Catalyst and method for aromatization of C.SUB.3.-C.SUB.4 .gases, light hydrocarbon fractions and aliphatic alcohols, as well as mixtures thereof

Abstract

The invention relates to hydrocarbon feedstock processing technology, in particular, to catalysts and technology for aromatization of C.sub.3-C.sub.4 hydrocarbon gases, light low-octane hydrocarbon fractions and oxygen-containing compounds (C.sub.1-C.sub.3 aliphatic alcohols), as well as mixtures thereof resulting in producing an aromatic hydrocarbon concentrate (AHCC). The catalyst comprises a mechanical mixture of 2 zeolites, one of which is characterized by the silica/alumina ratio SiO.sub.2/Al.sub.2O.sub.3=20, pre-treated with an aqueous alkali solution and modified with oxides of rare-earth elements used in the amount from 0.5 to 2.0 wt % based on the weight of the first zeolite. The second zeolite is characterized by the silica/alumina ratio SiO.sub.2/Al.sub.2O.sub.3=82, comprises sodium oxide residual amounts of 0.04 wt % based on the weight of the second zeolite, and is modified with magnesium oxide in the amount from 0.5 to 5.0 wt % based on the weight of the second zeolite. Furthermore, the zeolites are used in the weight ratio from 1.7:1 to 2.8:1, wherein a binder comprises at least silicon oxide and is used in the amount from 20 to 25 wt % based on the weight of the catalyst. The process is carried out using the proposed catalyst in an isothermal reactor without recirculation of gases from a separation stage, by contacting a fixed catalyst bed with a gaseous feedstock, which was evaporated and heated in a preheater. The technical result consists in achieving a higher aromatic hydrocarbon yield while ensuring almost complete conversion of the HC feedstock and oxygenates, an increased selectivity with respect to forming xylols as part of an AHCC, while simultaneously simplifying the technological setup of the process by virtue of using a reduced (inter alia, atmospheric) pressure.

Claims

1. A catalyst for the aromatization of mixtures of hydrocarbons and aliphatic alcohols, the catalyst comprising: a mixture of a first pentasil zeolite and a second pentasil zeolite; the first pentasil zeolite comprising a silica ratio SiO.sub.2/Al.sub.2O.sub.3=20 and oxides of rare earth elements in a quantity of between 0.5 to 2.0 weight % of the mass of the first pentasil zeolite; and, the second pentasil zeolite comprising a silica ratio SiO.sub.2/Al.sub.2O.sub.3=82, residual quantities of sodium oxide of 0.04 weight % of the mass of the second pentasil zeolite, and magnesium oxide in a quantity of between 0.5-5.0 wt. % of the mass of the second pentasil zeolite; wherein the mixture comprises a mass ratio of the first pentasil zeolite/second pentasil zeolite is between 1.7/1 and 2.8/1; and a binding agent; wherein the binding agent comprises silicon oxide and is between 20 to 25 weight % of the mass of the catalyst.

2. The catalyst of claim 1, wherein the binding agent further comprises aluminum oxide.

3. The catalyst of claim 2, wherein the aluminum oxide does not exceed 25 weight % of the mass of the binding agent.

Description

(1) The invention is illustrated by the following examples:

(2) Example 1. A catalyst containing a mechanical mixture of 2 zeolites75 wt. % in the composition of the catalyst: (1) a zeolite with a SiO.sub.2/Al.sub.2O.sub.3 molar ratio=20, pre-treated with an aqueous alkali solution (Na.sub.2O content0.5 wt. % based on this zeolite) and modified with lanthanum oxide2.0 wt. %, and (2) a zeolite with SiO.sub.2/Al.sub.2O.sub.3 molar ratio=82 with a residual quantity of sodium oxide of 0.04 wt. %, modified by magnesium oxide0.5 wt. %, which are taken in the ratio 2.8/1; with the remainder being a binding agent25 wt. % silicon oxide.

(3) Example 2. A catalyst containing a mechanical mixture of 2 zeolites80 wt. % in the composition of the catalyst: (1) a zeolite with a SiO.sub.2/Al.sub.2O.sub.3 molar ratio=20, pre-treated with an aqueous alkali solution (Na.sub.2O content0.5 wt. % based on this zeolite) and modified with cerium oxide0.5 wt. %, and (2) a zeolite with SiO.sub.2/Al.sub.2O.sub.3 molar ratio=82 with a residual quantity of sodium oxide of 0.04 wt. %, modified by magnesium oxide5.0 wt. %, which are taken in the ratio 1.7/1; with the remainder being a binding agent20 wt. % (a mixture of aluminum oxide and silicon oxide taken in the mass ratio 1/4).

(4) Examples 3-9. The process was carried out in an isothermal flow reactor with electric heating at a pressure in the range of 1-18 atm while contacting 100 cm.sup.3 of the catalyst, which is prepared according to examples 1 and 2 (the catalyst bed height being 25 cm) and heated to temperatures of 400-500 C., with the feedstock gas, said feedstock gas being pre-heated in a pre-heater to 150-250 C. and in the form of C.sub.3-C.sub.4 H/C gases, various low-octane hydrocarbon fractions (WFLH) or gasolines and oxygenates (methanol, ethanol, isopropanol), as well as mixtures of H/C with alcohols, at a gas feedstock space velocity of 300-1500 h.sup.1.

(5) The AHCC obtained during the reaction was accumulated over a period of 24 hours, and then the composition thereof was chromatographically determined according to ASTM 6729. In examples 6 and 10 (the comparison), continuous experiments were carried out for 300 hours.

(6) The hydrocarbon composition of the feedstock is listed in table 1.

(7) Example 10 (comparative example). The process was carried out according to example 3, with the exception of the fact that the process was carried out at a temperature of 520 C. and at a pressure of 8 atm (as in the prior art invention), and a propane-butane fraction without oxygenate additives (methanol) was used as the feedstock.

(8) TABLE-US-00001 TABLE 1 Mixture of propane-propylene Wide fraction Propane- fraction (PPF) + of light butane butane-butylene Composition, hydrocarbons fraction fraction (BBF) wt. % (WFLH) (PBF) (50/50 vol.) methane 0.1 ethane 3.4 0.3 propane 26.2 38.6 3.4 propylene 28.5 isobutane 12.2 20.7 29.6 n-butane 25.0 35.9 6.8 butylenes 31.7 isopentanes 10.3 cyclopentane 0.8 n-pentane 10.5 4.1 n-hexane 3.0 0.4 isohexanes 3.8 cyclohexanes 0.9 heptanes 2.9 octanes 0.9 TOTAL 100 100 100

(9) Table 2 contains specific data regarding the conversion of different types of gas and liquid low-octane hydrocarbon feedstock and aliphatic alcohols, as well as mixtures thereof, depending on the conditions of the aromatization process.

(10) TABLE-US-00002 TABLE 2 Material balances of aromatization. 10 Example No. 3 4 5 6 7 9 (comp) Catalyst according to example No. 1 2 1 1 1 2 2 Temperature, C. 500 490 400 500 480 450 520 Pressure, atm 18 8 4 6 1 6 8 Space velocity of gas supply, h.sup.1 300 1000 500 300 300 1500 300 Feedstock composition, vol. % n-butane 100 WFLH 100 75 methanol 100 30 25 Propane-butane fraction (PBF) 70 100 Propane-propylene fraction (PPF) + 80 butane-butylene fraction (BBF) (50/50 vol.) isopropanol 20 TOTAL: 100 100 100 100 100 100 100 Conversion of oxygenates, % 100 100 100 99.8 AHCC yield per pass of feedstock 34.6 46.4 50.5* 38.1* 52.2* 78.2* 29.2 (for the WC portion of the feedstock*), wt. %. Gas composition, wt. % CH.sub.4 17.3 6.8 17.1 14.3 10.0 6.8 43.7 C.sub.2H.sub.6 18.2 25.9 5.0 10.6 17.3 20.8 24.6 C.sub.2H.sub.4 0.1 0.3 11.5 5.8 5.9 3.3 trace C.sub.3H.sub.6 35.7 37.1 26.4 32.2 31.8 32.1 25.0 C.sub.3H.sub.6 0.2 0.5 12.0 8.1 6.3 4.5 0.2 i-C.sub.4H.sub.10 2.0 10.5 8.9 5.5 9.7 10.5 1.1 n-C.sub.4H.sub.10 23.7 15.0 12.6 18.2 13.8 18.3 1.9 C.sub.4H.sub.8 0.2 0.8 4.2 2.2 2.5 2.7 0.1 H.sub.2 2.6 3.1 1.7 2.9 2.6 1.0 3.4 CO.sub.x 0.6 0.2 0.1 Total, wt. % 100 100 100 100 100 100 100 Composition of AHCC, wt. %, including: aliphatic substances 0.9 19.2 0.8 0.4 1.2 8.2 0.9 benzene 14.9 12.0 7.5 8.2 7.8 6.1 21.0 toluene 30.1 30.8 36.4 27.8 24.8 32.2 37.1 xylenes + ethylbenzene 31.9 22.8 44.6 41.6 38.1 36.4 22.7 alkyl aromatics C.sub.9+ 22.2 15.2 10.7 22.0 28.1 18.1 18.3 Total ArH in the AHCC 99.1 80.8 99.2 99.6 98.8 91.8 99.1 composition: Time for 20% reduction in the ArH 270 185 yield, h *since oxygenates (oxygen-containing alcohols) are used in the feedstock composition, the AHCC yield is calculated for the H/C portion of the feedstock (as, for example, in the methanol molecule-CH.sub.3OH, the hydrocarbon portion is CH.sub.2, i.e. it makes up 43.8 wt. %).

(11) The technical result obtained by carrying out the proposed invention involves achieving an increased yield of AHCC (in one pass of feedstock without recirculating the separation gases) and increased selectivity for xylenes. Thus, comparing the indicators of the propane-butane fraction aromatization reaction according to the proposed method (example number 6) with the addition of an oxygenate (methanol) to the H/C feedstock with the prior art (comparative example number 10, without oxygenate additives), it is evident that with the catalyst proposed in the claimed invention, at a lower temperature (500 instead of 520 C.) and pressure (6 instead of 8 atm) a higher yield of AHCC is obtained in one pass of the feedstock (38.1% versus 29.2%). Furthermore, the ArH composition according to the proposed method is dominated by widely sought-after xylenes (the concentration of the C.sub.8 aromatic fraction in the composition of the AHCC is up to 41.6%), while, in example 10, the concentration thereof does not exceed 22.7%.

(12) A similar picture is also observed during aromatization of WFLH. From the comparison of examples no. 7 and 4, it is obvious that the addition of 25 vol. % methanol to the H/C feedstock leads to an increase in the AHCC yield of 5.8%, wherein the concentration of the C.sub.8 fraction, containing xylenes, in the AHCC composition increases from 22.8 to 38.1%; furthermore, atmospheric pressure is used, and the temperature of the process in example number 7 (with the addition of the oxygenate) is 10 C. lower. It should be noted that during joint treatment of an olefin-containing mixed fraction (PPF+BBF) and isopropanol (example number 9), the AHCC yield reaches 78.2% even at the relatively low temperature of 450 C.

(13) A significant result of the proposed invention is that mixing the gaseous H/C feedstock with oxygenates eliminates the need to pre-heat same to a temperature of approximately 550-575 C., as is done in the prior art invention during the aromatization of the propane-butane fraction, because during the conversion of the oxygenates, additional heat is given off which is required for carrying out the aromatization reaction. The streams of feedstock at the inlet to the reactor should be heated only to 150-250 C., and this can be provided for by recovering the heat from the hot gas stream of the product at the outlet from the reactor, which makes it possible to avoid using multiple-section furnaces (combustion heaters).

(14) The proposed method eliminates the need to convert individual C.sub.3+ and C.sub.5+ H/C in separate successive zones with a different temperature mode, as well as the need to recirculate gases. This leads to a significant reduction in energy consumption while simultaneously simplifying the technological implementation of the process.

(15) Furthermore, in the proposed method for the aromatization of C.sub.3-C.sub.4 gases, low-octane H/C fractions and aliphatic alcohols as well as mixtures thereof, the period of stable operation of the catalyst is significantly extended because reaction water is formed during the conversion of the oxygenates, and the process takes place under milder conditions (in terms of temperature and pressure). This is affirmed by the time for a 20% reduction in the yield of ArH, which is presented in table 2, and which according to the proposed method increases by at least 1.5 times.