TWI518070B - Separating styrene from c6-c8 aromatic hydrocarbons - Google Patents

Description

Separation of styrene from C6-C8 aromatic hydrocarbons

The present invention relates to a process for reducing the styrene content of a C6-C8 aromatic hydrocarbon blend, commonly referred to as BTX, in the refining of hydrocarbons by the use of a catalyst such as methanol in the presence of a catalyst selective for etherification. The C1-C3 lower alkyl alcohol of ethanol is reacted to form the corresponding styrene ether to convert the styrene in the BTX mixture, followed by separation of the styrene ether from BTX to form BTX substantially free of styrene. The resulting styrene ether can be decomposed to recover styrene. Alternatively, styrene ether can be blended into the gasoline as an oxygenating agent to improve combustion characteristics.

Refining liquid hydrocarbons and fractionation provides a range of hydrocarbon product streams. Further refining a stream such as a hydrocarbon feed, a non-hydrotreated pyrolysis gasoline from a steam cracker, a FCC petroleum brain or a non-hydrotreated coking petroleum brain to provide a predominantly comprising benzene, toluene, ethylbenzene, styrene, sulfur A mixture of a compound and a mixture of xylenes of a C6-C8 aromatic, commonly referred to as BTX. A method for producing BTX from the FCC petroleum brain is described in U.S. Patent No. 5,685,972, issued to A.S. Pat.

BTX is a valuable raw material for the manufacture of petrochemicals and polymers and is also used as a fuel for internal combustion engines. However, its styrene content tends to polymerize and form higher molecular weight compounds that can interfere with the processing of BTX into chemical feedstocks, or can cause gelatinous residue formation to hinder the feeding of BTX for combustion. Therefore, when you want When BTX is used as a petrochemical feedstock or a liquid fuel for an internal combustion engine, it is undesirable to have styrene present in the BTX. The styrene content in BTX is reduced by the conversion of styrene to ethylbenzene by hydrogenation. The "hydrotreating" stage in converting FCC petroleum brain into both BTX and high octane gasoline is described in U.S. Patent 5,685,972.

However, ethylbenzene and styrene are of lower value when burned as a fuel. The value of BTX with styrene removed is higher than that of BTX containing styrene. Furthermore, when compared to the conversion of styrene to ethylbenzene for use as a fuel, styrene itself is much more valuable in its recovery for the manufacture of polymers or petrochemicals. The methods disclosed in, for example, U.S. Patent Nos. 3,953,300, 4,031,153, and 5,849,982 are not effective in removing and recovering styrene from BTX fractions such as pyrolysis gasoline and FCC gasoline, which contain a large amount of sulfur compounds. This is because the reactivity of styrene with hydrogen is greater than that of thiophene sulfur during hydrotreating, and hydrotreating is the only way in which the purified styrene stream is desulfurized.

What is needed is a method for removing styrene from BTX fractions more efficiently than today's BTX refining and separation processes, and converting styrene into valuable polymers and petrochemicals.

According to one aspect of the invention, a method of reducing the styrene content of a C6-C8 aromatic hydrocarbon (BTX) blend from a liquid hydrocarbon refining stream is provided. A typical BTX-containing feed from a refinery contains about 33% styrene and 67% xylene.

In one embodiment, a hydrocarbon feed stream comprising BTX comprising styrene is fed to a catalytic converter in which most of the styrene is contained in the presence of a catalyst selective for etherification. In the presence of an acidic catalyst selective for etherification The C1-C3 lower alkyl alcohol which is preferably methanol or ethanol reacts to form the corresponding styrene ether. The resulting styrene ether is separated from the stream by distillation to form a fraction comprising a hydrocarbon comprising BTX having a greatly reduced styrene content but retaining a majority of the sulfur compound, and another stream comprising a styrene ether. The hydrocarbon stream containing residual unreacted styrene is hydrogenated to form a product stream, and the C6-C8 aromatic hydrocarbon substantially free of styrene is separated from the product stream. The styrene ether can then be decomposed to recover styrene and a C1-C3 lower alkyl alcohol. Alternatively, styrene ether can be blended into the gasoline as an oxygenating agent to improve combustion characteristics.

It should be noted that although methanol or ethanol is preferred, a C3 alcohol can also be used. However, it is more expensive.

In another embodiment of the invention, the selective etherification catalyst is a sulfonic acid based polymeric cation exchange resin. In another embodiment of the invention, the acidic catalyst is a sulfonic acid macroreticular polymeric resin based on a crosslinked styrene divinylbenzene copolymer, such as sold by Rohm & Haas as TM Amberlyst 15WET, 35WET and 70. These materials are well known to be selective for etherification reactions. For example, Amberlyst 15WET is used to produce MTEB and ETBE, so its reliability is well known. It should be noted that the 15WET, 35WET and 70 names are for variants that are suitable for use at different reaction temperatures. For example, Amberlyst 15WET is ideal for etherification reactions up to 120 °C, Amberlyst 35WET is ideal for etherification reactions up to 150 °C and Amberlyst 70 is etherified for upper temperature range The reaction is ideal. Details of the nature of these materials are available under the AMBERLYST polymerization catalyst in the Rohm & Haas catalog available online. Nation® SAC-13 is another polymeric acidic sulfonic acid catalyst that can be used. However, its activity is lower than that of the Amberlyst series.

In another embodiment of the invention, in the temperature range of 80 ° C to 150 ° C The etherification reaction is carried out. Amberlyst 15WET is stable in the temperature range of 80 ° C to 120 ° C. We have found that 100 ° C is optimal for its high selectivity to styrene ether.

In another embodiment of the invention, a molar excess of alcohol is used. Preferably, when the alcohol is methanol (MeOH), the molar ratio of MeOH:styrene is 5:1.

It is also contemplated that an inorganic acidic catalyst such as a sulfated zeolite can be used to catalyze etherification, but its activity is low.

As will be apparent from the subsequent [embodiments], the composition of the product stream will depend on the choice of design of the reactor system in which the process is to be performed.

10‧‧‧ device

12‧‧‧First Stage Hydrogenation Reactor

14‧‧‧First distillation tower

16‧‧‧Second Distillation Tower

18‧‧‧Second stage hydrogenation reactor

20‧‧‧Liquid-liquid extraction section

22‧‧‧hydrocarbon feedstock

24‧‧‧feed line

26‧‧‧ Hydrogen

28‧‧‧ Hydrogen feed line

30‧‧‧Light fractions

34‧‧‧Product stream

36‧‧‧Liquid bottom fraction

38‧‧‧Heavy fraction

42‧‧‧Light fraction

44‧‧‧Product stream

46‧‧‧Light extraction

50‧‧‧ products

100‧‧‧ device

102‧‧‧First Distillation Tower

104‧‧‧Second distillation tower

106‧‧‧etherification reactor

108‧‧‧ Third distillation tower

110‧‧‧First stage hydrogenation reactor

112‧‧‧Second stage hydrogenation reactor

114‧‧‧BTX extraction section

120‧‧‧ distillate

124‧‧‧ bottom fraction

126‧‧‧ bottom fraction

130‧‧‧ distillate

132‧‧‧ middle distillate

134‧‧‧C1-C3 low carbon alkyl alcohol

138‧‧‧Equilibrium mixture

140‧‧‧Bottom

144‧‧‧ distillate

145‧‧‧ distillate

146‧‧‧Product stream

148‧‧‧Product stream

150‧‧‧

154‧‧‧ products

200‧‧‧ device

214‧‧‧Product stream

216‧‧‧ fourth distillation tower

218‧‧‧ bottom fraction

222‧‧‧ distillate

300‧‧‧ device

302‧‧‧Prereactor

304‧‧‧ catalytic distillation tower

306‧‧‧C1-C3 low carbon alkyl alcohol

308‧‧‧ Logistics

310‧‧‧BTX product stream without styrene

312‧‧‧Liquid styrene ether stream

320‧‧‧Condenser

322‧‧‧ reboiler

400‧‧‧ device

402‧‧‧First reactor

404‧‧‧Second reactor

406‧‧‧ liquid feed

408‧‧‧Methanol

410‧‧‧ effluent

412‧‧‧ effluent

PFR1‧‧‧ plug flow reactor 1

PFR2‧‧‧ plug flow reactor 2

For a fuller understanding of the present invention and other objects and advantages,

Figure 1 is a schematic flow diagram labeled as prior art and a method for producing BTX.

2 is a schematic flow diagram of a first embodiment of a method for reducing styrene content in BTX by converting styrene to styrene ether.

3 is a schematic flow diagram of a second embodiment of a method for reducing styrene content in BTX by converting styrene to styrene ether.

4 is a schematic flow diagram of a third embodiment of a method for reducing styrene content in BTX by converting styrene to styrene ether in a device having a pre-reactor and a catalytic distillation column.

Figure 5 is a schematic representation of a two stage plug flow reactor for modeling methanol styrene ether synthesis.

Figure 6A is a schematic representation of the composition of the reaction mixture along with the first reactor illustrated in Figure 5 A graph of the distance, the first reactor is used to react methanol with styrene in p-xylene.

Figure 6B is a graph showing the compositional profile of the reaction mixture as a function of the distance along the second reactor illustrated in Figure 5, the second reactor being used to react additional methanol with styrene in p-xylene.

Figure 7A is a graph showing the composition profile as a function of the distance along the prereactor as illustrated in Figure 4 for reacting methanol with styrene in p-xylene to form a feed catalysis. The stream in the distillation column.

Fig. 7B is a graph showing the composition profile as a function of the height of the catalytic distillation column illustrated in Fig. 4.

Figure 8 is a graph illustrating the conversion of styrene to styrene ether using various catalysts according to the present invention.

The following description contains information obtained through laboratory experiments and simulations using ASPEN PLUS® software.

1 is a prior art and schematically illustrates a typical method for producing a BTX 50 having a reduced styrene content from a hydrocarbon feed 22. The hydrocarbon feed 22 can be any refinery stream containing a light aromatic having a higher styrene content, such as unhydrotreated pyrolysis gasoline, FCC petroleum brain or coker brain.

The apparatus 10 for use in the process has a series of reactors and columns comprising: a first stage hydrogenation reactor 12, a first distillation column 14, a second distillation column 16, a second stage hydrogenation reactor 18, and a liquid-liquid extraction zone. Paragraph 20.

Feeding the hydrocarbon feed 22 comprising styrene to the first stage reaction via feed line 24 In the first stage reactor, the hydrocarbon feed 22 is reacted on the first stage catalyst with hydrogen 26 fed via a hydrogen feed line 28. The catalyst is conventional Pd or Ni supported on alumina to convert the diene in the hydrocarbon feed 22 to a monoolefin. The product stream 34 from this reactor is fed to a first distillation column 14 where it is separated into a light fraction 30 comprising primarily C5 hydrocarbons and a liquid bottoms fraction 36. The liquid bottom fraction 36 is fed to a second distillation column 16 where it is separated into a heavy fraction 38 comprising C9 and higher hydrocarbons than C9, and a light comprising BTX, ethylbenzene and styrene. Fraction 42. The light fraction 42 is fed to a second stage hydrogenation reactor 18 where it is reacted with hydrogen 26 on a second stage catalyst. The catalyst is a conventional two-layer catalyst comprising a NiMo upper layer and a CoMo lower layer to convert the olefin to paraffin and to convert the sulfur compound to hydrogen sulfide. The hydrogen sulfide thus formed is removed from the mixture downstream of the second stage hydrogenation reactor 18. The product stream 44 from the second stage hydrogenation reactor 18 is fed to a liquid-liquid extraction section 20 where it is separated into light strips of residue 46 and contains BTX and less The product of ethylbenzene 50. This is the method currently used in most oil refineries. Hydrogenation of styrene (H2 consumption adds cost) to ethylbenzene (lower value). The advantages of the invention are then listed.

Referring to Figures 2 through 7B, three specific examples of the present invention will now be described, and the performance and advantages of the present invention over the prior art method illustrated in Figure 1 will be shown.

Figure 2 illustrates a first specific example of the method of the present invention. Apparatus 100 for use in the process includes a first distillation column 102, a second distillation column 104, an etherification reactor 106, a third distillation column 108, a first stage hydrogenation reactor 110, a second stage hydrogenation reactor 112, and a BTX extraction. Section 114. The styrene-containing hydrocarbon feed 22 is fed to a first column 102 where it is separated by distillation into a distillate 120 comprising predominantly C5 hydrocarbons and a C6-C8 enriched hydrocarbon It also contains bottom fraction 124 of styrene. The bottoms fraction 124 is fed to a column 104 where it is distilled to bottoms. Fraction 126, middle distillate 132 and distillate 130. Distillate 130 is rich in C6 and C7 aromatic hydrocarbons. The middle fraction 132 is rich in xylene, styrene and ethylbenzene, ie C8 aromatic hydrocarbons. The bottom fraction 126 primarily comprises C9+ hydrocarbons.

The middle distillate 132, C1-C3 lower alkyl alcohol 134 is fed to an etherification reactor 106 where it is reacted on an acidic catalyst (not shown) which is selective for etherification, An equilibrium mixture 138 (Reaction Formula 1) enriched in the corresponding styrene ether is formed, wherein the C1-C3 lower alkyl alcohol 134 is preferably methanol. Alternatively, ethanol can be used. It has been experimentally found that when the reaction 1 is carried out at about 100 ° C, the selective etherification catalyst is preferably an acidic resin such as Amberlyst 15 ^TM resin. When using Amberlyst 15WET or 35WET, tests with BTX feeds containing about 33% styrene and 67% xylene showed very little difference in activity.

C ₆ H ₅ CH=CH ₂ +CH ₃ OH ←→ C ₆ H ₅ CH(CH ₃ )OCH ₃ (1)

As shown in Fig. 8, other similar acidic resin catalysts as described above can also be used. In detail, Figure 8 illustrates a stirrer at 1000 rpm with a MeOH:styrene feed ratio of 5:1 at a temperature of 100 ° C using 10 g of various catalysts. The conversion of styrene to styrene ether at speed.

The liquid equilibrium mixture 138 is fed to a third distillation column 108 where it is fractionated into a styrene ether-rich bottoms 140, containing residual unreacted styrene and substantially all of the sulfur compounds. The xylene-containing distillate 144 and the distillate 145 containing mainly unreacted methanol. Distillate 145 is recycled to etherification reactor 106.

The distillate 130 from the second distillation column 104 is co-fed into the first stage hydrogenation reactor 110 together with the distillate 144 from the third distillation column 108 and hydrogen 26 at the first stage. In the hydrogenation reactor, it is reacted on a first stage catalyst (the same first stage catalyst as described above in [0018]). The product stream 146 from the first stage hydrogenation reactor 110 and the hydrogen 26 are fed to a second stage hydrogenation reactor 112 where it is in the second stage catalyst (and above [0018] The same second stage catalyst described above is reacted to saturate the olefin and desulfurize the sulfur compound. The first stage hydrogenation reactor 110 and the second stage hydrogenation reactor 112 operate under different conditions suitable for the various reactions and catalysts used in the various stages of the process, as will be familiar to those skilled in the art. See, for example, the announcement of Axens. The removed sulfur product stream 148 from the second stage hydrogenation reactor 112 is fed to a BTX extraction section 114 where it is separated into raffinate 150 and BTX-rich and substantially Product 154 free of styrene or styrene ether.

When the C1-C3 lower alkyl alcohol 134 is methanol and the methanol to styrene ratio is 1:1, we obtain 78.2% conversion in the single etherification reactor 106 illustrated in Figure 2. Optionally, in a modified form of apparatus 100, product stream 138 from etherification reactor 106 can be fed to at least one additional cascaded etherification reactor (not shown) where the at least one additional series is placed. In the etherification reactor, it is reacted with additional methanol. The conversion using a series of two etherification reactors was 94%. Details of this modification are given in the examples.

One concern is that methanol may be converted to dimethyl ether on the etherification catalyst (Scheme 2). The absence of detectable products resulting from such reaction (as determined by GC) was determined experimentally as indicated by the products listed in the tables in the Examples. The results indicate that the selectivity of the catalyst for the formation of styrene ether is greater than for the formation of dimethyl ether.

2 CH ₃ OH ←→ (CH ₃ ) ₂ O+H ₂ O (2)

Figure 3 is a schematic illustration of a second embodiment of the method of the present invention. Apparatus 200 for a second embodiment of the method contains many of the elements found in apparatus 100 and uses the same element symbols to identify such elements. The difference in the second embodiment of the process is that the C5 hydrocarbon-containing distillate 222 from the first distillation column 102 and the C6 and C7 hydrocarbon-containing distillate 130 from the second distillation column 104 are from the third distillation column. The distillate 144 of 108 is co-fed together into a first stage hydrogenation reactor 110 in which the olefin is passed through a first stage catalyst (the same as the first stage catalyst in [0018]) It is hydrogenated by reacting with hydrogen gas 26. In addition, product stream 214 from first stage hydrogenation reactor 110 is fed to a fourth distillation column 216 where it is separated into distillate 120 and bottoms fraction 218. Distillate 120 primarily comprises C5 hydrocarbons. The bottoms fraction 218 is fed to a second stage hydrogenation reactor 112 where the olefins and sulfur compounds are hydrogenated to form substantially free, in a first embodiment of the process using apparatus 100. Sulfur product stream 148.

It will be appreciated that additional stages with other hydrogenation reactors and distillation columns can be incorporated to further refine the BTX products of the above specific examples.

Figure 4 is a schematic illustration of a third embodiment of the method of the present invention. Apparatus 300 for use in a third embodiment of the method includes a pre-reactor 302 and a catalytic distillation column 304. First, the hydrocarbon feed 22 is first reacted in a pre-reactor 302 with a C1-C3 lower alkyl alcohol 306 selected from the group consisting of methanol and ethanol on a preferred acidic etherification catalyst as described above to form a corresponding styrene-rich, A stream 308 of residual unreacted styrene, residual unreacted C1-C3 lower alkyl alcohol, and C6-C8 aromatic hydrocarbon. Stream 308 and additional methanol or ethanol 306 are fed to catalytic distillation column 304 to react with residual unreacted styrene to recover substantially styrene free BTX product stream 310 and liquid styrene ether stream 312. Catalytic distillation column 304 includes a condenser 320 at the top and a reboiler 322 at the bottom. It should be noted that This particular example is only applicable to hydrocarbon feeds that are substantially pure BTX because no low carbon number and high carbon number hydrocarbons are removed from the feed. For this particular embodiment of the invention, the low carbon number C5 and high carbon number C9+ hydrocarbons are first separated by distillation and passed elsewhere to the refinery. This is described in Figure 1. Therefore, in this particular example, we only process fractions of the C6-C8 aromatic stream.

The method of modeling with ASPEN PLUS® has been characterized based on the results of the laboratory experiments described in the examples below, and its advantages have been identified.

The advantages of operating the method of the invention (especially for BTX aromatics from pyrolysis gasoline) when compared to prior art methods are:

• The BTX product contains almost no ethylbenzene produced by the hydrogenation of styrene. In the prior art methods, typically contain high amounts of ethylbenzene of C ₈ aromatics separated or sent to the gasoline pool, and thus have a low value. If the amount of remaining aromatic C ₈ of ethylbenzene was the excessively high, increasing the cost of downstream processing (e.g. purification xylol) of.

• Removal of most of the styrene prior to processing the stream in the hydrogenation reactor reduces the volume that must be treated through the reactors, and thus the ability of the reactors to treat the desired materials is enhanced. This is extremely significant because hydrogenation reactors are often the bottleneck in the process of petroleum brain crackers or gasoline crackers.

• In addition, low levels of residual styrene will extend the operating life of the catalyst in the hydrogenation reactor.

• There is no need to consume hydrogen to convert styrene to ethylbenzene, and thus the hydrogen consumption of the overall process is reduced.

● Styrene ether can be blended into gasoline as an oxygenating agent to improve combustion characteristics or it can be subdivided It is decomposed into styrene and methanol (reverse reaction of Reaction Scheme 1).

Example

Example 1. Methanol and styrene were reacted in p-xylene in a single etherification reactor.

The plug flow reactor (PFR) was modeled using the Aspen Plus (version 7.1) RPlug reactor model to react styrene with methanol (Reaction 1) to form methanol styrene ether (ie 1-methoxyl) Ethylbenzene is referred to as MSE in the table below. The laboratory rate data for the reaction in xylene solvent showed an empirical relationship that is proportional to the concentration of styrene and inversely proportional to the concentration of methanol. The model includes consideration of the methanol adsorption effect to account for the rate increase at low methanol concentrations, while also explaining the inhibition by methanol at high methanol concentrations. The reaction model also takes into account the inverse reaction by incorporating the equilibrium constant (K _eqm ) taken from the literature (Verevkin et al, J. Chem. Eng. Data, 46 , 984-990, 2001).

The vapor-liquid equilibrium calculation was performed using the NRTL-RK property method.

The binary pair parameters involving MSE and the binary interaction parameters of styrene-methanol were evaluated.

The reactor was designed as a plug flow reactor PFR. The size is for a 1 mol/h styrene flow rate in a feed mixture containing 0.35 mass fraction of styrene in xylene. Figure 5 is a schematic representation of a two stage plug flow reactor unit 400 for methanol styrene ether synthesis. Table 1 shows the operating parameters of the first reactor 402 (labeled PFR1) and the second reactor 404 (labeled PFR2). The tower is designed to operate at a pressure of 4 atm and a temperature of 100 °C. Liquid feed 406 containing styrene in xylene is mixed with stoichiometric stoichiometric methanol 408 equivalent to styrene and subsequently fed to first reactor 402. The effluent 410 from the first reactor 402 is mixed with another identical amount of methanol 408 and subsequently fed to the second reactor 404. The effluent 412 from the second reactor 404 is primarily the corresponding styrene ether. Therefore, the methanol and styrene used in the process The total feed ratio is 2:1. FIG. 6 illustrates a liquid composition profile along the length of the first reactor 402. It can be seen that a balanced composition is obtained 0.6 m from the inlet of the reactor. Table 2 is a summary of the logistics of the first reactor 402 (labeled PFR1) and the second reactor 404 (labeled PFR2). The styrene conversion in the first reactor 402 was 78.2% and the conversion of residual styrene from the first reactor 402 in the second reactor 404 was 73.5%, forming the total benzene of the corresponding methanol-styrene ether 408. The ethylene conversion was 94.2%. Thus, in one reactor with a methanol to styrene ratio of 1, there is 78.2% conversion. By adding 1 equivalent of methanol to the feed to the second reactor, the total conversion of styrene was 94%.

In view of the stability, optimum activity and selectivity of Amerlyst 15WET at a reaction temperature of 100 ° C, it is the catalyst used in the model calculation. Other reaction temperatures can be used depending on the catalyst selected.

Example 2. Ethanol and styrene were reacted in p-xylene in a series of two reactors.

In a similar set of measurements and models, we have shown that the reaction rates of ethanol and methanol are similar, and that a list of similar products in similar proportions is formed using either alcohol.

Example 3. Methanol and styrene were reacted in p-xylene in a series of pre-reactors and catalytic distillation columns.

Referring to Figure 4, an alternative configuration of apparatus 300 provides a third of the above methods. Body instance. The method involves a pre-reactor (PFR1) 302 upstream of a catalytic distillation (CD) column 304. The prereactor 302 is a plug flow reactor having the same operating conditions as PFR1 in Table 1 (corresponding to the first reactor 402 described in Example 1 and illustrated in Figure 5), and the catalytic distillation column 304 is in advance. Downstream of reactor 302. Catalytic distillation column 304 operates with full condenser 320 and reboiler 322. The modeled CD tower 304 has 15 stages and operates at a pressure of 1 atm. The reaction zone temperature is between 104 ° C and 133 ° C. The hydrocarbon feed 22 is mixed with a stoichiometric amount of methanol 306 equivalent to the styrene content of the hydrocarbon feed 22 and fed to the prereactor 302. The effluent from the prereactor 302 is fed over the second stage of the CD column 304. Additional methanol 306 is fed below stage 3 to react with residual styrene from the effluent from prereactor 302 and thereby achieve a high total styrene conversion (99%). Table 3 gives the operating parameters of the pre-reactor 302 and the catalytic distillation column 304. The total feed ratio for methanol:styrene used in the modeled process was 6:1. Table 4 is an overview of the logistics of pre-reactor 302 and catalytic distillation column 304, and Table 5 shows an overview of the various stages of catalytic distillation column 304.

1. wherein the etherification catalyst is an acidic cation exchange resin catalyst.

22‧‧‧hydrocarbon feedstock

26‧‧‧ Hydrogen

100‧‧‧ device

102‧‧‧First Distillation Tower

104‧‧‧Second distillation tower

106‧‧‧etherification reactor

108‧‧‧ Third distillation tower

110‧‧‧First stage hydrogenation reactor

112‧‧‧Second stage hydrogenation reactor

114‧‧‧BTX extraction section

120‧‧‧ distillate

124‧‧‧ bottom fraction

126‧‧‧ bottom fraction

130‧‧‧ distillate

132‧‧‧ middle distillate

134‧‧‧C1-C3 low carbon alkyl alcohol

138‧‧‧Equilibrium mixture

140‧‧‧Bottom

144‧‧‧ distillate

145‧‧‧ distillate

146‧‧‧Product stream

148‧‧‧Product stream

150‧‧‧

154‧‧‧ products

Claims (19)

A method for producing a C6-C8 aromatic hydrocarbon substantially free of styrene, comprising (a) providing a hydrocarbon feed comprising a C6-C8 aromatic hydrocarbon comprising styrene, and (b) providing the hydrocarbon feedstock The majority of the styrene is reacted with a C1-C3 lower alkyl alcohol in the presence of an acidic catalyst selective for etherification to form the corresponding styrene ether; (c) separating the feed by distillation A styrene ether and the hydrocarbons, (d) hydrogenating residual styrene in the hydrocarbon feed to form a product stream, and (e) separating a C6-C8 aromatic hydrocarbon substantially free of styrene from the product stream. The method of claim 1, comprising the preliminary step prior to step (b): distilling the hydrocarbon feed to obtain a C6-C8 aromatic hydrocarbon-rich stream; and distilling the C6-C8 aromatic hydrocarbon-rich The stream is obtained to obtain a first stream rich in C6 and C7 aromatic hydrocarbons, a second bottom stream mainly containing C9 and higher than C9, and a third stream rich in xylene and ethylbenzene and containing styrene, wherein The third stream is processed according to step (b). The method of claim 2, wherein in step (c), the feed containing styrene ether is separated by distillation to recover a liquid stream rich in the styrene ether and rich in hydrocarbons and containing residual unreacted Volatile stream of styrene. The method of claim 3, wherein in step (d), the volatile stream rich in hydrocarbons and containing residual unreacted styrene is combined with the first stream rich in C6 and C7 hydrocarbons, and The combined stream is hydrogenated in a continuous reactor to hydrogenate the olefin, sulfur compound and residual unconverted styrene to form a hydrocarbon product stream, and in step (e), the liquid product stream is separated from the hydrocarbon product stream by liquid-liquid extraction. A C6-C8 aromatic hydrocarbon substantially free of styrene. The method of claim 4, which comprises repeating step (b) before step (c) To form additional styrene ether. The method of claim 5, wherein the styrene-containing hydrocarbon feed is reacted with an alcohol selected from the group consisting of methanol and ethanol on an acid etherification catalyst in a series of continuous etherification reactors to form the corresponding styrene. An ether, which is fed to the reaction mixture effluent from an etherification reactor, and then fed to the lower etherification reactor in the series of reactors, whereby styrene is present in excess of the hydrocarbon feed. The total amount of methanol in excess. The method of claim 1, wherein the C1-C3 lower alkyl alcohol is used in step (b) in excess of the styrene molar excess. The method of claim 7, wherein the C1-C3 lower carbon alkyl alcohol is methanol or ethanol. The method of claim 8, wherein the etherification reaction is carried out at a temperature of from 80 °C to 150 °C. The method of claim 9, wherein the etherification reaction is carried out at a temperature of 100 °C. The method of claim 10, wherein the alcohol is methanol and the molar ratio of methanol:styrene is 5:1. The method of claim 8, wherein the acidic catalyst is an acidic cation exchange resin catalyst. The method of claim 1, wherein the hydrocarbon feed is a substantially pure C6-C8 aromatic hydrocarbon, wherein the hydrocarbon feed is first passed over a prereactor on an acidic catalyst selective for etherification. a C1-C3 lower alkyl alcohol selected from the group consisting of methanol and ethanol to react to form the corresponding styrene ether, residual unreacted styrene, residual unreacted C1-C3 lower carbon alkyl alcohol, and a product stream of a C6-C8 aromatic hydrocarbon, and feeding the product stream and another C1-C3 lower alkyl alcohol to a catalytic distillation column, recovering C6-C8 substantially free of styrene from the catalytic distillation column Aromatic hydrocarbons and liquid styrene ethers. The method of claim 13, wherein the C1-C3 lower alkyl alcohol is methanol or ethanol. The method of claim 14, wherein the etherification reaction is carried out at a temperature of from 80 °C to 150 °C. The method of claim 15, wherein the alcohol is methanol and the molar ratio of methanol:styrene is 5:1. The method of claim 16, wherein the acidic catalyst is an acidic cation exchange resin catalyst. The method of claim 1, further comprising the step (f) of decomposing the styrene ether in the product stream to recover styrene and alcohol. The method of claim 1, wherein the styrene ether is recovered for blending with gasoline to improve combustion characteristics.