EP2640680A1

EP2640680A1 - Method for removing high-boiling hydrocarbons from solvent flows

Info

Publication number: EP2640680A1
Application number: EP11794400.9A
Authority: EP
Inventors: Johannes Menzel; Holger Thielert
Original assignee: ThyssenKrupp Uhde GmbH
Current assignee: ThyssenKrupp Industrial Solutions AG
Priority date: 2010-11-16
Filing date: 2011-11-11
Publication date: 2013-09-25
Also published as: BR112013012047A2; US20140323790A1; CA2817854A1; WO2012065703A1; DE102010051396A1; RU2013124950A; US9249069B2

Abstract

The invention relates to a method for removing high-boiling hydrocarbons from water-soluble solvent flows, wherein said solvent flows are produced in industrial processes which circulate a solvent as a part of the process, and the solvent must be periodically or permanently freed of high-boiling hydrocarbons which influence the quality or the desired properties of the solvent in an unwanted way, and water is added for carrying out the method in a phase separator, so that the high-boiling hydrocarbons are separated off because of their immiscibility with water, and then the water-miscible phase containing water and solvent is returned to the process. By the method according to the invention the proportion of high-boiling hydrocarbons in circulating solvents in an industrial process can be kept permanently low.

Description

Process for removing high boiling hydrocarbons from solvent streams

The invention relates to a process for the removal of high-boiling hydrocarbons from water-soluble solvent streams, these solvent streams incurred in industrial processes, which lead a solvent as a process component in a circle, and the solvent must be periodically or permanently freed of high-boiling hydrocarbons, the quality or undesirably affect desired properties of the solvent, and water is added to perform the process in a phase separator, whereby the heavy hydrocarbons are separated because of their immiscibility with water, and then recycled the water and solvent-containing and water-miscible phase in the process , By the method according to the invention, the proportion of high-boiling hydrocarbons can be kept permanently low in circulating solvents in an industrial process.

Many industrial processes use solvents for execution, wherein the solvents are solid components of the process, which are circulated and needed because of their properties for the reaction. Typical processes include extractive distillation and gas purification processes. Since the solvents are frequently used for the purification of hydrocarbon-containing feedstocks, existing high-boiling hydrocarbon constituents from the feed mixture accumulate in the solvent streams. Often they affect their properties in an undesirable manner.

The accumulation of high-boiling hydrocarbons in solvents has a detrimental effect in many processes. Thus, the presence of these compounds, which may come from both the paraffinic and cyclic or aromatic compounds, may cause the solvent to foam. It may also be that, with a correspondingly high enrichment, the release effect of the solvent decreases. The accumulation of heavy hydrocarbons can mean that the required product quality can no longer be met. A separation by simple distillation is possible only in some cases, if, for example, the boiling point differences allow such separation and there is no formation of azeotropes. Distillation is associated with high costs or due to low boiling point differences with the solvents used often technically very expensive feasible. Often a thermal separation is practically impossible, since the solvent decomposes at elevated temperature and in the presence of higher water concentrations. It is therefore looking for ways to separate the high-boiling hydrocarbons in a simple manner from the solvents used in a technical process.

For this purpose, there are in the prior art methods which remove the unwanted high boilers due to their immiscibility with water from the process. This eliminates an energy-intensive distillation to remove these components. After the addition of water, the solvent, which is at least partially miscible with water, for the most part in the aqueous phase, while the high-boiling hydrocarbon passes completely into the water-immiscible phase. This is then separated and discarded, or the unwanted high boiler is removed by simple distillation from the water-immiscible phase. The solvent goes largely depending on the miscibility into the aqueous phase. This is then distilled to remove the water and the solvent returned to the process.

EP 0329958 A2 describes a process for preparing an aromatics concentrate suitable for use as a blending component for carburettor fuels, wherein feedstock hydrocarbon mixtures whose boiling range is substantially between 40 ° C and 170 ° C, without prior separation into individual fractions of an extractive distillation using N-substituted morpholines whose substituents have not more than seven carbon atoms are subjected as a selective solvent, so that the low-boiling non-aromatics with a boiling range up to about 105 ° C virtually completely and the higher-boiling non-aromatics with a boiling range between about 105 ° C and 160 ° C for the most part obtained as a raffinate, while the aromatics, which are used in whole or in part as a blending component, incurred in the extract of the extractive distillation, and the Schweraromatenabtrennung from the solvent while a partial flow of the recirculated water is added to the solvent and the heavy aromatics are removed as a light phase from the solvent Separate water mixture, which is then decomposed into its constituents and reused. The reprocessing step is energy intensive and therefore associated with high costs.

WO 2009043753 A1 teaches a process for the production of aromatic hydrocarbons selected from benzene, toluene, xylene, and ethylbenzene and mixtures thereof, from a hydrocarbon mixture, which also contains non-aromatic hydrocarbons and high boilers, wherein as a purification step for the aromatic hydrocarbons an extractive distillation is provided with an extractive solvent, and for separating the unwanted high-boiling constituents, a partial stream is separated from the extractive solvent, and the substream of the extractive solvent is extracted with water, so that a substantially free from high boiling aqueous extract phase and an organic phase containing the High boilers are obtained, and the aqueous extract phase for the recovery of the extractive solvent is distilled in purified form, so that the extractive solvent is recycled to the extractive distillation, and wherein prior to carrying out the extraction of the substream with water, a distillation is carried out in which a fraction of very high boiling hydrocarbons is separated from the substream of the extractive solvent. The process has the property that the extractive solvent must be distilled for recovery or must be expensively discharged from the process. This is associated with high costs. The additional distillation step to remove the high boiling hydrocarbons from the extractive solvent prior to the addition of water causes additional energy costs. It would therefore be advantageous to provide a method which separates the high-boiling hydrocarbons by adding water into a substream of an extracting solvent by forming second phases, the high-boiling and water-insoluble hydrocarbons by separation of the insoluble in water organic Phase, and the further workup of the water-soluble phase or the water-immiscible phase by distillation is unnecessary. The distillations mentioned in the prior art are characterized by a high expenditure of energy and influence the economy of the process in a negative way. There is therefore the task of providing a method which enables a purification of solvents used in industrial processes by separation of a partial stream of the solvent used, an addition of water and phase formation, wherein the undesirable high-boiling hydrocarbons by separation with water immiscible phase are separated from the process, and further processing of the aqueous phase from the process requires the least possible effort.

The invention solves this problem by a method which separates from the industrial process, which uses a solvent to be cleaned of heavy hydrocarbons, a partial flow, this partial flow provides with water, the mixing ratio with the water so provides that the formation of two not phases which are miscible with one another, performs a phase separation which removes water-immiscible phase with the undesired high-boiling components, which recirculates the water-miscible phase with the solvent in the process, wherein the recycling is designed so that further purification of the solvent is not required ,

Typical processes in which the process according to the invention is used are extractive distillations or gas scrubbing with absorbing solvents. The water-containing phase, which contains a large part of the solvent after the phase separation, depending on the miscibility, is returned to the process without further purification, wherein the recycle ratio is chosen so that the permissible water concentration in the solvent is not exceeded. The water introduced into the solvent circuit, since water is a low boiler, is discharged via one of the process steps present in the solvent cycle as a function of time. In an extractive distillation this can be exemplified by regenerative distillation. By means of this procedure, the water concentration in the process can be kept permanently low. In particular, a method for the removal of high-boiling hydrocarbons from water-soluble solvent streams in an industrial process, wherein A partial stream is taken from a solvent enriched with high-boiling hydrocarbons, which is led into a container, and

Water is added to this partial stream of solvent so that an aqueous and a nonaqueous phase are formed, and

• The hydrocarbon-containing phase is separated and withdrawn from the container, and

which is characterized in that

• The aqueous phase is recycled without further distillation in a suitable concentration in the process.

The container can be arbitrary. This may be a simple container suitable for separation and separation of immiscible phases, but it may also be an extractor which carries out both phases separately, and optionally interposing the water-miscible phase, around this phase in appropriate concentration to be able to trace back into the process. The container may also be a phase separator or additional phase separators may be interposed prior to initiation into the process to achieve complete phase separation.

The process for the removal of high-boiling hydrocarbons from water-soluble solvent streams is exemplified by an extractive distillation. By way of example, the process for removing high boiling point hydrocarbons from solvent streams is a process for gas scrubbing to separate unwanted gases from a gas mixture. An example of a suitable process for extractive distillation is EP 0792928 B1. An example of a suitable process for gas scrubbing is EP 1606041 B1. Ultimately, all process forms are possible in which a solvent with high-boiling substances accumulates and must be freed from these.

The water is added in an amount which allows a good phase separation, which is typically added to the solvent partial stream in the container in an amount of 5 to 90 wt .-%. On the container for phase separation sits in one embodiment of the invention, a cooler. Thereby For example, the temperature may be lowered to achieve efficient removal of the high boiling hydrocarbons. On the container for phase separation can sit for the same purpose a heater.

In one embodiment of the invention, the water concentration of the liberated from high-boiling hydrocarbons solvent immediately after recycling in the process 0.5 to 5 wt .-%. In a further embodiment, the water concentration of the solvent released from high-boiling hydrocarbons immediately after recirculation into the process is 1 to 2% by weight. As a result, the water can be returned to the process, without this having a disturbing effect on the solvent. The water concentration in the process, in the phase separation or in supply lines can be determined for this purpose by suitable measuring devices temporarily or permanently.

In one embodiment of the method, the water-containing phase is continuously metered into the solvent circuit during the return to the solvent process, so that the water concentration in the solvent released from the high-boiling hydrocarbons amounts to less than 0.5% by weight immediately after recycling to the process. is.

The added water is supplied to the solvent circuit and discharged according to the invention over time in the further course of the process over the solvent cycle already existing process steps. If it is an extractive distillation, the excess water is typically withdrawn via the top fraction of the regeneration column to remove the solvent ("stripping column"). The removal of the water after recycling into the solvent process thus takes place through the distillation columns or regeneration columns present in the extractive distillation ,

When the process is gas scrubbing, the excess water is conveniently taken up by the usually dry feed gas. The feed gas supplied to the bottom of the absorption column takes in countercurrent, theoretically, the water contained in the solvent, which is added to the top of the absorption column to the saturation limit, and thus the water-enriched product gas leaves the absorption column Head. The removal of the water after the return in the solvent process thus takes place by means of a flowing through the absorption column dry feed gas stream.

The invention has the advantage of allowing a simple separation of high-boiling substances from solvent mixtures, without an energy-consuming and thus economically unfavorable distillation of solvent is required. The water content of the solvent in the process is kept low by appropriate means, and the heavies and hydrocarbons are discharged from the process. As a result, the properties of the solvent over the service life of the process are largely retained.

The process flow of the method according to the invention is explained in more detail with reference to two drawings, wherein the inventive method is not limited to these embodiments. FIG. Figure 1 shows an extractive distillation equipped with water addition and phase separation tanks. FIG. Figure 2 shows a gas scrubber equipped with water addition and phase separation tanks.

FIG. 1 shows the process flow for the extractive distillation of a hydrocarbon mixture in which the hydrocarbon-containing feed mixture (1) is fed onto a column (2) for extractive distillation. The extractive distillation column (2) is equipped with a reboiler (2a). At the top of the column, a stream (3a) is obtained which is enriched with light distillation products. The product is returned via a reflux vessel (4) and a reflux pump (5) in the head of the extractive distillation column. A partial stream (3b), which also contains the discharged water in low concentration, is taken as product. At the bottom of the column, a distillation bottoms stream (3c) enriched in aromatic and heavier hydrocarbons is obtained, which also contains the extracting solvent. This is passed through a bottom-flow pump (6) into the regeneration column (7), which is of the distillation column type. There, the desired product which consists of aromatic hydrocarbons is obtained at the top of the column (8a) and the solvent is returned at the bottom of the column (8b). At the regeneration column (7) for the distillation of the solvent, the desired product is obtained from the extractive distillation. This is carried out via a cooler (9) and a reflux container (10) (FIG. 8c). This also contains the high-boiling hydrocarbons. The regeneration column (7) also contains a reboiler (7a) for heating the distillation stream (7b). The solvent (8b) is returned to the column (2) for extractive distillation. This stream (11) is fed via a pump (12), a side reboiler (13) for partial evaporation of the solvent in the extractive distillation column, a heat exchanger for preheating the feed mixture (1a), and a cooler (14) back into the extractive distillation column (2) , A partial stream (15) of the cooled solvent stream is branched off via a valve (16) and placed in a phase separation vessel (17) where water (18) is added. This results in the formation of two immiscible phases (19a, 19b). The lighter phase (19a) typically contains the heavier hydrocarbons and is separated and removed from the process (20a). This can be further processed as needed or used for heating purposes, for example. The heavier phase (19b) containing the purified solvent is also separated (20b) and returned to the process by means of a pump (21) via the valve (22) with the untreated partial flow (12a) (22a).

FIG. Figure 2 shows a process for gas scrubbing which contacts a feed gas (23) with an absorbing solvent in an absorption column (24), thereby liberating the feed gas (23) from undesired sour gases. This gives a purified product gas (25) for further use. The absorbed sour gas is carried out in a mixture with the absorbing solvent (26) from the absorption column (24) and led into a cascade of "flash" containers (27a-c). This is withdrawn from the solvent (26), which is withdrawn from the process and optionally reused to obtain a regenerated solvent (29) A partial stream of regenerated solvent (29a) is diverted via a valve (16) and into a phase separation vessel (17), where water (18) is added to give two phases (19a, 19b) The lighter phase (19a) is separated and removed from the process (20a), which can be further processed or added, as needed The heavier phase (19b) is separated (20b) and optionally by means of a pump (30) via the valve (22) in the absorption column (24) as a purified Solvent returned (22a). The transport of the regenerated solvent (22b) to the top of the Absorption column is effected by a circulation pump (12). The phase separation vessel (17) is cooled here with a cooler (17a). At the supply line of the regenerated solvent (21a) in the absorption column (24) sits an analyzer (31) for determining the water concentration.

[0024] List of Reference Numerals

1 feed mixture

1 a preheater or heat exchanger for feed mixture

2 column for extractive distillation

2a reboiler for extractive distillation column

3a stream at the top of the column for extractive distillation

3b overhead product stream from the column for extractive distillation

3c distillation bottoms stream

4 reflux tank

5 reflux pump

6 bottom-flow pump for the column for extractive distillation

7 regeneration column

7a reboiler for regeneration column

7b distillation stream

8a top product of the regeneration column

8b Regenerated solvent sump stream of the regeneration column

8c Executed aromatics-containing distillation product

9 coolers for regeneration tower head product

10 reflux containers

11 Regenerated solvent stream

12 pump for regenerated solvent

12a Main route of the solvent cycle

13 side reboiler

14 coolers

15 Solvent substream with heavy hydrocarbons

16 valve

17 phase separation container

17a cooler

18 water

19a Easier phase

19b heavier phase

20a High-boiling hydrocarbons

20b recycled water-containing phase with solvent pump

Valve

a recycle stream of regenerated solvent recycle stream of regenerated solvent

feed gas

absorption column

Purified product gas

Sour gas-containing solvent stream

a-c "Flash" container

a-c sour gas streams

Regenerated solvent

a partial stream of the regenerated solvent

pump

Analyzer for determining the water concentration

Claims

claims

A process for the removal of high boiling hydrocarbons (20a) from water soluble solvent streams (1) in an industrial process, wherein

• From a high-boiling hydrocarbons (20a) enriched solvent (1) a partial stream (15) is removed, which is guided into a container (17), and

• This solvent partial stream (15) is provided with water (18), so that it comes to form an aqueous (19b) and a nonaqueous (19a) phase, and

The hydrocarbon-containing phase (19a) is separated (20a) and withdrawn from the container (17),

characterized in that

The water-containing phase (19b) is returned to the solvent process without further distillation at a suitable concentration (20b).

Process for the removal of high-boiling hydrocarbons (20a) from solvent streams (1) according to Claim 1, characterized in that the process (2) for removing high-boiling hydrocarbons (20a) from solvent streams is an extractive distillation (2).

Method for removing high-boiling hydrocarbons (20a) from solvent streams (1) according to claim 2, characterized in that the removal of the water (18) after the return to the solvent process (22a) by the distillation columns (2) or regeneration columns (2) present in the extractive distillation ( 7).

Method for removing high-boiling hydrocarbons (20a) from solvent streams (1) according to Claim 1, characterized in that the process (24) for removing heavy-boiling hydrocarbons (20a) from solvent streams (22b) is a process for gas scrubbing (24). is.

5. A process for the removal of high-boiling hydrocarbons (20a) from solvent streams (1) according to claim 4, characterized in that the removal (25) of the water (18) after the return to the solvent process (22a, 22b) by means of a through the absorption column ( 24) flowing dry feed gas stream (23) takes place.

6. A process for the removal of high-boiling hydrocarbons (20a) from solvent streams (1) according to one of claims 1 to 5, characterized in that to the partial solvent stream (29a) in the container (17) water (18) in an amount of 5 to 90 % By weight is added.

7. A process for the removal of high-boiling hydrocarbons (20a) from solvent streams (1) according to any one of claims 1 to 6, characterized in that the water concentration of the high-boiling hydrocarbons (20a) freed solvent (19b) immediately after the return to the process (20b ) 0.5 to 5 wt .-% is.

8. A process for the removal of high-boiling hydrocarbons (20a) from solvent streams (1) according to any one of claims 1 to 6, characterized in that the water concentration of the high-boiling hydrocarbons (20a) freed solvent (19b) immediately after the return to the process (20b ) 1 to 2 wt .-% is.

9. A process for removing high-boiling hydrocarbons (20a) from solvent streams (1) according to one of claims 1 to 8, characterized in that the water-containing phase (19b) continuously metered into the solvent circuit (22a) during the return to the solvent process (20b) ( 22), so that the water concentration of the solvent released from high-boiling hydrocarbons (20a) immediately after the recycling (22) in the process (2) is less than 0.5% by weight.

10. A process for removing high-boiling hydrocarbons (20a) from solvent streams (1) according to one of claims 1 to 9, characterized in that on the container (17) for phase separation, a cooler

(17a) sits.

11. A process for the removal of high-boiling hydrocarbons (20a) from solvent streams (1) according to one of claims 1 to 9, characterized in that on the container (17) for phase separation, a heater sits.