Process for producing cumene and/or ethylbenzene from a mixed hydrocarbon feedstream

Abstract

A process for producing cumene and/or ethylbenzene from a mixed hydrocarbon feedstream comprising subjecting C6 cut separated from said mixed hydrocarbon feedstream to aromatization to provide an aromatization product stream and subjecting the thus obtained aromatization product stream to alkylation to produce an alkylated aromatic stream.

Claims

1. A process for producing alkylated aromatics comprising: (a) subjecting a mixed hydrocarbon feedstream to a separation to provide a C6 cut, wherein the C6 cut comprises iso-hexane; b) subjecting the C6 cut to aromatization to provide an aromatization product stream comprising 25-85 wt-% hexane; and (c) subjecting the aromatization product stream comprising 25-85 wt-% hexane to alkylation to produce an alkylated aromatic stream.

2. The process according to claim 1, wherein the separation of the mixed hydrocarbon feedstream to provide a C6 cut involves distillation under distillation conditions and wherein the distillation conditions are suitable to provide a C6 cut having a boiling point range of 45-90 C.

3. The process according to claim 1, wherein the aromatization comprises contacting the C6 cut with an aromatization catalyst under aromatization conditions.

4. The process according to claim 3, wherein the aromatization catalyst is a non-acidic zeolite comprising Ge as a framework element.

5. The process according to claim 3, wherein the aromatization catalyst is non-acidic by base-exchange and/or wherein the aromatization catalyst further comprises a hydrogenation metal.

6. The process according to claim 3, wherein the aromatization conditions comprise a temperature of 400-600 C., a pressure of 50-1000 kPa gauge, and a Weight Hourly Space Velocity of 0.1-20 h.sup.1.

7. The process according to claim 1, wherein the alkylation comprises contacting the aromatization product stream in the presence of ethylene with an alkylation catalyst under alkylation conditions to produce ethylbenzene, wherein said alkylation catalyst comprises beta zeolite, zeolite Y, ZSM-12, MCM-22, ZSM-5 and mordenite and wherein said alkylation conditions comprise a temperature of 120-250 C., a pressure of 1000-5000 kPa, a Weight Hourly Space Velocity of 0.5-20 h.sup.1, and a benzenelethylene molar ratio of 1-8.

8. The process according to claim 1, wherein the alkylation comprises contacting the aromatization product stream in the presence of propylene with an alkylation catalyst under alkylation conditions to produce cumene, wherein said alkylation catalyst comprises a zeolite selected from the group consisting of beta zeolite, zeolite Y, ZSM-12, MCM-22, ZSM-5 and mordenite and wherein said alkylation conditions comprise a temperature of 120-250 C., a pressure of 1000-5000 kPa, a Weight Hourly Space Velocity of 0.5-20 h.sup.1, and a benzene/propylene molar ratio of 1-8.

9. The process according to claim 1, wherein the mixed hydrocarbon feedstream comprises reformate.

10. The process according to claim 7, wherein said alkylation conditions comprise a temperature of 150-230 C., a pressure of 2500-3500 kPa, a Weight Hourly Space Velocity of 1-10 h.sup.1 and a benzene/ethylene molar ratio of 1-4.

11. The process according to claim 8, wherein said alkylation conditions comprise a temperature of 150-230 C., a pressure of 2500-3500 kPa, a Weight Hourly Space Velocity of 1-10 h.sup.1, and a benzene/propylene molar ratio of 1-4.

12. The process according to claim 1, wherein the C6 cut comprises 34-56 wt-% iso-hexane, based on a total weight of the C6 cut.

13. The process according to claim 1, wherein the aromatization product stream comprises 30-85 wt-% hexane.

14. The process according to claim 1, wherein the aromatization product stream comprises 50-60 wt-% hexane.

Description

(1) FIG. 1 shows the adiabatic temperature rise plotted against the dilution factor for diluted feedstock (Process conditions: pressure=30 bar, benzene/olefins molar ratio=2.5, Inlet temp=180 C.). The dilution factor as defined in the present invention is the weight fraction of the non-aromatics present in the diluted feedstock.

(2) FIG. 2 shows a reactor configuration in which the reactor consists of three beds 5, 6, and 7 in series. Fresh benzene stream 1 is mixed with the benzene recycle stream 2 from the benzene column in the downstream separation process. The propylene feed 3 is split and fed to each reactor stage. The fresh benzene stream 1 and propylene stream 3 provides the benzene to propylene stoichiometric ratio of 1:1. The mixed benzene stream 4 and propylene stream 3a is fed to the inlet of the first reactor bed 5. The effluent from 5 is mixed with stream 3b and fed to reactor bed 6. The sequence applies for reactor bed 7, i.e., the effluent from reactor bed 6 is mixed with stream 3c and fed to reactor bed 7. The product stream 8 is a mix of alkylated products such as cumene, diisopropylbenzene, triisopropylbezene, unreacted benzene, propane, n-hexane, and iso-hexanes.

(3) FIG. 3 shows a simple reactor configuration with a single bed 13. Fresh benzene stream 10 is mixed the benzene recycle stream 9 from the benzene column in the separation section of the alkylation process. The fresh benzene and the propylene stream 12 provides the benzene to propylene stoichiometric ratio of 1:1. The mixed benzene stream 11 is fed with the propylene stream into the reactor. The product stream 14 is a mix of alkylated products such as cumene, diisopropylbenzene, triisopropylbezene, unreacted benzene, propane, n-hexane, and iso-hexanes. Stream 14 is subjected to separation in the downstream process.

EXAMPLE 1

(4) Cs-Exchanged Pt/GeZSM-5 Aromatization Catalyst

(5) This catalyst consists of Pt dispersed on a basic ZSM-5 zeolite containing framework germanium (1% Pt/CsGeZSM-5). This catalyst may be prepared as described in U.S. Pat. No. 7,902,413 or US 2008/0293990 A1.

(6) Accordingly, Ge-ZSM-5 Zeolite may be prepared as follows: Solution #1 is made by diluting 15.84 g of 50 wt-% NaOH solution with 131.25 g of deionized (DI) water and subsequently dissolving 7.11 g of germanium dioxide. Solution #2 is made by diluting 3.84 g sodium aluminate solution (23.6 wt-% alumina and 19.4 wt-% sodium oxide) with 153.9 g DI water. Solution #1 is added to 150 g Ludox AS-40 (40 wt-% silica in a colloidal state) and vigorously stirred for 10 minutes to obtain a homogeneous mixture. Solution #2 is stirred into this mixture. After 15 minutes of vigorous agitation, 105.42 g of tetra-n-propyl ammonium hydroxide (TPAOH) is added and the mixture is stirred for 60 minutes. Finally, 23.32 g of glacial acetic acid is added to the gel to adjust the pH of the mixture to about 9. This mixture is loaded into a 1 L stainless steel autoclave and heated at 160 C. for 36 hours with stirring. Subsequently, the solids obtained are filtered from the mother liquor and washed with DI water. The solid is calcined at 550 C. for 6 hours in an oven with air flow. The MFI structure of the solid can be confirmed by measuring the powder X-Ray diffraction pattern.

(7) 8 grams of GeZSM-5 prepared as described above are washed with 200 ml of aqueous CsNO.sub.3 (0.5M) then filtered. The filtrate is then rewashed 3 more times with 0.5M CsNO.sub.3 and rinsed with distilled H.sub.2O on the final filtering. The zeolite powder is then calcined for 3 hours at 280 C. in air. Incipient wetness impregnation is carried out by adding drop wise a solution of 0.069 g Pt(NH.sub.2).sub.4(NO.sub.3).sub.2 dissolved in 1.343 g of deionized water to 3.508 grams of the Cs-exchanged Ge ZSM-5. The material is dried for 1 hour in a 110 C. drying oven then calcined at 280 C. for 3 hours. A representative elemental analysis gives 39.92 wt-% Si, 0.69 wt-% Al, 4.14 wt-% Ge, 5.03 wt-% Cs, and 0.90 wt-% Pt. The catalyst powder is typically pressed and sized to 20-40 mesh.

EXAMPLE 2

(8) Aromatization of C6 Heart Cut

(9) The experimental data as provided herein were obtained by modelling the product slates of an aromatization unit fed with reformate C6 heart cut feed. In this aromatization isohexanes (iso-C6) and normal hexanes (n-C6) are transformed into benzene, naphthenic species are dehydrogenated into benzene.

(10) Reaction tests are carried out using a 0.31 inch ID reactor tube containing a catalyst bed comprising 1 to 4.32 cm.sup.3 of the aromatization catalysts as described above in Examples 1 and 2. The bed is diluted to a total of 8 cm.sup.3 with inert silicon carbide to maintain constant length. Liquid n hexane is vaporized and passed over the catalyst bed at temperatures ranging from 500 to 540 C., pressures between 103 kPa absolute (15 psia) and 310 kPa absolute (45 psia), and liquid hourly space velocities ranging from 1 to 8 hr.sup.1. Products are analysed by on-line gas chromatography. Further experiments are carried out in two adiabatic pilot reactors connected in series, where n-hexane or light naphtha is vaporized and passed over a bed containing 80 g of catalyst per reactor, at an inlet temperature of 540 C., outlet temperatures at or above 450 C., and pressures ranging from 241 kPa absolute (35 psia) to 62 kPa absolute (9 psia). For these experiments, products are analysed both by on-line gas chromatography and by off-line analysis of collected liquid samples.

(11) The experimental data as provided herein were obtained by modelling the product slates of an aromatization unit fed with reformate C6 heart cut feed. In this example three cases are considered, i.e. a low, medium and high benzene concentration in the c6 heart cut feed. One-pass experiments allow the estimation of what conversions would be obtained in a complete process using partial recycle of unconverted hexanes; the predicted conversions are shown in Table 1:

(12) TABLE-US-00001 TABLE 1 Conversions for C6 hydrocarbons obtained in the aromatization experiment described above. % Benzene 0 iso-C6 25 n-C6 75 cyclo-C6 100

(13) A C6 cut from reformate may vary in composition. Roughly, the benzene content varies between 10-50 wt-% with the remainder being mainly paraffins, of which iso-paraffins are much more dominant. The naphthene content (mainly cyclohexane cyclo-C6) typically is below 10 wt-% since refinery reformers dehydrogenate the naphthenic species almost completely.

(14) TABLE-US-00002 TABLE 2 Three feed scenarios modelled in this example C6 heart cut feed composition (wt-%) LOW MEDIUM HIGH Benzene 17 35 50 iso-C6 56 44 34 n-C6 22 17 13 cyclo-C6 5 4 3 Sum 100 100 100

(15) Based on the examples explained above and given the obtained conversions explained in table 1 the following product slates are modelled for the three feed scenario's described in table 2.

(16) The tables below indicate the estimated effluent composition of an aromatization unit with Cs-exchanged Pt/GeZSM-5 aromatization catalyst.

(17) TABLE-US-00003 TABLE 3 Aromatization effluent composition in the aromatization unit with using Cs-exchanged Pt/GeZSM-5 aromatization catalyst as described in Example 1. All numbers in wt-%. Aromatization effluent composition LOW MEDIUM HIGH Benzene 46 58 70 iso-C6 42 33 25 n-C6 6 4 3 cyclo-C6 0 0 0 Hydrogen & Light gases 6 5 2 (C1-C4)

(18) Accordingly, it was found that n-C6, cyclo-C6 and the iso-C6 comprised in the C6 heart cut are converted into benzene when using a Cs-exchanged Pt/GeZSM-5 aromatization catalyst.

EXAMPLE 3

(19) Aromatic Alkylation

(20) In this example, the aromatic alkylation is carried with a model feed which is a diluted C6 stream containing 50 wt-% of benzene and the remaining diluted with iso-hexanes and n-hexane. The feed composition as used in this Example was 50 wt-% benzene, 34 wt-% iso-hexanes, 13 wt-% n-hexane, and 3 wt-% cyclohexane. The alkylation agent (olefin) is a mixture of ethylene and propylene at a weight ratio of 3:1.

(21) The reaction was carried out using a 3.5 mm ID reactor, which contains 1.35 ml catalyst volume available in an isothermal zone of 14 cm. This corresponds to approximately 0.1 ml catalyst/cm height. The catalyst is a BETA zeolite catalyst with Si/Al molar ratio of about 38. The undiluted zeolite is 0.65 g/ml in the reactor. The benzene to olefin molar ratio is 4, WHSV of 2 hr-1, reaction temperature of 200 C., and pressure of 25 bars. The product slate shows complete conversion of ethylene and propylene and 22% conversion of benzene. The combined selectivity of ethylbenzene and cumene is 87 wt-% while the polyalkylated byproducts (polyethylatedbenzene and ploypropylated benzene) is 13 wt-%. The amount of diluents in the product slates shows negligible conversion (<1%) which indicates that the n-hexane and iso-hexane acts as inerts in the alkylation reactor.

EXAMPLE 4

(22) Aromatic Alkylation Modelling

(23) The data as provided in this example were obtained by modelling the alkylation of the C6 fraction with propylene using an equilibrium reactor model. The feed compositions as used for the modelling experiments are described in Tables 4 and 5, below. The olefin stream contains 70 wt-% propylene and 30 wt-% propane. The reaction is carried out at 180 C. and 30 bar, with a benzene to propylene molar ratio of 2.5. Table 4 shows the result of the temperature rise and product selectivity using a single bed reactor. Table 5 shows the result of the temperature rise and product selectivity using a three staged reactor bed with interstage feeding of propylene. The effect of the diluents on the temperature rise is shown in FIG. 1.

(24) TABLE-US-00004 TABLE 4 Adiabatic temperature rise for a single staged reactor configuration C6 fraction Pure benzene Feed (wt-%) Benzene 40 100 Iso-hexane 56 0 n-hexane 4 0 T ( C.) 73 109 Selectivity (wt-%) Cumene 86 80 DIPB 12 16 TIPB 2 4

(25) The term selectivity is defined with respect to propylene as the weight of monoalkylated or polyalkylated product divided by the sum of the weight of monalkylated and polylaklylated products. For instance, the selectivity of cumene is the weight of cumene divided by the sum of the weight of cumene, DIPB, and TIPB. The results shown in Table 4 compares the exotherm for a diluted feed and pure benzene. A temperature rise of 73 C. indicates that the outlet reactor temperature is about 253 C., which is within the temperature range for alkylation reaction. For a pure benzene feedstock, the temperature rise of 109 C. amounting to an outlet temperature of 289 C. is undesirable for such process. Hence, explains why higher benzene to olefin ratio and/or interstage reactor beds are used to control the temperature rise. It is also expected that high amount of n-propylbenzene will be formed at high temperatures which impacts the purity of cumene. The selectivity of cumene also decreases at high temperatures.

(26) TABLE-US-00005 TABLE 5 Adiabatic temperature rise for interstaged reactor configuration C6 fraction Pure benzene Feed (wt-%) Benzene 40 100 Iso-hexane 56 0 n-hexane 4 0 T per stage ( C.) 28-30 43-51 Overall T ( C.) 63 89 Selectivity (wt-%) Cumene 88 86 DIPB 10 12 TIPB 2 2

(27) A separate embodiment of the invention also shows that the alkylation can be done in an interstaged reactor with at least three catalyst beds. In Table 5, an improved temperature control is achieved by also feeding propylene at each stage of the catalyst bed. The temperature rise per stage for the diluted feedstock is about 28-30 C., with the outlet temperature from the last reactor stage at 243 C. For the pure benzene feedstock, the reactor outlet temperature also decreased to 269 C. with a temperature rise of about 43-51 C. per stage. The result for the pure benzene feedstock using multiple reactor bed is similar to the result obtained in U.S. Pat. No. 8,242,320 at similar operating conditions. A temperature rise of about 50-61 C. per stage was reported. U.S. Pat. No. 8,242,320 also obtained a temperature rise of about 17-25 C. by recycling a portion of the reactor effluent but at the expense of low selectivity well below equilibrium level.

(28) The present invention affords us the opportunity to carry the alkylation reaction in a simple reactor configuration, which reflects in low capital cost of the equipment, produce high selective products, and obtain an improved temperature control in the alkylation reactor.