THE UNIVERSITY OF MICHIGAN INDUSTRY PROGRAM OF THE COJLLEGE OF ENGINEERING PRELIMINARY STUDIES ON EFFECTS OF GAMMA RADIATION ON THE CARBONIZATION OF COAL Roberto Trevino Shuya Fujii Harold Ohlgren December, 1957 IP-257

ACKNOWLEDGEMENTS The Dow Chemical Company and the Koppers Company both contributed to make these experiments possible; the former, by lending us the Chromatographic Analyzer for several months, and the latter, by providing the coal samples and by analyzing the physical properties of the coal before and after irradiation at room temperature, and determining the composition of gas evolved during this same room temperature test. Dr. J. J. Martin reviewed the experimental data and aided in interpreting the results. The authors are also very grateful to the staff of the Phoenix Memorial Project for making available the laboratory space and the radiation source for the performance of this work. -ii

ABSTRACT Powdered coal was subjected to radiation at room temperature to determine gas evolvement and changes in physical properties from radiation alone. Next, coal samples were submitted to the carbonization process at 450~, 600~, and 750~C both with and without radiation. The results of this series of experiments indicate that the volume of gas released under a 750~C heat cycle is much reduced swhen the heat cycle is combined with radiation. At 600~C this effect of reduced gas evolution with radiation is not conclusive. By analyzing gas composition by means of Orsat and gas chromatography methods, it was found that the ratio H2/CH4 always decreases when the carbonization process is performed under radiation. -.iii

TABLE OF CONTENTS Page Acknowledgements............................................. ii Abstract................................... iii List of Tables................................................v List of Figures.............................................. vi Introduction................................................. 1 History of Process and Purpose................................ 3 Irradiation of Coal at Room Temperature....................... 5 Eauipment for Carbonization.................................. 8 Method of Operation........................................... 14 Interpretation of Data............................... 19 Conclusions....................................... 22 Appendix..................................................... 28 Bibliography............................................. 30 -iv

LIST OF TABLES Table No. Page I Time-Temperature Data in a Radiation Run............ 25 II Results of Non-Radiation Runs.................... 26 III Results of Radiation Runs........................... 27 -v

LIST OF FIGURES Figure No. Page 1 Gieseler Plastometer Test. Effect of Irradiation with Co-60........................ 7 2 Apparatus Used in Coal Carbonization Experiments.. 10 3 Glass Condenser (Dimensions in cms)............... 11 4 Glass Scrubber (Dimensions in cms)................ 12 5 Carbonization Chamber Showing the Heating System.. 13 6 Typical Temperature History. Run 750-809......... 17 7 Time-Volume Curves at 7500C Runs................. 18 8 Influence of Radiation on HCv and...... 21 9 Changes of Gas Composition at Different Temperatures.................................... 24 -vi

CHAPTER I INTRODUCTION Although in recent years the use of radiation has become familiar in many different fields, it seems that in the particular area of coal chemistry, fundamential research remains to be performed in studying radiation effects. This is the first of a series of exploratory experiments at the University of Michigan to investigate she effects of radiation on carbonaceous materials. This investigation consisted of three separate steps. The first was purely exploratory, consisting of the irradiation of powdered coal in an open container at room temperature to see whether any measurable change occurred in the solid material. A physical effect was observed, leading to the first analytical part of the present study. This first analytical run was performed with the sample in a sealed tube, to determine quantitatively the physical changes occurring and to obtain an analysis of liberated gases under irradiation of coal at room temperature. The second analytical phase, with which the greater part of this report is concerned, dealt with the effects of radiation on the carbonization process. Carbonization of coal has been a well-known process for many years. However, the chemistry involved in the process is rather complex due mainly to the composition of coal itself. The existence of several varieties of coal makes the problem even more difficult.

-2The addition of radiation to the carbonization process can be expected to have: 1. A physical effect, with modification of coal and coke structures and a change in the mechanical properties of the solid product. 2. A chemical effect, causing the occurrence of certain reactions in addition to those normally observed. It can be expected that both physical and chemical properties of the products will be affected. The principles of the Gray-King coal testing method(l) were used, making necessary modifications which will be described later. The carbonization chamber was designed in such a way that it could be placed inside the 2-inch I.D. cylinder-shaped oobalt source. This arrangement of the source gives a radiation intensity of 850,000 R/hr. The released gases were collected as in the Gray-King method and were then analysed. Analyses were made of the percent of H2, C02, CO, 02)OH, CH 2H6 and higher HCO produced in radiation and non-radiation runs. Complete tabulation of these results are shown in Table II and Table III. No attempt has been made to correlate our results with expected theoretical results due to the complex chemistry involved in coal carbonization. The mechanisms which explain the effect of radiation in this case could be established only after many experimental sets of data and, of course, a better understanding of the chemical reactions that take place.

CHAPTER II HISTORY OF PROCESS AND PURPOSE The process known as carbonization of coal or coking was originated in England in 1700 and its historical importance is very often overlooked. It was actually this process which later made possible the tremendous industrial development which depended upon vast quantities of steel for heavy machinery and volume production of consumers products. Further improvements in the original process resulted in modern installations producing a great variety of chemicals in addition to gas and coke (solid residue of the carbonization). Coal carbonization products are not a major energy source in the United States, due to plentiful supplies of petroleum and natural gas. However, in those countries which do not have oil, coal and its derivatives remain the principal natural fuel. According to the temperature involved in the process, carbonization has been subdivided in three types: 1. High-temperature carb. (1500-2000~F) 800-1100~C 2. Mid-temperature carb. (1200-1300~F) 650-750~C 3. Low-temperature carb. (about 1000~F) \ 550~C Each temperature range results in a different product distribution. In these experiments we are concerned with low-temperature and mid-temperature carbonization, since the object of this work is to obtain a preliminary insight into the subject. -3

-4Current literature reports only a few studies in the effects of radiation on coal degradation. The results are gas desorption and changes in some mechanical properties.(2)'()' (4) This work reports specific radiation effects in the process of coal carbonization itself, the effort being confined to analyzing chemical changes only.

CHAPTER III IRRADIATION OF COAL AT ROOM TEMPERATURE* A ten-gram sample of coal was sealed in a glass tube 3/4" diameter and 2" long, evacuated to 0.2 microns. A vapor pressure equilibrium of 50 microns developed, at room temperature. This sample was subjected to a radiation dosage of approximately 100 megarep by exposure to 8.6 x 105 R/hr for 120 hours. A control sample was not irradiated. Gas Analysis Calculation from the initial and final pressures in the glass container and the free volume above the coal, indicated that approximately 1.5 cc of gas was evolved. Analysis by mass spectrometer showed the gas to have the following composition. Components Mole Per Cent (Water Free Basis) Carbon dioxide 1.2 Air 1.0O Ethane 0.1 Nitrogen and/or Carbon monoxide 2.9 (a) Methane 1.9 Hydrogen 93. + 0.5 (a) ca. 2.3% Nitrogen and ca. 0.6% carbon monoxide. Coal Analysis Proximate analyses, swelling indices and Gieseler Plastometer test data for both the irradiated and unirradiated coal are given below. * Analyses supplied by Koppers Company in private communication Sept. 1957. -5

-6Proximate Analyses and Free-Swelling Indices Blank Coal Irradiated Coal % Volatile Matter 30.3 29.8 % Fixed Carbon 64.0 64.4 % Ash 5.7 5.8 Free-swelling index 8-1/2 8-1/2 Gieseler Test Data Blank Coal Irradiated Coal Softening Temp. - C 310 320 Max. Fluidity Temp.- ~C 342 342 Solidification Temp.- OC 481 488 Max. Fluidity - Div. Per Min. 3150 5150 The Gieseler Plastometer test record furnished by The Koppers Company is reproduced as Figure 1.

rzj DIAL MOVEMENT- DIVISION PER MINUTE- oj -r C C rJ. O O- 0 0 000 0 000 0000, 0' i''(' r 1 T T T o C>D S?-OF TE MP co O (D --- --- ----- H I 0 D Itct ~~~~~~~~~~I +- 0 RD 0 CD M OD -I'0 CD N c) 0 0 H 0 PI ~O O l ---------- 0 OD FJ. SOLID TEMP ct O 0 0 03' c O

CHAPTER IV EQUIPMENT FOR CARBONIZATION The standard technique for high-temperature carbonization assay, known as the Gray-King method, proved to be suitable for the purposes of this work. The apparatus used in the set-up is represented diagrammatically in Figure 2, and scale drawings of certain parts are shown in Figure 3, 4, and 5. The tube (D) which is 2.8 cms. in diameter by 15 cms. long is charged with glass beads drenched with dilute sulfuric acid to absorb ammonia. The U-tube (C) acts as a condenser; it may be cooled externally and has an extension with a capacity of at least 5 ml. for the reception of the liquid products (tars). The gas holder (E), which is filled with a mixture of equal volumes of glycerin and water, is connected to a glass reservoir (G) by means of rubber or tygon tubing. This reservoir (G), which permits keeping the gas in (E) at atmospheric pressure, is suspended by a cord passing over a pulley and counterbalanced by a glass vessel (J) floating on the liquid in (K). This liquid comes from the gas holder (E) after it has been replaced by the released gas. The carbonization chamber (A), Figure 4, was designed instead of the conventional silica tube that is placed horizontally in the GrayKing method. In our case a vertical chamber was required being made of stainless steel tubing (Carpenter 220) with the following dimensions: O.D. 1.25 inches Thickness 0.12 inches Length 14.5 inches -8

-9The heating system consists of a resistance wire (Chromel-A, 16 gauge), which was wound alternately with asbestos cord. One asbestos layer was placed between the surface of the tube and the heating element and another was used to cover the element. Finally the whole assembly was wrapped with aluminum foil to reduce the heat losses to a minimum. The outer diameter was designed to fit the inner diameter of the Co source, 2 in. As a portion of the carbonization chamber was outside of the heated part, a solid metallic (S.S.) piece was put inside at the bottom of the chamber. The purpose of this was to raise the carbon sample to a region of uniform heat distribution. The temperature history of the process was obtained by a metallic-coated Chromel-Alumel thermocouple. The temperature was measured right in the center of the coal sample. It is reasonable to assume that a uniform heating was attained. Other accessories to the system include a Hg-differential manometer, which is connected to the gas holder. The rest of the connections and joints were made using glass and/or tygon tubing reinforced with copper wire to prevent gas leaks.

H hd HE ct' o ~D J -D GLASS SCRUBBER 0 W f\E GA_ S HOLDER K || F Hg - MANOMETER H. G GLASS RESERVOIR HUg~~ 0, —---— ~ ~H PULLEY eT J COUNTER POISE 0o3LS SRBE

-115.02.25 13.5 I15.~~,3.0 I.5 ~ 2.7135 2.75 Figure 3. Glass Condenser (Dimensions in cms)

-126.5 2.8 — ~ | 1 6.0 ~./ - 3.0 3.25 -- (DIMENSIONS IN CMS) Figure 4. Glass Scrubber (Dimensions in cms)

-13i! g 1 1\ JI A THERMOCOUPLE I, I1 I B GAS OUTLET I f F CHAMBER WALL G ASBESTOS SHEET H ALUMINUM FOIL I CHROMEL WIRE J ASBESTOS CORD I -- DI Figure 5. Carbonization Chamber Showing the Heating System

CHAPTER V METHOD OF OPERATION Coal was air dried at 105-110~C and ground to pass a 72-mesh B.S. Sieve. The carbonization chamber was charged with 40 gs. of airdried coal, and tightly closed using silver goop. Gas holder (E) had to be completely filled with a water-glycerin solution before the operation was started. Five cm. of sulfuric acid 0.1N was put in tube (D). The cold junction of the thermocouple was in ice and initial operating temperature for each run was about room temperature. The terminals of the heating wire were connected to power, and a final inspection of the flow lines and valves was made before starting the operation. For radiation runs, the apparatus was placed in the highradiation room and the carbonization chamber was arranged to fit into the center of the cobalt source, when this was raised. When the carbonization chamber is in the center of the source, the coal sample receives about 850,000 RPH. The heating procedure consisted of a rapid temperature increase up to 300~C followed by a controlled increase of five degrees per minute. This was attained by using a SECO Powerstat, and a typical time-temperature history, shown in Table I. See also Figure 6. The length of the run, 150 minutes, was kept constant for the three different carbonization temperatures. During the experiment, periodic volume readings were made to keep track of the time-volume behavior. Graphics illustrating these parameters are shown in Figure 7 -14

-15(1) The density of the gaseous phase is low when compared with the solid sample and therefore the frequency of gamma-interaction with molecules decreases proportionately. (2) The time of exposure of the gas molecules is rather short, since they occupy just a small portion of the chamber and shortly leave the region of high radiation. C. Some tendency of gamma-radiation breaking the bonds of CH- radicals attached to higher molecules, rather than freeing hydrogen atoms, is observed at 6000C. This can be represented by the following reactions ('). H H I I R - C -H R~ R — C —H H H (2) 7 I-. H R -- C — H c R -- C — H + H I I H H where R can represent one of the complex hydrocarbon radicals present in the coal. Reaction (1) could be followed by CH + H2 -, CH4 + H R + H2 - R + H and the hydrogen atoms would react with some other free radicals, being ultimately absorbed. The formation of CH2radicals also can be expected but in smaller amounts. CH2=

-16for several runs. At the end of the experiment, twenty or thirty minutes were allowed to cool the system. The final volume, adjusted atmospheric pressure, was then recorded. The next step consisted of weighing the solid and liquid products and analyzing the released gases. With this data it was then possible to estimate the balance of materials and thereby the quantitative success of the experiment. Gas analyses were made by two independent procedures: by means of an Orsat analyzer the percentage of H2, CO, C02 and 02 were determined; in addition a gas-chromatographic analysis was carried out to evaluate the quantitative composition of CH4, C2H2 and higher hydrocarbons. The correlation of both these results gives a fairly accurate picture of the gas composition and further enables us to make the balance of materials. The carbonization chamber and parts (D) and (C) were carefully washed with acetone after each run in order to assure a reliable quantitative analysis. Lack of time and facilities prevented us from making an analysis of the solid and liquid products.

-17800 / / 700 // 600 500 _ /' /G/ o / 0.A~ / W / 300 / / ~ ~~~~~~~~~~. W/ 0/ 300 _ i / 200 - / 400 _ / 0 10 20 30 40 50 60 70 80 90 100 110 20 130 140 150 TIME (min) Figure 6. Typical Temperature History. Run 750-809

6000 ^-X 5000 e i -; - o 0 0 / / L / L-rN 4000 / c TIME/ (') 3000 300 / ----— _ NON RAD RUNS Lii / --- - RADIATION RUNS /' C,) / /// 1000 / o r —! 0 TIME (min)

CHAPTER VI INTERPRETATION OF DATA Results from runs made at 450~C did not seem to throw much light on the problem; therefore, emphasis was placed on higher temperature runs. Volume of Gas Released At 600'C the volume released did not give any conclusive difference, since the radiation runs gave intermediate values, as may be observed in Tables II and III. However, at 750~C both radiation runs gave lower amounts of gases. H2 Content The observed difference is small at 600~C, but at 750~C there is a definite decrease under radiation. CH4 Content There were contradictory results in this matter. At 600~C, there was a slight increase in radiation runs, while at 750~C there was a decrease. (The decrease at 750~C was smaller than the increase at 600oC). CO Content The analysis revealed some increase in CO released when the runs were made under radiation. Content of Other Species From the series of runs made it is not possible to draw any conclusive result about variations of C02, 02, C2H6 and higher hydrocarbons. -19

-20Solid Product or Cokes In general, the weight of the cokes follows a correlated relationship with the volume of gas released. Further results concerned with possible changes in structural and/or mechanical properties are likely to be encountered, when a complete analysis of the collected samples is made. Correlations of the variation of H2 with respect to CH4 and higher hydrocarbons were made and are shown in Figure 8.

-2120. 1.5 _ 1.0 0.5 NON RAD --.- RAD TEMPERATURE ~C 0 I I 450 600- 750 8 7 6 5 ( 4 X 3N 2 - ---- NON RAD 1 _-~ o ^ -~ —RAD_ TEMPERATURE ~C 450 600 750 Figure 8. Changes of Gas Composition at Different Temperatures

CHAPTER VII CONCLUSIONS An early study of the data gave indications of a decrease in the ratio 2 which is inferred from data given in terms of percentCH4 ages of the volume released. Plots of H2/CH4 and H2/HCS vs. Temperature are shown in Figure 9. It can be noticed, however, that these curves follow a pattern that is established by the hydrogen itself, which shows an appreciable increase in volume released when the runs are made under radiation. In general the mechanisms involved in the processes are quite difficult to interpret. The most interesting fact is the cited decrease in hydrogen. The complexity of the chemical reactions that take place in coal carbonization makes the problem more difficult. On the basis of the exploratory purpose of this work, it is pertinent to postulate some of the possible mechanisms as well as pointing out some effects of radiation. A. The decrease of H2 produced can be caused by a polymerizing effect of gamma-radiation. This polymerization would hinder the release of H2. Such an effect would produce more complicated hydrocarbon molecules in the coal itself. One way of checking this possibility will be by means of the complete analysis of the cokes produced. B. The radiation can be expected to produce an effect either before or at the very instant of the gas evolution. It is quite unlikely that radiation has much effect in the gaseous phase itself because: -22

-23radicals would eventually increase the amount of hydrocarbons in the gas released. In some work (that has been done here, under the guidance of Dr. J. J. Martin) dealing with the effect of radiation upon hydrocarbons of high molecular weight an increase in methane formation has been observed. This mechanism (Reaction (1) could account partly for the results, at least at 600~C, reported here. At 750~, however, this effect could be counterbalanced by some other mechanism that we are not able to determine as yet. (Such as the polymerizing effect cited in B-(l)). D. Increase of C2H6 in the radiation runs is doubtful.

-2470 C| H 6-~~/ 9 60 s~~~~~~~~~~~~~~~~o~~~~~ 50 5_ r Figure 9a. Influence of Radiation Upon E/5~~~~~~~~~, - 450 600 750, 0 0 0 RAD 3 0 450 600 750 TEMPERATURE (~C) Figure 9b. Influence of Radiation Upon H-~

-25TABLE I TIME-TEMPERATURE DATA IN A RADIATION RUN TIME (min.) TEMP. (oC) AT TIME (min.) TEMP. (~C) T 0 30 - 62 560 9 2 42 12 64 571 11 4 74 32 66 582 11 6 108 34 68 594 12 8 177 69 70 605 11 10 227 50 72 614 9 12 243 16 74 624 10 14 256 13 76 636 12 16 268 12 78 648 12 18 283 15 80 660 12 20 298 15 82 671 11 22 310 12 84 678 7 24 323 13 86 688 10 26 335 12 88 699 10 28 347 12 90 708 10 50 357 10 92 717 9 32 367 10 94 728 11 34 377 10 96 737 9 36 389 12 98 748 11 38 404 15 100 755 7 4o 422 18 102 760 5 42 438 16 104 7-61 1 44 462 24 106 760 -1 46 480 18 108 756 -4 48 490 10 110 755 -1 50 498 8 115 754 -1 52 505 7 120 754 -0 54 514 9 125 753 -1 56 528 14 130 750 58 539 11 140 750 60 551 12 150 750.'''......50 7 5

-26TABLE II RESULTS OF NON-RADIATION RUNS Temp. (~C) 450 600 600 750 750 Run# 806 801 823 806 820 Coke (gs) 36.77 33.84 33.49 32.60 31.72 Tars (gs) 1.20 4.20 1.48 - 2.39 H20 (gs) 3.80 1.35 1.70 Gas Vo l(cm gas) 20 85.75 80.0 159.50 151.25 gr. of coal/ sample H2 2.14 24.44 25.04 73.69 72.45 CO2 1.60 2.31 2.40 3.35 2.42 0 - - 0.88 1.12 0.91 C0 0.58 2.83 2.24 6.06 4.69 CH4 5.76 36.96 33.60 53.43 56.72 C2H6 3.86 9.26 6.24 9.33 7.11 C0 3.82 6.69 4.98 6.86 4.84 C4 1.02 1.54 2.52 3.38 1.36 C5 1.30 1.29 1.98 2.26 1.06

-27TABLE III RESULTS OF RADIATION RUNS Temp. (~C) 450 600 600 750 750 Run # 805 802 825 809 827 Cokes (gs) 36.24 34.57 33.04 33537 33.175 Tars (gs) 1.0 2.9 1.40 1.78 1.645 HO2 (gs) 2.6 4.0 1.30 1.66 1.49 _jcmn3 of gas Gas ol r. coal) 21.25 76.50 86.25 130.00 138.75 gr. of coal / sample H2 2.55 21.80 24.15 50.83 56.89 CO2 1.74 2.14 2.59 2.34 2.77 0 - - 1.38 1.30 0.69 CO 0.53 2.60 1.72 2.21 4.58 CH4 6.88 33.05 39.93 56.16 52.31 C2H6 3.95 8.26 7.76 8.45 9.16 C3 3.76 5.74 5.43 5.33 7.63 C4 1.00 1.45 1.98 1.87 2.84 C5 0.85 1.45 1.47 1.51 2.01

CHAPTER VIII APPENDIX BALANCE OF MATERIAL - In order to evaluate the reliability of the experiments, material balances were made in most of the runs. The procedure was as follows: Solid and liquid products were weighed on the analytic scale. Released gas was allowed to cool and, the volume reading was made at room temperature. After the Orsat and Gas-Chromatography analysis, the composition data was used to calculate the weight of the gas mixture. Using the concept of average molecular weight, the expression PV = RT(1) can be used and m, the weight, found in grams. It is assumed that the mixture behaves ideally. This procedure can be illustrated in the case of run 750-809 (radiation run). Weight of cokes: 33,370 Weight of tars: 1,785 Weight of H 0: 1,665 36,820 grams The average molecular weight Mav = xAMA + xBMB + xCMC + (2) was calculated for all the components encountered in the gas mixture. In our case: -28

-29H2 -------------- ----- 0.391 x 2 = 0.782 CO2 ---------- ------ 0.018 x 44 = 0.790 02 --------—. ---- 0.010 x 32 = 0.320 CO ------------------------ 0.017 x 28 = 0.476 CH4 -------------- 0.432 x 16 = 6.920 6 —---------------------- 0.065 x 30 = 1.950 26 C3 -o —--------- ---- 0.04o x 44 = 1.800 C4 ------------------------- 0.014 x 58 = 0.810 c 4o.o12 x 78 = o.84o C ------------------------- 0.012 x 70 =0.840 14.688 = Mav. Solving equation (1) for M = E Mav RT where p = 1 atm. V = 5200 cm. R = 82.05 cm. atm./~K mol. T = 300~K mav = 14,688 1 x 5200 therefore m = x 14.688 82.05 x 300 m = 3.1 gs. The total weight of the products is coke and liquids. 36.820 weight of the gas...... 3.100 39.920 grs. A loss of 0.080 grams (0.2% of 40 grams) was found, which is a satisfactory result.

-30BIBLIOGRAPHY 1. Himus, G. W., Fuel Testing, Leonard Hill Lim., London, (1953). 2. "The Chemical Effect of Particles Upon Some Hydrocarbons in the Vapor State." J. Phys. Chem., 153, 56, (1952). 3. "The Radiation Chemistry of HC-Polymers, Polyethylene, Polymethylene and Octacosane." J. Phys. Chem., 599, 60, (1956). 4. "Radiolysis of Hydrocarbons Mixture." J. Phys. Chem., 560, 56, (1952). 5. Laidler, K. J., The Chemical Kinetics of Excited States, Oxford University Press, (1955). 5. Staecie, E. W. R., Atomic and Free Radical Reactions, Vol. 1, Reinhold Publishing Corp., New York, (1954). 7. Lowry, H. H., Chemistry of Coal Utilization, John Wiley and Sons, London, (1945).