2013
Znd. Eng. Chem. Res. 1991,30, 2013-2014
from the platinum value measured originally was less than 1%. However, due to the somewhat tedious treatment a systematic error remained. The mean platinum content of six different samples, each loaded by incipient wetness with 10 mg of Pt/g of catalyst, had been determined to 9.69 f 0.03 mg. If in kinetic measurements with Pt-Sn02 catalysts the observed reaction rate is, as usual, reported to the platinum weight of the catalyst sample, the use of the spectrophotometrically determined value of the platinum content will introduce an additional error of about 3%. Nevertheless, considering the limited precision of kinetic measurements which is rarely better than lo%, the analytical method described above is sufficiently accurate to characterize the platinum content of cordierite-supported Pt/SnO, oxidation catalysts. Acknowledgment U. Stenger has meticulously performed the chemical preparations and analysis.
Brunck, 0.;Holtze, R.Die Anwendung der Abatronschmelze in der analytischen Chemie. Angeru. Chem. 1932,45,331-334. Cmelins Handbuch der anorganische Chemie; Verlag Chemie: Berlin, 1939; System No. 68,Platin, Teil C 1, p 46. Gmelins Handbuch der anorganische Chemie, 8. Auflage; Verlag Chemie: Berlin, 1972;System No. 46,Zinn, Teil C 1, pp 105,112. Kolts, J. H.Oxidation of Carbon Monoxide and Cetalyst Composition Therefor. Eur.Pat. Appl. 88116581.5,1988,11 pp. Maziekien, I.; Ermanis, L.; Walsh, T. J. Assay Procedure for Platinum in Reforming Catalysts. Anal. Chem. 1960,32,645. Milner, 0. I.; Shipman, G. F. Calorimetric Determination of Platinum with Stannous Chloride. Anal. Chem. 1955,77,1476. Snell, F. D.;Snell, C. T. In Colorimetric Methods of Analysis; van Nostrand: Princeton, 1959; Vol. IIa, p 429. Wright, C. J.; Sampson, C. F. Tin Oxide Sola in Catalyst Preparation. Brit. Pat. Appl. P 8300554, 1983.
Hans-GClnther Lintz Znstitut fur Chemische Verfahrenstechnik Universitdt (TH)Karkrruhe, Postfach 6980 Kaiserstrasse 12,0-7500 Karlsruhe 1, Germany
Literature Cited Ayres, G. H.; Meyer, A. S. Spectrophotometric Study of the Platinum(1V)-Tin(I1) Chloride System. Anal. Chem. 1951,23,299.
Received for review January 17, 1991 Accepted May 24,1991
Transformation of Heavy Hydrocarbons into Benzene, Toluene, and Xylenes over Modified ZSM-5 Catalysts The transformation of heavy hydrocarbons (bp 623-673 K) over ZSM-5 catalyst modified with Zn (ZnZSM-5) and the combination of Zn, Nil and S elements (NiSZSM-5) was studied. The catalyst modified with the combination of Zn, Ni, and S elements had a better result. At the experimental conditions, the aromatics yield was 28.8 wt ?& and the concentration of aromatics in the gasoline fraction was 67.7 wt % for a reaction time of 9 h.
BTX compunds, namely, benzene, toluene, and xylenes, are consumed in large quantity as high-octane blending components. They are also an important source of petrochemicals. Most petroleum-derived aromatics are obtained by Pt reforming of nathphas. In the reforming, low-octane nathphas, boiling between about 338 and 473 K, are converted into high-octane gasolines containing a high concentration of aromatics. However, current Pt reforming processes are incapable of transformation of the heavy hydrocarbons, boiling above 473 K, which are often used in catalytic cracking processes to produce gasolines containing a little aromatics. Effective processes to convert the heavy hydrocarbons into aromatics would improve the availability of high-octane gasolines and increase the source of BTX as petrochemicals. The new technique of the synthesis of aromatics was reviewed by Hao (1987).' Aromatization of light hydrocarbons has been extensively studied. Chen and Yan (1986) reported a new process to produce aromatics (M2 forming) from light FCC (fluid catalytic cracking) gasoline and virgin nathphas.2 Wu et al. (1981) studied aromatization of C4hydrocarbons? Kitagawa et al. (1986) and Ono et al. (1987) researched the transformation of propane and but-1-ene into aromatics, r e s p e c t i ~ e l y .The ~ ~ ~formation of aromatics from methanol was reported by Pop et al. ( 1 9 W and Ono et al. (1988).' The aromatization of gasolines was investigated by Shen (1987)8 and Yang (1987).B Hu (1989) reported the aromatization of crude oil.l0 These studies were based on the ZSM-5 zeolite catalysts. The investigation of transformation of heavy hydrocarbons (bp 623-673 K) into aromatics over modified 0888-5885/91/2630-2013$02.50/0
ZSM-5 zeolite catalysts is presented in this paper. The zeolite sample with Si02/A1203= 53 was synthesized with n-butylamine. Ita structure was confirmed to be that of ZSM-5 zeolite by X-ray diffraction. The zeolite was converted into the ammonium form (NH4ZSM-5)by exchanging with an ammonium nitrate solution and calcined at 813 K to form HZSM-5. ZnZSM-5 was made by treating HZSM-5 with a zinc nitrate solution and had a zinc content of about 5 % by weight. It was p r o p e d that incorporation of zinc cations into ZSM-5 zeolite could increase the yield of aromatic hydrocarbons greatly!J' NiSZSM-5 was prepared by modification of ZnZSM-5 with a nickel nitrate solution and then with an ammonium sulfide solution. The reactions were carried out with a continuous-flow reactor at atmospheric pressure. The catalyst was packed in a reactor made of a stainless-steel tube (8-mm i.d.1 placed in a vertical furnace. The NiSZSM-5 catalyst was heated under a hydrogen stream at 773 K for 2 h. By this treatment, nickel cations were expected to be partly reduced into nickel metal atoms. ZnZSM-5 was not treated with hydrogen. Reaction conditions were temperature 773 K, weight hourly space velocity (WHSV) 3.5 h-l, and reactant (g):stream (g):hydrogen or nitrogen (mol) 1:l:O.W. The effluent was collected with an ice trap. The gasoline fraction was distilled, and ita aromatics composition was analyzed by a gas chromatograph equipped with a thermal conductivity detector. The reactant was a heavy distillate oil. Its properties are shown in Table I. The reaction over ZnZSM-5 was carried out with nitrogen as a carrier gas, and the results are given in Table 0 1991 American Chemical Society
2014 Ind. Eng. Chem. Res., Vol. 30, No. 8, 1993 Table I. ProDerties of the Reactant boiling range, K coagulation point, K flash point, K chemical composition," wt % alkanes cycloalkanes mononuclear aromatics dinuclear aromatics others Table 11. Results with ZnZSM-5 reaction time, h 1 carrier gas nitrogen liquid recovery, wt YO 70.1 carbonaceous deposition, w t % gasoline yield, wt YO 34.8 aromatics yield, wt YC 28.7 product distribution of gasoline fraction, wt YO benzene 16.7 toluene 35.4 ethylbenzene 3.1 20.2 p-xylene m-xylene 5.0 o-xylene 1.3 Cg aromatics 0.9 nonaromatics 17.4 xaromatics 82.6
623-673 303 383 63.1 24.8 6.5 2.0 0.4 5.5
9
nitrogen nitrogen 74.0 26.8 17.4 13.2 27.4 0.5 17.4 4.4 1.0 0.5 35.2 64.8
80.4 0.6 26.4 15.9 12.5 25.4 0 16.8 4.3 1.1
0 39.9 60.1
11. Table I1 shows that ZnZSM-5 could aromatize the heavy hydrocarbons to give a high yield of BTX especially at the beginning of the reaction, so there is the possibility of producing BTX from heavy hydrocarbons. However, the activity of the catalyst decreased gradually with reaction time. In order to develop a new aromatization process based on this reaction, it is critical to maintain the activity of the catalyst as long as possible. Shen (1987) reported that the carbonaceous deposition on the surface covered the active site of aromatization and decreased the aromatization activity of the catalyst.* Even though the mechanism of the carbonaceous deposition has not been well established, it is assumed that the deposition contains polynuclear aromatics and even graphite, which are formed by dehydrogenation and aromatization of the hydrocarbons during the reaction. It was reported12that the combination of nickel and sulfur elements could catalyze the hydrocracking of polynuclear aromatics better than mononuclear aromatics. Polynuclear aromatics are the components of the carbonaceous deposition left on the surface of the catalyst. Thus it is postulated that the introduction of nickel and sulfur elements to the ZnZSM-5 zeolite catalyst functions in part by suppressing the formation of the polynuclear aromatics, changing the carbonaceous deposition into light hydrocarbons, keeping the surface of the catalyst clean, and having the aromatization activity of the catalyst remain longer. Table I11 gives the results with the NiSZSM-5 catalyst. Comparing the the results in Table I11 with those in Table 11, we can see that liquid recovery, gasoline yield, and aromatics yield with NiSZSM-5 catalyst were higher and also more stable than those with ZnZSM-5 as the reaction went on. The data in Table I11 also show that the carbonaceous deposition was formed less on the surface of NiSZSM-5 than on the surface of ZnZSM-5. Therefore, we could infer that the higher and the more stable aromatics yield with the NiSZSM-5 resulted from the formation of less carbonaceous deposition, which could poison the active sties of the aromatization. The higher liquid recovery and gasoline yield resulted from the aromatization of light hydrocarbons, which were formed by cracking or hydrocracking during the reaction, into BTX, which were in the gasoline fraction.
Table 111. Results with NiSZSM-5 reaction time, h 1 4 carrier gas hydrogen hydrogen liquid recovery, wt ?& 84.1 85.4 carbonaceous deposition, wt YG gasoline yield, wt '70 41.7 43.0 aromatics yield, wt % 31.0 30.5 product distribution of gasoline fraction, wt '7~ benzene 6.0 6.3 toluene 37.9 33.8 ethylbenzene 3.0 2.9 p-xylene 22.3 22.6 m-xylene 2.7 2.8 o-xylene 1.5 1.4 C9 aromatics 0.9 1.1 nonaromatics 25.7 29.1 xaromatics 74.3 70.9
7
9
hydrogen hydrogen 84.8
85.2 -0.2
43.2 28.6
42.6 28.8
6.0 32.6 2.5 21.4 1.9
5.9 34.6 2.1 20.9 2.0 1.2 1.0 32.3 67.7
1.1 0.7 33.8 66.2
A t the reaction temperature 773 K, WHSV 3.5 h-l, reactant (g):steam (g):hydrogen (mol) 1:1:0.044, and reaction time 9 h, the transformation of heavy hydrocarbons into aromatics gives 28.8 wt % and a 67.7 wt % concentration of aromatics in the gasoline fraction. These resulb provide the basis for the development of a new kind of catalytic process for the production of high-octane gasoline and aromatics which are of importance to the petrochemical industry. Nomenclature HZSM-5 = H-form ZSM-5 zeolite catalyst ZnZSM-5 = HZSM-5 modified with zinc NiSZSM-5 = ZnZSM-5 modified with nickel and sulfur Registry No. Ni, 7440-02-0; S, 7704-34-9; Zn, 7440-66-6; benzene, 71-43-2; toluene, 108-88-3; ethylbenzene, 100-41-4; p xylene, 106-42-3; m-xylene, 108-38-3; o-xylene, 95-47-6.
Literature Cited (1) Hao, G. Z. Advance in the Technology of Aromatics Production. Shi You Hua Gong 1987,16 (5), 375-383. (2) Chen, N. Y.; Yan, T. Y. M2 Forming-A Process for Aromati-
zation of Light Hydrocarbons. Ind. Eng. Chem. Process Des. Deu. 1986, 25, 151-155. (3) Wu, Z. N.; Wu, Z. J.; Ge, X. D.; Chen, Y. B.; Yang, J. G.; He, W.
L. Aromatization of C, Hydrocarbons with HZSM-5 Catalyst. Hua Dong Hua Gong Xue Yuan Xue Bao 1981,4, 1-11. (4) Kitagawa, H.; Sendoda, Y.; Ono, Y. Transformation of Propane into Aromatic Hydrocarbons over ZSM-5Zeolites. J . Catal. 1986, 101, 12-18.
(5) Ono, Y.; Kitagawa, H.; Sendoda, Y. Transformation of But-1-ene into Aromatic Hydrocarbons over ZSM-5 Zeolite. J. Chem. Soc., Faraday Trans. 1 1987,83 (9) 2913-2923. (6) Pop, G.; Maria, G.; Straja, S.; Mihall, R. Selective Methanol Conversion to BTX. Ind. Eng. Chem. Process Res. Deu. 1986,25, 208-213. (7) Ono, Y.; Adachi, H.; Sendoda, Y. J. Chem. SOC., Faraday Trans. I 1988, 84 (4), 1091-1099. (8) Shen, L. N. Aromatization of Hydrocarbons. Shi You Hua Gong 1987, 16 (8), 541-546. (9) Yang, X. K. Aromatization of Hydrocarbons. Shi You Hua Gong 1987, 16 (9), 611-615. (10) Hu, R. L. Test of Cracking/Aromatization of Crude Oil. Shi You Xue Bao (Shi You Jia Gong) 1989,5 (4), 25. (11) Lin, S. X. Shi You Lian Zhi Gong Cheng; Petroleum Industry Press: Beijing, 1988; pp 27-28. (12) Pines, H. The Chemistry of Catalytic Hydrocarbon Conuersions; Academic Press: New York, 1981; pp 110-118.
Duoli Sun,* Zhenge Zhao Shenyang Institute of Chemical Technology Shenyang, People's Republic of China I I0021 Received for review February 20, 1991 Accepted May 29, 1991
