DE102011102971A1 - Process for the production of ethylene - Google Patents

Abstract

Process for the production of ethylene, comprising the steps: feeding an ethanol-containing stream (S) into at least one reactor (10-13) and dehydrating ethanol contained in the stream (S) in the at least one reactor (10-13) with the formation of ethylene . According to the invention, the material stream (S) is compressed by means of a pump (6) before it is fed into the at least one reactor (10-13).

Description

The invention relates to a process for the production of ethylene according to the preamble of claim 1.

In such a method z. B. fed an ethanol-containing stream in at least one reactor and dehydrated there to form ethylene.

The recovery of ethylene from ethanol by dehydration on a heterogeneous catalyst is a technology that is interesting because of their characteristics (very high selectivity, very high conversion) and relatively simple decomposition parts for smaller production quantities.

The invention is therefore based on the problem of designing a method of the type mentioned, in particular in the aforementioned area, cost-effectively and efficiently.

This problem is solved by a method having the features of claim 1.

Thereafter, it is provided that the liquid stream is compressed only before feeding (upstream) in the at least one reactor by means of a pump (high pressure pump) or a pumping means, d. h., Is brought by means of said pump to a predefinable pressure. Of course, the pumping means may comprise a plurality of pumps upstream of the at least one reactor.

Preferably, it is further provided that that ethylene-containing material stream is withdrawn from the at least one reactor. The gaseous reaction product (stream) is then preferably cooled, wherein a part condenses, in particular the water split off during the dehydration.

For cooling, on the one hand, the material flow (feed stream) to be introduced into the at least one reactor (see below), in particular in combination with a second cooling water stream, is recommended. It can also be integrated with sufficient availability, only a cooling water circuit. The biphasic material stream resulting from cooling, comprising an ethylene-containing gas phase, is preferably fractionated into a first column (eg stripper) connected to the reactor for further fractionation, in particular for washing off at least one water-soluble constituent (eg in the form of oxygenates such as ketones , Esters and / or ethers) from the gas phase.

In this case, the two-phase stream is preferably driven in the first column in countercurrent to fresh water fed at the top of the column. At the bottom of the first column, an ethanol-containing phase can then be withdrawn, which is added in particular to the material stream to be introduced into the at least one reactor, wherein that phase is previously passed through a membrane filter, in particular for concentrating the ethanol contained therein.

According to the invention, said material stream is preferably pressurized prior to feeding into the at least one reactor such that the material stream still has a pressure required for fractionating or washing out the at least one water-soluble constituent even after said cooling when feeding into said first column.

In other words, in particular a compression of the liquid feed (stream) in the form of aqueous ethanol by means of a (high pressure) pump is carried out, wherein the pressure is raised so far that after cooling of the reaction mixture is at least one pressure, as it is for further fractionation is required (eg washing out of water-soluble constituents, see above). As a result, it is possible in particular to dispense with the conventional, cost-intensive, multistage crude gas compression with intermediate cooling and condensate separation. Instead of washing out water-soluble constituents or in addition thereto, the said further fractionation may also comprise other process steps (see below).

Thus, it is preferably provided that the two-phase (ethylene-containing) stream is withdrawn from the first column and is subjected to an acid gas scrubbing to remove CO ₂ in a second column with the first column flow or pressure-conducting second column.

For this purpose, the said stream is preferably countercurrent to a NaOH-containing stream (to form water and Na ₂ CO ₃ ) driven, in particular a carbonate-containing phase from the bottom the second column is withdrawn, and preferably wherein the thus purified and withdrawn from the second column ethylene-containing two-phase material flow is dried over a molecular sieve or by means of a molecular sieve. Instead of NaOH and other alkaline chemically or physically acting, known in the art detergent can be used.

Furthermore, the (ethylene-containing) stream withdrawn from the second column is preferably fed into a third column which is connected to the second column in a fluid or pressure-conducting manner to remove heavy C ₃₊ components (hydrocarbons having three or more than three carbon atoms). In this case, those heavy components accumulate in the bottom of the third column and are withdrawn there from the third column. The stream containing the lighter C ₁ / C ₂ components (one or two carbon atoms per molecule), on the other hand, is withdrawn from the top of the third column and preferably fed to a further fractionation.

For removing lighter components, such as. B. CO and / or CH ₄ is finally preferably the withdrawn from the third column (ethylene-containing) stream fed into a third column with the fluid or pressure-conducting connected fourth column, wherein a (final purified, concentrated) ethylene-containing gaseous phase from the sump the fourth column is withdrawn, and wherein those light components are collected in the head of the fourth column and withdrawn there.

Preferably, the pressure of the stream is adjusted by means of the pump so that it is 10 bar to 30 bar, preferably 15 bar to 25 bar in the removal of the stream in the form of an ethylene-containing (gaseous) phase from the bottom of the fourth column.

For this purpose, the material stream to be introduced into the at least one reactor is preferably compressed to from 20 to 100 bar, preferably to from 30 to 40 bar, before it is introduced into the at least one reactor. The ethanol content of the stream before being fed into the at least one reactor is preferably 40% by volume to 99.9% by volume, more preferably 60% by volume to 96% by volume and particularly preferably 70% by volume to 90% by volume.

Furthermore, the at least one reactor in a variant of the invention is preferably at least one isothermal reactor in which the dehydration of the ethanol is carried out at (substantially) constant temperature. A heating of the material flow (heat tracing) can be made via a heat transfer medium, z. B. in the form of steam, oil or a molten salt.

In an alternative embodiment of the invention it is provided that the at least one reactor is designed as an adiabatic reactor. In an adiabatic system, apart from radiation losses across the reactor wall, there is approximately no heat exchange with the environment. With good heat insulation of the reactor, the adiabatic reaction is technically easy to implement. Preferably, it is provided that, after passing through the at least one adiabatic reactor, the stream passes through at least one further, preferably two further, most preferably three further adiabatic reactors which are connected to one another by pressure or flow (adiabatic bed cascade).

In the case of several adiabatic reactors, it is preferably provided that the stream is heated in each case between two such adiabatic reactors, the stream in each case in particular being heated to a temperature between 300 ° C. to 500 ° C., preferably 350 ° C. to 480 ° C., most preferably between 400 ° C to 450 ° C is heated.

For dehydrating the ethanol in the said reactors, it is preferably provided that they each contain at least one catalyst bed which is charged with the stream, wherein those catalyst beds preferably comprise an Al ₂ O ₃ or a ZSM5 catalyst.

Preferably, after passing through the entirety of the adiabatic or isothermal reactors, the stream (gaseous reaction product) is cooled by means of an indirect heat exchange with the stream to be introduced into the at least one reactor in a heat exchanger, so that in particular the water split off during the dehydration condenses out.

This indirect heat exchange can also be used to heat the stream prior to feeding into said reactors. In this case, the material stream to be fed in is preferably completely evaporated and / or superheated. The heat exchange can also be carried out with another process stream be, especially in the form of steam (high-pressure steam). For heating the material flow, this can also be heated in a furnace chamber.

The ethanol for the fed into the reactors stream (feed) is preferably withdrawn from the top of a distillation column, which is charged in particular with crude ethanol produced by fermentation, in particular a withdrawn from the bottom of the distillation column ethanol-containing liquid phase for concentrating the ethanol in that phase is sent through a membrane filter. Preferably, that ethanol-containing phase after passing through the membrane filter is added to the said, from the top of the distillation column withdrawn ethanol-containing material stream.

In the aforementioned fermentation, alcohol (ethanol) is obtained in a known manner from sugars with the aid of microorganisms. In general, yeast is used. The sugars come z. B. from plants.

Further details and advantages of the invention will be explained by the following description of an embodiment with reference to the figure.

It shows:

1 a schematic representation of a plant or a process for the production of ethylene from ethanol.

1 shows a plant (arrangement) 1 or a corresponding method for the inventive (heterogeneous catalytic) dehydration of ethanol (EtOH) to ethylene. For this purpose, the attachment 1 four interconnected, adiabatically operated reactors 10 - 13 on.

According to the invention, a compression of a liquid feed (stream) S, which contains aqueous ethanol (EtOH (aq)), by means of a pump, in particular in the form of a high-pressure pump 6 , performed. In this case, the pressure of the stream S is preferably raised so far that even after cooling of the reaction mixture (stream) S is still a pressure as required for the further fractionation.

First, this is done in an upstream, bioprocessing process step by fermentation in a fermentation facility 2 obtained crude ethanol separated from the yeast constituents of the fermentation broth and concentrated over a line 3 a distillation column 4 fed. At the head 40 the distillation column 4 then an ethanol-rich phase can be withdrawn, while one from the bottom of the distillation column 4 withdrawn phase via a line 36 for increasing the product yield and process water treatment through a membrane filter 38 is given. With this a low-ethanol permeate for easy introduction into a municipal / industrial wastewater treatment plant is obtained, on the other hand, an ethanol- and intermediate rich retentate for return to the head 40 the distillation column 4 withdrawn stream S in terms of yield increase.

The ethanol-rich material flow S is then via a line 5 the pump 6 supplied and in particular to 20 bar to 100 bar, preferably compressed to 30 bar to 40 bar. The ethanol content of the stream S is in particular 40% by volume to 99.9% by volume, preferably 60% by volume to 96% by volume and particularly preferably 70% by volume to 90% by volume.

The compression is followed by heating, complete evaporation and overheating of the feed S. For this purpose, a heat coupling with a hot reactor effluent is preferred, ie, the stream S is from the pump 6 starting via a line 7 in a heat exchanger 8th fed, in which the stream S z. B. in countercurrent or other driving in indirect heat exchange with that from the reactors 10 - 13 withdrawn stream S occurs. This will be the from the reactors 10 - 13 cooled stream S cooled and the in the reactors 10 - 13 to be fed stream S heated accordingly.

Alternatively, however, another suitable process stream, for. B. HD steam, use or the aqueous ethanol solution S are conditioned in a corresponding furnace chamber.

After heating the stream S (feed) in the heat exchanger 8th the stream S is via a line 9 in the head 14 a first reactor 10 entered, with at least a section 9a of the said lead 9 by means of a heating medium 17 is heated to raise the temperature of the stream S. Within the first, adiabatically operated reactor 10 the stream S is on a catalyst bed 15 abandoned, which contains a highly selective Al ₂ O ₃ or ZSM5 catalyst. At the swamp 16 of the first reactor 10 the stream S, in which now ethylene is enriched accordingly, withdrawn again and via a line 10b , in turn, at least in sections by means of the heating means 17 is heated (section 10a ) in the head 14 a second reactor 11 fed, in which the heated stream S in turn on a catalyst bed 15 is abandoned (Al ₂ O ₃ - or ZSM5). In the same way is still a third and a fourth (analogue) catalyst 12 . 13 traversed by the stream S, with a section 11a one the second with the third reactor 11 . 12 connecting line 11b and a section 12a one the third with the fourth reactor 12 . 13 connecting line 12b again by means of the heating medium 17 be heated to the adiabatic operation of the reactors 10 - 13 to ensure.

Intermediate heating by means of a heating medium 17 is necessary because the dehydration is an endothermic reaction (+44.6 kJ / mol) in an adiabatic reactor 10 - 13 a drop of 180 to 200 K occurs, depending on the importance of side reactions. Since there is no appreciable activity of said catalyst in such a drop, at least part of the intermediate (stream S) becomes the reactor 10 - 12 taken and overheated again. This intermediate heating is carried out at least once, preferably up to three times. At the same time, these points can also be points for intermediate feeds of fresh feed (ethanol-rich stream S).

Alternatively to an adiabatic bed cascade 10 - 13 For example, an isothermal reactor with a heat tracer can be provided which heats the material stream via a heat transfer medium (eg steam, oil, molten salt).

Preferred heating levels for the adiabatic process, d. h., for said intermediate heating, are each at 300 ° C to 500 ° C, preferably at 350 ° C to 480 ° C, most preferably at 400 ° C to 450 ° C. In an isothermal reactor would be about 20 K to 30 K below the max. Inlet temperature of the adiabatic bed remain.

That from the swamp 16 of the fourth reactor 13 withdrawn gaseous reaction product (stream S) is then passed through a conduit 18 to the heat exchanger 8th passed and cooled there, with a part condensed, in particular the split-off water. For cooling in the heat exchanger 8th offers itself - as already indicated above - on the one hand to be heated feed stream (flow) S, possibly in combination with a second cooling water flow. It can also be integrated with sufficient availability, only a cooling water circuit.

The cooled, two-phase reaction product (stream) S is via a line 19 in a first column 20 (Stripper) passed to wash out the water-soluble reaction products as completely as possible from the gas phase with supply of fresh water and a circulation stream of the aqueous phase. The thus purified from oxygenates such as ketones, esters and ethers gas stream (stream S), which consists essentially of olefins, can head 21 the first column 20 are deducted and still contains traces of CO, CH ₄ and CO ₂ . The latter is removed in an acid gas wash. For this purpose, the stream S is via a line 23 in a second column 24 and run in countercurrent with a NaOH-Storm (other detergents can also be used, see above). Accordingly, on the head 25 the second column, a purified from CO ₂ stream S are deducted. A corresponding carbonate-containing phase is at the bottom 26 subtracted from the second column. The thus purified gas is preferably dried over a molecular sieve to obtain the quality standard "Chemical Grade Ethylene".

The further purification to "Polymer Grade Ethylene" comprises a C ₃₊ separation (molecules having three or more than three carbon atoms) in one with the second column 25 over a line 27 connected third column 28 (C ₃₊ components are added to the sump 30 the third column 28 deducted) and a separation of the traces of CO and CH ₄ over the head 33 a fourth column (distillation column) 34 over a line 31 with the third column 28 connected is.

The final pressure of the purified ethylene coming from the bottom of the fourth column 34 is withdrawn, is 10 bar to 30 bar, preferably 15 bar to 25 bar.

The ones from the swamp 22 the first column 20 withdrawn phase can be used to recover the contained ethanol via a line 35 through the membrane filter 38 be directed, so that one ethanol-rich phase via another line 50 the feed stream (stream) S can be added before compacting.

As a result of the compaction in the liquid phase, the operating costs (steam or electricity) in the process according to the invention are considerably lower. An example for comparison (same condition conditions for feed and product): The production of one ton of ethylene with the process described herein requires less than 5 kW of compression power, the conventional multi-stage compression process in fractionation has a consumption of 60 to 70 kW compaction performance per ton of ethylene.

A further advantage is that with the method according to the invention no strong olefin-containing stream must be compressed, which is known to fouling (in the compressor stages) tends, which can reduce the availability of plants previously known type.

Contrary to expectations, a comparably high conversion of ethanol to ethylene can be achieved with the process according to the invention at identical temperature. This was not to be expected a priori in the gaseous reaction with doubling the number of moles. Likewise, the higher pressure can significantly increase the space-time yield from an LHSV in the range of 0.1 to 0.2 to 1 to 1.2 l / h. Thus, the process requires only about 15% to 20% as much catalyst and reactor volume as the previously known reference method with multiple compressor stages, which leads to further savings based on the total investment.

Furthermore, several laboratory experiments were carried out (no optimized conditions, the numbers are only for comparison for different experimental conditions), whereby pressure, temperature and ethanol concentration were varied.

These experiments were carried out as follows:
An ethanol-water mixture was pumped to an evaporator. Subsequently, the evaporated ethanol was catalytically dehydrated in a tubular reactor (internal diameter 33.7 mm). The tube reactor was filled with 64 ml-160 ml of catalyst (acidic alumina).

The single-phase product stream was cooled (0-20 ° C) and the two resulting phases separated in a pressure vessel (decanter). The gas phase was continuously quantified by means of a gas meter.

The liquid phase was drained and weighed after the experiment. Both phases were analyzed in detail by gas chromatography. In addition, a GO-MS was also used to identify by-products.

A) Comparison 5 and 30 bar:

Example 1:

• Temperature: 431 ° C
• Pressure: 5.0 bar
• LHSV: 1.1 h-1
• Ethanol in water: 90 wt%
• Yield: 96 wt%

Example 2:

• Temperature: 431 ° C
• Pressure: 30,0 bar
• LHSV: 1.2 h-1
• Ethanol in water: 90 wt%
• Yield: 93 wt%

B) Comparison of 75 wt%, 90 wt% and 96 wt% ethanol:

Example 3

• Temperature: 402 ° C
• Pressure: 30,0 bar
• LHSV: 1.2 h-1
• Ethanol in water: 96 wt%
• Yield: 90 wt%

Example 4:

• Temperature: 402 ° C
• Pressure: 30,0 bar
• LHSV: 1.2 h-1
• Ethanol in water: 90 wt%
• Yield: 90 wt%

Example 5:

• Temperature: 402 ° C
• Pressure: 30,0 bar
• LHSV: 1.2 h-1
• Ethanol in water: 75 wt%
• Yield: 87% by weight.

LIST OF REFERENCE NUMBERS 1 Arrangement for producing ethylene from ethanol 2 fermentation facility 3 . 5 . 7 . 9 . 10b . 11b . 12b . 18 . 19 . 23 . 27 . 31 . 35 . 36 . 37 . 39 . 50 management 4 distillation column 6 pump 8th heat exchangers 9a . 10a . 11a . 12a line section 10 . 11 . 12 . 13 reactor 14 . 40 . 21 . 25 . 29 . 33 head 15 catalyst bed 16 . 41 . 22 . 26 . 30 . 34 swamp 17 heating 20 . 24 . 28 . 32 column 38 membrane filter

Claims (15)

Process for the production of ethylene, comprising the steps: - feeding an ethanol-containing material stream (S) into at least one reactor ( 10 - 13 ), and - dehydrating ethanol contained in the stream (S) in the at least one reactor ( 10 - 13 ) under formation of ethylene, characterized that the stream (S) before being fed into the at least one reactor ( 10 - 13 ) by means of a pump ( 6 ) is compressed. A method according to claim 1, characterized in that the following further steps are provided: - removing an ethylene-containing material stream (S) from the at least one reactor ( 10 - 13 Cooling the ethylene-containing material stream (S) to form a two-phase material stream (S) comprising water and an ethylene-containing gas phase, wherein in particular the water split off by dehydration of the ethanol present in the stream (S) condenses, and - feeding the two-phase material stream (S ) into one with the at least one reactor ( 10 - 13 ) flow-connected first column ( 20 ) for fractionating the stream (S), in particular for washing out at least one water-soluble constituent from the ethylene-containing gas phase in the first column ( 20 ), - wherein the stream (S) before feeding into the at least one reactor ( 10 - 13 ) is compressed so that the stream (S) even after said cooling during feeding into said first column ( 20 ) has a pressure required for said fractionation. Process according to Claim 1 or 2, characterized in that the stream (S) before being fed into the at least one reactor ( 10 - 13 ) is compressed to 20 to 100 bar, preferably to 30 to 40 bar. Method according to one of the preceding claims, characterized in that the ethanol content in the stream (S) before feeding into the at least one reactor ( 10 - 13 ) 40% by volume to 99.9% by volume, preferably 60% by volume to 96% by volume and particularly preferably 70% by volume to 90% by volume. Method according to one of the preceding claims, characterized in that the at least one reactor ( 10 - 13 ) is an isothermal reactor. Method according to one of the preceding claims, characterized in that the at least one reactor ( 10 - 13 ) is an adiabatic reactor, wherein in particular the stream (S) after passing through the at least one reactor ( 10 - 13 ) at least one further, preferably two further, most preferably three further adiabatic reactors ( 11 - 13 ), wherein the stream (S) in particular before a reactor ( 10 - 13 ) and / or between two reactors ( 10 - 13 ) is heated in each case, the stream (S) in particular to a temperature between 300 ° C to 500 ° C, preferably 350 ° C to 480 ° C, most preferably between 400 ° C to 450 ° C is heated. Method according to one of the preceding claims, characterized in that the stream (S) in the at least one reactor ( 10 - 13 for dehydrating ethanol present in the stream (S) to at least one catalyst bed ( 15 ), which has an Al ₂ O ₃ or a ZSM5 catalyst. Process according to Claim 2 or according to one of Claims 3 to 7 as far as dependent on Claim 2, characterized in that the stream (S) after passing through the at least one reactor ( 10 - 13 ) by an indirect heat exchange with the in the at least one reactor ( 10 - 13 ) to be introduced stream (S) is cooled. Method according to one of the preceding claims, characterized in that the stream (S) before feeding into the at least one reactor ( 10 - 13 ) is heated, completely evaporated and / or superheated, in particular by an indirect heat exchange with one of the at least one reactor ( 10 - 13 ) withdrawn stream (S) and / or another process stream, in particular in the form of steam and / or by heating in a furnace chamber. Process according to Claim 2 or according to one of Claims 3 to 8 as far as dependent on Claim 2, characterized in that the two-phase material stream (S) from the first column ( 20 ) and to remove CO ₂ in a second column ( 24 ) is subjected to an acid gas scrubbing, wherein said stream (S) is driven in particular countercurrent to a NaOH-containing stream, in particular the thus purified ethylene-containing two-phase stream (S) is dried by means of a molecular sieve, and wherein in particular the stream (S) before feeding into the at least one reactor ( 10 - 13 ) is compressed so that the stream (S) even when feeding into said second column ( 24 ) has a pressure required for sour gas scrubbing. A method according to claim 10, characterized in that the from the second column ( 24 ) withdrawn stream (S) for removing heavy C ₃₊ components in a third column ( 28 ) fed with a C ₃₊ -containing phase from the sump ( 30 ) of the third column ( 28 ), and wherein a C ₁ / C ₂ -containing stream (S) from the head ( 29 ) of the third column ( 28 ), and in particular the stream (S) before being fed into the at least one reactor ( 10 - 13 ) is compressed so that the stream (S) even when feeding into said third column ( 28 ) has a pressure required to remove the C ₃₊ components. A method according to claim 11, characterized in that the from the third column ( 28 ) withdrawn stream (S) for removing light components, in particular in the form of CO and / or CH ₄ , in a fourth column ( 32 ), wherein an ethylenhaltige phase from the sump ( 34 ) of the fourth column ( 32 ), and wherein those light components from the head ( 33 ) of the fourth column ( 32 ) subtracted from. A method according to claim 12, characterized in that the pressure of the sump ( 34 ) of the fourth column ( 32 ) withdrawn ethylene-containing phase is 10 bar to 30 bar, preferably 15 bar to 25 bar. Method according to one of the preceding claims, characterized in that the ethanol-containing material flow (S) before compression by means of the pump ( 6 ) on the head ( 40 ) a distillation column ( 4 ) is withdrawn, which is fed in particular with crude ethanol produced by fermentation, in particular one from the sump ( 41 ) of the distillation column ( 4 ) withdrawn ethanol-containing liquid phase for concentrating the ethanol in that phase through a membrane filter ( 38 ) and in particular that ethanol-containing phase after passing through the membrane filter ( 38 ) the said, out of the head ( 40 ) of the distillation column ( 4 ) withdrawn ethanol-containing material stream (S) in particular before the compression of the stream (S) is added. Process according to claim 2 or any of claims 3 to 14 as far as dependent on claim 2, characterized in that from the sump ( 22 ) of the first column ( 20 ) an ethanol-containing phase is withdrawn through a membrane filter ( 38 ) is concentrated to concentrate ethanol contained in that phase, wherein said phase is added in particular to the stream (S) before compacting.

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