Ind. Eng. Chem. Prod. Res. Dev. 1984, 23, 476-479
470
Hydrogen Cyanide Synthesis Catalyzed by Alumina in the Presence of Hydrogen Sulfide under Simultaneous Formation of Aluminum Nitride Wolfgang A. Hlllebrand’ Bergbau-Forschung GMBH, Franz-Flscher- Weg 6 1, 4300 Essen 13, West Germany
The alumina-catalyzedhydrogen cyanide formation from methane and ammonia is increased 4-fold when 10 vol. % hydrogen suWMe Is added. Effecting an HCN yield of 80% (based on NH, fed), the catalyst system provides
an activity similar to R/A1203. More than inhibiting coke formation, H2S surprisingly brings about a complete conversion of aluminum nitrlde, whlch in turn promotes further the conversion of ammonia and methane to hydrogen cyanide. The system offers a new route to the production of HCN from coke oven and refinery sour gases. Possibly there are still more applications of AIN as a catalyst.
Introduction Many industrial chemicals are produced from or with hydrogen cyanide. Accordingly, the hydrogen cyanide production capacities exceed 250000 tpa in the United States. The cyanide is synthesized predominantly by reacting methane with ammonia on noble metal catalysts. In the Andrussow process (Andrussow, 1935) methane, ammonia, and oxygen (from air) convert to hydrogen cyanide according to the overall equation NH,
+ CHI + ,l2O2
lo00 *c
HCN
+ 3H20
AH = -474 kJ/mol While the process is simple, the HCN concentration in the product gas is rather low and the HCN yield (about 6070, based on ammonia) is moderate. In the BMA process (Endter, 1958), no oxygen is used and both the HCN concentrations in the product gas and the yields (8045%) are higher 1200 “C
+
NH3
Pt/A1,0,- HCN + 3/2H2
AH = 252 kJ/mol The net reaction is endothermic, so indirect heating is required to achieve the high temperature needed. As a consequence, the reactor is made up from many parallel ceramic tubes internally coated with platinum. In the Shawinigan process (Shine, 1971) hydrocarbon gases are reacted with ammonia in a fluidized bed consisting of coal particles which are directly heated with electric current. This noncatalytic process gives the advantage of a wider range of potential feedstocks. It will, however be restricted to sites where low-cost electric power is available. The Andrussow process, as well as the BMA process, requires pure gases. Sulfur compounds and hydrocarbons other than methane cause deactivation of the catalyst by poisoning and by coke formation. The aim of the work reported here was to develop a catalyst as well cheap as a resistant to sulfur compounds and to hydrocarbons. In other words, this catalyst should provide the option of using raw feedstocks such as refinery
* Firma UHDE GmbH, Deggingstr., 4600 Dortmund 1,West Germany. 0196-432118411223-0476$01.50/0
gases and coke oven plant ammonia. The observation that alumina is capable of catalysing the reaction of ammonia with methane has been made long ago. Kotake (1956) found a suitable catalyst for the synthesis when he used A1203-Th02. He also noted a promoting effect of H2S or CS2 on the reaction. The main disadvantage of A1203catalysts is the methane being required in large excess amounts; otherwise ammonia mainly converts to nitrogen and hydrogen. A great surplus of methane has the consequence that coke formation is enhanced and thus the catalysts deactivate. So until now there were neither satisfactory yields nor did A1203catalysts have acceptable lifetimes.
Experimental Section Catalyst Samples. Various commercial grade types of alumina extrudates were tested. Before use they were heated under nitrogen for 1 h at 1100 “C. Apparatus. A simplified scheme of the equipment used is shown in Figure 1. Hydrocarbon gases, nitrogen, ammonia, hydrogen sulfide, and hydrogen flows could individually be adjusted by thermal mass flow controllers. The mixed gases passed through a preheater into the reactor. The reactor consisted of a quartz tube (id. 3 cm) which could be heated up to 1300 “C with an electric oven. The catalyst bed had a volume of 100 mL. The bed temperature was measured by means of a thermocouple. Typical reaction temperature was 1030 f 5 “C. The product gases were passed through H2S04and KOH for NH,,HCN, and H2S absorption and were subsequently metered. Analyses. The off-gas was analyzed by means of a gas chromatograph using a 6 f t by l/* in. column packed with Porapak Q and a thermal conductivity detector. N2,CHI, NH,, H2S, and HCN were traced. The methane and CO concentrations in the off-gas were continuously monitored with an “UNOR” infrared analyzer. In addition to the chromatographic analysis, NH,, H2S, and HCN were chemically determined from seperate samples: NH, by titration with sulfuric acid, H2S by titration with iodine, and HCN by the bromocyanogen method. Results and Discussion Effects of H2S Addition. The addition of H2S to the feed gas mixture consisting of hydrogen, methane, and ammonia increased the yield of HCN far more than previously observed. Thus Kotake et al. (1956) observed an 30% yield increase in the presence of CS2. They used an 0 1984 American Chemical Society
lnd. Eng. Chem. Rod. Res. Dev., VoI. 23,No. 3, 1984 477
Table 11. Properties of the Catalysts Used surface pore compacted HCN yield,' area, volume, bulk density, mol of HCN/100 g/mL mol of NH8 cat. m2/g mL/g 0.65 69.3 &% 230 0.70 D10-10' AI,OSR1O-ll' 300 n.d. 0.80 60.0 ALO, SCS 100 0.51 0.73 65.8
ic6
ac::
f
Figure 1. Flow sheet of experimental equipment: (a) maen flow controllers; (h) oven; (c) reactor; (d) catalyst bed; (e) wet gas meter. ",el6 "CN
CO
rsm
:". no
x BO
60
A1203SCS 25OC AI,O,SCS m
250
0.56
0.68
63.2
320
0.45
0.76
58.4
a
AliOiSCM 270 0.63 0.66 61.8 25ff SiO, D11-11' 180 0.90 0.43 14.2 activated 300 n.d. n.d. 23.1 carhon quartz wool n.d. n.d. n.d. 7.0 'Conditions: 100 mL of catalyst, 1030 'C, 70 L/h H2, 30 t / h CH,, 29.5 L/h NH,, 20 L/h H& yields given after 1 h. 'BASF. (Rhone poulene. Yield HCN jm01f100mOI NH,]
I
IC/
40
20
0
0 0
15
10
"0l.X
H,s
Figure 2. Influence of HIS on HCN yield, conversion of NHa and CH,; (100 mL) Ai,O, (BASFDlO-10);conditions: 1030 "C. 70 L/h H,: 30 L/h CH,; 29.5 L/h NH,; yield and conversion given after 1 h run time. Table 1. Selectivety of the Formation of NI. ECN, and Coke with and without Hydrogen Sulfide (Conditions as in Figure 1) H,S. vol '70 0 10
sN:
SHCN'
0.81
0.18
0.10
0.90
SC' 0.15 0.00
'Mol of Nlmoi of NH, converted. 'Mol of HCN/mol of NH, converted. ?Mol of Cjmol of CH, converted.
AI@-ThO2 catalyst and a 2 1 ratio of CH,:NH,. In our experiments we used nearly stoichiometric amounts of ammonia and methane and pure AI,O,. Under these conditions the increase of HCN yield effected by H$ was more than 4-fold. AI can be seen in Figure 2, with no H,S present there is only little formation of HCN (1400 "C) according to the equation A1203 + 3C + Nz 2A1N + 3CO (3)
-
-
Probably the following reaction takes place A1203 + 2HCN 2A1N + 2CO + HzO
(4)
Figure 4 shows the X-ray diffraction pattern of BASF D10-10 samples before reaction, after 4 h, and after 70 h of operation, respectively. Already after 4 h significant amounts of A1N have formed. After 70 h solely A1N can be found with X-ray diffraction analysis. In the absence of H a , alumina conversion proceeds very slowly (Figure 5). After 4 h only traces of A1N are detectible. Carbon deposition into the alumina pores obvi-
ously prevents aluminum nitride formation. In Table I11 some structural properties of 7-Alz03and aluminum nitride are listed for comparison. A1N has a smaller specific surface area and a larger average pore diameter. The conversion of M,O3 to ALN was investigated in more detail in a 73-h run. A feed gas mixture made up from hydrogen, methane, ammonia, and hydrogen sulfide initially gave 65% HCN yield, based on the ammonia fed (Figure 6). After 5 h NH3 conversion and HCN yield began to increase and reached their maximum levels after about 24 h run duration. These values (HCN yield 80%, and NH3 conversion) remained constant for another 34 h after which the run was terminated. The alumina conversion was complete after about 20 h. During this time CO in the off-gas dropped to a zero concentration. Another run with no hydrogen present in the feed gas but with otherwise the same conditions showed a similar overall pattern (Figure 7). The higher HCN concentration in the gas, however, effected a much faster alumina conversion. Correspondingly, the maximum yield was reached in only 13 h while carbon monoxide formation was initially
479
Ind. Eng. Chem. Prod. Res. Dev. 1904, 23, 479-482
surplus of propane caused immediate catalyst deactivation. Once coke formation had started it proceeded very rapidly. With no hydrogen addition, pure propane, or mixtures of propane and methane, the catalyst activity dropped dramatically. (See Table V.) Conclusion and Significance Hydrogen sulfide has some beneficial effects upon the synthesis of hydrogen cyanide. First, it enhances strongly in regard to the formation the catalytic properties of A1203 of HCN. A 5 1 0 % hydrogen sulfide concentration in the feed gas increases the HCN yield about fourfold. Second, H2S prevents deactivation due to coke formation. Third, only in the presence of H2S is the yA120, completely converted to aluminum nitride. Along with this conversion HCN formation is increased. The new process can be used with gas streams for coke oven plants as with refinery sour gases and sour natural gas. If acetone cyanhydrin is the desired product, it is not necessary to separate H2S and HCN before the gas is treated with acetone. Aluminum nitride itself may be used as a catalyst in further processes. Moreover, A1N is a material of some interest for the electronic industry. Registry No. NH,, 14798-03-9;CH,, 74-82-8; H2S,7783-06-4; A1203, 1344-28-1;AlN, 24304-00-5; HCN, 74-90-8. Literature Cited
Table V. Other Hydrocarbons as Feedstocks for HCN HCN yield! mol/100 N/C molofNH, cokef coke oven gaso 0.76 88.2 no H2/propaneb 1.07 84.2 no H2/CH,/propanec 1.00 85.2 no H,/CH,/n-butaned 1.00 87.2 no Cii, /propanee 1.00 74.3 Yes '100 L/h. b70 L/h H2, 12.5 L/h C3HB,40 L/h NH3, 20 L/h H,S. c70 L / h H,, 25 L/h CH,, 5 L / h CaHn,40 L / h NHn, 20 L/h His. d70 L j h Hi, 25 L j h CH4; 5 L/h C4Hli, 45 L/h NH;, 20 L/h H2S. e50 L/h CHI, 5 L/h C3Hs,65 L/h NH3,20 L/h H2S. '1030 "C, 100 mL D10-LO, after 6 h run time.
very high and CO dropped to a zero level within the same time. HCN Yield from Further Hydrocarbons. Checking whether coke oven plant or refinery gases are suitable feedstocks for the production of HCN, supplemental runs were made with coke oven gas, propane, and butane, respectively. Coke oven gas (composition, see Table IV) gave a very high HCN yield (88.2%),which is partly due to the very low N/C ratio (0.76) prevailing in this experiment. No carbon formed, though. Replacing 5% methane with propane at a 1:l N/C ratio and with hydrogen added gave an 85% HCN yield. Butane led to an 87% yield under the same conditions. No catalyst fouling because of coke formation was observed. Replacing the methane entirely with propane and maintaining the hydrogen level resulted in a HCN yield of 84%. Coke formation could be avoided, but short interruption of the H2S addition or a small
Andrussow, L. Angew. Chem. 1035, 48, 593. Endter, F. Chem. Ing. Tech. 1058, 30, 305. Kotake, M.; Nahagawa, M.; Ohara, T.; Harada, K.; Ninaniya, M. Kogyo Kaga hu Zasshi 1058, 59, 121.
Shlne, N. B. Chem. Eng. Prog. 1071, 67(2), 52.
Received for review January 23, 1984 Accepted March 5, 1984
Benzophenone via Nitric Acid Oxidation of 1,l-Diphenylethane Johann G. D. Schulz and Anatoll Onopchenko" Gulf Research & Development Company, Products and Alternate Energy Research and Development Divisions, Pittsburgh, Pennsylvania 15230
The discovery that 1, ldiphenylethane is present in the fuei-valued polyethylbenzene residues, available from commercial production of ethylbenzene, prompted us to utilize this feedstock for the preparation of benzophenone via nitric acid Oxidation. Optimum conditions for oxidation include a temperature of 150-160 OC and incremental addiion of nitric acid. Oxidations at atmospheric pressure at reflux (100 "C),or those under autogeneous pressure below 150 O C , led to significant formation of nitration products.
Introduction Until recently, 1,l-diphenylethane hm been unavailable commercially, and low yields (-25%) associated with its synthesis discouraged its use as a chemical feedstock (Bayer, 1873,1874; Spilker and Schade, 1932; Watanabe et al., 1977). Higher yields of 1,l-diphenylethane were obtained by mercury salt-catalyzed alkylation of benzene with acetylene in sulfuric acid (40-50%), probably the best method for preparing 1,l-diphenylethane today (Reichert and Niewland, 1923). In recent years, it became evident that a byproduct stream from the commercial alkylation of benzene with ethylene to produce ethylbenzene contains significant quantities of 1,l-diphenylethane (Watanabe et al., 1977). Utilization of this feedstock in the synthesis of benzophenone via nitric acid oxidation is therefore po0196-432118411223-0479$01.50/0
tentially attractive. Most benzophenone is manufactured today by Friedel-Crafts chemistry. Nitric acid oxidation of diphenylmethane to produce benzophenone has been known, but this procedure has not yet reached commercial significance (Rivkin, 1938; Bengtsson, 1955; Nakamura, 1971). The mechanism of nitric acid oxidation of diphenylmethane has been the subject of several papers (Ogata et al., 1969a,b; Ogata and Tezuka, 1970). Unfortunately, the reaction conditions reported for diphenylmethane are not suited for commercial production, requiring the use of 30-6570 nitric acid, solvents, and long reaction times. Uncontrollable exotherms are also encountered with low productivity. In contrast to the use of diphenylmethane, 1,l-diphenylethane has never been oxidized with nitric acid to produce benzophenone, al0 1984 American Chemical Society
