Process for producing C2-C4 olefins from methanol

Abstract

The invention relates to a process for the preparation of C2-C4 olefins from methanol, comprising the following steps: A) feeding a feed stream A comprising methanol into a dimethyl ether fixed bed reactor and catalytically converting methanol to dimethyl ether to obtain a product stream A1 comprising dimethyl ether, methanol and water vapor; b) mixing stream A1 with one or more hydrocarbon recycle streams R comprising C2-C6 hydrocarbons and catalytically converting it in an olefin fixed bed reactor to a crude product stream B comprising C2-C4 olefins, C5-C6 hydrocarbons and C6 + hydrocarbons; c) cooling the crude product stream B to obtain a hydrocarbon crude product stream C; d) separating the hydrocarbon crude product stream C into at least one stream comprising ethylene, at least one stream comprising propylene, at least one stream comprising butene, at least one stream comprising C5-C6 hydrocarbons, and at least one byproduct stream N comprising C6 + hydrocarbons; e) recycling a portion of the C2-C4 olefins selected from the group consisting of ethylene, propylene and butenes obtained in step D) and at least a portion of the C5-C6 hydrocarbons obtained in step D) as one or more hydrocarbon recycle streams R to step B); f) obtaining from these streams obtained in step D) at least one value product stream F1 comprising ethylene, at least one product stream F2 comprising propylene and optionally one or more value product streams F3 comprising butene; g) feeding at least a portion of the product stream F2 comprising propylene to an olefin metathesis reactor and converting propylene to a product stream G comprising ethylene and butene, leaving a substream F4 of stream F2 as a valuable product stream; h) separating from the product stream G a value product stream H1 comprising ethylene and a value product stream H3 comprising butene; i) optionally recycling at least a portion of the butene present in the value product stream H3 to step B), leaving a substream H4 as the value product stream; k) discharging the at least one byproduct stream N comprising C6 + hydrocarbons; wherein 30% to 60% by weight of ethylene, 30% to 60% by weight of propylene and 0% to 30% by weight of butene are present and recovered as valuable products, based on 100% by weight of C2-C4 olefins present as valuable products in streams F1, F3, F4, H1 and H3 or H4, and recycling from 0% to 10% of ethylene, from 30% to 60% of propylene and from 40% to 80% of butene into step B) based on C2-C4 olefins present in the one or more recycle streams R and in the valuable product and byproduct streams F1, F3, F4, H1, N and H3 or H4, and directing from 20% to 40% of propylene into the olefin metathesis reactor based on the crude product stream B, and recycling from 0% to 10% of ethylene, from 30% to 60% of propylene and from 40% to 80% of butene into step B) based on the C2-C4 olefins present in the one or more recycle streams R and in the valuable product and byproduct streams F1, F3, F4, H1, N and H3 or H4. Or 5% to 30% of ethylene, 0% to 10% of propylene and 40% to 85% of butene are recycled to step B) on the basis of C2-C4 olefins present in the one or more recycle streams R and the valuable product and byproduct streams F1, F3, F4, H1, N and H3 or H4, and 50% to 70% of propylene is directed to the olefin metathesis reactor on the basis of the crude product stream B.

Description

[0001] The present invention relates to a process for preparing C2-C4 olefins from methanol.

[0002] It is known that propylene can be produced by converting a methanol / dimethyl ether mixture in a fixed-bed reactor (methanol to propylene, MTP reactor). Known fixed-bed reactors operate with zeolite catalysts at temperatures of about 480°C.

[0003] US 2010 / 145125 A1 discloses a method for producing light olefins by converting methanol and ethanol. The method comprises feeding a first portion of feed into a reaction zone containing a catalyst via a distributor at the bottom of a fluidized bed reactor, feeding a second portion of feed into the reaction zone from at least one location above the distributor, contacting the feed with the catalyst and reacting to produce a stream containing ethylene and propylene, wherein the first and second portions of feed each independently contain methanol and / or ethanol, provided that the entire feed contains both methanol and ethanol and the weight ratio of methanol to ethanol in the entire feed is in the range of 99:1 to 0.1:1.

[0004] CN 216106699 U discloses a method for producing ethylene, propylene, and butenes by catalytic dehydration of methanol. The system comprises a reaction unit and a separation unit, wherein the reaction unit includes a preliminary reactor, a process steam column, and a main reactor, and the separation unit includes a quencher and a compressor. The main reactor contains a ZSM-5 molecular sieve catalyst; the separation unit includes an ethylene column, a propylene column, and a butene column. Ethane, propane, butane, and C5 and C6 hydrocarbons are partially recycled to the main reactor; the remaining components are discharged as by-products. This unit can also be used to produce butene while reducing the amount of recycled hydrocarbons and lowering the unit's energy consumption. Only saturated hydrocarbons are recycled to the main reactor.

[0005] CN 110218138 A discloses a method for increasing olefin yield in a methanol-to-propylene (MTP) process, wherein C2, C4, and C5-C7 hydrocarbons are recycled to the MTP reactor. In one example, in a 500,000 t / a methanol-to-propylene plant, the methanol feed is 210 t / h, and the recycled C2, C4, and C5-C7 hydrocarbon feeds are 27 t / h, 40 t / h, and 150 t / h, respectively. Ethylene production is 1.5 t / h, and propylene production is 60 t / h.

[0006] There is no mention of a co-feed of ethanol. The product of value obtained is very predominantly propylene.

[0007] US 11,136,278 B2 discloses a process for converting propylene to ethylene, the process comprising feeding a propylene feed stream to a C3 metathesis reactor and converting it into ethylene and 2-butene; separating in a fractionation system into an ethylene fraction, a C3 fraction, a C4 fraction, and a C5+ fraction; feeding at least a portion of the C3 fraction to a C3 metathesis reactor to produce additional ethylene; feeding the C4 fraction to a C4 isomerization / metathesis reaction zone and converting the C4 fraction by: (i) isomerizing a portion of the 2-butene to 1-butene, (ii) metathesizing 1-butene and 2-butene to propylene and 2-pentene, and / or (iii) metathesizing 1-butene itself to ethylene and 3-hexene; obtaining a product stream comprising ethylene, propylene, butenes, pentenes, and hexenes and feeding it to the fractionation system.

[0008] US 11,046,627 B2 discloses a process for preparing propylene from ethylene and butene, the process comprising:

[0009] (a) producing a first product stream comprising ethylene and a second product stream comprising butenes in a methanol to propylene (MTP) system comprising a zeolite catalyst and a methanol to olefins (MTO) system comprising a silicoaluminophosphate (SAPO) molecular sieve catalyst, wherein the MTP or MTO system comprises:

[0010] (i) a first reactor that converts methanol into dimethyl ether; and

[0011] (ii) a second reactor that converts dimethyl ether to a C2+ product stream comprising propylene, ethylene, and butenes;

[0012] (b) feeding the first and second product streams to a metathesis reaction unit and converting the ethylene and butenes into a metathesis product stream comprising propylene and unconverted ethylene and butenes;

[0013] (c) separating propylene from unconverted ethylene and butenes to produce a propylene product stream and a stream comprising unconverted ethylene and butenes;

[0014] (d) recycling the stream comprising unconverted ethylene and butenes from step (c) to the MTP or MTO system.

[0015] EP 2 892 863 B1 comprises a process for preparing linear butenes from methanol, comprising the following steps: a) providing methanol; b) converting the methanol in a first reaction stage into a first reaction mixture comprising dimethyl ether and water, with or without unconverted methanol; c) converting the dimethyl ether in a second reaction stage into a second reaction mixture comprising propene and further hydrocarbons having 2, 4 and 5 carbon atoms, wherein the second reaction stage is at least partially fed by the first reaction mixture; d) working up the second reaction mixture to obtain a propene-rich fraction and at least one propene-low fraction, wherein the propene-low fraction is partly returned to the second reaction stage; e) converting the propene in a third reaction stage into a third reaction mixture comprising ethylene and linear butenes selected from the group consisting of 1-butene, cis-2-butene, trans-2-butene, wherein the third reaction stage is at least partially fed by the propene-rich fraction; f) working up the third reaction mixture into a target fraction rich in linear butenes and an ethylene-rich fraction.

[0016] The object of the present invention is to provide a flexible process for preparing C2-C4 olefins from methanol in a methanol to olefins process (MTO process), wherein the proportions of ethylene, propylene and butenes in the valuable product stream obtained from the process can be varied within wide ranges and the volume of the recycle stream which is recirculated into the MTO process can be reduced overall.

[0017] This object is achieved by a process for preparing C2-C4 olefins from methanol, comprising the following steps:

[0018] A) feeding a feed stream A comprising methanol into a dimethyl ether fixed bed reactor and catalytically converting the methanol into dimethyl ether to obtain a product stream A1 comprising dimethyl ether, methanol and water vapor;

[0019] B) mixing the stream A1 with one or more hydrocarbon recycle streams R comprising C2-C6 hydrocarbons and catalytically converting them in an olefin fixed bed reactor into a stream comprising C2-C4 olefins, C5-C6 hydrocarbons and C6 + a crude hydrocarbon product stream B;

[0020] C) cooling the crude product stream B to obtain a hydrocarbon crude product stream C;

[0021] D) separating the crude hydrocarbon stream C into at least one stream comprising ethylene, at least one stream comprising propylene, at least one stream comprising butenes, at least one stream comprising C5-C6 hydrocarbons, and at least one stream comprising C6 + a hydrocarbon by-product stream N;

[0022] E) recycling a portion of the C2-C4 olefins selected from ethylene, propylene and butenes obtained in step D) and at least a portion of the C5-C6 hydrocarbons obtained in step D) as one or more hydrocarbon recycle streams R to step B);

[0023] F) obtaining from the streams obtained in step D) at least one product stream F1 comprising ethylene, at least one product stream F2 comprising propylene and optionally one or more product streams F3 comprising butenes;

[0024] G) feeding a portion of the product stream F2 comprising propene to an olefin metathesis reactor and converting the propene into a product stream G comprising ethylene and butenes, leaving a substream F4 of stream F2 as a valuable product stream;

[0025] H) separating from the product stream G a product-of-value stream H1 comprising ethylene and a product-of-value stream H3 comprising butenes;

[0026] I) optionally recycling a portion of the butenes present in the product of value stream H3 into step B), leaving stream H4 as product of value stream;

[0027] K) discharging the at least one C6 + a hydrocarbon by-product stream N;

[0028] in

[0029] Based on 100% by weight of the C2-C4-olefins present as valuable products in the streams F1, F3, F4, H1 and H3 or H4, 30% to 60% by weight of ethylene, 30% to 60% by weight of propylene and 0% to 30% by weight of butenes are present and recovered as valuable products, and based on the C2-C4-olefins present in the one or more recycle streams R and the valuable products and by-product streams F1, F3, F4, H1, N and H3 or H4, 0% to 10% of the ethylene, 30% to 60% of the propylene and 40% to 80% of the butenes are recycled to step B) or 5 to 30% of ethylene, 0 to 10% of propylene and 40 to 85% of butenes, based on the C2-C4 olefins present in the recycle stream(s) R and the valuable products and by-product streams F1, F3, F4, H1, N and H3 or H4, are recycled to step B), and 50 to 70% of propylene, based on the crude product stream B, are directed to the olefin metathesis reactor.

[0030] Olefin metathesis allows the composition of non-ideal olefin products to be closely aligned with the desired olefin product composition. The alternative is to recycle the unwanted olefins, which, on the one hand, increases the recycle volume and, therefore, the separation intensity (power and steam requirements) of the MTO process. On the other hand, due to the numerous chemical reactions during the MTO process, adjusting the olefin product range solely by recycling the unwanted olefins is only possible with a high level of development intensity and rapidly leads to an increase in the amount of by-products.

[0031] In a preferred embodiment, the method of the present invention comprises the following steps:

[0032] A1) feeding a feed stream A comprising methanol into a dimethyl ether fixed bed reactor and catalytically converting the methanol into dimethyl ether to obtain a product stream A1 comprising dimethyl ether, methanol and water vapor;

[0033] A2) mixing at least a portion of the product stream A1 with at least one hydrocarbon recycle stream R comprising C2-C6 hydrocarbons and a steam stream to obtain a second feed stream A2;

[0034] B1) heating the second feed stream A2 in one or more heat exchangers to a temperature in the range of 430° C. to 500° C. and feeding it to an olefin fixed bed reactor, wherein the heating can also be carried out before mixing the individual substreams in step A2) to obtain the feed stream A2;

[0035] B2) catalytic conversion of feed stream A2 at a temperature in the range of 430°C to 520°C into a mixture comprising ethylene, propylene, butenes, additional C2-C6 hydrocarbons, C7 + a crude product gas stream B of hydrocarbons, methanol, and water vapor;

[0036] C1) cooling the crude product gas stream B to a temperature in the range of 170° C. to 220° C. in one or more heat exchangers by heat exchange with the feed stream A2;

[0037] C2) further cooling the crude product gas stream B to a temperature in the range of 30° C. to 60° C. under condensation of water and methanol by contact with at least one aqueous quench circulation stream K to obtain a water- and methanol-depleted hydrocarbon crude product gas stream C;

[0038] D) separation of the crude hydrocarbon gas stream C into a product-of-value stream comprising propene, optionally a product-of-value stream comprising ethylene, a product-of-value stream comprising butenes, at least one recycle stream comprising C5-C6 hydrocarbons, and at least one recycle stream comprising C6 + Hydrocarbon by-product stream.

[0039] In step A1), a feed stream A comprising methanol is fed into a dimethyl ether fixed bed reactor and the methanol is catalytically converted into dimethyl ether to obtain a product stream A1 comprising dimethyl ether, methanol and water vapor.

[0040] If, based on 100% by weight of the C2-C4-olefins obtained as products of value, 30 to 60% by weight of ethylene, 30 to 60% by weight of propylene and 0 to 30% by weight of butenes are obtained as products of value, the present invention comprises conducting 20 to 40% of propylene, based on the crude product stream B, to the olefin metathesis reactor and recycling 0 to 10% of ethylene, 30 to 60% of propylene and 40 to 80% of butenes, based on the C2-C4-olefins present in the one or more recycle streams R and the products of value and by-product streams F1, F3, F4, H1, N and H3 or H4, to step B).

[0041] Alternatively, 50 to 70% of the propylene, based on the crude product stream B, can be directed to the olefin metathesis reactor and 5 to 30% of the ethylene, 0 to 10% of the propylene and 40 to 85% of the butenes, based on the C2-C4 olefins present in the recycle stream(s) R and the valuable product and by-product streams F1, F3, F4, H1, N and H3 or H4, are recycled to step B).

[0042] 100% by weight of products of value are based on the C2-C4-olefins present in streams F1, F3, F4, H1 and H3 or H4 which are not recycled and not fed to the metathesis reactor.

[0043] The dimethyl ether fixed-bed reactor can be designed in various ways. Typically, a feed gas stream A containing methanol is heated to a temperature above 250°C and fed into the fixed-bed reactor. The catalyst used is typically gamma-alumina. The conversion temperature is between 250°C and 450°C, and the pressure is between 1 bar and 25 bar, for example, 4 bar. The methanol conversion is typically 50% to 90%, preferably 65% ​​to 85%, for example, 75%.

[0044] In step A2), at least a portion of the stream A1 is mixed with one or more hydrocarbon recycle streams R comprising C2-C6 hydrocarbons and a steam stream to obtain a feed gas stream A2. Typically, this portion of stream A1 is at least 50% by weight and preferably up to 90% by weight. Another portion A1-2 of stream A1, preferably at least 10% by weight, can be fed directly into one or more trays of a fixed-bed olefin reactor. This portion of stream A1 is typically cooled before being fed into the trays of the fixed-bed olefin reactor, preferably to a temperature in the range of 30°C to 60°C. This substream A1-2 is preferably fed into the reactor in liquid form.

[0045] If the olefin fixed bed reactor is operated and cooled isothermally, the cooling of the substream A1-2 can also be omitted. Isothermal operation can be achieved, for example, in the manner described in WO 2017 / 102096 A1.

[0046] For example, a fixed-bed olefin reactor can be equipped with heat transfer surfaces that operate, for example, with liquid salt or high-pressure steam as the heat transfer medium. As the heat transfer medium flows through the heat transfer surfaces in the reactor, the generated heat of reaction is removed from the reactor, and the reactor is thus operated isothermally. In order to achieve the desired product distribution in the product gas stream B, substream A1-2 can also be fed to an intermediate stage of the fixed-bed olefin reactor.

[0047] The at least one hydrocarbon recycle stream R from steps D) and optionally G) of the removal of C2-C4 olefins typically comprises C2-C6 hydrocarbons. Depending on the proportions in which ethylene, propylene, and butenes are obtained as valuable products, the at least one hydrocarbon recycle stream typically comprises C2-C4 hydrocarbons in an amount of 40% to 90% by weight. Prior to mixing, the at least one hydrocarbon recycle stream typically has a temperature in the range of 100° C. to 175° C., preferably in the range of 130° C. to 160° C.

[0048] The product stream A1 from the dimethyl ether fixed-bed reactor is also mixed with a steam stream. The steam stream is typically at a temperature in the range of 100° C. to 200° C., preferably in the range of 100° C. to 150° C. The feed stream A2 thus obtained typically comprises 20% to 80% by weight, preferably 30% to 60% by weight, of steam. It typically further comprises 1% to 10% by weight of methanol, 0% to 15% by weight of ethanol, 1% to 20% by weight of dimethyl ether, and 10% to 50% by weight of C2-C6 hydrocarbons.

[0049] In step B1), feed stream A2 is heated in one or more heat exchangers to a temperature generally in the range of 430° C. to 500° C. and fed into the olefin fixed bed reactor. This heating can also be carried out before mixing the individual substreams in step A2).

[0050] Typically, the feed stream A2 is at a temperature in the range of 430° C. to 500° C., for example 470° C., when fed to the olefin fixed bed reactor. The feed stream A2 can be heated to this temperature by heat exchange with the crude product gas stream B from the olefin fixed bed reactor, by direct electrical heating, or by heating via combustion of a separate fossil energy carrier.

[0051] Then in step B2), the olefins are catalytically converted into a fixed bed reactor containing ethylene, propylene, butene, other C2-C6 hydrocarbons, C7 +The product gas stream B comprises hydrocarbons, methanol and water vapor. The conversion is usually carried out over a zeolite catalyst, preferably a catalyst based on ZSM-5 zeolite. The reaction temperature is usually 430°C to 500°C, preferably 460°C to 480°C. The pressure is usually 1.3 to 2.5 bar. The resulting crude product gas stream B2 preferably has the following composition: 1% to 15% by weight of ethylene, 1% to 30% by weight of propylene, 35% to 80% by weight of water, 10% to 50% by weight of C2-C6 hydrocarbons (especially butenes, and saturated C4 and C5 hydrocarbons and C6 + hydrocarbons), and 0.01 to 1.5 wt % of methanol and dimethyl ether.

[0052] The olefin fixed bed reactor is typically in the form of a tray reactor. The number of trays is preferably 4 to 6. In one embodiment, up to 50% by weight of the gas stream A is directly fed into one or more trays, preferably all trays, of the olefin fixed bed reactor. In another embodiment, methanol is directly fed into one or more trays, preferably all trays of the olefin fixed bed reactor.

[0053] The crude product gas stream B is at a temperature of generally 430 to 520°C, preferably 460 to 480°C, on leaving the reactor.

[0054] In a preferred step C1), the crude product gas stream B is cooled in one or more heat exchangers by heat exchange with the feed gas stream A2 to a temperature in the range of 170° C. to 220° C. After this cooling step, the temperature of the crude product gas stream B is typically 160° C. to 220° C., preferably 170° C. to 210° C., for example 190° C.

[0055] In a preferred step C2), the crude product gas stream B is further cooled to a temperature in the range of 30°C to 60°C by contact with one or more aqueous quench recycle streams under condensation of water and methanol to obtain a water-depleted and methanol-depleted hydrocarbon crude product gas stream C. The hydrocarbon crude product gas stream C thus obtained essentially comprises ethylene, propylene, further C2-C6 hydrocarbons and C7 + hydrocarbon.

[0056] In step D), one or more product streams comprising C2-C4 olefins are separated from the crude hydrocarbon product gas stream C, and at least one recycle stream R comprising C2-C6 hydrocarbons is obtained. The (entire) recycle stream R may comprise or be formed from a plurality of individual recycle streams R1, R2, R3, etc. Typically, the entire recycle stream R comprising C2-C6 hydrocarbons comprises essentially, i.e., comprises to an extent of >95% by weight, C2-C6 hydrocarbons.

[0057] Typically, step D) comprises steps D1) to D7):

[0058] D1) compressing the hydrocarbon crude product gas stream C to obtain a product containing propylene and C4, C5 and C6 + a liquid hydrocarbon stream D11 of hydrocarbons and a gaseous hydrocarbon stream D12 comprising ethane, ethylene and propylene;

[0059] D2) separating water from the liquid hydrocarbon stream D11 by phase separation to obtain a liquid hydrocarbon stream D21;

[0060] D3) separating a stream D31 comprising propylene from the liquid hydrocarbon stream D21 to obtain a stream D31 comprising C4, C5 and C6 + or separating a stream D31 comprising propylene and C4 hydrocarbons to obtain a stream D32 comprising C4, C5 and C6 hydrocarbons; + a stream D32 of hydrocarbons;

[0061] D4) from the containing C4, C5 and C6 + The hydrocarbon stream D32 is separated into C6 + a hydrocarbon by-product stream D41 to obtain a stream D42 comprising C4, C5 and C6 hydrocarbons; stream D41 optionally comprises aromatic C6 hydrocarbons, and stream D42 optionally comprises aliphatic C6 hydrocarbons;

[0062] D5) separating a stream D51 comprising propylene from the gaseous hydrocarbon stream D12 comprising ethane, ethylene and propylene to obtain a stream D52 comprising ethane and ethylene;

[0063] D6) separating a stream D61 comprising butenes from the stream D42 comprising C4, C5 and C6 hydrocarbons to obtain a stream D62 comprising C5 and C6 hydrocarbons; and or separating a stream D63 comprising propylene from the stream D31 to obtain a stream D64 comprising butenes;

[0064] D7) obtaining at least one recycle stream R from one or more streams selected from the group consisting of the stream D42 comprising C4, C5 and C6 hydrocarbons, the stream D62 comprising C5 and C6 hydrocarbons, the stream D31 comprising propylene, the stream D51 comprising propylene, the stream D63 comprising propylene, the stream D61 comprising butenes, the stream D64 comprising butenes, and the stream D52 comprising ethane and ethylene.

[0065] Steps D3), D4), D5), and D6) are carried out in standard distillation equipment. Suitable distillation equipment generally includes equipment known to those skilled in the art for such separation tasks. In addition to the actual column body with internals, a distillation column typically includes a top condenser and a reboiler. The column body can be equipped with, for example, structured packing, random packing, or trays. The distillation equipment can be designed and operated according to the general knowledge of those skilled in the art.

[0066] In step E), a portion of the C2-C4 olefins and at least a portion of the C5-C6 hydrocarbons are recycled as one or more hydrocarbon recycle streams R to step B).

[0067] In step F), at least one product of value stream F1 comprising ethylene, at least one product of value stream F2 comprising propylene and possibly one or more product of value streams F3 comprising butenes are obtained.

[0068] Propylene can be obtained as a valuable product from stream D31 or D63 and D51. Ethylene can be obtained as a valuable product from stream D52. Butenes can be obtained from streams D61 and / or D64.

[0069] One or more recycle streams R may be obtained from one or more of the above-mentioned streams D31 , D42, D51 , D52, D61 , D62, D63 and D64.

[0070] In step G), at least a portion of the valuable product stream F2 comprising propene is fed to an olefin metathesis reactor, and the propene is converted into a product stream G comprising ethylene and butenes.

[0071] The conversion is typically carried out in the gas phase. Suitable metathesis catalysts include, for example, tungsten oxide on silica (WO3 / SiO2), cobalt molybdate on alumina (CoO-MO3 / Al2O3), and rhenium oxide on alumina (Re2O7 / Al2O3). As described in US Pat. No. 11136278, the reaction can be carried out at a temperature ranging from 50°C to 650°C and a pressure range of 0 to 40 barg.

[0072] The metathesis reaction of propylene involves the disproportionation of propylene into ethylene and 2-butene. This is an equilibrium reaction. The metathesis catalyst may also include an isomerization catalyst, such as magnesium oxide (MgO), which catalyzes the isomerization of 2-butene to 1-butene.

[0073] A product stream G comprising ethylene, propylene and butenes is obtained.

[0074] In step H), a product of value stream H1 comprising ethylene and a product of value stream H3 comprising butenes are separated from the product stream G.

[0075] Separation H) usually includes

[0076] H1) separating a valuable product stream H1 comprising ethylene from the product stream G as a top draw stream in an ethylene separation column to obtain a bottom draw stream comprising propene and butenes;

[0077] H2) In a propylene separation column, a stream H2 comprising propylene is separated from a bottom draw stream comprising propylene and butenes as a top draw stream to obtain a bottom draw stream comprising butenes. The latter can be obtained directly as a valuable product stream H3 or alternatively further purified by distillation.

[0078] The propene-comprising stream H2 is preferably recycled to the metathesis reactor.

[0079] In step I), at least part of the butene-comprising product of value stream H3 is optionally recycled into step B).

[0080] In one embodiment of the invention, 50% to 100% of the butenes present in the product of value stream H3 are recycled to step B). Alternatively, a portion of streams D61 and / or D64 corresponding to the same amount of butenes can be recycled.

[0081] In step K), the C6 + A hydrocarbon by-product stream, which may be stream D41.

[0082] The present invention is illustrated in detail by the following examples.

[0083] Examples

[0084] The following scenarios 1-3 were simulated computationally. The results obtained show the composition and relative mass flow rates of the valuable product stream, the by-product stream, and the recycle stream. The ratios of olefins entering the recycle and metathesis streams were varied. The numbers are weight ratios.

[0085] In order to determine preferred scope, on laboratory scale, carry out catalytic experiment, based on this laboratory scale calculation, have the expected conversion and the mass flow rate in the industrial process of preliminary reactor, tray reactor and separation section.The analysis to this system causes the scheme 1-3 of report in table 1.Table 2-4 shows the relative mass flow rate and the total composition of main product stream and by-product stream and also recycle stream.As can be seen from the table, metathesis can reduce the quantity of by-product and the volume of return flow, and therefore can improve energy efficiency and the mass efficiency of this method.Simultaneously, obtained the expectation alkene of wider scope than prior art.

[0086]

[0087] Table 2

[0088]

[0089] Table 3

[0090]

[0091] Table 4

[0092]

Claims

1. A method for preparing C2-C4 olefins from methanol, the method comprising the following steps: A) feeding a feed stream A comprising methanol into a dimethyl ether fixed bed reactor and catalytically converting the methanol into dimethyl ether to obtain a product stream A1 comprising dimethyl ether, methanol and water vapor; B) mixing the stream A1 with one or more hydrocarbon recycle streams R comprising C2-C6 hydrocarbons and catalytically converting them in an olefin fixed bed reactor into a stream comprising C2-C4 olefins, C5-C6 hydrocarbons and C6 + a crude hydrocarbon product stream B; C) cooling the crude product stream B to obtain a hydrocarbon crude product stream C; D) separating the crude hydrocarbon stream C into at least one stream comprising ethylene, at least one stream comprising propylene, at least one stream comprising butenes, at least one stream comprising C5-C6 hydrocarbons, and at least one stream comprising C6 + a hydrocarbon by-product stream N; E) recycling a portion of the C2-C4 olefins selected from ethylene, propylene and butenes obtained in step D) and at least a portion of the C5-C6 hydrocarbons obtained in step D) as one or more hydrocarbon recycle streams R to step B); F) obtaining from the streams obtained in step D) at least one product stream F1 comprising ethylene, at least one product stream F2 comprising propylene and optionally one or more product streams F3 comprising butenes; G) feeding at least a portion of the product stream F2 comprising propene to an olefin metathesis reactor and converting the propene into a product stream G comprising ethylene and butenes, leaving a substream F4 of stream F2 as a valuable product stream; H) separating from the product stream G a product-of-value stream H1 comprising ethylene and a product-of-value stream H3 comprising butenes; I) optionally recycling at least a portion of the butenes present in the product of value stream H3 to step B), leaving substream H4 as product of value stream; K) discharging the at least one C6 + a hydrocarbon by-product stream N; in Based on 100% by weight of the C2-C4-olefins present as valuable products in the streams F1, F3, F4, H1 and H3 or H4, 30% to 60% by weight of ethylene, 30% to 60% by weight of propylene and 0% to 30% by weight of butenes are present and recovered as valuable products, and based on the C2-C4-olefins present in the one or more recycle streams R and the valuable products and by-product streams F1, F3, F4, H1, N and H3 or H4, 0% to 10% of the ethylene, 30% to 60% of the propylene and 40% to 80% of the butenes are recycled to step B) or 5 to 30% of ethylene, 0 to 10% of propylene and 40 to 85% of butenes, based on the C2-C4 olefins present in the recycle stream(s) R and the valuable products and by-product streams F1, F3, F4, H1, N and H3 or H4, are recycled to step B), and 50 to 70% of propylene, based on the crude product stream B, are directed to the olefin metathesis reactor.

2. The method according to claim 1, wherein Steps A) to D) include the following steps A1), A2), B1), B2), C1), C2) and D): A1) feeding a feed stream A comprising methanol into a dimethyl ether fixed bed reactor and catalytically converting the methanol into dimethyl ether to obtain a product stream A1 comprising dimethyl ether, methanol and water vapor; A2) mixing at least a portion of the product stream A1 with at least one hydrocarbon recycle stream R comprising C2-C6 hydrocarbons and a steam stream to obtain a second feed stream A2; B1) heating the second feed stream A2 in one or more heat exchangers to a temperature in the range of 430° C. to 500° C. and feeding it to an olefin fixed bed reactor, wherein the heating can also be carried out before mixing the individual substreams in step A2) to obtain the feed stream A2; B2) catalytic conversion of feed stream A2 at a temperature in the range of 430°C to 520°C into a mixture comprising ethylene, propylene, butenes, additional C2-C6 hydrocarbons, C6 + a crude product gas stream B of hydrocarbons, methanol, and water vapor; C1) cooling the crude product gas stream B to a temperature in the range of 170° C. to 220° C. in one or more heat exchangers by heat exchange with the feed stream A2; C2) further cooling the crude product gas stream B to a temperature in the range of 30° C. to 60° C. under condensation of water and methanol by contact with at least one aqueous quench circulation stream K to obtain a water- and methanol-depleted hydrocarbon crude product gas stream C2; D) separating the crude hydrocarbon stream C into a stream D1 comprising ethylene, a stream D2 comprising propylene, a stream D3 comprising butenes, at least one stream D4 comprising C5-C6 hydrocarbons, and at least one stream D5 comprising C6 + A hydrocarbon by-product stream N.

3. The method according to claim 1 or 2, wherein: Step D) comprises steps D1) to D7): D1) compressing the hydrocarbon crude product gas stream C to obtain a product containing propylene and C4, C5 and C6 + a liquid hydrocarbon stream D11 of hydrocarbons and a gaseous hydrocarbon stream D12 comprising ethane, ethylene and propylene; D2) separating water from the liquid hydrocarbon stream D11 by phase separation to obtain a liquid hydrocarbon stream D21; D3) separating a stream D31 comprising propylene from the liquid hydrocarbon stream D21 to obtain a stream D31 comprising C4, C5 and C6 + or separating a stream D31 comprising propylene and C4 hydrocarbons to obtain a stream D32 comprising C4, C5 and C6 hydrocarbons; + a stream D32 of hydrocarbons; D4) from the containing C4, C5 and C6 + The hydrocarbon stream D32 is separated into C6 + a hydrocarbon by-product stream D41 to obtain a stream D42 comprising C4, C5 and C6 hydrocarbons; stream D41 optionally comprises aromatic C6 hydrocarbons, and stream D42 optionally comprises aliphatic C6 hydrocarbons; D5) separating a stream D51 comprising propylene from the gaseous hydrocarbon stream D12 comprising ethane, ethylene and propylene to obtain a stream D52 comprising ethane and ethylene; D6) separating a stream D61 comprising butenes from the stream D42 comprising C4, C5 and C6 hydrocarbons to obtain a stream D62 comprising C5 and C6 hydrocarbons; and or separating a stream D63 comprising propylene from the stream D31 to obtain a stream D64 comprising butenes; D7) obtaining at least one recycle stream R from one or more streams selected from the group consisting of the stream D42 comprising C4, C5 and C6 hydrocarbons, the stream D62 comprising C5 and C6 hydrocarbons, the stream D31 comprising propylene, the stream D51 comprising propylene, the stream D63 comprising propylene, the stream D61 comprising butenes, the stream D64 comprising butenes, and the stream D52 comprising ethane and ethylene.

4. The method according to any one of claims 1 to 3, wherein In step I), 50% to 100% of the butenes present in the product of value stream H3 are recycled to step B).

Images