Depannvnt of CHEMICAL ENGINEERING

Documen C ntr

NORTH CAROLINA AGRICULTURAL AND TECHNICAL STATE UNIVERSITY

GREENSBORO 2741 1

TELEPHONE (9101 334-7564 FAX (9101 334-7904

1 Center

U.S. D e p m e n t of Energy Pittsburgh Energy Technology Center

Pittsburgh, PA 15236-0940 P.O.BOX 10940, MS 921-118

FEFI 2 5 m Q t

SUBJECT Quarterly Technical Report for U.S. DOE Grant No.: DE-FG22-92MT92020

Dear Sir,

Three copies of the quarterly technical progress report for the period April 1,1996 to June 30, 1996 for the above grant are enclosed. If you have any concerns about the repop, please feel free to contact me.

Sincerely,

Vinayak N. Kabadi Grant PI

cc: Dr. Psalmonds, Division of Research, NCA&TSU

An Equal Opponuniry [Affirmative Action Employer

A Conm'ruenr Instirution of THE UNIVERSITY OF NORTH CAROLINA

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QUARTERLY TECHNICAL REPORT April 1,1996 to lune 30,1996

Project Title

Improvement of Hydrogen Solubility and Entrainment in Hydrocracker Feedstocks U.S. DOE Grant No.: DE-FG22-92MT92020

Investigator

Vinayak N. Kabadi, Department of Chemical Engineering, North Carolina A&T State University, Greensboro, NC 2741 1

Project Objectives and Scope:

The objective of this project is to determine the conditions for the hydrogen-heavy oil feed preparation so as to optimize the yield of hydrocracking reactions. Proper contacting of hy- drogen with heavy oil on the catalytic bed is necessary to improve the yields of the hydro- cracking reactions. It is most desirable to have the necessary amount of hydrogen available either in the dissolved or in entrained state, so that hydrogen diffusion to the reaction site does not provide rate controlling resistance to the ovpall rates of hydrocracking reactions. This projecr proposes to measure solubility and entrainment data for hydrogen in heavy oils at conditions such as in hydrocrackers, and investigate the improvement of these properties by usage of appropriate additives. Specifically, measurements will be carried out at temperatures up to 300 "C and pressures up to 120 atmospheres. Correlations for solubility and entrainment kinetics will be developed from the measured data, and a method for estimating yield of hy- drocracking reactions using these conelations will be suggested. Exxon Research and Engi- neering Company will serve as private sector collaborator providing A&T with test samples and some technical expertise that will assure successful completion of the project.

Technical Highlights and Milestones:

The final experimental measurements €or hydrogen solubility in hydrocarbons are in progress. The nevel experimental apparatus has been successfully operated for these measurements. The apparatus wil l be utilized for many more measurements of solubility of gases in liquids in the future. The calibration procedures and some of the initial data measurements are summa- rized in the attached write-up.

Portions of this document m y be illegible in electronic image products. h a g s are produced fhm the best available 0-4 dOrrlmt!Ilti

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An experimental method for measuring the solubility of hydrogen gas in liquid

Hexadewne is being developed utilizing a Gas Chromatograph outfitted with both Flame

Ionization Detector (FlD) and Thermal Conductivity Detector (TCD) for detection, laboratory PC

with Waters Dynamic Solutions Baseline 810 chromatography software for analysis, and an

equilibrium cell of in-house design with associated piping. The basic principle of operation of the

apparatus involves the sparging of hydrogen gas through tiquid hexadecane at different

pressures and temperatures as specified by the experimental parameters and withdrawing both

liquid and vapor phase samples to be analyzed with the gas chromatograph. As this experiment

involves equilibrium compositions, care must be taken to ensure a condition of equilibrium exists

before experimental data may be obtained. The chemicals involved in the experiment shall all be

of HPLC grade or higher or of the highest grade possible for all liquids and the gases shall be of

Ultra Pure Carrier grade.

PRELIMINARY STUDIES

Prior to obtaining any experimental data, development of a suitable method is required.

The method is the plan order of operations necessary to perform the actual experiment and

analyze the data. The experimental operation was developed by Kabadi and involves charging

the equilibrium cell with approximately 75 milliliters of Hexadecane, sealing it to ensure a

leakproof seal, and sparging hydrogen gas through it. The hydrogen gas shall be supplied by

cylinder via piping network inclusive of a digital flow meter. The gas shall be introduced to the

cell through four inlet ports at the poles of the base of the cell at the specified pressure and

flowrate. Exit of the gas product shalt be through a single exhaust port at the top of the cell which

terminates inside the laboratory exhaust hood. Cell pressure shall be maintained by a control

valve in the exit gas stream line. Sample extraction shalt be performed utilizing two sample

valves, a three port sampling vafve and a six port routing valve. The carrier gas stream (argon)

shall flow continuously to the Gas Chromatograph (GC) through the six port routing valve. The

sample, vapor or liquid, shall be selected by the three port valve and directed io the six port

valve where it is combined with the carrier gas for routing to the GC.

Purging of the entire sampling loop is effected with the six port valve also. When sample

analysis is not required, the contents of the sample loop is routed to a vent in order to assure an

uncontaminated sample for the subsequent analysis. The size of the sample is determined

through the selection of the appropriate external sample loop and shall be the same for both the

liquid and vapor samples. The entire equilibrium cell and sampling and routing valves shall be

maintained at the desired operating temperature through the use of a laboratory oven in which

they shall be placed. The exit line to the GC shall be maintained at the desired temperature with

the use of an electrical heating tape.

Due to the expected change in volume due to the vaporization of the liquid hexadecane

in the liquid sample, and the fact that the external sample loop shall be utilized for both the vapor

and liquid samples, it is probable that differing volumes of the sample will be required depending

on the phase of the sample. Consequently, determining the appropriate sample size for actual

injection is of extreme importance. The GC measures total amounts of components which pass

through it. In general, detectability can be accurate in the range from 1 - 1000 ppm. Relatively

small amounts of compounds may be analyzed with very good results. However, if excessive

amounts of compunds are introduced, the results show marked deterioration of indicator peaks

and consequently degrade the accuracy of the analysis. Because of this, division of the sample

entering to the GC from the six port valve must be performed as necessary to produce good,

accurde, and reproducable results. Spliting this stream is achieved through the use of the PSS

(Programable Split Splitless) injector on the GC. By instituting a split flow configuration, a

fraction of the total incoming sample may be routed to the GC and the remainder vented out.

The primary concern is the determination of the appropriate split ratio. As the total incoming

sample size is determined by the size of the external sample loop, the split ratio will be

dependant upon that volume and the maximum allowable sample volume for which the GC

produces satisfactory results.

The initial step in determing the split ratio was to determine the maximum sample size which

may be injected to the GC. This was done by doing manual injections of differing amounts to the

GC and obtaining the corresponding chromatographs. Two FID sensitivity settings are available

the GC which allow for differing amounts of components to be introduced. Only one sensativity

setting exists for the TCD. Injections were made using both FlD sensitivity settings. The FID shall

be used to detect hexadecane amounts while the TCD shall detect hydrogen amounts. Injections

of pure components were made and the corresponding chromatograph analyzed visually for

satisfactory peak definition. The desired camer gas flowrate was specified to approximately 10

milliliters per minute and the detector temperature was set to 300 degrees Celsius. The first set

of injections were made at FID sensitivity of 20 as we expected a large amount of liquid sample

to be analyzed since the split ratio was unknown. The choice of external sample loops for the

apparatus was previously limited to either a five microliter or two microliter loop.

Beginning with a 5 microliter injection, available sample loops are 5 and 2 microlitersie

loop volumes ( 5 and 2 microliters ) chromatograph 1 was produced. Good peak definition was

demonstrated but an additional smaller peak was noted a s well as a prominent tail. Possible

explanations for these phenomena included an incorrect oven ramp rate and an elongated

elution time due to the amount of the sample. A second injection was made at the same

conditions but incorporated a sample split of 99.4390617% a s shown in chromatograph 2. A

definate decrease in the associated tail is noted a s well as secondary peak size. The total area of

the tail was somewhat undetectable at the specified sensitivity range. As the total sample

injected was approximately .02805 microliters, a study was performed at the more sensitive FID setting with a smaller sample size. Incorporating a 94.43175% split (approximately 95%), a total

sample size of .02273 microliters was injected which produced a well defined peak a s shown in

chromatograph 3. Again a tailing effect was noted but was overall much less pronounced. It was

decided however that the higher FID sensitivity setting would be the most appropriate for our

analysis. Chromatograph 4 shows the peak generated by a .2 microliter injection of hexadecane.

Again a definate tail is noted. Also, the peak height was almost maximum full scale deflection

indicating the maximum sample size which will produce a satisfactory result. Chromatograph 5

shows the peak generated by an injection of approximately .002128 microliters of hexadecane.

This was achieved using the maximum available split on the instrumentand an injection of .4

microliters of hexadecane. The resulting peak shows good definition and the integrating software

was able to make clear distinctions between the peak starYstop points and the rising baseline.

Chromatographs 4 and 5 indicate hexadecane limits of .2 microliters and .002 microliters. The

primary problem s t i l l remaining was the tail of the peak. It was believed that the tail was

attributable to elution of hexadecane beyond the compounds retention time. Studies were

performed in order to determine if the tail couid be deminished and the total hexadecane sample

could be consolidated into one peak. Variations in the operating parameters of the developed

method, it was hope, could remedy the problem. Injections of .1 microliters were used utilizing

differing oven ramp rates. Previously a s shown in chromatograph 4, a .2 microliter sample had

produced a somewhat satisfactory peak with a prominent tail. Using .1 microliter injections

should produce viable peaks with a somewhat lessened tail effect. Chromatographs 5 through 8

show the results of these injections. A s evidenced, the altering of the ramp rate has a definate

effect on the associated tail. In each case, it was found that the tail was actually hexadecane

which eluted beyond the actual retention time of the compound and therefore was part of the

sample which was not being accounted for in the peak analysis. Chromatograph number 6, for

instance indicated two major peaks, one for hexadecane at a retention time of about 7 to 8

minutes and another “unknown” peak at about 15 to 16 minutes, and a hump at about 9 minutes.

As the only compound injected in the sample was hexadecane, both peaks must be attributed to

hexadecane. However, the peak integration performed by the software indicated multiple

compunds and consequently the actual amount of hexadecane reported would be erroneous.

The valley existing between the peaks caused the software to denote two peaks. Removal of the

valley would allow proper integration. Chromatograph number 7 shows the effect of increasing

the ramp rate to 45 degrees a minute. The hump at 9 minutes disappeared but the prominence

of the valley increased. The hexadecane peak height increased substantially a s the overall size

of the associated tail decreased but did not become negligible. Chromatograph number 8 shows

the effect of a ramp rate of 25 degrees per minute. The valley has almost disappeared and the

total sample is compacted into a much more satisfactory single unit. However a valley does exist

at roughly 10 to 11 minutes. Chromatograph number 9 shows the effect of a ramp rate of 15

degrees per minute. No valley exists at all and the entire sample has been incorporated into one

single peak. Another study at a ramp rate of 5 degrees per minute was planned but the expected

improvement in peak shape didn’t appear to justify the expected increase in total sample run

time (approximately 78 minutes). A .1 microliter sample size indicates a split flow ratio of 9.5%

with the maximum available split previously demonstrated to 99.46796206%

Hydrogen studies were performed also to determine the maximum amounts of hydrogen

which could be detected without significant peak distortions like hexadecane. In addition, as the

amount of hydrogen expected to be in the liquid sample is somewhat miniscule, the lower limit of

hydrogen detectability was of extreme importance. The TCD has only one sensitivity setting and

therefore must be able to detect extremely small amounts a s well as possibly large amounts of

hydrogen. Chromatographs 10 through 19 show the results of injections of varoius volumes of hydrogen gas injected at atmospheric pressure and room temperature. In each case a

satisfactoiy peak was obtained and indicated an upper limit in excess of 500 microliters

(chromatograph 19). Three samples were injected consecutively and the resulting peaks plotted

in the chromatograph. In each case, the total sample was accounted for in the peak integration

performed by the software. The top of the third peak was cut off by the plotter possibly because it

exceeded a 1 volt deflection. On manual integration however, the well defined top was evident.

A lower limit of .15 microliters was indicated in chromatograph 18 by a hydrogen peak at

approximately three fourths of a minute.

EXPERIMENTAL SCHEDULE

The following exercises are to be performed next (within the next 10 days):

1) Replication of manual injection studies utilizing the actual equilibrium cell to

verify reproducability of data by alternate method.

Fully define all operating parameters of the experimental method inclusive of

adjustments to oven temperatures and times to obtain an optimum method.

Develop calibration methodology for pure component samples and mixed

samples. Produce associated calibration curves necessary to perform

experiments.

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