Zeolite catalysts in the upgrading of low-octane hydrocarbon feedstocks to unleaded gasolines

Catalysts in Petroleum Refining and Petrochemical Industries 1995 M. Absi-Halabi et al. (Editors) 9 1996 Elsevier Science B.V. All fights reserved.

477

Z E O L I T E CATALYSTS IN THE UPGRADING OF L O W - O C T A N E H Y D R O C A R B O N F E E D S T O C K S TO UNLEADED GASOLINES

V. G. Stepanov, K. G. lone and G. P. Snytnikova Scientific - Engineering Centre Novosibirsk, 630090, Russia

"Zeosit",

G. K. Boreskov Institute o f

Catalysis

1. ABSTRACT Processing different hydrocarbon raw materials into high-octane gasolines over zeolite-containing catalysts with pentasil structure has been studied in the absence of hydrogen in dependence on the technological parameters of the process. Correlations have been found between the hydrocarbon composition of the feed and the yield of gasoline and its composition. The possibility of increasing the octane numbers of light petroleum naphtha and gas condensate from 56-60 to 85-90 MON without hydrogen application has been shown. For low-octane number raw material, upgrading the catalyst IC30 without previous hydropurification of the feed results in a decrease of the total sulfur content in synthesised gasolines to 0.1 wt % and simultaneous improvement in their antidetonate parameters. The non-hydrogen transformation of light petrol fractions of oils and gas condensates over IC-30 catalysts to increase the octane number and to reduce the sulphur content was performed on a pilot and industrial scale over three years. 2. I N T R O D U C T I O N Nowadays because of deterioration of the ecological situation worldwide, there is a tendency towards reduction in the use of leaded gasoline followed by a complete cessation of its use. As a result, increasing interest is shown in development of new catalysts and processes based on them that allow, first the obtaining of gasoline with sufficiently high octane numbers, and second the involvement of unconventional hydrocarbon feedstocks, e.g. gas condensates, petroleum gas, gas gasoline, etc., into standard gasoline production. It is well known that zeolites with pintail structures are active in reactions of isomerization, cracking, aromatization, alkylation, etc., which makes possible their use as an active component of catalysts for a number of processes. Thus, ZSM-5 zeolites are used as catalysts for the transformation of lower alkanes into aromatics [1]; Ni/ZSM-5 zeolite is applied in the M-Forming process to increase octane numbers of reformates [2]; catalysts prepared on the basis of pentasil-type zeolites are employed in "zeoforming" - the process of unleaded high-octane gasoline obtaining from gas condensate and gas gasoline fractions [3-7]. Here we describe the results of systematic investigations of zeolite H-ZSM-5-type behavior during the processing of different hydrocarbon raw materials with gasoline boiling ranges that depend on reaction conditions.

478 3. EXPERIMENTAL PROCEDURE The catalyst containing H-ZSM-5 zeolite (SIO2/A1203=96, Na20<0.1 wt.%) granulated with 7-A1203 as a binder was investigated in a fixed-bed, down-flow, electrically heated reactor (10 ml, fraction 0.25-0.50 mm) at a temperature interval (TO of 300-460~ pressures (P) of 0.1-0.4 MPa and LHSV of 0.5-7.0 h~. The feed was delivered to the reactor by a metering liquid pump. Overpressure was maintained by N2 from buffer capacity at its consumption 21/h. Reaction products after reactor were passed through a cold-water condenser and then separated into gas and liquid (catalysate) phases. It was established, by independent experiments with quartz instead of catalyst, that in the reactor catalysis as described does not take place. The yield of catalysate was 90 wt % and that of the uncondensed C4-C6 fraction was about 10 wt %. Before the experiment the catalyst sample was activated in air flow in situ at 500~ for 2h, and then was blown by N2 at the same temperature for 0.5 h. During the experiments, i.e., a period of 4 h with hourly collection of probes for gas chromatographic analysis changes in catalyst stability and selectivity were not observed. Light gasoline fractions of oils and gas condensates from different deposits, gas petroleum, reformates, and reforming rafinates as well as model hydrocarbon mixtures were used as feedstocks. 4. RESULTS AND DISCUSSION The hydrocarbon composition of gasoline produced from different raw materials under the same process conditions may essentially differ individually as well as in groups. The main differences are observed in the composition of the paraffin-naphthene fraction of gasoline, and aromatics are represented basically by the toluene-xylene fraction. As a result of the transformation of hydrocarbon feedstocks over H-ZSM-5/AI203 catalyst, hydrocarbon and fraction composition of liquid products widen which leads to an increase of the end boiling point of the catalysate. Simultaneously, the formation of C1 - C4 hydrocarbons and of a small amount of H2 (not more than 3-4 wt % in the gas phase) occurs. The composition of the gaseous products obtained (P>5 MPa) differs only slightly. 4.1 The influence of the reaction temperature

With elevation of temperature, gas formation increases (Figure l a). The content of methane and ethane in the gas phase is increased, the portion of butanes is reduced and the concentration of propane, the main gaseous product, passes through its maximum. Increasing Tr from 340 to 450~ in process under atmospheric pressure leads to the growth of the C2-C4 olefin content from 5 to 20 wt % in the gas phase. When P>0.5 MPa the process temperature actually does not influence the concentration of the gas phase. It does not exceed 3-5 wt %. With an increase of the Tr obtained, the end boiling point ofcatalysates also rises to 220280~ depending on the conditions of the process; the portion of distilled off fraction >195~ is equal to 2-8 vol %. In this case, the content ofparaffines and naphthenes in the gasoline fraction decreases while that of aromatic hydrocarbons increases. It has been shown by the independent experiments that for the model hydrocarbon mixture (isooctane : n-octane : cyclohexane = 1 : 1 : 1 wt), the degree of conversion of isoparaffines owing to shape selectivity is much smaller than that of n-paraffines and

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Figure 1. Influence of process temperature, pressure and LHSV on the yield and hydrocarbon composition of the gas phase during the conversion of: (a)gas condensate (45-125~ P=IMPa, LHSV = 2 hl, (b) oil fraction (85-180~ at T=360~ LHSV = 2 h"~ and (r gas condensate (60-155~ at T=380~ P =lMpa. (1- gas yield; 2- content of methane+ethane; 3-propane; 4- butanes; and 5- C2-C4-olefins in C1-C4-fraction).

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Figure 2. Model hydrocarbon mixture conversion vs. temperature at P=I MPa, LHSV = 2 h"1. (1- yieM of gasoline fraction; 2- content of Cs+ n-paraffines; 3isoparaffines; 4- naphthenes; and 5- aromatics). naphthenes; along with the rise of Tr, the content of naphthenes and n-paraffines in catalysate falls, the amount of aromatics increases and the isoparaffine passes through its maximum (Figure 2). Increase in T, lead to substantial changes in the composition of the n-paraffines fraction; the portion of n-C7+ is essentially reduced and that of n-C4-C5 is increased. The dependence of the individual composition of the aromatic fraction of gasoline on Tr is of a more complicated nature, that depends on the composition of the initial raw materials. In general, with T, increasing from 360~ to 450~ the amount of benzene and toluene in the aromatic fraction increases while that of the C9+ aromatics is reduced (Figure 3).

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Figure 3. Dependence of distribution of aromatics on reaction temperature at P = 1 MPa and LHSV = 2 h~. At the transformation of sulfur- and high-sulfur containing hydrocarbon fractions, the desulphurization of gasoline takes place and sulfur evolves in the gas phase in H2S. With increases of the process temperature, the degree of desulphurization increases; then it stabilizes and can reach 95-96 wt %. Liquid products contain about 300-600 PPM total sulfur. With increases of the process temperature, the yield of the gasoline fraction falls and the content of high-octane components is increased while the quantity of total sulfur and lowoctane components is reduced. 4.2 The influence of LHSV With an increase of the LHSV of reaction products, decreasing gas yield and increasing liquid hydrocarbon yields are observed, caused by the diminution of the stock conversion degree. In gaseous products, with increases in the LHSV, the content of Ci-C2 paraffines decreases while the concentration of C2-C4 olefines increases slightly (Figure lc). In gasoline obtained with an increase of the LHSV from 0.5 to 7.0 h"1 , the content of initial stock components, paraffines and naphthenes, increases practically linearly while the amount of aromatic hydrocarbons decreases (Figure 4). On the whole, with increasing the LHSV, increases the yield of gasoline fraction, but the amount of high-octane hydrocarbons in it diminishes and that of the low-octane components rises. 4.3 Composition and properties of the gasoline obtained

When performing the process, the reactions of C-C bond cleavage, isomerization, hydrogen transfer, alkylation of hydrocarbon stock components and intermediates taking place on the active surface of the zeolite result in the transformation of low-octane hydrocarbons (nalkanes, monomethylalkanes and naphthenes) into high-octane components (isoparaftines and arenes). Strongly branched stack paraffines, as a result of shape selectivity of the catalyst, in all practicality, do not undergo the conversion, which preserves the high-octane feed components. The gasoline obtained corresponds to standard motor fuels (Table 1).

481

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LHSV, h t Figure 4. Gasoline yield and composition vs. space velocity at the conversion of gas condensate (33 - 155~ at Tr = 420~ P = 1 Mpa. (1- yield of gasoline; 2content ofn-paraffmes; 3- iso+~cloparatNaes; and 4- arenes in C5+-fraction. Table 1 Composition and octane numbers of feedstocks and gasoline obtained N

1

2 3

Index

Groupcomposition,wt% C3-C4 Normal alkanes Cyclo + iso-alkanes Arenes Total S content, wt % Fractional composition, ~ Initial boiling point 10 vol %

4

.......................................... F.~..d..s.tp..e.~......~.......a...n...d...g...m....o.!.i.n..e....(.G..) "......................................... Gas Gasoline Gas Condensate Pet.Naphtha F G F G F G F G

50 90 End boiling point MON

2.2 33.1 64.1 0.6 0

5.1 5.3 32.8 56.8 0

30.8 61.5 7.7 0

3.2 6.7 34.3 54.8 O.

.1

.1

.1

1

33 63 82 105 109 68

35 58 112 169 193 86

44 63 94 137 149 66

35 56 94 157 181 86

1.8 31.5 51.1 15.6 1.3

7.0 11.2 38.2 43.6 0.06

36 56 89 109 134 56

31 45 98 150 185 80

32.7 44.2 23.1 0.05

2.3 16.8 48.3 32.6 0.02

85

35 67 115 163 196 78

108

128 159 185 62

The middle-and wide-pore zeolites were investigated in comparison with ZSM-5. As a result of these investigations the technology of the new catalyst IC-30 was developed for low octane number hydrocarbon mixture upgrading. The technology for obtaining high-octane, unleaded gasoline was elaborated on a pilot-scale using real feedstocks: 9 From the low-octane gasoline fraction of gas condensates at the Novo-Urengoy gascondensate plant and Luginetsk deposit; 9 From compressates of oil gas, at the Nizhne-Vartovsk gas plant. (This installation has been in operation for 3 years.); 9 From sulfur-containing gas condensates, at the Orenburg gas-refining plant.

482 5. CONCLUSION Hydrocarbons of different nature having low octane numbers can be converted into gasoline with the properties of motor fuels using middle-and wide-pore-type zeolites. The yield and composition of gasoline obtained are determined by the composition of the initial feed as well as the process conditions. Depending on process conditions, increases in octane numbers from 56 MON to 85-86 MON and higher are possible. The successful industrial application of this technology and type of catalyst has been in progress in the northern Siberia for three years. REFERENCES 1. Y.Ono, Transformation of lower alkanes into aromatic hydrocarbons over ZSM-5 zeolites, Catal. Rev. Sci. Eng. 34(3) (1992) 179-226. 2. Y.Chen, W.E.Garwood and R.H.Heck, Ind. Eng. Chem. Res., 26 (1987) 706 3. K.G.Ione, V.G.Stepanov et al. Patent of Russia Federation No.1325892. Method of producing gasoline fractions. 18.03.1993, appl. 03.10.1984. 4. V.G.Stepanov, K.G.Ione et al. Patent of Russia Federation No.1141704. Method of producing motor fuels from gas condensate. 18.03.1993, appl. 17.06.1983. 5. G.P.Snytnikova, M.N.Radchenko, K.G.Ione, V.G.Stepanov. The production of high-octane gasoline fractions. Gas Industry (Russia) No.4 (1988) 54-55. 6. V.G. Stepanov, A.J. Getinger, G.P. Snytnikova, V.L. Nebykov, K.G. Ione. Catalyic upgrading of gas gasoline of Nijnevartovsk plant on zeolite catalyst. Nettepererabotka and nettehimia, No.12, (1988) 3-6. 7. V.G. Stepanov, G.P. Snytnikova, L.G. Agabalian, K.G. Ione. Autogasolines from fractions of gas condensate. Gas industry (Russia), No. 1 (1989) 54-57.