Process for producing c2-c4 olefins from methanol

Abstract

The invention relates to a process for producing C2-C4 olefins from methanol, the process having the steps of: A) feeding a feed stream A containing methanol into a dimethyl ether solid-bed reactor and catalytically reacting methanol to form dimethyl ether, wherein a product stream A1 containing dimethyl ether, methanol and water vapour is obtained; B) mixing the stream A1 with one or more hydrocarbon return streams R containing C2-C6 hydrocarbons and catalytically reacting in an olefin solid-bed reactor to form a raw product stream B containing C2-C4 olefins, C5-C6 hydrocarbon and C6 +-hydrocarbons; C) cooling the raw product stream B, wherein a hydrocarbon raw product stream C is obtained; D) separating the hydrocarbon raw product stream C into at least one ethylene-containing stream, at least one propylene-containing stream, at least one stream containing butylenes, at least one stream containing C5-C6 hydrocarbons and at least one by-product stream N containing C6 +-hydrocarbons; E) returning a portion of the C2-C4 olefins recovered in step D), selected from ethylene, propylene and butylenes, and at least a portion of the C5-C6 hydrocarbons recovered in step D) as one or more hydrocarbon return streams R in step B); F) recovering at least one ethylene-containing useful-product stream F1, at least one propylene-containing product stream F2 and optionally one or more useful-product streams F3 containing butylenes from the streams recovered in step D); G) feeding at least a portion of the propylene-containing product stream F2 into an olefin metathesis reactor and reacting propylene to form a product stream G containing ethylene and butylenes, wherein a partial stream F4 of the stream F2 remains as a useful-product stream; H) separating an ethylene-containing useful-product stream H1 and a useful-product stream H3 containing butylenes from the product stream G; I) optionally returning at least a portion of the butylenes contained in the useful-product stream H3 in step B), wherein a partial stream H4 remains as a useful-product stream; K) discharging the at least one by-product stream N containing C6 +-hydrocarbons; characterised in that, based on 100 wt.% of the C2-C4 olefins contained in the streams F1, F3, F4, H1 and H3 or H4 as useful products, 30 to 60 wt.% ethylene, 30 to 60 wt.% propylene and 0 to 30 wt.% butylenes are contained and recovered as useful products, and, based on the C2-C4 olefins contained in the one or more return streams R and the useful- 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 butylenes in step B) are returned and, based on the raw product stream B, 20 to 40% of the propylene is conveyed into the olefin metathesis reactor, or, based on the C2-C4 olefins contained in the one or more return streams R and the useful- and by-product streams F1, F3, F4, H1, N and H3 or H4, 5 to 30% of the ethylene, 0 to 10% of the propylene and 40 to 85% of the butylenes in step B) are returned and, based on the raw product stream B, 50 to 70% of the propylene is conveyed into the olefin metathesis reactor.

Description

[0001] Process for the production of C2-C4 olefins from methanol Description The invention relates to a process for the production of C2-C4 olefins from methanol. It is known to produce propylene by reacting a methanol / dimethyl ether mixture in a fixed-bed reactor (methanol-to-propylene, MTP reactor). Known fixed-bed reactors are operated with zeolite catalysts at temperatures of approximately 480°C. US 2010 / 145125 A1 discloses a process for producing light olefins by converting methanol and ethanol. The process comprises feeding a first partial feed via a distributor at the bottom of a fluidized-bed reactor to a reaction zone containing a catalyst, feeding a second partial feed from at least one point above the distributor to the reaction zone, contacting the feed with the catalyst, and reacting to form a stream containing ethylene and propylene.wherein the first and second subfeeds each independently comprise methanol and / or ethanol, with the proviso that the feed as a whole comprises both methanol and ethanol, and the weight ratio of methanol to ethanol in the feed as a whole is in the range from 99:1 to 0.1:1. CN 216106699 U discloses a process 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 comprises a pre-reactor, a process vapor column, and a main reactor, and the separation unit comprises a quencher and a compressor. The main reactor contains a ZSM-5 molecular sieve catalyst, and the separation unit comprises 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.Other components are discharged as by-products. The unit can also produce butenes while reducing the amount of recycled hydrocarbons and lowering the unit's energy consumption. Only saturated hydrocarbons are recycled to the main reactor. CN 110218138 A discloses a process for increasing the yield of olefin in a methanol-to-propylene (MTP) process, in which C2 hydrocarbons, C4 hydrocarbons, and C5-C7 hydrocarbons are recycled to the MTP reactor. In one example, in a 500,000 t / year methanol-to-propylene plant, the methanol feed is 210 t / h and the recycled C2, C4, and C5-C7 hydrocarbons 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. The co-feed of ethanol is not mentioned. Propylene is predominantly obtained as a valuable product. US 11,136278 B2 discloses a process for converting propylene to ethylene, comprising feeding a propylene feed stream into a C3 metathesis reactor and converting it to ethylene and 2-butene; separating it 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 the C3 metathesis reactor to produce additional ethylene; Feeding the C4 fraction into a C4 isomerization / metathesis reaction zone and converting the C4 fraction by: (i) isomerization of a portion of the 2-butenes to 1-butene, (ii) metathesis of the 1-butene and 2-butene to propylene and 2-pentene, and / or (iii) autometathesis of the 1-butene to ethylene and 3-hexene; obtaining a product stream comprising ethylene, propylene, butenes, pentenes, and hexenes and feeding it into the fractionation system. US 11,046,627 B2 discloses a process for producing propylene from ethylene and butylene.comprising: (a) producing, in a methanol-to-propylene (MTP) system comprising a zeolite catalyst, and a methanol-to-olefin (MTO) system comprising a silicoaluminophosphate (SAPO) molecular sieve catalyst, a first product stream comprising ethylene and a second product stream comprising butylene, wherein the MTP or MTO system comprises: (i) a first reactor that converts methanol to dimethyl ether; and (ii) a second reactor that converts the dimethyl ether to a C2+ product stream comprising propylene, ethylene, and butylene; (b) feeding the first and second product streams to a metathesis reaction unit and converting the ethylene and butylene to a metathesis product stream containing propylene and unreacted ethylene and butylene; (c) separating the propylene from unreacted ethylene and butylene,to produce a propylene product stream and a stream containing unreacted ethylene and butylene; (d) recycling the stream containing the unreacted ethylene and butylene from step (c) to the MTP or MTO system. EP 2892863 B1 describes a process for producing linear butenes from methanol, comprising the steps: a) providing methanol; b) converting the methanol in a first reaction stage to a first reaction mixture containing dimethyl ether, water, and optionally unreacted methanol; c) converting dimethyl ether in a second reaction stage to a second reaction mixture containing propene and other hydrocarbons having two, four, and five carbon atoms, wherein the second reaction stage is fed at least partially from the first reaction mixture; d) working up the second reaction mixture to obtain a propene-rich fraction and at least one propene-poor fraction,wherein the propene-poor fraction is partially recycled to the second reaction stage; e) converting propene in a third reaction stage into a third reaction mixture containing ethene and linear butenes selected from the group comprising 1-butene, cis-2-butene, trans-2-butene, wherein the third reaction stage is at least partially fed from the propene-rich fraction; f) processing the third reaction mixture into a target fraction rich in linear butenes and into an ethene-rich fraction. The object of the invention is to provide a flexible process for producing C2-C4 olefins from methanol in a methanol-to-olefin process (MTO process), in which the proportions of ethylene,Propylene and butenes in the valuable product streams obtained from the process can be varied within wide ranges and the amount of recycle streams recycled into the MTO process can be reduced overall. This object is achieved by a process for producing C2-C4 olefins from methanol, comprising the steps of: A) feeding a methanol-containing feed stream A into a dimethyl ether fixed-bed reactor and catalytically converting methanol to dimethyl ether, obtaining a product stream A1 comprising dimethyl ether, methanol, and steam; B) mixing stream A1 with one or more hydrocarbon recycle streams R comprising C2-C6 hydrocarbons and catalytically converting the stream in an olefin fixed-bed reactor to form a crude product stream B comprising C2-C4 olefins, C5-C6 hydrocarbons, and C6. +-hydrocarbons; C) cooling the crude product stream B, whereby a hydrocarbon crude product stream C is obtained; D) separating the hydrocarbon crude product stream C into at least one ethylene-containing stream, at least one propylene-containing stream, at least one butene-containing stream, at least one C5-C6 hydrocarbon-containing stream and at least one C6 +-hydrocarbon-containing by-product stream N; E) recycling a portion of the C2-C4 olefins obtained in step D), selected from ethylene, propylene and butenes, and at least a portion of the C5-C6 hydrocarbons obtained in step D) as one or more hydrocarbon recycle streams R in step B); F) obtaining at least one ethylene-containing valuable product stream F1, at least one propylene-containing product stream F2 and optionally one or more butene-containing valuable product streams F3 from the streams obtained in step D); G) feeding a portion of the propylene-containing product stream F2 into an olefin metathesis reactor and converting propylene to a product stream G comprising ethylene and butenes, wherein a partial stream F4 of the stream F2 remains as the valuable product stream; H) Separation from the product stream G of an ethylene-containing valuable product stream H1 and a butene-containing valuable product stream H3;I) optionally recycling a portion of the butenes contained in the valuable product stream H3 to step B), leaving a stream H4 as the valuable product stream; K) discharging the C6; +-at least one by-product stream N containing hydrocarbons; characterized in that, based on 100% by weight of the C2-C4 olefins present as valuable products in 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 obtained as valuable products, and, based on the C2-C4 olefins present in the one or more recycle streams R and the valuable 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) and, based on the crude product stream B, 20 to 40% of the propylene is fed to the olefin metathesis reactor, or, based on the C2-C4 olefins contained in the one or more recycle streams R and the value and by-product streams F1, F3, F4, H1, N and H3 or H4, 5 to 30% of the ethylene,0 to 10% of the propylene and 40 to 85% of the butenes are recycled to step B), and, based on the crude product stream B, 50 to 70% of the propylene is fed to the olefin metathesis reactor. Olefin metathesis can be used to specifically approximate a non-ideal olefin product composition to the desired olefin product composition. The alternative is to recycle the unwanted olefins.This, on the one hand, increases the recycle quantity and thus the separation effort (power and steam requirements) of the MTO process. On the other hand, adjusting the olefin product spectrum solely by recycling the undesired olefins is only possible with considerable development effort due to the numerous chemical reactions during the MTO process and quickly leads to an increase in by-product quantities. In a preferred embodiment, the process according to the invention comprises the steps: A1) feeding a methanol-containing feed stream A into a dimethyl ether fixed-bed reactor and catalytic conversion of methanol to dimethyl ether, obtaining a product stream A1 containing dimethyl ether, methanol, and steam; A2) mixing at least a portion of the product stream A1 with at least one hydrocarbon recycle stream R containing C2-C6 hydrocarbons and a steam stream,wherein a second feed stream A2 is obtained; B1) heating the second feed stream A2 in one or more heat exchangers to a temperature in the range from 430 to 500°C and feeding it into an olefin fixed bed reactor, wherein the heating can also take place before mixing individual substreams to form the feed stream A2 in step A2); B2) catalytic conversion of the feed stream A2 at a temperature in the range from 430 to 520°C to a crude product gas stream B comprising ethylene, propylene, butenes, further C2-C6 hydrocarbons, C7, +-hydrocarbons, methanol and water vapor; C1) cooling the crude product gas stream B in one or more heat exchangers to a temperature in the range from 170 to 220°C by heat exchange with the feed stream A2; C2) further cooling the crude product gas stream B to a temperature in the range from 30 to 60°C by contacting it with at least one water-containing quench cycle stream K, wherein water and methanol are condensed out and a hydrocarbon crude product gas stream C depleted in water and methanol is obtained; D) separating the hydrocarbon crude product gas stream C into a propylene-containing valuable product stream, optionally an ethylene-containing valuable product stream, a butene-containing valuable product stream, at least one C5-C6 hydrocarbon-containing recycle stream and at least one C6 +-hydrocarbon-containing by-product stream. In step A1), a methanol-containing feed stream A is fed into a dimethyl ether fixed-bed reactor, and methanol is catalytically converted to dimethyl ether, obtaining a product stream A1 containing dimethyl ether, methanol, and steam. If, based on 100% by weight of the C2-C4 olefins obtained as valuable products, 30 to 60% by weight of ethylene, 30 to 60% by weight of propylene and 0 to 30% by weight of butenes are to be obtained as valuable products, according to the invention, based on the crude product stream B, 20 to 40% of the propylene are fed into the olefin metathesis reactor and, based on the C2-C4 olefins present in the one or more recycle streams R and the valuable 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).Alternatively, based on the crude product stream B, 50 to 70% of the propylene can be fed into the olefin metathesis reactor and, based on the C2-C4 olefins present in the one or more recycle streams R and the valuable and by-product streams F1, F3, F4, H1, N, and H3 or H4, 5 to 30% of the ethylene, 0 to 10% of the propylene, and 40 to 85% of the butenes can be recycled in step B). 100 wt. % of valuable products refers to the C2-C4 olefins present in streams F1, F3, F4, H1, and either H3 or H4 that are not recycled and not fed into the metathesis reactor. The dimethyl ether fixed-bed reactor can be designed in various ways. Generally, the methanol-containing feed gas stream A is heated to a temperature above 250 °C and fed into the fixed-bed reactor. Gamma-alumina is generally used as the catalyst.The reaction temperature is between 250 and 450°C and the pressure is between 1 and 25 bar, for example 4 bar. The methanol conversion is generally from 50 to 90%, preferably from 65 to 85%, for example 75%. In a step A2), at least a portion of this 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. This portion of stream A1 generally amounts to at least 50% by weight and preferably up to 90% by weight. A further portion A1-2 of stream A1, preferably at least 10% by weight, can be fed directly to one or more trays of the olefin fixed-bed reactor. This portion of stream A1 is generally cooled before being fed into the trays of the olefin fixed-bed reactor, preferably to a temperature in the range of 30 to 60°C. This partial stream A1-2 is preferably fed into the reactor in liquid form.Cooling by substream A1-2 can also be omitted if the olefin fixed-bed reactor is operated and cooled isothermally. Isothermal operation can be carried out, for example, in the manner described in WO 2017 / 102096 A1. Heat exchanger surfaces can be installed in the olefin fixed-bed reactor, which are operated, for example, with molten salt or high-pressure steam as the heat transfer medium. As the heat transfer medium flows through the heat exchanger surfaces in the reactor, the resulting reaction heat is removed from the reactor, thus operating the reactor isothermally. To adjust the desired product distribution in the product gas stream B, a substream A1-2 can also be fed to an intermediate stage of the olefin fixed-bed reactor. The at least one hydrocarbon recycle stream R, which originates from the separation of the C2-C4 olefins in steps D) and optionally G), generally contains C2-C6 hydrocarbons.Depending on the proportions of ethylene, propylene, and butenes obtained as products of value, the at least one hydrocarbon recycle stream contains C2-C4 hydrocarbons, generally in total amounts of 40 to 90% by weight. The at least one hydrocarbon recycle stream generally has a temperature in the range from 100 to 175°C, preferably in the range from 130 to 160°C, before mixing. Product stream A1 from the dimethyl ether fixed-bed reactor is further mixed with a steam stream. The steam stream generally has a temperature in the range from 100 to 200°C, preferably in the range from 100 to 150°C. The feed stream A2 thus obtained generally contains 20 to 80% by weight, preferably 30 to 60% by weight, of steam. It generally also contains 1 to 10 wt% methanol, 0 to 15 wt% ethanol, 1 to 20 wt% dimethyl ether and 10 to 50 wt% C2-C6 hydrocarbons.In step B1), the feed stream A2 is heated in one or more heat exchangers to a temperature generally in the range of 430 to 500°C and fed into an olefin fixed-bed reactor. The heating can also take place before the mixing of individual substreams in step A2). Generally, the feed stream A2 has a temperature in the range of 430 to 500°C, for example 470°C, upon feeding into the olefin fixed-bed reactor. The heating of the feed stream A2 to this temperature can be achieved by heat exchange with the raw product gas stream B of the olefin fixed-bed reactor, by direct electrical heating, or by heating by combustion of a separate fossil fuel. This is followed in step B2) by catalytic conversion in the olefin fixed bed reactor to a product gas stream B containing ethylene, propylene, butenes, further C2-C6 hydrocarbons, C7. +- hydrocarbons, methanol, and steam. The reaction is generally carried out over a zeolite catalyst, preferably over a catalyst based on a ZSM-5 zeolite. The reaction temperature is generally from 430 to 500°C, preferably from 460 to 480°C. The pressure is generally from 1.3 to 2.5 bar. The resulting crude product gas stream B2 is preferably composed as follows: from 1 to 15% by weight of ethylene, from 1 to 30% by weight of propylene, from 35 to 80% by weight of water, from 10 to 50% by weight of C2-C6 hydrocarbons, in particular butenes and saturated C4 and C5 hydrocarbons, and also C6 +-hydrocarbons and 0.01 to 1.5% by weight of methanol and dimethyl ether. The olefin fixed-bed reactor is generally designed as a tray reactor. The number of trays is preferably 4 to 6. In one embodiment, a total of up to 50% by weight of gas stream A is fed directly to one or more trays of the olefin fixed-bed reactor, preferably all trays of the olefin fixed-bed reactor. In a further embodiment, methanol is fed directly to one or more trays of the olefin fixed-bed reactor, preferably all trays of the olefin fixed-bed reactor. The crude product gas stream B has a temperature of generally 430 to 520°C, preferably 460 to 480°C, upon exiting the reactor. In a preferred step C1), the crude product gas stream B is cooled in one or more heat exchangers to a temperature in the range of 170 to 220°C by heat exchange with the feed gas stream A2.After this cooling step, the temperature of the crude product gas stream B is generally from 160 to 220°C, preferably from 170 to 210°C, for example 190°C. In a preferred step C2), the crude product gas stream B is further cooled to a temperature in the range from 30 to 60°C by contacting it with one or more water-containing quench cycle streams, water and methanol being condensed out and a hydrocarbon crude product gas stream C depleted in water and methanol being obtained. The hydrocarbon crude product gas stream C thus obtained essentially comprises ethylene, propylene, further C2-C6 hydrocarbons and C7. +-hydrocarbons. In a step D), one or more product streams comprising C2-C4 olefins are separated from the hydrocarbon crude product gas stream C, and the recycle stream R comprising at least one C2-C6 hydrocarbon is obtained. The (total) recycle stream R can comprise a plurality of individual recycle streams R1, R2, R3, etc. or be formed from them. In general, the entire recycle stream R comprising C2-C6 hydrocarbons essentially contains, i.e., >95 wt.%, C2-C6 hydrocarbons. In general, step D) comprises steps D1) to D7): D1) compression of the hydrocarbon crude product gas stream C, wherein a propylene, C4, C5 and C6 +-hydrocarbons-containing liquid hydrocarbon stream D11 and a gaseous hydrocarbon stream D12 containing ethane, ethene and propylene are obtained; D2) separating water from the liquid hydrocarbon stream D11 by phase separation, whereby a liquid hydrocarbon stream D21 is obtained; D3) separating a propylene-containing stream D31 from the liquid hydrocarbon stream D21, whereby a C4, C5 and C6 + -hydrocarbons-containing stream D32 is obtained; or separation of a stream D31 containing propylene and C4 hydrocarbons, wherein a C4, C5 and C6 + -hydrocarbons-containing stream D32 is obtained; D4) Separation of a C6 + -hydrocarbon-containing by-product stream D41 from the C4, C5 and C6 +-hydrocarbons-containing stream D32, whereby a C4, C5 and C6 hydrocarbon-containing stream D42 is obtained; optionally the stream D41 contains aromatic C6 hydrocarbons and the stream D42 contains aliphatic C6 hydrocarbons; D5) separating a propylene-containing stream D51 from the ethane, ethene and propylene-containing gaseous hydrocarbon stream D12, whereby an ethane and ethene-containing stream D52 is obtained; D6) separating a butene-containing stream D61 from the C4, C5 and C6 hydrocarbon-containing stream D42, whereby a C5 and C6 hydrocarbon-containing stream D62 is obtained; and / or separating a propylene-containing stream D63 from the stream D31, whereby a butene-containing stream D64 is obtained; D7) Obtaining at least one recycle stream R from one or more of the streams selected from the C4, C5 and C6 hydrocarbon-containing stream D42,the C5 and C6 hydrocarbon-comprising stream D62, the propylene-comprising stream D31, the propylene-comprising stream D51, the propylene-comprising stream D63, the butene-comprising stream D61, the butene-comprising stream D64, and the ethane and ethene-comprising stream D52. Steps D3), D4), D5) and D6) are carried out in conventional distillation apparatus. Suitable distillation apparatuses are, in principle, those known to the person skilled in the art for such separation tasks. In addition to the actual column body with internals, the distillation column also contains, as usual, a top condenser and a bottom evaporator. The column body can, for example, be equipped with packings,packed beds or trays. The distillation apparatus can be designed and operated using the general knowledge of the person skilled in the art. 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). In step F), at least one ethylene-comprising valuable product stream F1, at least one propylene-comprising valuable product stream F2 and, if appropriate, one or more butene-comprising valuable product streams F3 are obtained. Propylene can be obtained as valuable product from streams D31 or D63 and D51. Ethylene can be obtained as valuable product from stream D52. Butenes can be obtained from stream D61 and / or D64. The recycle stream(s) R can be obtained from one or more of the above-described streams D31, D42, D51, D52, D61, D62,D63 and D64. In step G), at least a portion of the propylene-containing valuable product stream F2 is fed into an olefin metathesis reactor, and propylene is converted to a product stream G containing ethylene and butenes. The conversion generally takes place in the gas phase. Suitable metathesis catalysts include, for example, tungsten oxide on silicon dioxide (WO3 / SiO2), cobalt molybdate on aluminum oxide (CoO-MO3 / Al2O3), and rhenium oxide on aluminum oxide (Re2O7 / Al2O3). The conversion can take place, as described in US11136278, in a temperature range from 50 to 650 °C and a pressure range from 0 to 40 bar(g). The metathesis reaction of propylene involves a disproportionation of propylene to ethylene and 2-butene. This is an equilibrium reaction. The metathesis catalyst may additionally comprise an isomerization catalyst, for example magnesium oxide (MgO),which catalyzes the isomerization of 2-butene to 1-butene. A product stream G is obtained which contains ethylene, propylene, and butenes. In step H), an ethylene-containing valuable product stream H1 and a butene-containing valuable product stream H3 are separated from the product stream G. The separation H) generally comprises H1) the separation of an ethylene-containing valuable product stream H1 from the product stream G in an ethylene separation column as the top draw stream, whereby a bottom draw stream containing propylene and butenes is obtained; H2) the separation of a propylene-containing stream H2 from the bottom draw stream containing propylene and butenes in a propylene separation column as the top draw stream,wherein a bottom draw stream comprising butenes is obtained. This can be obtained directly as valuable product stream H3 or, if appropriate, further purified by distillation. The propylene-containing stream H2 is preferably recycled to the metathesis reactor. If appropriate, in a step I), at least a portion of the butene-containing valuable product stream H3 is recycled to step B). In one embodiment of the invention, 50 to 100% of the butenes present in the valuable product stream H3 are recycled to step B). Alternatively, a portion of the streams D61 and / or D64 corresponding to the same amount of butene can be recycled. In step K), a C6, +-hydrocarbon-containing by-product stream is discharged from the process. This can be stream D41. The invention is explained in more detail by the following examples. Examples The following cases 1 - 3 were simulated computationally. The compositions and relative mass flows of the desired product streams, by-product streams, and recycle streams were obtained as a result. The proportions of olefins in the recycle and metathesis were varied. Data are given in weight ratios. To determine the preferred ranges, catalytic experiments were carried out on a laboratory scale, and on this basis the expected conversions and mass flows in an industrial process with a pre-reactor, tray reactors, and separation section were calculated. An investigation of this system led to cases 1 - 3, which are shown in Table 1.Tables 2–4 show the relative mass flow rates and overall composition of the main and by-product streams, as well as the recycle streams. As can be seen in the tables, metathesis can reduce the number of by-products and the amount of recycle stream, thus improving the energy and mass efficiency of the process. At the same time, a broader desired olefin spectrum is obtained than with the state of the art. Table 1 Case 1 Case 2 Case 3 Min Max Min Max Min Max Recycled portion of C2H4 from the crude product stream. [1] 0% 0% 0% 10% 10% 30% Recycled portion of C3H6 from the crude product stream [1] 60% 100% 20% 40% 0% 10% Portion of C3H6 from the crude product stream fed into the metathesis reactor [1] 20% 40% 50% 70% Recycled portion of C4H8 from the crude product stream [1] 40% 70% 30% 100% 30% 100% Recycled part of C2H4 relative to C2H4 in the recycling, the value and by-products [2]0% 0% 0% 10% 5% 30% Recycled part of C3H6 relative to C3H6 in the recycling, the value and by-products [2] 60% 100% 30% 60% 0% 10% Recycled portion of C4H8 relative to C4H8 in the recycling, value-added products and by-products [2] 40% 70% 40% 80% 40% 85% [1] After separation in step D) [2] After separation in step D) and step H)

[0002] Table 2 Case 1: No metathesis unit Value products By-products Recycle Relative mass flow 1.00 1.72 3.08 Mass fraction MeOH - - - DME - 0.01 0.01 H2O - - - H2 - 0.00 - CO2 - 0.00 - CH4 - 0.02 - C2H4 0.35 - - C3H6 0.38 - 0.43 C4H8 0.27 0.00 0.11 C5H10 - 0.02 0.01 C6+ Olefins - 0.01 0.01 C2H6 - 0.07 - C3H8 - 0.11 0.21 C4H10 - 0.19 0.13 C5H12 - 0.11 0.06 C6+ Paraffins - 0.06 0.03 aromatics - 0.41 - N2 - - -

[0003] Table 3 Case 2: No recycled C2H4 Value products By-products Recycling Relative mass flow 1.00 0.88 1.85 Mass fractions MeOH - - - DME - 0.04 - H2O - - - H2 - 0.00 - CO2 - 0.00 - CH4 - 0.02 - C2H4 0.36 - - C3H6 0.41 - 0.18 C4H8 0.23 0.00 0.21 C5H10 - 0.02 0.01 C6+ Olefins - 0.02 0.01 C2H6 - 0.16 - C3H8 - 0.11 0.02 C4H10 - 0.01 0.49 C5H12 - 0.12 0.06 C6+ Paraffins - 0.07 0.03 Aromatics - 0.42 - N2 - - -

[0004] Table 4 Case 3: no recycled C3H6 Value products By-products Recycling Relative mass flow 1.00 0.88 0.85 Mass fraction MeOH - - - DME - 0.04 - H2O - - - H2 - 0.00 - CO2 - 0.00 - CH4 - 0.01 - C2H4 0.37 - 0.05 C3H6 0.39 - - C4H8 0.24 0.01 0.62 C5H10 - 0.02 0.02 C6+ olefins - 0.01 0.01 C2H6 - 0.05 0.01 C3H8 - 0.09 C4H10 - 0.21 0.12 C5H12 - 0.11 0.11 C6+ paraffins - 0.06 0.06 Aromatics - 0.38 - N2 - - -

Claims

Claims 1. A process for the preparation of C2-C4 olefins from methanol, comprising the steps of: A) feeding a methanol-containing feed stream A into a dimethyl ether fixed-bed reactor and catalytically converting methanol to dimethyl ether, obtaining a product stream A1 comprising dimethyl ether, methanol and steam; B) mixing the stream A1 with one or more hydrocarbon recycle streams R comprising C2-C6 hydrocarbons and catalytically converting the stream A1 in an olefin fixed-bed reactor to a crude product stream B comprising C2-C4 olefins, C5-C6 hydrocarbon and C6 +-hydrocarbons; C) cooling the crude product stream B, whereby a hydrocarbon crude product stream C is obtained; D) separating the hydrocarbon crude product stream C into at least one ethylene-containing stream, at least one propylene-containing stream, at least one butene-containing stream, at least one C5-C6 hydrocarbon-containing stream and at least one C6 +-hydrocarbon-containing by-product stream N; E) recycling a portion of the C2-C4 olefins obtained in step D), selected from ethylene, propylene and butenes, and at least a portion of the C5-C6 hydrocarbons obtained in step D) as one or more hydrocarbon recycle streams R in step B); F) obtaining at least one ethylene-containing valuable product stream F1, at least one propylene-containing product stream F2 and optionally one or more butene-containing valuable product streams F3 from the streams obtained in step D); G) feeding at least a portion of the propylene-containing product stream F2 into an olefin metathesis reactor and converting propylene to a product stream G comprising ethylene and butenes, wherein a partial stream F4 of the stream F2 remains as the valuable product stream;H) Separation from the product stream G of an ethylene-containing valuable product stream H1 and a butene-containing valuable product stream H3, I) optionally recycling at least a portion of the butenes contained in the valuable product stream H3 to step B), leaving a partial stream H4 as the valuable product stream; K) Discharge of the C6; + -hydrocarbons containing at least one by-product stream N; characterized in that, 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 wt.% butenes are contained and are obtained as valuable products, and, based on the C2-C4 olefins contained in the one or more recycle streams R and the valuable 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 in step B) and, based on the crude product stream B, 20 to 40% of the propylene are fed to the olefin metathesis reactor, or, based on the C2-C4 olefins contained in the one or more recycle streams R and the valuable and by-product streams F1, F3, F4, H1, N and H3 or H4, 5 to 30% of the ethylene, 0 to 10% of the propylene and 40 to 85% of the butenes are recycled to step B) and 50 to 70% of the propylene, based on the crude product stream B, is fed into the olefin metathesis reactor.

2. The process according to claim 1, wherein steps A) to D) comprise the subsequent steps A1), A2), B1), B2), C1),C2) and D) comprise: A1) feeding a methanol-containing feed stream A into a dimethyl ether fixed bed reactor and catalytically converting methanol to dimethyl ether, obtaining a product stream A1 comprising dimethyl ether, methanol and steam; 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, obtaining a second feed stream A2; B1) heating the second feed stream A2 in one or more heat exchangers to a temperature in the range from 430 to 500°C and feeding it into an olefin fixed bed reactor, wherein the heating can also take place before the mixing of individual partial streams to form the feed stream A2 in step A2); B2) catalytic conversion of the feed stream A2 at a temperature in the range of 430 to 520°C to a crude product gas stream B containing ethylene, propylene, butenes,other C2-C6 hydrocarbons, C6, + -hydrocarbons, methanol and water vapor; C1) cooling the crude product gas stream B in one or more heat exchangers to a temperature in the range from 170 to 220°C by heat exchange with the feed stream A2; C2) further cooling the crude product gas stream B to a temperature in the range from 30 to 60°C by contacting it with at least one water-containing quench cycle stream K, wherein water and methanol are condensed out and a hydrocarbon crude product gas stream C2 depleted in water and methanol is obtained; D) separating the hydrocarbon crude product stream C into an ethylene-containing stream D1, a propylene-containing stream D2, a butene-containing stream D3, at least one C5-C6 hydrocarbon-containing stream D4 and at least one C6 + -hydrocarbon-containing by-product stream N.

3. Process according to claim 1 or 2, characterized in that step D) comprises steps D1) to D7): D1) compression of the hydrocarbon crude product gas stream C, wherein a propylene, C4, C5 and C6 + -hydrocarbons-containing liquid hydrocarbon stream D11 and a gaseous hydrocarbon stream D12 containing ethane, ethene and propylene are obtained; D2) separating water from the liquid hydrocarbon stream D11 by phase separation, whereby a liquid hydrocarbon stream D21 is obtained; D3) separating a propylene-containing stream D31 from the liquid hydrocarbon stream D21, whereby a C4, C5 and C6 + -hydrocarbons-containing stream D32 is obtained; or separation of a propylene and C4-hydrocarbons-containing stream D31, wherein a C4-, C5- and C6- + -hydrocarbons-containing stream D32 is obtained; D4) separation of a C6 +-hydrocarbon-containing by-product stream D41 from the C4, C5 and C6 +-hydrocarbons-containing stream D32, whereby a C4, C5 and C6 hydrocarbon-containing stream D42 is obtained; optionally the stream D41 contains aromatic C6 hydrocarbons and the stream D42 contains aliphatic C6 hydrocarbons; D5) separating a propylene-containing stream D51 from the ethane, ethene and propylene-containing gaseous hydrocarbon stream D12, whereby an ethane and ethene-containing stream D52 is obtained; D6) separating a butene-containing stream D61 from the C4, C5 and C6 hydrocarbon-containing stream D42, whereby a C5 and C6 hydrocarbon-containing stream D62 is obtained; and / or separating a propylene-containing stream D63 from the stream D31, whereby a butene-containing stream D64 is obtained;D7) Obtaining at least one recycle stream R from one or more of the streams selected from the C4, C5, and C6 hydrocarbon-containing stream D42, the C5 and C6 hydrocarbon-containing stream D62, the propylene-containing stream D31, the propylene-containing stream D51, the propylene-containing stream D63, the butene-containing stream D61, the butene-containing stream D64, and the ethane- and ethene-containing stream D52.

4. The process according to any one of claims 1 to 3, characterized in that in step I) 50 to 100% of the butenes present in the desired product stream H3 are recycled to step B). Alternatively, a portion of the streams D61 and / or D64 corresponding to the same amount of butene can be recycled.;