4. Physical Chemistry

Engr. Yvonne Ligaya F. Musico 1

PHYSICAL CHEMISTRY


Why is Physical Chemistry important in the study of Environmental Engineering?

Applied physical chemistry procedures is used to solve common environmental engineering problems.


TOPICS

Gas Laws and Relationships

Stoichiometry

Equilibrium Chemistry

Common Treatment Processes in Environmental Engineering


GAS LAWS AND RELATIONSHIPS


Gases

Indefinite shape

Indefinite volume

Take the shape and volume of container

Particles are far apart

Particles move fast

high Kinetic Energy - particles can separate

and move throughout container


Henry’s Law

It states that the amount of gas that dissolves in a liquid is proportional to the partial pressure that the gas exerts on the surface of the equation


Henry’s Law

CA = KHPA

Where

CA = concentration of A [mol/L] or [mg/L]

KH = Henry’s Law constant [mol/L.atm] or [mg/L.atm]

PA = partial pressure of A [atm]


Sample Problem 1

Summer water temperatures of 25 to 30oC are typical for many surface waters in United States. The Henry’s law constant for oxygen in water is 61.2 mg/L.atm at 5oC and 40.2 mg/L at 25oC. What is the solubility of oxygen at 5oC and at 25oC?


Air Stripping

It is a common method of removing dissolved gases from water and wastewater. Gases commonly removed include ammonia, carbon dioxide, and hydrogen sulfide.


Sample Problem 2

An air-stripping tower is used to remove dissolved carbon dioxide from a groundwater supply. If the tower lowers the level to twice the equilibrium concentration, what amount of dissolve gas will remain in the water after treatment? The partial pressure of carbon dioxide in the atmosphere is 1 x 10-3.5 atm.


Ideal Gas Law

PV = nRT

Where

P = absolute pressure [atm]

V = volume [L]

n = number of moles [mol]

T = absolute temperature [K]

R = gas constant [0.0821 L.atm/mol.K]


Sample Problem 3

Anaerobic microorganisms metabolize organic matter to carbon dioxide and methane gases. Estimate the volume of gas produced (at atmospheric pressure and 25oC) from the anaerobic decomposition of 1 mol of glucose. The reaction is

C6H1206 3CH4 + 3CO2


Dalton’s Law of Partial Pressure

Dalton's Law

The total pressure of a mixture of gases is equal to the sum of the partial pressures of the gases in a mixture

Ptotal = PA + PB + PC + …..Pi


Stoichiometry

It deals with numerical relationships between reactants and products in chemical reactions.

Stoichiometric analysis can be used to determine the product yield for a given amount of reactant converted.


Example of Stochiometric Analysis

Nuetralization of hydrochloric acid with lime

2HCl + Ca(OH)2 CaCl2 + 2H2O

Oxidation of acetic acid to carbon dioxide and water.

CH3COOH + 2O2 2CO2 + 2H2O


Theoretical Oxygen Demand (ThOD)

It is an environmental engineering application of stoichiometry.

The estimation of the amount of oxygen a known organic chemical will consume as it is converted to carbon dioxide and water.

It is simply the amount of oxygen required to convert the material to carbon dioxide and water.



It can be used to analyze a variety of different aqueous reactions of interest to the environmental engineer – or the environmental engineering student.



Example:

1. Determining the amount of base to add to an acid spill

2. The amount of acid to neutralize a basic process wastewater

3. The solubility of metal in a chemical waste stream

4. Estimating the removal of phosphorus in a wastewater treated with lime

5. Solubility of mercury complexed in seawater.


Mass Balances

A mass balance is written statement or equation that describes the different species in which a component may exists.


The Carbonate System

Carbon dioxide and carbonates are crucial in water chemistry.


Units of Expression

Molarity

Normality


Adsorption

It is a surface phenomenon in which a solute (soluble material) concentrates or collects at a surface.

This contrasts with ABSORPTION, which a substance penetrates the material.


Adsorption

Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or a liquid (adsorbent), forming a film of molecules or atoms (the adsorbate).


Adsorbents Characteristics and General Requirements

Adsorbents are used usually in the form of spherical pellets, rods, moldings, or monoliths with hydrodynamic diameters between 0.5 and 10 mm.



They must have high abrasion resistance, high thermal stability and small pore diameters, which results in higher exposed surface area and hence high surface capacity for adsorption.



The adsorbents must also have a distinct pore structure which enables fast transport of the gaseous vapors.


Adsorbents

Silica gel is a chemically inert, nontoxic, polar and dimensionally stable (< 400 °C) amorphous form of SiO2.

Zeolites are natural or synthetic crystalline aluminosilicates which have a repeating pore network and release water at high temperature.


Adsorbents

Activated carbon is a highly porous, amorphous solid consisting of microcrystallites with a graphite lattice, usually prepared in small pellets or a powder. It is non-polar and cheap.


Carbon Adsorption

Activated carbon can be used to remove toxic organics from both water and air.

It is commonly used in aquarium filters.


Carbon Adsorption

It is used in some potable water plants to remove organics before or after chlorination, in industrial wastewater treatment to remove a variety of organics, and occasionally to remove residual organics following conventional wastewater treatment.


Carbon Adsorption

It is used in air pollution control to remove organic contaminants from contaminated air before discharge.


Mathematical Models to Predict the Mass of Solute Removed per Mass of Adsorbent

Freundlich Isotherm

Langmuir Isotherm


Freundlich Isotherm

qe = _x_ = KCe1/n

m

Where:

qe = mass of solute adsorbed per mass of

adsorbent used [mg adsorbed/mg carbon]

x = mass of solute adsorbed [mg or mol]

m = mass of adsorbent [mg]

K = experimental constant

n = experimental constant


Linearized Freundlich Equation

log (x/m) = log K + (1/n) log Ce

If log (x/m) is plotted versus log Ce, the data should fit a straight line.


Langmuir Isotherm

qe = _x_ = _KQ0Ce__

m 1 + KCe

Where:

qe = mass of solute adsorbed per mass of

adsorbent used [mg adsorbed/mg carbon]

x = mass of solute adsorbed [mg or mol]

m = mass of adsorbent [mg]

K = experimental constant [L/mg]

Q0 = constant representing the mass of solute

adsorbed per mass of adsorbent at saturation


Linearized Langmuir Isotherm

_1__ = _1_ + _1_ _1_

x/m Q0 KQ0 Ce

If (1/qe) is plotted versus (1/Ce), the data fit a straight line.


Linearized Langmuir Isotherm


Sample Problem 1

A pharmaceutical manufacturer plans to install a new industrial production process. The waste stream for the process is expected to have a concentration of 7.5 mg/L methylene blue at a flow rate of 25 gpm. The company plans to use carbon adsorption data were obtained from the laboratory. The liquid volume in each flask was 200 mL. Determine if either or both isotherms are applicable (plot a straight line in linearized form). Find both the Freundlich parameter K and 1/n and Langmuir parameters K and Qo if applicable. Estimate the amount of activated carbon require to remove the contaminant each year if the carbon is removed by an adsorption column that reaches the equilibrium with at the carbon at the 7.5 mg/L concentration.


Sample Problem 1

Mass of Adsorbent, mg

Initial Concentration, mg/L

Final Concentration, mg/L

98.6 25 0.04

58.1 25 0.11

26.3 25 0.49

15.7 25 1.2

8.8 25 3.2

2.9 25 10.2

0.8 25 19.7

Blank 25 25


Sample Problem 2

-Endosulfan is an organic insecticide commonly used on vegetables and ornamental flowers. Carbon adsorption data for it is listed in the table. The initial concentration was 0.082 mg/L. Calculate the Langmuir constant. What qe (mass adsorbed/mass of carbon) would be required to attain a contaminant concentration of 0.02 mg/L? The flask volume was 250 mL (0.25 L).


Sample Problem 2

Carbon Dose, mg Cf, mg/L

0 0.082

0.2 0.052

0.625 0.017

1.25 0.008

2.5 0.004


Ion Exchange

An adsorption in which one ion is exchanged for another ion of like charge.

an exchange of ions between two electrolytes or between an electrolyte solution and a complex.

In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion exchangers'.


Ion Exchange


Application of Ion Exchange

Most typical example of application is preparation of high purity water for power engineering, electronic and nuclear industries; i.e. polymeric or mineralic insoluble ion exchangers are widely used for water softening, water purification, water decontamination, etc.



Ion exchange is a method widely used in household (laundry detergents and water filters) to produce soft water. This is accomplished by exchanging calcium Ca2+ and magnesium Mg2+

cations against Na+ or H+ cations



Ion exchange chromatography is a chromatographical method that is widely used for chemical analysis and separation of ions.



Ion exchangers are used to enrich and purify precious metals, including uranium, lutetium, neodymium, samarium, and thallium.

An important area of the application is extraction and purification of biologically produced substances such as amino acids and proteins.

http://en.wikipedia.org/wiki/Metal

http://en.wikipedia.org/wiki/Uranium

http://en.wikipedia.org/wiki/Lutetium

http://en.wikipedia.org/wiki/Neodymium

http://en.wikipedia.org/wiki/Samarium

http://en.wikipedia.org/wiki/Thallium



Industrial and analytical ion exchange chromatography is another area to be mentioned.

Ion exchangers are used in nuclear reprocessing and the treatment of radioactive waste.



Ion Exchange is also widely used in the food & beverage, hydrometallurgical, metals finishing, chemical & petrochemical, pharmaceutical, sugar & sweeteners, ground & potable water, nuclear, softening & industrial water, semiconductor, power, and a host of other industries.



Ion exchange resins in the form of thin membranes are used in chloralkali process, fuel cells and vanadium redox batteries.

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4. Physical Chemistry