the abstract until after you’ve completed the report.

Before writing the abstract, it is often helpful to summarize each section of the report (introduction, methods and materials, procedure, results, discussion, and conclusion) in one sentence. Then try to arrange this information into a short paragraph. Remember, the abstract should be a precise and specific summary.

3. Introduction

Pertinent background and explanatory information about your experiment must be presented if your audience is to ‘connect the dots’ of later sections of your report. Typically there is both an organizational need and a technical problem, so you should briefly introduce the purpose of the study, the nature of the technical problem, and argue for this work’s importance by putting it in the context of the industrial practices or the state of knowledge. This information emanates from the problem statement, scenario, or other context of the assignment.

4. Literature Review/Theory

The Literature Review and/or Theory section is a brief review of relevant ideas from the major field and a more intensive coverage of the specific topic at hand – in your own words. Only pertinent articles or textbook materials relevant to the assigned topics are cited. The literature may reveal conflicting views and opinions on the topic; these are included in the review in an unbiased way. The underlying physical principles, laws and governing equations relevant to the problem are presented. State the assumptions and limitations of the theory. Charts, diagrams, and other exhibits may be used in developing and explaining the theory, especially if they aid clarity and conciseness. The relationship between academic/laboratory and industrial perspectives (Connection and

application of concepts from the pilot-process to the real industrial processes) must be explained.

5. Methodology

Assumption and justification involved while doing the experiment and preparing the report may also included. Importance and information on precautious/safety aspect of the experiment may also highlighted and discussed, if any. This rewrite should now reflect the actual experimental program as implemented by your team, and thus be consistent with the upcoming Results and Discussion sections.


6. Results

The Results section delivers the evidence that will help answer the questions raised by the objectives of the investigation, should prepare readers for the more detailed upcoming discussion, and justify the conclusions that will be drawn next.

Observations, data and calculated results (in consistent units) are often presented best as graphs or charts, particularly if it will be important to illustrate trends. However, tables make sense when you need to present accurate data and specific facts or demonstrate the relationships between numerical and/or descriptive data. Figures and tables should include – whenever possible – published, theoretical, and/or model/simulation values available from the literature or produced programmatically. Tables of raw experimental data are not placed in this section; they are reported in appendices. Other results that do not relate directly to the upcoming discussion can either be reported in the Appendix, or by reference to the Lab Prep Report. Data are often summarized or reduced for presentation. Reducing the data allows generalizations to be made and trends to be pointed out.

Obviously, then, charts and tables must be accompanied by appropriate text. Every figure or table itself is numbered and supplied with a brief but descriptive title or caption. Build graphics and other visual displays so that, with their accompanying description, they are self-explanatory. Consult a good reference for guidelines on producing quality graphs and tables. The Results section text briefly explains how the results were obtained from the experimental data, the associated quantitative uncertainty (e.g., confidence limits, standard error, etc.), references to appropriate equations or sample calculations, and any critical assumptions or approximations made in obtaining the results. However, best practice in bringing together your exhibits and your words is accomplished by referring readers to graphics explicitly and telling them what trends to notice.

7. Discussion

If the Results section delivers the evidence, the Discussion section makes the case in court. In the Discussion section, you explain what your experimental results mean by relating them to the concepts and ideas presented in the Introduction and Literature Review/Theory sections.

There are many questions that could be answered in this section so you should not limit yourself to those offered here as examples. Answer the questions that make most sense for your work.

Do the results agree with theory, with the work of others, with models/simulation? If so, how? If not, why not? Can the disagreement be explained?

What are the most probable sources of experimental error and have these affected your ability to draw conclusions? How might these errors have been reduced or eliminated?

Did your results reveal problems with the experimental plan, method, or equipment? How might these be improved?

Were your assumptions suspect or reliable?


What definite conclusions can you draw from your results? What conclusions are more speculative?

What implications do your results have on theory and current industrial practices? What questions remain unanswered? What questions should be answered next?

In this section, you may also criticize the lab experiment and make recommendations or improvement. Such criticisms and recommendations, however, should focus on the lab as a learning experience; mere complaints about faulty equipment or amount of time spent are not appropriate.

8. Conclusion

Draw conclusion from the results and discussion that answer the objectives of the experiment. Then go on to explain your conclusions that summarizes and reflects the results and discussion.

9. Nomenclature

All symbols and acronyms used in the report and its appendices must be listed and defined in a Nomenclature section with the consistent set of units used for calculation/reporting of results. Symbols are arranged in alphabetical order, Latin terms (e.g., a, b, D, Re, Pr, etc.) first, followed by Greek (e.g., α, β, ρ, etc.), and finally subscripts (e.g., i, j, k, etc.). Greek and subscript sets are headed by the titles ‘Greek’ and ‘Subscripts’.

In addition to the Nomenclature section proper, introduce these symbols where they first appear using either running text or a list set off from the running text. If a dozen or fewer symbols are used in this report, you may rely on the in-text introduction of symbols and acronyms alone and forego a separate Nomenclature section altogether.

10.References

The Literature Cited section includes all references from which material in this report was taken. It does not include materials consulted but not cited. It does include citations listed in any appendix document (e.g., citing of handbooks from which properties data have been taken). A report without ANY cited literature is typically not a

credible piece of work. Citing the literature typically strengthens any case you are making in your own reporting.

The in-text citations themselves should give the page number(s) relevant to the actual material cited. The in-text citation plus the full reference in the Literature Cited section make it possible for the reader to find the material.

11.Appendices

Appendices may include raw data, calculations, graphs, and other quantitative materials that were part of the experiment, but not reported in any of the above sections. Refer to each appendix at the appropriate point (or points) in your report. For example, at the end of your results section, you might have the note, See Appendix A: Raw Data Chart.


Adapted from: Unit Operations Laboratory Syllabus, Cain Department of Chemical Engineering, Louisiana State University; Fluid Mechanics Laboratory, Polymer Engineering Laboratory 2, Faculty of Chemical Engineering, Universiti Teknologi Malaysia.


LIST OF EXPERIMENTS

EXPERIMENT 1: SIEVINGEXPERIMENT 2: FLUIDIZED BEDEXPERIMENT 3: VACUUM FILTRATIONEXPERIMENT 4: TRAY DRYEREXPERIMENT 5: SPRAY DRYEREXPERIMENT 6: EVAPORATIONEXPERIMENT 7: VAPOUR-LIQUID EQUILIBRIUM


EXPERIMENT 1SIEVING

Background of Experiment

Sieving refers to the separation of a mixture of particles of different sizes using sieves each with a uniform sized opening. Standard sieves of specified opening sizes are used. Sieves are stacked with the sieve with the largest opening on the top and the material is separated into fractions by shaking. The material between two sieves is smaller than the upper sieve opening but larger than the smaller sieve opening.

Many natural and manufactured materials occur in a disperse form, which means that it consist of differently shaped and sized particles. The particle size distribution, i.e. the number of particles of different sizes, is responsible for the determination of important physical and chemical properties such as:

mechanical bulk behavior surface reaction taste miscibility filtration properties conductivity

This list could be continued at great length. The examples clearly show how important it is to have knowledge of the particle distribution, particularly within the context of quality assurance in the production of bulk goods. If the particle distribution changes during the manufacturing process then the quality of the finished product will also change. Only a continuous monitoring of the particle size distribution can guarantee a constant product quality.

Objective of Experiment

In this experiment, students will determine the particle distribution using sieving method.

Scopes of Experiment

Given a sample of particulate solid, you are assigned to conduct sieving experiment using sieve shaker with designated dimension (with mesh openings that reveal particle distribution at critical sizes). If the particle range of material representing feed to a screen or product from a crusher is wide, you have to use a large sample (from 500 to 1,000 grams). If the material is finely ground, use a smaller sample of 25 to 100 grams. From this experiment, you should determine the particle distribution. The steps required must be repeated at least three times to get more accurate result.

Description of Experiment


Particle size determination methods

There are different methods in determining the particle distribution (Figure 1.1). The choice of a particular method depends primarily on the dispersion status, i.e. on the degree of fineness of the sample.

Figure 1.1: Particle Size Determination Methods (Retsch; Solution in Milling & Sieving, 15th Dec 2010)

The oldest and best-known method is particle size determination by sieve analysis. The particle size distribution is defined via the mass or volume. Sieve analysis used to divide the granular material into size fractions and then to determine the weight of these fractions. In this way a relatively broad particle size spectrum can be analyzed quickly and reliably (Retsch; Solution in Milling & Sieving, 15th Dec 2010).


(a) (b)

Figure 1.2: (a) Sieve shaker (b) Sieves with different mesh openings (Retsch; Solution in Milling & Sieving, 15th Dec 2010)

Experimental Procedures

Performing a Sieve Analysis

You can begin your particle size distribution analysis after you properly collect, prepare and size a sample. Select test sieves with mesh openings that reveal particle distribution at critical sizes. These are usually stated in a product specification or determined by material processing requirements.

To perform the analysis, do the following:

1. Stack the sieves on top of each other with the coarsest (largest opening) on the top of the stack.

2. Put the bottom pan under the finest (smallest) opening sieve. This pan collects “fine” material that passes through the last one.

3. Use a laboratory scale (accurate to .1 gram) to weigh an empty container (such as an extra empty bottom pan) and establish the tare weight.

4. Weigh the sample material.5. Empty the sample into the top of the stack. Make sure you do not overload the

surface as this causes “blinding” or blocking of the openings.6. Put the stack into the sieve shaker.7. Place a cover on the top of the stack. (If do not have the cover, you need to

determine the sieving loss)8. Make sure the stack is securely in place.9. Set the proper length of time to agitate the material.10. Turn on the shaker and run the test.

11. After the shaker stops, empty the material from the coarsest sieve into the empty container that you weighed in step (3). Use a soft bristle brush to gently brush the underside of the sieve to remove all of the particles.

12. Tap the side of the frame with the handle of the brush to clean the remaining material from the sieve.


13. Weigh the contents in the part to the nearest 1/10 gram and record the data.14. Return the material to its original sample container.15. Repeat steps 11 through 14, using the container referenced in step (3) for each

sieve, including the fine material in the bottom pan.16. Total the weights to make sure the sum of the retained material and the material

in the bottom pan is as close as possible to the original weight. Check your specification for allowable variation.

17. Divide the weight obtained from each sieve by the weight of the original sample. Record the percentage for each sieve.

18. Calculate and record the cumulative percentages as required.19. Repeat all the steps above for 3 times.

Experimental Result

Based on the above procedures, you need to identify what kind of data you should extract from the experimental work. Then, all the data must be recorded in a table. Example of the table of experimental result is as Table 1.1:

Table 1.1: Experimental result of sieving

RunMesh

openings (mm)

Mean Particle Size, Dpi (mm)

Sieving Loss (g)

Mass Fraction, p3

(%)

Cumulative fractions for particle size less than Dpi

(%)

1

2

3

Result Discussion

Questions

The following questions must be explained explicitly in the result discussion.


1. What is the fractions, p3 of the samples in each class of particle size. (This can be shown graphically in bar charts or histogram). Sample of the graph is as follows:

Figure 1.3: Fractions,

2. Sorting can be expressed by various statistical methods. The simplest of these is the measurement of the central tendency of which there are three commonly used parameters: the median, the mode, and the mean. Therefore, based on your answer in (1), what is the median, the mode and the mean of your results and how does the figure reflect the sieve analysis.

3. Plot the cumulative percentage of particle size that less than the mean particle size, Dpi for each mesh opening of the sieve. Then, determine the particle size at the cumulative percentage of 16%, 50% and 84%.

4. Calculate the particle size distribution using the following equation:

Particle Distribution =P84−P16

2


EXPERIMENT 2FLUIDIZED BED


The upward flow of fluid through a bed of particles is a situation encountered both in nature, as with the natural movement of ground water, crude petroleum or natural gas, through porous media, and in industrial operations such as backwashing filters, ion- exchange processes, extraction of soluble components from raw materials and for certain types of chemical reactor. It is well known that if the particles are loosely packed and the pressure drop due to the flow through the bed is equivalent to the weight of the bed, the phenomenon of fluidization occurs. The fluidized state occurs naturally is so-called ‘quick sand’ and industrially, use is made of the high rate of solids mixing that accompanies fluidization for various operations such as drying, coating, heat transfer and chemical reaction.

This equipment is designed to allow the study of the characteristics of flow through both fixed and fluidized bed of solid particles. Although the majority of fixed and fluidized bed situations encountered by practicing engineers are three dimensional, in order that students can readily observe the important phenomenon of bubbling that occurs in gas-solid systems when the gas velocity is in the excess of that required for fluidization. The transparent walls allow studies to be made of bubble behaviour in the gas-solid system.


In this experiment, students are required to study the behaviour of fluidization.


In this experiment, you have to investigate the principles of fluidization of fine sand using fluidized bed. For different air flow rate supplied to the system, you need to further study the characteristics of fluidized bed such as the thickness and the condition of fluidized bed formed, and also the pressure drop.


Many important industrial processes rely upon intimate contact between a fluid (liquid or gas) and a granular material. In early applications, the fluid flowed through a static bed of granules supported on a grid provided the material is suitable, great improvement in mixing and contact is achieved if the granule size is properly matched to the upward velocity of the fluid. The particles of material will be supported by the drag forces and the bed is said to be "fluidized". The fluidized beds show following liquid or fluid like properties.

The principle of operation of fluidized systems are based on the fact that if a gas is allowed to flow through a bed of particulate solids at velocity greater than the settling velocity of the particles and less than the terminal velocity for pneumatic conveying and equal to the minimum velocity of fluidization (V mf ), the solids get partially suspended in

the stream of upward moving gas. The gas stream negates the gravitational pull due to weight of particles to enable the suspended state of the solid.


The resultant mixture of solids and gas behave like a liquid and thus rightly solids are called Fluidized. The solid particles are continually caught up in eddies and fall back in a random boiling motion so that each fluidized particle is surrounded by the gas stream for efficient drying or granulation or coating purpose. In the process of fluidization there occurs an intense mixing between the solids or gas resulting in uniform condition of temperature, composition and particle size distribution throughout the bed.

A mass of finely divided solids is transformed into a fluidized bed by lifting action of gas passing through it. Thus three stages can be identified in the process of fluidizing a bed of solids basing on the velocity of gas flow through it. They include:

Fixed bed or Static Bed Expanded bed or particulate fluidization. Mobilized bed

As shown in Figure 2.1 below, the velocity of the fluid through the bed opposite to the direction of gravity determines whether the bed is fixed, expanded, or is swept out. This led to the development of the concept of minimum fluidization velocity (V mf ) at which the bed just begins to fluidize. Thus the primary concern is to measure and optimize the V mf for efficient fluidization.

(a) Slow flow rate (b) Intermediate flow rate (c) High flow rateFigure 2.1: Fixed, Fluidized, and Mobilized beds.

The fixed bed (a) occurs when the approach velocity or superficial velocity, ( V o ) , is much smaller than the minimized fluidization velocity,( V mf ). The fluidized bed (b) occurs when the approach velocity is intermediate between the minimum fluidization velocity and the terminal velocity. The pneumatically mobilized bed (c) occurs when the approach velocity is much greater than the particle terminal velocity, (U t ).

Experimental Result

Based on the above objective, you need to identify the required data to investigate the fluidization process. Then, all the data must be recorded in a table.


Example of the table of experimental result is as Table 2.1:

Table 2.1: Experimental result of fluidizationAir flow rate,

L/minThickness of the bed of fine sand,

cm

Pressure drop, mmH2O

Observation (fluidized bed of

fine sand)

Result Discussion

Questions


1. Plot a graph of (log) pressure drop versus (log) air flow rate. Explain the curve obtained from the experimental result based on the condition of fluidized bed of fine sand observed during the experimental work.

2. Determine the fluidization point and what is the air flow rate at the fluidization point?

3. Calculate the bed void fraction, εM of the fluidized bed of the fine sand.


EXPERIMENT 3VACUUM FILTRATION


In another class of mechanical separations, placing a screen in the flow through which they cannot pass imposes virtually total restraint on the particles above a given size. The fluid in this case is subject to a force that moves it past the retained particles. This is called filtration. The particles suspended in the fluid, which will not pass through the apertures, are retained and build up into what is called a filter cake. Sometimes it is the fluid, the filtrate that is the product, in other cases the filter cake.

The fine apertures necessary for filtration are provided by fabric filter cloths, by meshes and screens of plastics or metals, or by beds of solid particles. In some cases, a thin preliminary coat of cake, or of other fine particles, is put on the cloth prior to the main filtration process. This preliminary coating is put on in order to have sufficiently fine pores on the filter and it is known as a pre-coat.


In this experiment, students will be carrying out the experiment of vacuum filtration to characterize the flow through the cake in a simple laboratory test.


In this experiment, you will be doing a simple experiment on vacuum filtration. From this experiment you need to record the time taken for the filtration process of various amount of filtrate at different vacuum pressure. So that, at the end of experiment, you need to study the relationship between the specific resistance of the filter cake and the medium, and the vacuum pressure.


Cake Filtration

Cake filtration consists of passing a solid suspension (slurry) through a porous medium or septum (e.g. a porous membrane, a woven wire). The solids in the slurry are retained on the surface of the medium where they build up, forming an increasing thicker cake. As more slurry is filtered the solids retained on the medium provide most of filtering action. Head losses in the cake will control the filtrate flow rate. In cake filtration the cake is the real filtering element. Vacuum filtration is one of cake-forming filters.

Basic Principles of Filtration


To some extent one would expect that a high pressure driving force would be beneficial for liquid removal, but the effect is limited because some cakes are compressible. In these cases, then, vacuum filtration would be more efficient. With a compressible cake, the act of forcing liquid through the already collected solids (the cake) result in these solids being pressed together forming a dense matt. This dense matt, which requires a greater force to penetrate, thus produces a denser matt, which requires even higher forces which produce an even denser matt and so on. This problem multiplies exponentially with the thickness of the cake layer. Figure 3.1 illustrates this phenomenon. Normally one can expect a ‘best overall efficiency’ if the cake thickness is kept well below its theoretical maximum and the driving force is not the maximum available. This is true in general, but especially so in those cases where the solids have to be washed, extracted or subsequently impregnated.

Figure 3.1: Filter cake formation (BHS Filtration, 20th Dec 2010)

The Analysis of Filtration

The analysis of filtration is largely a question of studying the flow system. The fluid asses through the filter medium, which offers resistance to its passage, under the influence of force which is the pressure differential across the filter. Thus, we can write the familiar equation:

rate of filtration = driving force/resistance

Resistance arises from the filter cloth, mesh, or bed, and to this is added the resistance of the filter cake as it accumulates. The filter-cake resistance is obtained by multiplying the specific resistance of the filter cake, that is its resistance per unit thickness, by the thickness of the cake. The resistances of the filter material and pre-coat are combined into a single resistance called the filter resistance. It is convenient to express the filter resistance in terms of a fictitious thickness of filter cake. This thickness is multiplied by the specific resistance of the filter cake to give the filter resistance. Thus the overall equation giving the volumetric rate of flow dV/dt is:

dV/dt = (ADP)/R

As the total resistance is proportional to the viscosity of the fluid, we can write:

R = mr(Lc + L)


where R is the resistance to flow through the filter, m is the viscosity of the fluid, r is the specific resistance of the filter cake, Lc is the thickness of the filter cake and L is the fictitious equivalent thickness of the filter cloth and pre-coat, A is the filter area, and DP is the pressure drop across the filter.

If the rate of flow of the liquid and its solid content are known and assuming that all solids are retained on the filter, the thickness of the filter cake can be expressed by:

Lc = wV/A

where w is the fractional solid content per unit volume of liquid, V is the volume of fluid that has passed through the filter and A is the area of filter surface on which the cake forms.

The resistance can then be written

R = mr[w(V/A) + L) (1)

and the equation for flow through the filter, under the driving force of the pressure drop is then:

dV/dt = ADP/mr[w(V/A) + L] (2)

Equation 2 may be regarded as the fundamental equation for filtration. It expresses the rate of filtration in terms of quantities that can be measured, found from tables, or in some cases estimated. It can be used to predict the performance of large-scale filters on the basis of laboratory or pilot scale tests. Two applications of Equation 2 are filtration at a constant flow rate and filtration under constant pressure.


Experimental Result


Table 3.1: Experimental result of vacuum filtration

Volume of wastewater

fed, cm3

Time, s Cumulative volume of

filtrate generated,

cm3

100 mmHg

200 mmHg

300 mmHg

400 mmHg

5101520253035405055

Where;VF = Cumulative of filtrate generated

Result Discussion

Questions


1. Plot a graph of VF versus time and calculate the filtrate flow.

2. Plot a graph of t/ VF versus VF for every vacuum pressure. From the graph, determine the filtration constant.

3. Calculate the specific resistance of the filter cake and the specific resistance of the medium.

4. Discuss the relationship of between the specific resistance of the filter cake and the vacuum pressure; and between the specific resistance of the medium and the vacuum pressure. Explain the effect of vacuum pressure on both parameters.


EXPERIMENT 4TRAY DRYER


The term "drying" is a relative one, and simply means that there is a further reduction in the moisture content from some initial level provided by mechanical dewatering to some acceptable lower level. For example, moisture content of 10-20% by volume would normally allow particles to flow freely, yet suppress dust formation. The necessity for drying may be to make a product suitable for sale or for subsequent processing, e.g. example paint pigments; of for subsequent processing, e.g in pyrometallurgical operations.

When a solid dries, two fundamental and simultaneous processes occur:

Heat is transferred to evaporate liquid; Mass is transferred as a liquid or vapor within the solid and as a vapor from the

surface.

These factors governing the rates of these processes determine the drying rate. Commercial drying operations may utilize heat transfer by convection, conduction, radiation, or a combination of these. Industrial dryers differ fundamentally by the methods of heat transfer employed. However, irrespective of the mode of heat transfer, heat must flow to the outer surface and then into the interior of the solid.

Careful consideration of many factors is necessary in the final selection of the most suitable type of dryer for a particular application. Some of these factors are:

Properties of the material being handled Drying characteristics of the material Flow of the material to and from the dryer Product qualities Recovery problems Facilities available at the site of the proposed installation.


In this experiment, students will be exposed to the operation of tray dryer whereby they are required to study the drying behaviour of a non-porous solid.


After drying the solid experimentally using tray dryer, you need to analyse the experimental data relating moisture content to time and it should be represented by typical drying curves. Besides, the study of drying behaviour can be carried out further by determining the drying rate of the solid and also by calculating the heat and mass transfer coefficient during the constant rate period.



When a solid is dried experimentally, data are usually obtained relating moisture content to time. Consider the drying of a non-porous, insoluble material such as sand or rice in a tray. The surface of the rice is exposed to a drying medium such as hot dry air passing over the surface. Figure 4.1 shows the typical drying curves in investigating the drying behaviour of a substance.

*

X E1 = equilibrium moisture content

Figure 4.1: The typical drying curves

To experimentally determine the rate of drying for a given material, a sample is usually placed on a tray. If it is a solid material it should fill the tray so that only the top surface is exposed to the drying air stream. By suspending the tray from a balance in a cabinet or duct through which the air is flowing, the loss in weight of moisture during drying can be determined at different time intervals without interrupting the operation. The velocity, humidity, temperature, and direction of the air should be the same and constant to simulate drying under constant drying conditions. In this course, a tray dryer as shown in Figure 4.2 is used to perform this experimental work.

Figure 4.2: Tray dryer

The Drying Curve

For each and every product, there is a representative curve that describes the drying characteristics for that product at specific temperature, velocity and pressure conditions.


This curve is referred to as the drying curve for a specific product. Variations in the curve will occur principally in rate relative to carrier velocity and temperature. The curve is extremely valuable in understanding idiosyncrasies associated with the drying of each unique product.

In discussing the drying process, typically, there two fundamental temperatures involved. The dry bulb temperature is the temperature of a body or air as measured with a conventional thermometer. In process applications, it is the process control set point of a dryer. It is also referred to as just "temperature”. Meanwhile, wet bulb temperature is different. It is called “wet” because a permeable membrane such as wet gauze is used in conjunction with a regular thermometer to obtain the reading. The gauze is wrapped around the bulb of the thermometer and inserted into the gas stream. Because the water is evaporating off the gauze in the gas stream, evaporative cooling ensures that the temperature is lower than a dry bulb thermometer in the same gas stream. Physically obtaining this reading is tricky because the reading is meaningful only at a constant rate of evaporation. Too much or too little water will affect the reading, and it takes practice to obtain the correct value. The dry and wet bulb temperatures are fundamentals in defining the properties of the air.

Figure 4.3: Different phases in drying processes; initial period, constant rate period and falling rate period. (Process Heating; The Drying Curve, 15th Dec 2010)

Figure 4.3 represents a typical drying curve for virtually any product. Drying occurs in three different periods, or phases, which can be clearly defined. The first phase, or initial period, is where sensible heat is transferred to the product and the contained moisture. This is the heating up of the product from the inlet condition to the process condition, which enables the subsequent processes to take place. In some instances, pre-processing can reduce or eliminate this phase. For example, if the feed material is

coming from a reactor or if the feed is preheated by a source of waste energy, the inlet condition of the material will already be at a raised temperature. The rate of evaporation increases dramatically during this period with mostly free moisture being removed.


During the second phase, or constant rate period, free moisture persists on the surfaces and the rate of evaporation alters very little as the moisture content reduces. During this period, drying rates are high, and higher inlet air temperatures than in subsequent drying stages can be used without detrimental effect to the product. There is a gradual and relatively small increase in the product temperature during this period.

Interestingly, a common occurrence is that the time scale of the constant rate period may determine and affect the rate of drying in the next phase. The third phase, or falling rate period, is the phase during which migration of moisture from the inner interstices of each particle to the outer surface becomes the limiting factor that reduces the drying rate.

Experimental Procedures

The equipment setup of this experiment is shown in Figure 4.

1. Weigh the cooked rice before adding some water. The rice should be removed from the container and drained excess “free water”.

2. Distribute about 1000 g of the wet rice between all four trays. The initial moisture content should be more than 10%. The total weight of the wet rice should be noted before drying commences.

3. At some arbitrary time (t=0), switch on and set the fan speed control to mid-position (5) and the heater power control to position 8, letting them remain constant throughout the experiment.

4. Wait until the dryer reaches a steady state temperature.5. Record the wet and dry bulb temperatures at the three locations (inlet air

position, and both before and after the drying trays, see positions 1,2 and 3 shown in Figure 4.4) for time = 0 s and record the air velocity.

6. While the material is being dried, record the following:a. The total weight of rice in the trays at regular time intervals until drying is

complete, i.e., the weight remains constant. (At the beginning use short time intervals since the drying is fast and then make it long as the drying becomes slow).

b. The wet and dry bulb temperatures at the three locations and the air velocity.


Figure 4.4: Schematic diagram of tray dryer

Experimental Result

Based on the above procedures, you can plan the time intervals for the data recording. It is recommended for you to record the data for every two minutes within the first 10 minutes, then you can increase the time interval as the drying progresses. You need to record the experimental result until the process is complete i.e. the weight is constant.

Example of the table of experimental result is shown as Table 4.1 (you can modify the table according to your needs):


Table 4.1: Experimental result of tray dryer

Surface area of 4 trays (cm2)

Weight of empty trays (kg)

Weight of cooked rice (kg)

Weight of wet rice (kg)

Weight of dry rice (kg)

Time (min) 0 1 2 4 6 8 10 14 18 22 26 30 35 40 45

Dry bulb temperatur

e

*1

*2

*3

Wet bulb temperatur

e

*1

*2

*3

Weight of wet rice

(kg)


Result Discussion

Questions


1. Using the weights measured during the experiment calculate the dry basis moisture content of the sample at given values of time:

X=W−W s

W s, kg total water

kg dry solid

W is the weight of the wet solid (total water+dry solid) and Ws is the weight of the dry solid.

2. Plot the drying curve (moisture content versus time)

3. Calculate the drying rate at given values of time. The drying rate R is calculated for each point by:

R=−W s

A, dXdt

4. Plot the drying rate curve (drying rate versus moisture content).

5. From the drying rate curve estimate the drying rate within the constant rate period, Rc and the critical moisture content, Xc.

6. Calculate the heat and mass transfer coefficients during the constant rate period.

7. Estimate the time of drying during the constant-rate period and the falling period and hence calculate the total drying time. Compare your results with the experimentally measured one.


EXPERIMENT 5SPRAY DRYER


Spray drying is a very widely applied, technical method used to dry aqueous or organic solutions, emulsions etc., in industrial chemistry and food industry. Dry milk powder, detergents and dyes are just a few spray dried products currently available. Spray dryingcan be used to preserve food or simply as a quick drying method. It also provides the advantage of weight and volume reduction. It is the transformation of feed from a fluid state into a dried particulate form by spraying the feed into a hot drying medium. Intensive research and development during the last two decades has resulted in spray drying becoming a highly competitive means of drying a wide variety of products. The range of product applications continues to expand, so that today spray drying has connections with many things we use daily.

The spray drying process transforms fluid feed into a dried product in a single operation. Basically, spray drying is accomplished by atomizing feed liquid into a drying chamber through a rotating wheel or nozzle, where the small droplets are subjected to a stream of hot air and converted to powder particles as a result of moisture evaporation. The resulting rapid evaporation maintains a low droplet temperature so that high drying air temperatures can be applied without affecting the product. The drying proceeds until the desired moisture level in the products is reached.

As the powder is discharged from the drying chamber, it is passed through a powder/air separator and collected for packaging. Most spray dryers are equipped for primary powder collection at efficiency of about 99.5%, and most can be supplied with secondary collection equipment if necessary.


In this experiment, students will study the process of spray drying which is applied to dry aqueous or organic solutions, emulsion, etc.


In this experiment, you need to study spray drying process including its principles of transformation of feed from liquid state into a dried particulate form, the application of the process, the uses of spray dryer and type of spray dryers. You have to produce your own product from the spray dryer, then the density of the product obtained from the experiment should be compared to the standard density. You need to investigate the instrument settings, namely inlet temperature, feed rate, spray air flow in order to further study the product parameters such as temperature load, final humidity, particle size and yield. Besides, you can also compare the density of the product obtained in this experiment to the standard density.



Spray drying is suited for most real or colloidal solutions, for emulsions and dispersions as long as the dried product behaves like a solid.

Figure 5.1: Spray drying of inorganic or organic product (BÜCHI Labortechnik AG, 2002)

As shown in Figure 5.1, an aqueous solution of the product (A) is dispersed into fine droplets (B) using a two fluid nozzle. The solvent evaporates immediately surrounding the product in a vapour cloud that protects the product from thermal load. As soon as the critical concentration is exceeded, nucleation starts forming a solid shell. After the solvent is dried away from the surface, the interface moves into the core (second step of drying).The final product (C) is a fine, amorphous or crystallized material. Spraying highly concentrated solution results in a more porous final product.

In principal, the spray drying process is dependent upon the solution flow rate, solution temperature, air flow rate, air temperature and feed concentration. These instrument settings are in a combined system influencing the product parameters; temperature load, final humidity, particle size and yield. The time of drying the droplets is very short in comparison with most other drying processes. Low product temperature and short drying time allow spray drying of very heat-sensitive products. The optimisation of instrument settings is usually made in trial and error process. Some initial conditions can be found in the application database for equal or similar products.

Spray drying is used to dry pharmaceuticals, foods, dairy products, blood plasma, numerous organic and inorganic chemicals, ceramic powders, detergents and other products. The application depends on the kind of product used, such as viscosity, density, additives etc. Therefore, the given parameters cannot precisely be overtaken. Table 5.1, Table 5.2, Table 5.3 and Table 5.4 show some application of spray drying process.

Table 5.1: Foodstuffs (BÜCHI Labortechnik AG, 2002)


Table 5.2: Aromas, cosmetics, cleaners and detergents (BÜCHI Labortechnik AG, 2002)

Table 5.3: Medical and pharmaceutical products (BÜCHI Labortechnik AG, 2002)

Table 5.4: Chemical products (BÜCHI Labortechnik AG, 2002)


Experimental Result

In this experiment, you need to identify what kind of data that should be extracted from the experimental work. All the data must be recorded in a table.

Before you run the experiment, make sure the weight of beaker, inlet air temperature and outlet temperature are recorded. If possible, during the process, you are required to record the inside temperature of the spray dryer at steady state condition and the pressure of the compressed air supplied to the atomizer. Then, after completing the experimental work, record the total time required for the drying process and weigh the collected particulate sample.

Example of the table of experimental result is shown as Table 5.5, Table 5.6, and Table 5.7:

Table 5.5: Experimental result for Calculation of Particulate DensityData for Calculation of Particulate Density:


Total weight, gWeight of beaker, gWeight of sample, gStandard volume (VR), cm3 6.28Volume of sample cell (VC), cm3 11.67Total drying time, min

Table 5.6: Experimental result of inlet and outlet temperatureOperation state Inlet temperature, oC Outlet temperature, oCBefore experimentDuring experimentAfter experiment

Table 5.7: Experimental result of pressure, volume of particular powder and density of particulate powder

Data #1 #2 #3P1

P2

VP

Density of particulate powder

Where;

VP = Volume of particulate powder, cm3

VR = Standard volume, cm3

VC =Volume of sample cell, cm3

P1 = Pressure; after applying pressure on the standard densityP2 = Pressure; after taking VC into account


Result Discussion

Questions


1. Draw the process block diagram (PBD) and process flow diagram (PFD) for the entire spray drying system. Explained the process thoroughly.

2. Using the equation below, calculate the volume of particulate powder obtained in this experiment, and then determine its density. Compare the calculate density and the standard value, and discuss the difference.

V P= V R [( P1

P2 )−1]3. Using the temperature measured during the experiment, calculate the

performance of spray drying which is measured in terms of thermal efficiency. If the drying process is assumed to be adiabatic, that is, the heat loss is negligible; the overall thermal efficiency (ηoverall) can be approximated to the relation:

ηoverall= (T Ai−T Ao

T Ai−T∞ )×100 %

Where TAi and TAo are the inlet and outlet air temperatures, respectively and T∞

is the ambient air temperature.

4. What kind of modification of the existing system would you suggest to increase the recovery percentage of product?


EXPERIMENT 6EVAPORATION


Tradition leads us to believe that evaporation is one of the oldest techniques known to humanity. It is nevertheless regarded now as an essential unit operation in modern Chemical Engineering. The aim of evaporation is to concentrate a solution consisting of a volatile solvent and a non-volatile solute. This unit operation is achieved by vaporizing part of the solvent to produce a concentrated solution. Most evaporation operation used by industry uses water as the solvent.

Typical examples of evaporation are concentration of aqueous solutions of sugar, sodium chloride, sodium hydroxide, milk, and orange juice. The climbing film evaporator is a special type of evaporator, which provides a high heat transfer coefficient and a short residence time for the solution being evaporated. Multi-tube evaporators are used to concentrate solutions such a fruit juices that can be damaged by prolonged heat. They are usually operated under vacuum, which reduces the evaporation temperature and increases the heat flux.


In this experiment, students are assigned to study the operation of evaporator.


In this experiment, you have to perform single effect evaporation experiments using a climbing film evaporator under atmospheric pressure. Then, based on the collected data, you are required to perform mass and energy balances for a single effect climbing film evaporator.


Evaporation is a widely used process in engineering as a simple technique to concentrate solutions. It is used when one component is volatile and the remaining components are essentially non-volatile. It is used in numerous industries to concentrate aqueous solutions. It has been widely used as a means of desalting seawater. For this use, chemical engineers have developed a highly heat-integrated approach to maximize the thermal efficiency. The key to obtain a high-energy efficiency is the use of multi-effect evaporation as illustrated in Figure 6.1:


Figure 6.1: Standard flow of multi effect evaporator system

The cascade takes vapour from the first unit and uses it to boil the solution. The same concept is used for the second unit and can be followed by further contacting units. The only requirement is that the pressure in each stage is lower than the previous one: this allows the vapour to provide the necessary temperature driving force to boil the solution. The optimal number of units in a multi-effect evaporation process requires a process analysis of the trade off between energy savings and the capital costs for the contacting units.

The experimental unit in the Unit Operations Laboratory is a single evaporation unit. It allows a study of the heat transfer characteristic of the unit, essential for process design and to provide the experimental data for the generation of a complete heat and material balance.

The Single Effect Evaporator

The typical evaporator is made up of three functional sections: the heat exchanger, the evaporating section, where the liquid boils and evaporates, and the separator in which the vapour leaves the liquid and passes off to the condenser or to other equipment. In many evaporators, all three sections are contained in a single vertical cylinder.

In the centre of the cylinder there is a steam heating section, with pipes passing through it in which the evaporating liquors rise. At the top of the cylinder, there are baffles, which allow the vapours to escape but check liquid droplets that may accompany the vapours from the liquid surface. A diagram of this type of evaporator, which may be called the conventional evaporator, is given in Figure 6.2.


Figure 6.2: Single effect evaporator

In the heat exchanger section, called a calandria in this type of evaporator, steam condenses in the outer jacket and the liquid being evaporated boils on the inside of the tubes and in the space above the upper tube plate. The resistance to heat flow is imposed by the steam and liquid film coefficients and by the material of the tube walls. The circulation of the liquid greatly affects evaporation rates, but circulation rates and patterns are very difficult to predict in any detail. Values of overall heat transfer coefficients that have been reported for evaporators are of the order of 1800-5000 J m-2 s-1 °C-1 for the evaporation of distilled water in a vertical-tube evaporator with heat supplied by condensing steam. However, with dissolved solids in increasing quantities as evaporation proceeds leading to increased viscosity and poorer circulation, heat transfer coefficients in practice may be much lower than this.

As evaporation proceeds, the remaining liquors become more concentrated and because of this the boiling temperatures rise. The rise in the temperature of boiling reduces the available temperature drop, assuming no change in the heat source. And so the total rate of heat transfer will drop accordingly. Also, with increasing solute concentration, the viscosity of the liquid will increase, often quite substantially, and this affects circulation and the heat transfer coefficients leading again to lower rates of boiling. Yet another complication is that measured, overall, heat transfer coefficients have been found to vary with the actual temperature drop, so that the design of an evaporator on theoretical grounds is inevitably subject to wide margins of uncertainty.

Perhaps because of this uncertainty, many evaporator designs have tended to follow traditional patterns of which the calandria type of Figure 6.2 is a typical example.

Experimental Result


Table 6.1: Experimental result of evaporation


Pressure, bar Time, s T1, oC T2, oC Volume, ml Refractive index,

nDV3 V5 V3 V5

0.5

05

1015202530

1.0

05

1015202530

1.5

05

1015202530

Result Discussion

Questions


1. Draw the process block diagram (PBD) and the process flow diagram (PFD) for the entire evaporation system studied in this experiment. Explain the process thoroughly.

2. A key aspect of this experiment is the heat and material balance. This is essential information for any engineering process.

a. Perform a material balance:

Total balance:F = L + V

Where;F: feed mass flow rateL: concentrated liquid mass flow rateV: Evaporated water mass flow rate

Solute balance:F xF = L xL


Where;xF: mass fraction of solids in feedxL: mass fraction of solids in concentrate

b. Perform an energy balance and calculate heat losses:

Energy balance for the steam side is,

q = S(HS - hS ) = Sλ

Where;q: rate of heat transfer through heating surface from steamHS: specific enthalpy of steamhS: specific enthalpy of condensateλ : latent heat of condensation of steamS: mass flow rate of steam.

Energy balance for the liquor side is,

q = L hL + V HV – F hF + heat losses

Where;hL: specific enthalpy of concentrateHV: specific enthalpy of vaporHF: specific enthalpy of feed

3. Calculate the evaporator (or steam) economy.*Note: See Geankoplis (reference # 1) pp. 489-519.

4. The heat and material balance results can be used to calculate the process efficiency:

weight water product

weight steam used

The data also allows an analysis of the heat exchanger and a determination of the overall heat transfer coefficient.

5. Plot a graph of refractive index versus concentration of salt solution for the standard mixture, and discuss the findings.

6. Plot a graph of steam pressure versus concentration of salt solution obtained from the evaporation process, then discuss the result.

7. Compare the concentration of salt solution obtained at V3 and V5 and discuss the difference and the factors that influence the findings.



EXPERIMENT 7VAPOUR-LIQUID EQUILIBRIUM


Vapour-liquid equilibrium are the fundamental properties whose knowledge is required, for example, in the design of separation columns in chemical industries. Many experiments are necessary to obtain such equilibrium data, at least for binary systems, where non-idealities in both phases must be determined. Therefore further improvements to theoretical models for describing and predicting these non-idealities are indispensable.

At low pressure, deviations from ideal behaviour are due mainly to the liquid phase. The association of one or more components in a liquid mixture and the chemical forces due to electrical charge exchange between an associating and an active compound influence strongly the excess properties of associated solutions and the fluid phase equilibrium. These effects are in many cases stronger than those due to physical forces.


The objective of this experiment is to produce vapour-liquid equilibrium at atmosphere pressure and to measure equilibrium temperatures and compositions.


In this experiment, a mixture of methanol – water will be used. From the experimental result in terms of refractive index and the boiling point for different composition, you need to produce a graph of vapour-liquid equilibrium for the mixture of methanol – water.


In the analysis of vapour-liquid equilibrium diagram, we shall consider only 2-component mixture, e.g. A (more volatile) and B (less volatile). Two types of vapour–liquid equilibrium diagrams are widely used to represent data for two-component (binary) systems. The first is a “temperature versus x and y” diagram (Txy) or it is called as phase diagram. The x term represents the liquid composition, usually expressed in terms of mole fraction. The y term represents the vapour composition.

The second diagram is a plot of x versus y. This diagram is also known as equilibrium curve. These types of diagrams are generated at a constant pressure. Since the pressure in a distillation column is relatively constant in most columns (the exception is vacuum distillation, in which the pressures at the top and bottom are significantly different in terms of absolute pressure level), a Txy diagram, and an xy diagram are convenient for the analysis of binary distillation systems. The Figure 7.1 below shows a constant pressure phase diagram for an ideal solution (one that obey Raoult's Law).


Figure 7.1: Constant pressure phase diagram

Usually the mole fraction of the more volatile component is plotted on the horizontal axis, whereby x is the mole fraction in the liquid phase and y is the mole fraction in the vapour phase.

From the above constant pressure phase diagram; it shows that:

Since the boiling point of pure A (tA at xA = 1.0) is lower than boiling point of pure B (tB at xA = 0.0, i.e. xB = 1.0), therefore component A is more volatile than component B where A has a lower boiling point than B.

Boiling point and condensation point changes with concentration: Saturated liquid curve : x vs. T, bubble point curve Saturated vapour curve : y vs. T, dew point curve

At each temperature, the vapour and the liquid are in equilibrium

Three different regions exist where only vapour, only liquid and a vapour-liquid mixture can exist.

The upper curve in the diagram is called the dew-point curve while the lower one is called the bubble-point curve. The dew-point is the temperature at which the saturated vapour starts to condense. The bubble-point is the temperature at which the liquid starts to boil.

The region above the dew-point curve shows the equilibrium composition of the superheated vapour while the region below the bubble-point curve shows the equilibrium composition of the subcooled liquid.

For example, when a subcooled liquid with mole fraction of A=0.4 (point A) is heated, its concentration remains constant until it reaches the bubble-point (point B), when it starts


to boil. The vapour evolved during the boiling has the equilibrium composition given by point C, approximately 0.8 mole fraction A. This is approximately 50% richer in A than the original liquid.

Meanwhile, Figure 7.2 below (left) showed an example of typical equilibrium curve for a binary mixture on x-y plot. It contains less information than the phase diagram (i.e. temperature is not included), but it is most commonly used. It is useful for graphical design in determining the number of theoretical stages required for a distillation column.

Figure 7.2: Constant pressure equilibrium curve or x-y plot


Experimental Result

In this experiment, you need to identify the required data from the experimental work in order to produce the graph of vapour-liquid equilibrium for the studied system. Then, all the data must be recorded in a table.


Table 7.1: Experimental result of vapour-liquid equilibriumVolume, ml Refractive Index

Methanol Water Liquid phase before heating

Liquid phase after

heating

Vapour phase

Boiling point, oC

50 200100 150125 125150 100200 50

Result Discussion

Questions


1. Draw the process flow diagram for the entire vapour-liquid equilibrium system. Explain the process thoroughly.

2. Plot a graph of refractive index versus mol fraction of methanol (before heating).

3. Plot Txy diagram of methanol-water system. Then compare the experimentally obtained temperature and composition values at equilibrium with the literature results. Discuss the factors that influence the findings.

4. Describe the uses of VLE diagram.


Table 7.2: Equilibrium data for methanol-water system

Vapor-Liquid Equilibriumof Methanol-Water System

P = 760 mm Hg; T = 64.6°C - 72.0°C

BPTemp.

°C

% by mole methanol

liquid vapor

72.0 56.5 80.5

71.5 58.5 81.6

71.4 60.0 83.1

70.6 66.2 85.7

69.9 67.5 86.5

69.6 70.0 87.4

69.1 71.4 87.8

67.8 80.0 91.8

66.9 85.0 93.0

66.50 88.08 94.17

66.2 89.0 95.6

66.1 90.0 96.1

65.7 92.0 96.5

65.4 95.0 98.1

64.95 96.57 95.69

64.70 98.71 97.78

64.6 100.0 100.0

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SEPARATION PROCESSES LABORATORY II · Web viewThis laboratory manual is prepared by the Department of Chemical Engineering, Faculty of Chemical Engineering for the Separation Processes