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OF BLEACHABILITY TO PULPINQ Ecoxonrv FIGURE 6. RELATION
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give the screened pulp yield as shown by the middle curve of Figure 6A. The lower curve gives the tons of bleached pulp (all pulps having the same color) produced from 100 tons of wood as calculated from the chemical shrinkage data given in Figure ID. Figure 6B gives the tons of chlorine required to bleach the pulp produced from 100 tons of wood as calculated from Figure 1C. Figure 6Ct gives the value of the bleached pulp (at 55 dollars per ton) and the cost of chlorine (at 60 dollars per ton). The value of the bleached pulp less the cost of chlorine (Figure 6D) gives the economic efficiency of the entire process. The curve shows that the bleached pulp has a maximum net value when the wood was cooked to produce a pulp with a bleachability of 6.0. If a mill superintendent insists on keeping chlorine costs below one dollar to bleach the pulp produced from a ton of wood, he is losing approximately 40 cents per ton of wood cooked. On the basis of a sulfite mill that requires 200 tons of wood (approximately 200 cords) per day, this amounts to a loss Of 8o
Acknowledgment the unbleached pulp will not vary with bleachability. Likewise, the cost of labor, equipment, etc., for bleaching %-ill not change with bleachability because a plant built t o accommodate 100 tons of pulp per day could handle 105 tons with no added cost. Therefore, the items to be considered are increase in the quantity of screenings, chemical shrinkage, and the quantity of chlorine t o bleach the pulps t o the same color with increasing bleachability, together with the value of a ton of bleached pulp and the cost of a ton of available chlorine. For convenience, in this presentation bleached pulp will be valued a t 55 dollars a ton whereas a ton of available chlorine will cost 60 dollars. The upper curve of Figure 6A shows the total yield of unbleached pulp us. bleachability. Plant experience indicates that the quantity of screenings increases from 0.5 per cent (basis, oven-dry wood) a t a bleachability of 3.5 to 1.5 per cent a t bleachability 7.0. Therefore, this amount ie deducted to
The author takes this opportunity to state his indebtedness to C. L. R. deWet and Gordon Welch of the Kimberly-Clark Corporation and to Clyde Arrington, formerly of this corporation, who capably did the experimental work reported here.
Literature Cited (1) Davis, M. N., Paper Trade J.,101, S o . 1, 36-44 (1935). (2) Hagglund, Erik, Paper I n d . , 13, 511-15, 518 (1931). (3) John, Hans, and Poppe, F. W., Paper Trade J . , 99, No. 9, 36-7 (1934). (4) Rauchberg, Herbert, Papier-Fabr., 29, 491-7, 516-24, 535-41 (19313. ( 5 ) Rothchild, H. A., et al., PuZp &. Paper Mag. Can., 28, 567-70, 584 (1929). ( 6 ) Swanson, W. H., and Monsson, Vi'. H., Paper Trade J.,82, No. 9, 6 2 4 (1926).
RECEWED May 5, 1936. Presented before the Division of Cellulose Chemistry at the 9lst Meeting of the American Chemical Society, Kansas City. Mo., April 13 to 17, 1936.
NATURAL GAS Conversion to Carbon Monoxide and Hydrogen
0
F THE possible uses of the methane in natural gas as a raw,material in chemical industry, its utilization as a source of hydrogen for ammonia synthesis or for hydrogenation is especially attractive. Hydrogen may be produced from natural gas by thermal cracking of the methane to yield carbon and hydrogen, or by steam conversion of the methane to yield carbon monoxide and hydrogen, with subsequent steam conversion of the carbon monoxide a t 500" C. The thermal cracking process is used in industry to obtain hydrogen for ammonia synthesis (8) and to obtain lampblack only (7). Since the hydrogen made contains 5 to 20 per cent undecomposed methane, it must be purified before use by cooling and washing with liquid nitrogen. Because of the expensiveness of such purification and the comparatively low yield of hydrogen (half that obtained from steam conversion),
W. A. KARZHAVIN Nitrogen Research Institute, Moscow, U. S. S. R.
this process is t o be preferred over the steam conversion process only when it is desirable to produce hydrogen and lampblack simultaneously. Although establishment of equilibrium (3) a t 800" C. for a mixture of one volume of methane and two of steam leaves only 0.3 per cent undecomposed methane, the rate of reaction without a catalyst is very low a t 800" C. and becomes high enough for industrial purposes only a t 1400" C. Nickel catalysts (4) are effective in speeding up the reaction, and with them the process may be carried out a t 1000" to 1100 " C. The high temperature to which the reactants must be heated and the endothermicity of the conversion reaction require large quantities of heat. The supplying of this heat constitutes the chief problem in the application of the steam conversion process. Plants in France and Germany (8), employing the process for the conversion of methane in coke-
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oven gas, produce this heat by intermittently burning a The process of converting natural gas with steam to produce part of the gas in the reaction carbon monoxide and hydrogen is tested on a semi-industrial scale. chamber, which is filled with It consists in heating a gas-steam mixture in an apparatus, prorefractory material. Since the gas-steam mixture is heated vided with chamotte regenerative packing, and passing it over a only to 1200" C. and no catalyst nickel catalyst. The methane content of the converted gas is, on is used, methane decomposithe average, 0.8 per cent. tion is incomplete and the During conversion 1.9 cubic meters of steam (1.5 kg.) are added hydrogen must be purified for to 1 cubic meter of the natural gas, and 3.3 cubic meters of converted ammonia synthesis by 1 0 7 ~ temperature cooling. gas are produced containing 64 per cent hydrogen and 22 carbon Employment of catalysts in monoxide. The total consumption of natural gas per cubic meter the intermittent process makes of a pure nitrogen-hydrogen mixture is 0.44 cubic meter, taking it possible to obtain corninto account the gas consumption both for the conversion and for plete conversion of methane at the heating of the packing. One cubic meter of the reaction temperatures low enough to permit the use of commonly chamber volume can yield 24 cubic meters of converted gas per hour. available refractory materials. Laboratory experiments by the author and bv Hawk, Its percentage composition, which remained practically constant, Golden, Storch, and Fieldner (1) showed that a nickel catalyst was : is suitable. The author has extended his experiments in a specially constructed semi-works plant. Katural gas from the Dag-ogni field near Derbent (Caucasus) was used.
Apparatus and Procedure REACTION CHAMBER.The reaction chamber (Figure 1) was a sheet steel cylinder with a lining of refractory fire-clay brick 500 mm. thick. The lower part was filled with regenerative packing of fire-clay brick, the upper part with nickel catalyst and pieces of fire clay. The total volume taken up by the regenerative packing and catalyst was 22 cubic meters. The fire clay used throughout was of good quality with a melting point of 1730" C. and a softening point of 1420" C. under standard loading (2 kg. per sq. cm.). The strain under standard loading mas 4 per cent at 1490' C. and 40 per cent a t 1600" C. Provisions were made to measure temperature over the catalyst, under the catalyst, and under the regenerative packing. Orifices were installed for the measurement of flows of natural gas, steam, and air. C.ATA+YST.The catalyst was prepared by impregnating pieces of fireclay brick with nickel nitrate and drying them. The nickel content of the total charge was 36 kg. Reduction \vas accomplished with natural gas at the beginning of the operation. STEAMAICD AIR SUPPLY. Steam was delivered to the plant at a pressure of 1 to 1.5 atmospheres. Air was supplied by a fan which maintained a pressure up to 300 mm. water column and had a capacity of 55 cubic meters per minute. NATURAL GAS SUPPLY.Katural gas n-as supplied through a 4-inch (10.2-cm.) pipe line directly from the well, without any pretreatment except passage through mud-and-water separators.
Sulfur compounds were present to the extent of 0.1 gram per cubic meter (4.4 grains per 100 cubic feet). Preliminary laboratory tests (4, 5 ) had shown that this amount of sulfur compounds reduced the activity of the nickel catalyst only slightly, especially at high temperatures, and accordingly no steps were taken to remove them from the gas. PROCEDURE. The conversion was carried out as follows: The mixture of natural gas and steam entered the lower part of the reaction chamber and passed upward, being heated by the hot regenerative packing and catalyst. The converted gas left the upper part of the chamber at a b o u t 1100" C. No attempt was made to recover the heat in it, and it passed directly to a tubular water cooler. When the regenerative packing had cooled, the conversion process was i n t e r r u p t e d and the c h a m b e r reheated by combustion of natural gas with 20 to 30 per cent excess air. The flow of c o m b u s t i o n p r o d u c t s Tvas downward.
Operation without Catalyst The first experiments were carried out with no catalyst in the reaction chamber. Gas was supplied a t the rate of 1.2 to 3.3 cubic meters per minute and steam a t the rate of 1.7 to 5.4 kg. per minute. Conversion periods lasted 10 to 18 minutes. The degree of conversion was found to depend much more on reaction temperature than on flow through the reaction chamber. The results, plotted in Figure 2 , show the relation between methane content of the converted gas and reaction temperature. Simultaneously with the interaction of methane and steam, thermal decomposition of methane occurred to a small extent. Part of the lampblack so produced was carried out with the gas, and part settled out on the packing and was burned during the heating period. Obseryations showed that lampblack
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was formed chiefly in the upper, hotter part of the packing; the lower the concentration of methane in the gas a t this point, the less lampblack is formed. These observations are confirmed by Kassel (6). During these tests the gas resulting from the partial decomposition of methane was passed through a second reaction chamber containing nickel catalyst for completion of the reaction. Continuous operation for 3 months proved that the catalyst retained its activity. The lampblack carried along with the gas from the first reaction chamber had no harmful effect. From these results it was concluded that the reaction could be carried out essentially to completion in a single reaction chamber, containing both regenerative packing and catalyst.
Operation with Catalyst Xormal operating conditions and results obtained were as follows : Natural gas flow during conversion period, 3.3 cubic meters (0' C. and 760 mm.) per minute.
Steam flow, 5 kg. per minute. Temperature at top of reaction chamber at beginning of conversion period, 1350' C. (flame temperature). Temperature at top of reaction chamber at end of conversion period, 1280" C. Temperatures at middle of reaction chamber, E%O" to 900" C. Length of conversion periods, 10 minutes. Methane content of converted gas, 0.4 t o 1.2 per cent. Average percentage composition of converted gas:
Yield of converted gas, 530 cubic meters per hour. Natural gas converted per cubic meter converted gas, 0.30 cubic meter. Natural gas burned per cubic meter converted gas, 0.16 cubic meter. Total natural gas consumed per cubic meter converted gas, 0.46 cubic meter. The quantity of steam used amounted to 1.9 volumes per volume of natural gas supplied for conversion. This is almost double the requirement for complete reaction to yield carbon monoxide and hydrogen. Actually, considerable quantities of carbon dioxide were also formed. The relatively high nitrogen content of the converted gas (4.2 per cent) resulted from inadequate purging of the reaction chamber with steam at the beginning of the conversion period. If the hydrogen is intended for ammonia synthesis, a hydrogen-nitrogen mixture is required, and no steam purge should be used. Mixing all of the products of combustion which remain in the reaction chamber with the converted gas would raise the nitrogen content of the mixture t o 6 per cent. It was noted during operation that the methane content of the converted gas was low a t the start when the reaction chamber was hot, and gradually increased as the conversion period was prolonged and the packing became cool. Accordingly, to obtain converted gas low in methane, the conversion period should be short. I n an industrial plant it should be
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altogether practical, with automatic controls, to operate with conversion periods of only 10 minutes. Operation of the experimental plant demonstrated that the nickel catalyst retains its activity quite well under the working conditions described, and that it can be used satisfactorily for a t least 3 months, the duration of the tests.
Production of Nitrogen-Hydrogen Mixture for Ammonia Synthesis To produce 1 cubic meter of converted gas of the composition shown, 0.30 cubic meter of natural gas is required. If 85 per cent of the carbon monoxide is converted to hydrogen in a subsequent conversion a t 500" C., 0.827 cubic meter of hydrogen or 1.10 cubic meters of nitrogen-hydrogen mixture will be produced. If 5 per cent of the hydrogen is lost during purification, the practical yield of pure nitrogen-hydrogen mixture may be estimated as 1.05 cubic meters per cubic meter of converted gas. For 1 cubic meter of pure nitrogenhydrogen mixture, 0.95 cubic meter of converted gas and 0.29 cubic meter of natural gas (to conversion) are used. Since, for the conversion of 1 cubic meter of natural gas, 0.54 cubic meter must be burned to supply heat, to obtain 1 cubic meter of pure nitrogen-hydrogen mixture, 0.15 cubic meter of natural gas must be burned. The total quantity of natural gas consumed per cubic meter of nitrogen-hydrogen mixture is therefore 0.44 cubic meter. Steam required for the conversion process can be obtained by cooling the converted gas to 300" C. in a waste-heat boiler, about 2.1 cubic meters being obtainable per cubic meter of natural gas supplied for conversion. The size of the reaction chamber can be based on the yield of 530 cubic meters of converted gas per hour from 22 cubic meters of space occupied by packing and catalyst-that is, 24 cubic meters of converted gas per hour per cubic meter of reaction chamber volume. The process is simple and no difficulties should be encountered in its large-scale operation. It is estimated that a reaction chamber and waste-heat boiler can be conveniently installed for the production of 3000 to 4000 cubic meters of nitrogen-hydrogen mixture per hour.
Acknowledgment The author expresses his deep gratitude to all who participated in this investigation and especially to N. P. Electronoff, B. N. Ovchinnikoff, I. G. Dreizer, and Z. M. Smirnova.
Literature Cited (1) Hawk, Golden, Storch, and Fieldner, IND. ENG.CHEM.,24, 23 (1932). (2) Hirsch, Industl-ie chimique, 1931, No.213,731. (3) Karzhavin, J . Chem. Ind. (Moscow), 1932, No. 6,24. (4) Karzhavin, Boguslavski, and Smirnova, Ibid., 1933, NO. 8, 31. (5) Karzhavin, Leibush, Ovohinnikov, and Margulis, Ibid., 1934. No. 5, 45. (6) Kassel, J. Am. Chem. Soc., 54, 3949 (1932). (7) Moore, IND. ENG.CHEM.,24, 21 (1932). (8) Rosenstein, Chem. & Met. Eng., 38,636 (1931). RECEIVED May 4, 1936.
