NAVAL STORES FROM PINE B Y FLUIDIZED BED DISTILLATION I . H.
K I M 1 AND H. C . LEWIS
Georgia Institute of Technology, Atlanta, Ga.
The aim of this research was to explore the possibilities of fluidized bed distillation for recovering naval stores from pine. A result of special interest to naval stores plants is the discovery lhat the heat generated by mechanical subdivision of pine wood is enough to vaporize appreciable amounts of turpentine and pine oil. The remainder is easily distilled a t 250” F. with no detectable chemical reaction. At 440” F. three quarters of the rosin is distillable to yield an F grade crude rosin. The rest is essentially undistillable. The rate of distillation appears influenced b y a chemical reaction in which steam participates. The role of the sieam needs to b e clarified. In the lighl of the experiments fluidized bed distillaiion seems well worth considering as a means of recovering naval stores from waste wood,
described, the raw material was pitchof Southern pine. However, the results may be applicable to the waste wood from a variety of operations in the lumber and paper industries. and to the digestor charge in a sulfate paper mill, if the industry should develop a digestor in which cooking liquor is mixed with wood in powdered form. Another possible use is in certain specialized undertakings, such as the production of juniper oil. At present. almost all the naval stores obtained from pine stumps are recovered by solvent extraction. Stumps are reduced to chips, which are then extracted with a solvent. Yields based on the amount and analysis of the chips are good, and product quality is high. However. rates of extraction are low7 because of the time needed for the solvent to penetrate to the interior of the chips. There is also a significant ex pense for solvent recovery. Instead of using solvent extraction it might be possible to grind stumps to powder and steam-distill in a fluidized bed. The dry powdered wood obtained as a by-product could be used directly as a fuel, compressed into briquets, or gasified or activated in another fluidized bed operation. Still another possible treatment is destructive distillation, followed by burning, briquetting, gasification, or activation of the resultant charcoal. The gas required for fluidization during destructive distillation could be made by gasifying a portion of the charcoal or by boiling diphenyl or some similar substance. No quantitative information is available on the cost of grinding pine stumps to powder. However. the material is far easier to subdivide than a typical ore, and the grinding of ores is an extremely low cost operation. This article is a report on laboratory studies of the grinding and distillation of pine stumps. The experiments were at temperatures high enough to distill the naval stores, yet low enough to avoid destructive distillation of cellulose and lignin. Of especial interest to existing solvent extraction plants is the discovery that the heat generated by mechanical subdivision N THE EXPERIMENTS
I soaked stumps
of pine stumps can be enough to vaporize appreciable amounts
of turpentine and pine oil. Machines used to reduce stumps to chips should be tested to determine the magnitude of these vaporization losses under plant conditions. Composition of Pine Stumps
In addition to cellulose, lignin, and water, pine stumps contain six distinct groups of chemical compounds : bicyclic terpenes, monocyclic terpenes, terpene alcohols and ketones, resin acids, neutral distillable resinous compounds, and a “dark rosin” fraction, essentially nondistillable. The bicyclic terpenes are the main constituent of commercial turpentine, the alcohols and ketones are the main constituents in pine oil, and commercial pale rosin is largely resin acids and neutral distillable compounds. The exact nature of the neutrals is unknown, but the fraction is a relatively small one. The compounds in dark rosin have a much darker color than pale rosin, are much less acidic, and have a considerably higher softening point. There is also evidence that these substances are of far higher molecular weight than the resin acids.
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TEMPERATURE,
Present address, University of Massachusetts, Amherst, Mass. 148
I&EC PROCESS D E S I G N AND DEVELOPMENT
I
Figure 1.
OC
Vapor pressures of terpenes
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HEATING ELEMENT STEAM MAIN
TO VET TEST METER
ICE AND WATER
PREHEATERS
Figure 2.
Vapor Pressures
The chemical similarity of the bicyclic terpenes is reflected in the fact that the vapor pressure curves of the various members of the group are all close together, the curve for the fraction as a whole being almost identical with that of the main constituent, a-pinene. I n the same way, the vapor pressure curve of the monocyclic fraction is well represented by the curve for dipentene, and the curve for the alcohol and ketone fraction by a-terpineol. The data of Ha\vkins and Armstrong ( 2 ) on a-pinene and of Pickett and Peterson ( 9 ) on dipentene and a-terpineol are shown in Figure 1. Pickett and Peterson also give the vapor pressures of several other terpenes. The limited information available on the vapor pressure of abietic acid (6, 8 ) indicates that it is of the order of 0.5 to 1.0 mm. of Hg a t 200' C. The vapor pressures of other distillable resinous compounds are presumably of about the same magnitude. Experimental
Fresh pine stump chips (Southern pine) were obtained from the Hercules Powder Co. T o prevent oxidation. the chips were shipped and stored in a n atmosphere of carbon dioxide. The chips and the products of distillation were analyzed for moisture content, bicyclic terpenes (reported as turpentine). monocyclic terpenes, terpene alcohols and ketones (reported as pine oil), rosin, and dry wood, free of moisture and naval stores. by conventional methods of extraction. distillation, and vapor chromatography (5). The crude rosin was tested for softening point by the Hercules drop method ( 3 ) ,acid number by the standard ASTM method (7), and color. Because of the small amounts of the samples available for testing, the reported cdors are only approximate. The chips were ground in a micropulverizer and sieved to obtain a fraction ranging in size from 100 to 250 Tyler mesh. T o eliminate vaporization of naval stores during the grinding, extraordinary measures were found necessary. In the first place, the chips were mixed thoroughly with small pieces of dry ice and chilled i n a dry ice chest for 1 hour. Then for about 5 minutes before grinding, the pulverizer was run and charged liberally with dry ice, in order to chill all parts of the machine. Finally. during the grinding itself the machine was charged ivith 10 parts of dry ice per part of chips, dry ice was continuously supplied to the storage container for the charge, and the charge was slowly fed to the machine. Preliminary experiments showed there is a slight tendency for powdered stumps to cake a t distilling temperatures, but the aggregates are small and fragile and collapse very easily upon mechanical agitation of the bed. Accordingly, the still was provided with four vertical blades attached to a shaft rotating at 88 r.p.m. The main body of the still, shown in Figure 2,
Apparatus
was a 30-inch length of ordinary 2-inch pipe, schedule 40, and could be charged with u p to 55 grams of fresh powder. T h e fluidized bed was supported by means of a l/s-inch thick brass plate perforated with 0.076-inch holes on a triangular spacing and a t a center to center distance of l/s inch. The preheaters had sufficient capacity to preheat the fluidizing gas to the temperature of the fluidized bed. Operation was essentially a t atmospheric pressure. The steam rate was normally about 250 grams per hour. When the gas was steam, the rate was determined by measuring the water accumulated in the condensate receiver. When the gas was noncondensable, its velocity was measured by the rotameter.
A sample of the powder charged to each run was analyzed. As might be expected, the moisture content varied somewhat; but the analysis of undistilled powder on a dry basis was almost constant. A typical sample contained 0.97% turpentine, 0.727, monocyclic terpenes, 2.087, pine oil, 30.670 rosin, and 65.6% wood (all percentages by weight on a moisturefree basis). Results
Losses during Grinding. When the standard procedure described above was used, the product of a typical grind contained 95% of the turpentine in the feed to the grinding machine, 94% of the monocyclic terpenes, 98% of the pine oil, 977, of the rosin. and 100% of the dry Xvood. O n the other hand, when the charge was chilled with dry ice for an hour before the start of grinding but the machine itself was not cooled, no dry ice was added to the feed during grinding, and the rate of feeding was much faster, only 297, of the turpentine in the charge appeared in the product and only 45% of the monocyclic terpenes; 89% of the less volatile pine oil was recovered, 89% of the rosin, and 1007, of the dry wood. Obviously, if neither the feed nor the machine had been chilled at all, the subdivision of pine stumps would have resulted in vaporization of very large percentages of the turpentine, monocyclics, and pine oil. On a plant scale, an) material vaporized in this way can be recovered by using an enclosed machine and draiving vapors from the enclosure into a recovery system. Losses during Distillation. Sufficient data were obtained in each run to permit material balances. Two typical balances are shown in Table I ; losses of turpentine, monocyclic terpenes, pine oil, and dry wood were small. However, the loss of rosin was 16y0in 1 hour at 250' F. and 25y0 in 45 minutes a t 440 F.
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The increase of rosin "disappearance" Mith time of distillation a t 250' F. is shown in Figure 3. Figure 4 is a similar plot for 440' F. I n the runs a t 440' F. the charge was a powder previously stripped of volatile naval stores by distillation for 40 minutes at 250' F.
TIME, MINUTES
Figure 3.
Disappearance of rosin during distillation a t
250°F.
Table 1. Typical Material Balances Run No. .4-29 A-42 Temp., O F. 250 440 Time. minutes 60 45 Steam rate, grams per hour 270 260 Charge, grams 46.6 40.3
Charge Moisture, yo .4nalysis, dry basis, % Turpentine Monocyclics Pine oil Rosin \2'ood Input, grams Turpentine Monocyclics Pine oil Rosin rt'ood
Overhead products
0
13.2 0.84 0.71 2.08 30.6 65.7
28.4 71.6
0,344 0,290 0,852 12.53 26.7
11.4 28.9
Grams
% of
Grams
Input Turpentine Monocyclics Pine oil Rosin \Vood Rrsidue in still Turpentine Monocyclics Pine oil Rosin \2'ood
0.333 0.290 0.830 0 0 0 0 0 10.5 26.6
96.8 100.0 97.4 0 0
% of
Input
8.0 2.9
70.2 10.0
0.2 25.9
1.8 89.6
0.3
2.6
2.9 0.1
25.4 0.4
0 0
0 83.8 99 6
Deposit on wall Rosin Loss
Turpentine Monocyclics Pine oil Rosin \Toad
150
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0.011 0 0.022 2.03 0.1
3.2 0 2.6 16.2 0.4
PROCESS DESIGN AND DEVELOPMEN1
The apparent loss of rosin seems to be due laryely, if not entirely, to a change in solubility of part of the original rosin under the influence of heat. Kosin in undistilled stumps is soluble in benzene; and benzene \vas therefore used to extract rosin from the various samples of powdered stiimps, whether fresh or distilled. If fresh powder after extraction with benzene was then extracted lvith furfural. no loss in weight of \vood was observed. However! if distilled poLvder from a given run was extracted first u i t h benzene and then with furfural. the Xvood suffered a loss in weight amounting to about 80% of the rosin "disappearance" calculated for that run on the basis of extraction with benzene. A study of the nature of the furfural extract \vas made difficult by the fact that distillation of furfural alone develops color and also a nonvolatile residue. I t was simply observed qualitatively that the furfural extract was very dark. \Vhile a change in the benzene solubility of rosin during heating seems to account for most of the rosin disappearance, it does not account for all of it. Hence? checks were made on several other possible causes of loss. I n every case, the results were negative. For example, when steam was used as the fluidizing gas, the vent line from the condensate receiver was tested to see if any noncondensable gases were being evolved as a result of thermal decomposition of rosin. IVhen helium was used as the fluidizing gas. the exit gas stream was analyzed for water. -411 aqueous and organic layers discarded in the analytical procedures were analyzed for rosin. I n addition, all deposits remaining in the still, the lines, and the condenser a t the end of each run Ivere carefully collected and rveighed. I n every case the amounts involved were either too small to be detected or, if detectable, much too small to account for the calculated disappearance. Effect of Temperature. Figure 5 shows the results of a series of steam distillations a t varying temperatures. Each run was 2 hours long. T h e plot brings out the great difference in volatility between rosin on the one hand and turpentine, monocyclics, and pine oil on the other. Evidently, a t temperatures u p to 300' F., one can distill the more volatile materials completely with no detectable evolution of rosin. To distill rosin, much higher temperatures are necessary. However, from a practical point of view temperatures in the neighborhood of 450' F. are about the upper limit, since above this temperature the danger of serious thermal degradation of the dry wood increases rapidly (7). I n a commercial operation, one Jvould probably use t\vo stages, distilling turpentine. monocyclics, and pine oil in the first stage a t 300' F. and rosin in a second stage a t 450' F. A striking feature of Figure 5 is that the apparent disappearance of rosin is 20 to 25y0 of the rosin in the charge at all temperatures investigated. Apparently 20 to 25Yc by weight of the rosin in decayed stumps of Southern pines is sensitive to even mild heating, which readily converts it from a benzenesoluble state to a state insoluble in benzene but soluble in furfural. This fraction is also of extremely l o ~ vvolatility, being essentially undistillable a t a temperature as high as 450' F. -4fter conversion to the benzene-insoluble state the fraction is very dark and therefore low grade rosin. I n the original rosin it is probably the well-known dark fraction, which is insoluble in hexans but soluble in furfural. Distillation of Turpentine, Monocyclics, and Pine Oil. T h e progress of steam distillation a t a constant temperature of 250' F. is shown in Figure 6. As can be seen, under the conditions employed it required about 40 minutes to complete the distillation. However, in these experiments the charge contained essentially all of the naval stores in the original chips
before grinding. If the grinding is conducted without any chilling of chips or machine, much of the turpentine, monocyclics. and pine oil can be vaporized in the machine and then recovered. In this case, the charge to the still !vi11 contain relatively little of the volatile naval stores; and the time required for distillation \vi11 be only a fraction of that shown in Figure 6. The temperature of distillation can be raised from 250" to 300" F. without detectable evolution of rosin. The higher temperature would undoubtedly be preferable in a commercial operation. The charge to each run shown in Figure 6 contained only a few grams of turpentine, monocyclic terpenes, and pine oil; yet it required 40 minutes and a steam rate of over 250 grams per hour to complete the distillation. Obviously, the ratio of steam to organic distillate was uneconomically high for a commercial still. O n the other hand, fluidization under vacuum is entirely practical. I n a commercial operation, one could easily reduce the steam-distillate ratio to a reasonable value by operating the still under vacuum. .i\ final point must be made about Figure 6. The slope of rach curve is proportional to the rate of evolution of the constituent in question, and in each case the slope is essentially constant until the final stages of distillation. This means that the partial pressures of turpentine, monocyclic terpenes, and pine oil in the top gas all remained constant from the start of distillation until tht. final stages. This srrongly suggests the evisrence of an equilibrium limitation. In fact: i t seems likely that mixing of the bed in a vertical direction was small and that equilibrium between the upflowing steam and the fluidized bed \.vas approached within a vertical disrance short compared to the depth of the bed. The assumption of an equilibrium limitation can be checked by an estimate of partial pressures in the top gas and partial pressures in equilibrium with fresh powder a t 250" F. During rhe constant rate period approximatel). 4.16c0 of the turpentine distilled per minut?; 3.647, of the monocyclics. and 2.607, o f the pine oil. The average charge for each run contained 0.400 gram of turpentine. 0.341 gram of rnonocyclics, and 0.676 gram of pine oil; and the average steam rate \vas 4.35 grams per minute. If one assumes an average molecular Lveight of 136 for turpentine, 136 for rnonocyclics. and 154 for pine oil and a total pressure of 760 mm., the partial pressures of turpentine. monocyclics, and pine oil in the top gas are 3.8, 2.8, and 3.5 mm. of Hg. respectively. The average composition of the charge on a weight basis \vas 0.887% turpentine, 0.757% monocyclic terpenes, 1.47% pine oil. 29.970 rosin. and the rest dry lvood. If one assumes the above molecular iveights and a molecular weight of 302 for rosin, the molal composition of the naval stores in the Xvood is 5.4% turpentine, 4.6% rnonocyclics. 7.9%, pine oil, and rosin. From Figure 1. the vapor pressures of a-pinene, dipentene, and a-terpineol at 250" F. (121' C.) are 285, 165, and 34 mm. of Hg, respectively. Assuming that these values apply to turpentine. monocyclic terpenes. and pine oil, respectively, rosin is nonvolatile, solutions of turpentine, monocyclics. and pine oil in rosin obey Raoult's law! and there is no reduction of parrial pressure due to adsorption of naval stores by \vood, one finds the equilibrium partial pressures to be 15.4 mm. for turpentine, 7.6 mm. for rnonocyclics, and 2.7 mm. for pine oil. While the equilibrium pressures of the turpentine and monocyclics are higher than the partial pressures in the top %as, the orders of magnitude are the same and it is possible that actual equilibrium pressures are some\vhat lower than
0
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TIME, MINUTES
Figure 4. 440°F.
Disappearance of rosin during distillation at
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ROSIN IN D I S T I L L A T E PLUS ROSIN DEPOSITED ON THE UPPER PORTION OF T H E INSIDE WALL OF THE S T I L L
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ROSlh REMAINING IN T H E WOOD-'-,.,
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DISTILLATE
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DURATION OF RUNS 2 HOURS IN EACH RUN D I S T I L L A T I O N O F TURPENTINE MONOCYCLIC TERPENES A h D PINE O I L COMPLETE IN EACP R U h
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TEMPERATURE
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Figure 5. Effect of temperature on rate of distillation of fresh wood 100 4 e r
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Figure 6.
40
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Distillation of fresh wood at 250°F. Effect of time on yields
the calculated ones! because of adsorption effects. Evidentl>-, the conjecture that the top gas is substantially at equilibrium \vith the fresh charge until the last stages of distillation is not far Lvrong. If the picture outlined above is true, at any instant during the progress of distillation most of the distillation was occurring in a relatively thin horizontal slice of the bed and the rest of the bed was practically inactive. Presumably, the distilling capacity of the still per unit volume could have been increased by using a higher steam rate (in so far as this could have been done Lvithout excessive entrainment) or by employing a bed of less height and greater diameter. VOL. 2
NO. 2
APRIL
1963
151
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Figure 7.
Distillation of rosin from wood at 440°F. Effect of time on yields
STEAM
140
A
NITROGEN
0
HELIUM
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ACID NUMBER OF ROSIN IN ORIGINAL WOOD 145 ACID NUMBER OF ROSIN IN CHARGE 146
1
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$
120
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HELIUM
40
ROSIN DISTILLED OVERHEAD,
Figure
9.
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NITROGEN
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100
WT. 5 OF ROSIN
I N CHARGE
60
Distillation of rosin from wood a t
440°F. 152
I & E C PROCESS D E S I G N A N D DEVELOPMENT
Distillation of Rosin. Figure 7 shows that the distillable rosin in pine stumps-Le., 75 to 80% of the rosin as it exists in the original stumps-can be steam-distilled in approximately an hour at 440' F. and atmospheric pressure. The charge was previously denuded of turpentine, monocyclics, and pine oil by distillation for 40 minutes a t 250' F. If the powder had not been denuded of turpentine, etc., before distillation at 440' F., it would have taken twice as long to distill the rosin (see Figure 5). An effect of this sort is to be expected from the fact that presence of turpentine, monocyclics, and pine oil during the early stages of distillation of rosin reduces the concentration of rosin in the solution and hence its partial pressure. If it is assumed that the average molecular weight of the initial distillate is the same as that of abietic acid, the initial rate of distillation shown by Figure 7 equals 0.068 gram mole per hour. This corresponds to a partial pressure of 3.6 mm. of Hg in the initial distillate at 440' F. (227' C.). The vapor pressure of abietic acid, it will be recalled, is 0.5 to 1.0 mm. of Hg a t 200' C. Any quantitative comparison between the partial pressure of rosin at 227' C. and the vapor pressure of abietic acid at 200' C. is impossible, because there are so many compounds in rosin besides abietic acid. However, the two pressures are of the same order of magnitude. When a charge previously denuded of turpentine, etc., was distilled for 1 hour at 440° F. in a current of nitrogen instead of steam, only 32.3% of the rosin in the charge was vaporized. In other words, the average rate of distillation was 0.54% per minute. This compares with 72.8% in 45 minutes, or 1.6% per minute, for distillation in steam. To put it another way, the average rate of distillation in nitrogen was only 34% of that in steam. When a similar charge was distilled for an hour a t 440' F. in helium, the average rate of distillation was 51% of that in steam. I n both cases, the linear gas velocity was the same as in distillations with steam. Both the crude rosin in the charge and all the rosin distillates were F grade in color. The rosin extracted with benzene from wood after distillation was much darker than B grade. The softening point of distilled rosin was always 86-7' C., which is typical of crude wood rosin (4). Figures 8 and 9 show how the acid numbers of the total distillate and the rosin remaining in the wood were affected by the amount of rosin distilled. From the information on distilling rates and acid number, one can draw some interesting conclusions. I t is obvious from Figures 8 and 9 that the resin acids are more volatile than the other distillable compounds in rosin, and that the factor which controls the rate of distillation of rosin must be entirely different from that which controls the distillation of turpentine, monocyclics, and pine oil. With the latter, each fraction distills at constant rate during most of the distillation. With the rosin the composition of the distillate changes continuously. I n the case of the turpentine, etc., the top gas appears to be saturated; one would therefore expect the rate of distillation to be the same in nitrogen or helium as in steam. In the case of rosin, the nature of the carrier gas has an important effect on distillation rate. Assume for the moment that the rate of distillation of rosin is controlled by the rate of diffusion of rosin vapor from the surface of the wood particles into the main body of the fluidizing gas. If this is c o r r x t , the rate should be approximately inversely proportional to the '/o power of the molecular weight of the fluidizing gas. On this basis the ratio of the distilling
rate in helium to that in nitrogen would be 1.4. The observed ratio, 51/34 or 1.5, agrees as closely as one could expect in view of all the assumptions and measurements involved. However, on the same basis the predicted rate of distillation in steam is only 10% greater than that in nitrogen. T h e observed rate in steam is 300y0 of that in nitrogen. Clearly some factor besides diffusional resistance must be at work in the case of steam. A clue as to what this factor might be is the location of the nitrogen and helium points on Figures 8 and 9. As these figures sholv, the use of steam not only speeds u p the distillation a great deal; it also makes the distillate and residue noticeably more acidic. Evidently the absence of steam makes it possible for the relatively volatile resin acids to be dehydrated to form the relatively nonvolatile anhydrides. I n the presence of steam, dehydration is suppressed; and the rate of distillation is increased. Conclusions
More information on the effect of steam pressure is needed. If the rate of distillation of rosin is relatively insensitive to the partial pressure of steam, one may be able to steam-distill rosin with reasonable success at high vacuum, thus economizing on steam. If, on the other hand, the distilling rate is sensitive to steam pressure, it may actually be advantageous to use steam under pressure and recover the heat by using a waste heat boiler in place of a condenser.
Acknowledgment
The financial aid of the Georgia Engineering Experiment Station is gratefully acknowledged. The authors much appreciate information and samples provided by C. L. Tyler, chief chzmist of the Hercules Powder Co.3 naval stores plant at Brunswick, and R. V. Lalvrence, director of the C.S.D.A. Naval Stores Experiment Station a t Olustee. literature Cited
(1) American Society for Testing Materials, Philadelphia, Pa., “Standard Methods of Test for Acid Number of Rosin,” ASTM Designation D 465-51, 1958. (2) Hawkins, J. E., .4rmstrong, G. T.: J . Am. Chem. Soc. 7 6 , 3756 11954). (3)’ He&ules Powder Co., LYilmington, Del., “Lt’ood Rosins and Stabilized Rosins,” 1957. (4) Humphrey, I. W., 2nd. Eng. Chem. 35, 1062 (1943). (5) Kim, I. H.. Ph.D. thesis in chemical engineering, Georgia Institute of Technoloev. 1960. (6) Landau, E. F., “Cayboxylic Acids,” Encyclopedia of Chemical Technology, R. E. Kirk and D. F. Othmer, eds., 1st ed., pp. 139-51, Interscience, New York, 1947. (7) Lawrence, R. V., personal communication. (8) Lombard, R., Frey, J. M., Bull. SOL.Chin. France 1948, 1194. (9) Pickett, 0. A., Peterson, J. M., 2nd. Eng. Chem. 21, 325 (1929). RECEIVED for review July 11, 1962 ACCEPTEDOctober 5 , 1962 Division of Wood, Cellulose, and Fiber Chemistry, 144th Meeting, ACS, Los Angeles, Calif., March 1963. Condensation of Ph. D. thesis of I. H. Kim, School of Chemical Engineering, Georgia Institute of Technology, Atlanta, Ga., August 1960.
REACTIVITY OF COALS IN HIGH-PRESSURE GASIFICATION WITH HYDROGEN AND STEAM HARLAN L. FELDKIRCHNER AND HENRY
R. LINDEN
Insritule of Gas Technology, Chicago 16, Ill.
The rates of reaction of various coals and chars with hydrogen, steam, and hydrogen-steam mixtures were measured a t pressures up to 2500 p.s.i.g. and temperatures up to 1700” F. A rapid-charge, semiflow reactor system was used in which very short coal heatup and product gas residence times were obtained. The primary variables studied were temperature, carbon conversion, total pressure, and feed gas composition. By means of the novel experimental technique employed, it was possible to follow directly the course of the coal-hydrogen-steam reactions during the initial high-rate period. The information obtained is of value in the design of reactors for conversion of coal i o methane.
NE
of the major obstacles to the design of a reactor for
0 direct conversion of coal to gas of high heating value by
destructive hydrogenation a t high pressure (hydrogasification) has been the lack of information on the rate and course of the reactions during the initial period of rapid conversion of the more reactive coal constituents. Kinetic studies have generally been made with highly devolatilized chars and carbons to avoid the problem of changes in feed composition during heatup.
Where the rates of formation of low molecular weight hydrocarbons from reactive coals and low-temperature chars have been measured, experimental conditions did not permit both rapid heatup and short product gas residence times to minimize side and secondary reactions. The primary variables affecting the rate of hydrogasification are coal reactivity, temperature, pressure, and feed gas composition. T h e coal reactivity, in turn, varies with the initial VOL. 2
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APRIL 1963
153
