WO2012163481A1

WO2012163481A1 - Process for preparing ethylene

Info

Publication number: WO2012163481A1
Application number: PCT/EP2012/002122
Authority: WO
Inventors: Marianne Ponceau; Florian Winkler; Volker Göke; Markus Fritsch
Original assignee: Linde Aktiengesellschaft
Priority date: 2011-05-31
Filing date: 2012-05-16
Publication date: 2012-12-06
Also published as: DE102011102971A1

Abstract

A process for preparing ethylene, comprising the steps of: feeding an ethanol-containing stream (S) into at least one reactor (10-13) and dehydrating ethanol present in the stream (S) in the at least one reactor (10-13) to form ethylene. According to the invention, the stream (S) is compressed by means of a pump (6) before being fed into the at least one reactor (10-13).

Description

description

Process for the production of ethylene

The invention relates to a process for the production of ethylene according to the

Preamble of claim 1.

In such a method, e.g. fed an ethanol-containing material 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, due to its characteristics (very high selectivity, very high conversion) and relatively simple decomposition parts is also interesting 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 envisaged that the liquid stream is compacted prior to feeding (upstream) into the at least one reactor by means of a pump (high-pressure pump) or a pumping means, that is, brought to a predefinable pressure by means of said pump. 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Preferably, it is further provided that that ethylene-containing material stream is withdrawn from the at least one reactor.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, whereby a part condenses, in particular the water split off during the dehydration.

For cooling, on the one hand, the material to be heated (feed stream) to be introduced into the at least one reactor is provided (see below), in particular in FIG Combination with a second cooling water flow. It can be sufficient if

Availability also only a cooling water circuit can be integrated. The resulting by cooling two-phase flow containing a

The ethylene-containing gaseous phase is preferably fed into a first column (e.g., stripper) pressure-connected to the reactor for further fractionation, especially for washing out at least one water-soluble constituent (e.g., in the form of oxygenates such as ketones, esters, and / or ethers) from the gaseous phase.

In this case, the two-phase stream is preferably 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, the said stream is preferably pressurized prior to feeding into the at least one reactor such that the stream still has a fraction for fractionating or washing out the at least one water-soluble stream even after said cooling when feeding into said first column

Component required pressure.

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 to the extent that after cooling of the reaction mixture is at least one pressure, as he also for the other

Fractionation is required (e.g., washing out of water-soluble components, 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, the said further fractionation can also other

Procedural steps include (see below).

Thus, it is preferably provided that the two-phase (ethylene-containing) material flow from the Column flow or pressure connected second column a

Sour gas washing is subjected.

For this purpose, the said stream is preferably countercurrent to a NaOH-containing stream (to form water and Na ₂ C0 ₃ ) driven, in particular a carbonate-containing phase from the bottom of the second column is withdrawn, and preferably the thus purified and from the dried second column withdrawn ethylene-containing biphasic Stoffstromjjber 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 ₃₊ -Bestandteilen (hydrocarbons with three or more than three carbon atoms) is preferably the withdrawn from the second column (ethylene containing) material stream for the removal of heavy C in a column with the second

Fed fluid or pressure-conducting third columns. 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.

Finally, to remove light constituents, such as CO and / or CH ₄ , the (ethylene-containing) material stream withdrawn from the third column is fed into a fourth column which is fluidly or pressure-conductively connected to the third column, one (final purified, concentrated) ethylene-containing gaseous phase is withdrawn from the bottom of the fourth column, 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 stream (heat tracing) can be carried out via a heat transfer medium, e.g. 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 over the

Reactor wall, approximately no heat exchange with the environment instead. 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 is preferably provided that they each contain at least one catalyst bed, which is acted upon by the material flow, wherein those catalyst beds preferably have an Al ₂ 0 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. It is the

fed stream is preferably completely evaporated and / or superheated. The heat exchange can also be carried out with another process stream, in particular in the form of steam (high-pressure steam). To heat the stream this can also be heated in a Oferiraum.

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 prepared 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 said to be from the top of the distillation column

withdrawn ethanol-containing material stream added.

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 are derived e.g. 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:

Fig. 1 is a schematic representation of a system or a method for

Production of Ethylene from Ethanol. FIG. 1 shows a plant (arrangement) 1 or a corresponding process for the inventive (heterogeneous-catalytic) dehydration of ethanol (EtOH) to ethylene. For this purpose, Appendix 1 shows four interconnected, adiabatic

operated reactors 10 - 13 on.

According to the invention, a compression of a liquid feed (stream) S containing aqueous ethanol (EtOH (aq)) is carried out by means of a pump, in particular in the form of a high-pressure pump 6. 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 further fractionation.

First, the crude ethanol obtained in a preceding bioprocessing process step by fermentation in a fermentation unit 2 is separated from the yeast components of the fermentation broth and fed to a distillation column 4 via a line 3 for concentration. At the top 40 of the

Distillation column 4 can then be withdrawn from a ethanol-rich phase, while a withdrawn from the bottom of the distillation column 4 phase is passed through a line 36 to increase the product yield and process water treatment through a membrane filter 38. 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 recycling in the withdrawn from the head 40 of the distillation column 4 stream S in terms of yield increase.

The ethanol-rich stream S is then fed via a line 5 of the pump 6 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 compaction is followed by a warming, 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 fed from the pump 6, starting via a line 7 in a heat exchanger 8, in which the flow S, for example, in countercurrent or other driving in indirect Heat exchange with the withdrawn from the reactors 10 - 13 stream S occurs. As a result, the stream S withdrawn from the reactors 10-13 is cooled and the stream S fed into the reactors 10-13 is heated accordingly. Alternatively, however, may also be another suitable

Process stream, e.g. HD steam, use or the aqueous Ethahollösung S are conditioned in a furnace chamber accordingly.

After heating the stream S (feed) in the heat exchanger 8, the stream S is entered via a line 9 in the head 14 of a first reactor 10, wherein at least a portion 9a of said line 9 is heated by a heating means 17 to the temperature of the Material stream S to raise. Within the first, adiabatically operated reactor 10, the stream S is fed onto a catalyst bed 15 which contains a highly selective Al ₂ O ₃ or ZSM5 catalyst. At the bottom 16 of the first reactor 10, the stream S, in which now ethylene

enriched accordingly, again withdrawn and fed via a line 10b, which in turn is at least partially heated by the heating means 17 (Section 10a) in the head 14 of a second reactor 1 1, in which the heated stream S is in turn fed to a catalyst bed 15 (Al ₂ 0 ₃ - or ZSM5). In the same way, a third and a fourth (analogous)

Catalyst 12, 13 of the stream S, wherein a portion 11 a of the second with the third reactor 1 1, 12 connecting line 11 b and a portion 12 a of the third with the fourth reactor 12, 13 connecting line 12 b again by means of the heating means 17th be heated to ensure the adiabatic operation of the reactors 10-13.

Intermediate heating by means of the heating means 17 is necessary because the dehydration is an endothermic reaction (+44.6 kJ / mol) in which a drop of 180 to 200 K occurs in an adiabatic reactor 10-13, as the case may be Meaning of side reactions. Since there is no appreciable activity of said catalyst in such a drop, at least a portion of the intermediate (stream S) is removed from the reactor 10 - 12 and again superheated. These

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). As an alternative to an adiabatic bed cascade 10 -13, 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, ie, for said intermediate heating, are each at 300 ° C to 500 ° C, preferably 350 ° C to 480 ° C, most preferably 400 ° C to 450 ° C. In an isothermal reactor would be about 20 K to 30 K below the max. Inlet temperature of

remain adiabatic bed.

The withdrawn from the sump 16 of the fourth reactor 13 gaseous

Reaction product (stream S) is then passed via a line 18 to the heat exchanger 8 and cooled there, with a part condensed, in particular the split-off water. For cooling in the heat exchanger 8 offers itself - as already indicated above - on the one hand to be heated feed stream (stream) 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 passed via a line 19 in a first column 20 (stripper) to wash out the water-soluble reaction products as completely as possible from the gas phase while supplying fresh water and a circulation stream of the aqueous phase. The purified as oxygenates such as ketones, esters and ethers gas stream (stream S), which consists of olefins essentially can be withdrawn at the head 21 of the first column 20 and still contains traces of CO, CH ₄ and C0. ₂ The latter is removed in an acid gas wash. For this purpose, the stream S is introduced via a line 23 into a second column 24 and driven in countercurrent with a NaOH Storm (other detergents can also be used, see above). Accordingly, at the top 25 of the second column of a C0 ₂ purified stream S can be deducted. A corresponding carbonate-containing phase is withdrawn at the bottom 26 of 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" (polymer grade ethylene) comprises a C ₃₊ separation (molecules having three or more than three carbon atoms) in a third column 28 (C _3, connected to the second column 25 via a line 27 ₊ Components are withdrawn at the bottom 30 of the third column 28) and a separation of the traces of CO and CH ₄ via the head 33 of a fourth column (distillation column) 34, which is connected via a line 31 to the third column 28.

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

The withdrawn from the bottom 22 of the first column 20 phase can for

Recovery of the ethanol contained therein are passed through a line 35 through the membrane filter 38, so that an ethanol-rich phase can be added via a further line 50 to the feed stream (stream) S 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 one LHSV in the range of 0.1 to 0.2 to 1 to 1.2 1 / h. Thus, the process requires only about 15% to 20% as much catalyst and reactor volume as the previously known reference method with several

Compressor levels, which leads to further savings in relation to 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 in a tubular reactor

(Inside diameter 33.7 mm) catalytically dehydrated. 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, GC-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: 90wt%

Yield: 96wt%

Example 2:

Temperature: 431 ° C Pressure: 30,0 bar

LHSV: 1, 2 h-1

Ethanol in water: 90wt%

Yield: 93wt%

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

Example 3

Temperature: 402 ° C

Pressure: 30,0 bar

LHSV: 1, 2 h-1

Ethanol in water: 96wt%

Yield: 90% by weight Example 4:

Temperature: 402 ° C

Pressure: 30.0 bar

LHSV: 1, 2 h-1

Ethanol in water: 90wt%

Yield: 90wt%

Example 5:

Temperature: 402 ° C

Pressure: 30,0 bar

LHSV: 1, 2 h-1

Ethanol in water: 75wt%

Yield: 87wt%. LIST OF REFERENCE NUMBERS

Arrangement for producing ethylene from ethanol

fermentation facility

, 5, 7, 9, 10b, 1b, 12b, 18, 19, 23, 27, 31, conduit

5, 36, 37, 39, 50

distillation column

pump

heat exchangers

a, 10a, 11a, 12a line section

0, 11, 12, 13 reactor

4, 40, 21, 25, 29, 33 head

5 catalyst bed

6, 41, 22, 26, 30, 34 swamp

7 heating means

0, 24, 28, 32 column

8 membrane filters

Claims

claims

Process for the preparation of ethylene, comprising the steps:

- Feeding an ethanol-containing stream (S) in at least one reactor (10-13), and

Dehydration of ethanol contained in the stream (S) in the at least one reactor (10-13) with formation of ethylene, characterized in that the stream (S) prior to feeding into the at least one reactor (10-13) by means of a pump (6) is compressed.

2. The 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 of the ethylene-containing material stream (S) to form a two-phase

Material stream (S) containing water and an ethylene-containing gas phase, wherein in particular condensed by dehydration of the stream contained in the stream (S) ethanol condensed water, and

- Feeding the two-phase stream (S) in a with the at least one reactor (0- 3) 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) prior to feeding into the at least one reactor (10-13) is compressed so that the stream (S) even after said cooling when feeding into said first column (20) to said fractionation required pressure. Method according to claim 1 or 2, characterized in that the

Material stream (S) before being fed into the at least one reactor (10-13) to 20 to 100 bar, preferably to 30 to 40 bar compressed.

Method according to one of the preceding claims, characterized

characterized in that the ethanol content in the stream (S) before

Feeds into the at least one reactor (10-13) is 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

characterized in that the at least one reactor (10-13) is an isothermal reactor.

Method according to one of the preceding claims, characterized

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 Runs reactors (11-13), wherein the stream (S) in particular in front of a reactor (10-13) and / or between two reactors (10-13) is heated in each case, wherein the material flow (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 in the stream (S) contained ethanol is applied to at least one catalyst bed (15) comprising an Al ₂ 0 ₃ - or a ZSM5 catalyst having.

Method according to claim 2 or according to one of claims 3 to 7 as far back referring to claim 2, characterized in that the stream (S) after passing through the at least one reactor (10-13) by a indirect heat exchange with the in the at least one reactor (10-13) to be introduced stream (S) is cooled.

9. The method according to any one of the preceding claims, characterized

characterized in that the material stream (S) is heated, completely evaporated and / or superheated before being fed into the at least one reactor (10-13), 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.

10. The method according to claim 2 or according to one of claims 3 to 8 so far

With reference to claim 2, characterized in that the two-phase stream (S) from the first column (20) is withdrawn and subjected to the removal of C0 ₂ in a second column (24) an acid gas scrubbing, wherein said stream (S) in particular in Countercurrent is driven to a NaOH-containing stream, wherein 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) prior to feeding into the at least one reactor (10-13) so densified is that the material flow (S) even at

Feeding into said second column (24) has a pressure required for acid gas scrubbing.

A process according to claim 10, characterized in that the stream (S) withdrawn from the second column (24) is fed into a third column (28) for removing heavy C ₃₊ components, a C ₃₊ -containing phase consisting of the bottoms (30) of the third column (28) is withdrawn, and wherein a C ₁ / C ₂ -containing stream ^' (S) from the head (29) of the third column (28) is withdrawn, 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 third column (28) has a pressure required for removing the C ₃₊ components.

12. The method according to claim 1 1, characterized in that from the third column (28) withdrawn stream (S) for the removal of light Ingredients, in particular in the form of CO and / or CH ₄ , in a fourth column (32) is fed, wherein an ethylene-containing phase from the sump (34) of the fourth column (32) is withdrawn, and wherein those light components from the head (33) of the fourth column (32) are deducted.

1 3. The 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 1 5 bar to 25 bar. 14. The method according to any one of the preceding claims, characterized

characterized in that the ethanol-containing material stream (S) before the compression by means of the pump (6) from the head (40) of a distillation column (4) is withdrawn, which is fed in particular with crude ethanol produced by fermentation, in particular one from the sump (41 ) is fed to the distillation column (4) withdrawn ethanol-containing liquid phase for concentrating the ethanol in that phase through a membrane filter (38), and wherein

in particular that ethanol-containing phase after passing through the

Membrane filter (38) the said, from the head (40) of the distillation column (4) withdrawn ethanol-containing material stream (S) is added in particular before the compression of the stream (S).

1 5. The method of claim 2 or one of claims 3 to 14 so far

With reference to claim 2, characterized in that from the sump (22) of the first column (20) an ethanol-containing phase is withdrawn, which is passed through a membrane filter (38) to concentrate contained in that phase ethanol, said phase in particular the Material stream (S) is added before compacting.