WO2025190833A1

WO2025190833A1 - A process and plant for removing water from a crude composition containing water, phenol and bisphenol a

Info

Publication number: WO2025190833A1
Application number: PCT/EP2025/056388
Authority: WO
Inventors: Chris Lu; Chao YUNG-KANG; Ulric SEAH
Original assignee: Sulzer Management AG
Current assignee: Sulzer Management AG
Priority date: 2024-03-11
Filing date: 2025-03-10
Publication date: 2025-09-18
Anticipated expiration: 2026-09-11

Abstract

A process for removing water from a crude composition containing water, phenol and bisphenol A, wherein the process comprises the steps of: a) feeding the crude composition into a dividing-wall distillation column and distilling it therein so as to obtain an overhead composition, a side composition and a bottom composition, wherein the bottom composition is a dewatered bisphenol A composition, b) subjecting the overhead composition obtained in step a) to a liquid-liquid extraction with an extracting agent in an extraction column so as to obtain a raffinate composition being enriched in water and an extract composition being enriched in phenol, and 15 c) feeding the extract composition obtained in step b), the side composition obtained in step a) and an extracting agent being the same as that used in step b) separately from each other into a distillation column and distilling these therein so as to obtain an overhead composition containing the extracting agent and water as well as a bottom composition containing phenol.

Description

A process and plant for removing water from a crude composition containing water, phenol and bisphenol A

The present invention relates to a process and to a plant for removing water from a crude composition containing water, phenol and bisphenol A.

Bisphenol A is an important raw material for industrial processes and in particular an important comonomer for the production of a variety of polymers, such as polycarbonates, epoxy resins, polysulfones, polycyanurates, polyetherimides and others. Bisphenol A is typically synthesized by performing a condensation reaction of acetone and phenol to bisphenol A and water, thus leading to a reaction mixture or crude composition, respectively, containing the synthesized bisphenol A, the coproduct water, non-reacted acetone, non-reacted phenol and side-products. Thereafter, the crude composition is purified, in order to reduce the content of water, acetone and phenol to a sufficiently low level allowing the purified bisphenol A to be used in the desired application, for instance as comonomer in a polymerization reaction to epoxy resin.

Usually, the crude bisphenol A containing composition is processed in two subsequent distillation steps, wherein the second distillation step is performed as azeotropic distillation using an entrainer, such as ethylbenzene, in order to break the water-phenol azeotrope. More specifically, in the first upstream distillation step, comparably pure bisphenol A is separated from the crude composition as bottom composition, whereas the overhead composition contains water, acetone, phenol and side-products. Thereafter, the water is separated in the second downstream azeotropic distillation from the phenol and acetone. However, this process is very energy intensive, because the large amount of water included in the crude composition must be heated twice. More specifically, the crude composition containing mainly water and bisphenol A and smaller amounts of the non-reacted acetone and phenol is firstly heated in the first distillation column, in order to separate the bisphenol A from the crude composition. The water containing overhead composition is then condensed, partially recycled as reflux into the first distillation column, whereas the remaining portion of the condensed overhead composition is then led into the downstream azeotrope distillation column, in which the overhead composition including large amounts of water is heated/evaporated for a second time.

In view of this, the object underlying the present invention is to provide a process and a plant for removing water from a crude composition containing water, phenol and bisphenol A and in particular further containing acetone, which leads to dewatered bisphenol A, but which is characterized by a low energy consumption.

In accordance with the present invention, this object is satisfied by providing a process for removing water from a crude composition containing water, phenol and bisphenol A, wherein the process comprises the steps of: a) feeding the crude composition into a dividing-wall distillation column and distilling it therein so as to obtain an overhead composition, a side composition and a bottom composition, wherein the bottom composition is a dewatered bisphenol A composition, b) subjecting the overhead composition obtained in step a) to a liquid-liquid extraction with an extracting agent in an extraction column so as to obtain a raffinate composition being enriched in water and an extract composition being enriched in phenol, and c) feeding the extract composition obtained in step b), the side composition obtained in step a) and an extracting agent being the same as that used in step b) separately from each other into a distillation column and distilling these therein so as to obtain an overhead composition containing the extracting agent and water as well as a bottom composition containing phenol. This solution bases on the finding that by first separating the crude bisphenol A containing composition in a dividing-wall column into an overhead composition mainly consisting of water and minor amounts of phenol and acetone, into a side composition mainly consisting of phenol and minor amounts of water and acetone and into a dewatered bisphenol A composition, from which only the side composition with a comparable low water content is sent directly to a downstream distillation column functioning as extracting agent recovery distillation column, but the overhead composition mainly consisting of water and minor amounts of phenol and acetone is subjected to a liquid-liquid extraction so as to separate the major water portion contained in the overhead composition of the dividing-wall distillation column as raffinate composition from the extract composition having a comparable low water content and comparable high phenol content, wherein only the extract composition having a comparable low water content is led into the extracting agent recovery distillation column, only a comparable small amount of the water being contained in the crude composition needs to be heated twice. Namely, only the comparable small portions of the water being contained in the side composition being obtained in the dividing-wall distillation column and of the water being contained in the extract composition being obtained in the liquid-liquid extraction step are led into the extracting agent recovery distillation column and have to be heated/evaporated therein, whereas the major amount of water, which is separated in the liquid-liquid extraction step as raffinate composition, is not at all led into the extracting agent recovery distillation step and thus does not need to be heated/evaporated twice. In addition, because the major portion of the phenol being contained in the crude composition is separated from the water in the crude composition as side composition and is directly led into the extracting agent recovery distillation and not to the liquid-liquid extraction, the liquid-liquid extraction is only performed with a comparable small volume of the crude composition and thus requires only comparable low amounts of extracting agent. Another advantage of the method in accordance with the present invention is that in steps b) and c) the same extracting agent is used. Thereby the management of two different streams, namely of a first extracting agent stream on the one hand and of a different second extracting agent stream on the other hand, can be reduced to the management of only one stream. All in all, the implementation of a divided-wall distillation column in combination with an extraction column allows to obtain a dewatered bisphenol A composition and to reduce the energy consumption of the process by at least 30% in comparison to a prior art process, in which the crude composition is separated in a regular distillation column without dividing wall into an overhead composition and a pure bisphenol A composition as bottom composition, whereafter the whole overhead composition is led to an azeotrope distillation.

The present invention is not particularly limited concerning the kind and content of the impurities in the crude composition containing bisphenol A. The process in accordance with the present invention has been shown to be particularly suitable to dewater a crude composition, which contains, based on 100% by weight of the crude composition, 15 to 35% by weight of bisphenol A, 1 to 5% by weight of water, 0.5 to 5% by weight of acetone and 60 to 80% by weight of phenol. More preferably, the crude composition contains, based on 100% by weight of the crude composition, 20 to 30% by weight of bisphenol A, 1 .5 to 2.0% by weight of water, 0.8 to 2.9% by weight of acetone and 65 to 75% by weight of phenol.

Also concerning the kind of dividing-wall distillation column used in step a), the present invention is not particularly restricted. Thus, any distillation column comprising a dividing wall, which separates at least a longitudinally extending section of the dividing wall, seen in its cross-section, into two sub-sections may be used. Preferably, the dividing wall is arranged at least essentially vertical downwards in the dividing-wall distillation column. At least essentially vertically downwards means in accordance with the present invention that the angle between the dividing wall and the length axis of the dividing-wall distillation column or vertical direction, respectively, is at most 20°, preferably at most 10°, more preferably at most 5° and most preferably 0°. In accordance with a particularly preferred embodiment of the present invention, the crude composition is fed in step a) into a middle dividing-wall distillation column. A middle dividing-wall distillation column is according to the present invention defined as a dividing-wall distillation column, which comprises a dividing wall extending from a point being located below the top of the distillation column at least essentially vertically downwards to a point being located above the bottom of the dividing-wall distillation column so as to subdivide the dividing-wall distillation column into a top section being located above the dividing-wall, into a bottom section being located below the dividing-wall and into a middle section comprising a first middle subsection being located on one side of the dividing wall and a second middle subsection being located on the opposite side of the dividing wall. Good results are in particular obtained, when the dividing wall extends, seen from the bottom to the top of the dividing-wall distillation column, from a point being located at 10 to 45% of the distance from the bottom to the top of the dividing-wall distillation column to a point being located at 50 to 90% of the distance from the bottom to the top of the dividing-wall distillation column and preferably from a point being located at 25 to 40% of the distance from the bottom to the top of the dividing-wall distillation column to a point being located at 60 to 80% of the distance from the bottom to the top of the dividing-wall distillation column. Moreover, it is preferred that the dividing wall extends, seen from the bottom to the top of the dividing-wall distillation column, over 5 to 90%, more preferably over 20 to 80% and most preferably over 30 to 70% of the distance from the bottom to the top of the dividing-wall distillation column.

In a further development of the idea of the present invention, it is suggested that the dividing wall subdivides the middle section of the dividing-wall distillation column, seen in cross-section of the dividing-wall distillation column, in about two equally sized subsections or halves, respectively. Therefore, it is preferred that one of the first and second middle subsections covers at least 30%, more prefer- ably at least 40%, yet more preferably at least 45% and most preferably 50% of the total area of the cross-section of the middle section of the dividing-wall column, whereas the other of the first and second middle subsections covers the remainder to 100% of the total area of the cross-section of the middle section of the dividingwall column. For instance, one subsection covers 43% and the other 57% of the total area of the cross-section or both subsections cover each exactly 50% of the total area of the cross-section. If the total area of the cross-section of the middle section varies over the axial length of the middle section, the above numeric values are related to the average total area of the cross-section of the middle section.

Preferably, the distillation is performed in step a) at a temperature of 0 to 200°C and at a pressure of 10 to 150 MPa and more preferably at a temperature of 80 to 160°C and at a pressure of 10 to 80 MPa.

In accordance with a further preferred embodiment of the present invention, the dewatered bisphenol A composition, which is obtained in step a) as bottom composition in the dividing-wall distillation column, contains, based on 100% by weight of the dewatered bisphenol A composition, at least 15% by weight, preferably at least 20% by weight and more preferably at least 30% by weight, such as 20 to 40% by weight, of bisphenol A and up to 80% by weight, such as 60 to 80% by weight, or up to 70% by weight of phenol. The dewatered bisphenol A composition may contain, based on 100% by weight of the dewatered bisphenol A composition, traces of impurities, such as up to 0.1% by weight of water and up to 0.1% by weight, such as 7 to 100 ppm, of acetone. The content of these impurities may be further reduced and phenol may be removed from the dewatered bisphenol A composition by subjecting the dewatered bisphenol A composition to a further purification step, such as evaporation and/or crystallization. In turn, the overhead composition preferably contains, based on 100% by weight of the overhead composition, 30 to 80% by weight of water, 10 to 50% by weight of acetone and 0 to 20% by weight of phenol.

The overhead composition obtained in the dividing-wall distillation column may be led directly to the extraction column used in step b). However, preferably, as in usual distillations, it is preferred that the overhead composition being withdrawn from the dividing-wall distillation column used in step a) is first condensed in a condenser to a condensed overhead composition, from which a portion is recycled as reflux into the upper section of the dividing-wall distillation column, whereas the remaining portion of the condensed overhead composition is led into the extraction column.

In a further development of the idea of the present invention, it is proposed that the extracting agent used in steps b) and c) is selected from the group consisting of methyl isobutyl ketone, diisopropyl ether, ethylbenzene, toluene, hexane, octane, benzene, heptane, cyclohexane, hexadecance and arbitrary combinations of two or more of the aforementioned compounds. Good results are in particular obtained, when in steps b) and c) ethylbenzene and/or methyl isobutyl ketone is used as extracting agent, wherein ethylbenzene is most preferred.

The present invention is not particularly limited concerning the kind of liquid-liquid extraction performed in step b), i.e. concerning the kind of liquid-liquid extraction column used in step b). However, it is preferred that the liquid-liquid extraction in step b) is performed in an agitated extraction column. Particular good results are obtained, when the liquid-liquid extraction in step b) is performed in an agitated countercurrent extraction column. Performing the liquid-liquid extraction in step b) in an agitated extraction column leads to an increased efficiency of the liquid-liquid extraction, thus allowing to minimize the amount of extracting agent being necessary for the liquid-liquid extraction. The agitated liquid-liquid extraction column preferably comprises at least one and more preferably a plurality, such as 2 to 80 and more preferably 5 to 40, agitated internals being disposed within the liquid-liquid extraction column. For instance, each of the agitated internals comprises one or more rotating shafts, each of which being connected with one or more agitators being preferably selected from the group consisting of discs, blades, paddles, turbine impellers, fins and arbitrary combinations of two or more of the aforementioned agitators. In addition thereto, the agitated liquid-liquid extraction column comprises an inlet line for the extracting agent, an inlet line for the overhead composition being obtained in the dividing-wall distillation column of step a), an outlet line for extract and an outlet line for raffinate. Preferably, the inlet line for extracting agent and the inlet line for the overhead composition being obtained in the dividing-wall distillation column of step a) are arranged on opposite ends of the liquid-liquid extraction column. Likewise, it is preferred that the outlet line for extract and the outlet line for raffinate are arranged on opposite ends of the liquid-liquid extraction column, preferably with the outlet line for extract and the inlet line for the overhead composition being obtained in the dividing-wall distillation column of step a) being arranged on the same end of the liquid-liquid extraction column and with the outlet line for raffinate and the inlet line for extracting agent being arranged on the opposite end of the liquid-liquid extraction column.

Good results are in particular obtained, when the agitated liquid-liquid extraction column comprises two or more compartments, which are separated from each other by static partition plates, wherein at least some and preferably all of the compartments comprise a rotating shaft comprising one or more agitators being preferably selected from the group consisting of discs, blades, paddles, turbine impellers, fins and arbitrary combinations of two or more of the aforementioned agitators. For instance, the liquid-liquid extraction column, in which the agitated liquid-liquid extraction is performed, may be embodied as a Kuhni column and the like.

Preferably, the liquid-liquid extraction is performed in the liquid-liquid extraction column during step b) at ambient temperature and at ambient pressure.

For instance, the raffinate composition obtained in step b) may contain, based on 100% by weight of the raffinate composition, 90 to 99.99% by weight and preferably 95 to 99.99% by weight of water, wherein the remainder to 100% by weight of the raffinate composition are the extracting agent and impurities, such as 0 to 1% by weight of phenol and 0 to 0.1 % by weight of acetone.

In a further development of the idea of the present invention, it is suggested that the extract composition obtained in step b) contains, based on 100% by weight of the extract composition, 0.5 to 25% by weight and preferably 1 to 10% by weight of phenol. The remainder to 100% by weight of the extract composition are the extracting agent and impurities, such as 0 to 10% by weight of water and 0 to 10% by weight of acetone.

In accordance with the present invention, the extracting agent used in step c) is the same as the extracting agent used in step b), because thereby the management of two different streams, namely of a first extracting agent on the one hand and of a different second extracting agent on the other hand, can be reduced to the management of only one stream. Most preferably, the extracting agent used in step c) is - as the extracting agent used in step b) - ethylbenzene.

In accordance with a further preferred embodiment of the present invention, the extracting agent is fed in step c) into the distillation column at a location being above the location at which the extract composition obtained in step b) is fed into the distillation column, wherein the location at which the extract composition ob- tained in step b) is fed into the distillation column is above the location at which the side composition obtained in step a) is fed into the distillation column.

Preferably, the extracting agent is fed in step c) into the distillation column at a location being located 0 to 50%, preferably 1 to 30% and most preferably 5 to 20% of the distance from the top to the bottom of the distillation column below the top of the distillation column. Moreover, it is preferred that the extract composition is fed into the distillation column at a location being below that at which the extracting agent is fed into the distillation column and being located 20 to 80%, preferably 30 to 70% and most preferably 40 to 65% of the distance from the top to the bottom of the distillation column below the top of the distillation column. In turn, the side composition is preferably fed into the distillation column at a location being below that at which the extract composition is fed into the distillation column and being preferably located 60 to 100%, preferably 70 to 99% and most preferably 75 to 95% of the distance from the top to the bottom of the distillation column below the top of the dividing-wall distillation column.

Preferably, the distillation is performed in step c) at a temperature of 70 to 250°C and at a pressure of 0.02 to 0.50 MPa and more preferably at a temperature of 100 to 210°C and at a pressure of 0.05 to 0.20 MPa.

In a further development of the idea of the present invention, it is proposed that the overhead composition obtained in the distillation column contains, based on 100% by weight of the overhead composition, 85 to 100% by weight extraction agent and 0 to 15% by weight of water and minor impurities, such as up to 0.5% by weight of acetone.

In accordance with a further particularly preferred embodiment of the present invention, the extracting agent is recovered from the overhead composition being obtained in the distillation column used in step c), before it is recycled into the liquid-liquid extraction step b) and into the distillation step c). More specifically, it is preferred that the overhead composition obtained in step c) is led for this purpose into a liquid-liquid separator, in which the overhead composition is separated, if necessary after having been condensed, into a first liquid composition and into a second liquid composition, wherein the first liquid composition is enriched in the extracting agent and has a lower density than the second liquid composition being enriched in water, and wherein the first liquid composition is at least partially fed as extracting agent into the distillation column used in step c). The overhead composition obtained in the distillation column may be led directly to the liquid-liquid separator. However, preferably, as in usual distillations, it is preferred that the overhead composition being withdrawn from the distillation column used in step c) is first condensed in a condenser to a condensed overhead composition, which is then led into the liquid-liquid separator, which preferably comprises an outlet line for the first liquid composition and an outline line for the second liquid composition, wherein the outline line for the first liquid composition splits into two lines so that a portion of the first liquid composition is recycled as reflux into the upper section of the distillation column, whereas the remaining portion of the first liquid composition is preferably recycled into the liquid-liquid extraction column.

The present invention is not particularly limited concerning kind of liquid-liquid separator. Preferably, the liquid-liquid separator is a settler, in which the first and second liquid compositions separate from each other by gravity. A suitable example for such a settler is a horizontal vessel comprising one or more at least essentially vertically arranged separation walls, wherein at least essentially vertically arranged means in accordance with the present invention that the angle between the separation wall and the vertical direction is at most 20°, preferably at most 10°, more preferably at most 5° and most preferably 0°. Good results are in particular obtained, when the one or more separation walls extend from the bottom of the horizontal vessel over 50 to 95% and preferably 60 to 90% of the height of the horizontal vessel. More preferably, the horizontal vessel comprises one such separation wall. Thereby, the second liquid composition having a higher density settles in the first section of the horizontal vessel being located upstream of the separation wall below the first liquid composition so that only the first liquid composition may flow over the upper edge of the separation wall into the second section of the horizontal vessel being located downstream of the separation wall, whereas the second liquid composition remains in the first section of the horizontal vessel and is withdrawn therefrom, whereas the first liquid composition is withdrawn from the horizontal vessel from its second section.

In a further development of the idea of the present invention, it is proposed that a portion of the first liquid composition being obtained in the aforementioned liquidliquid separator is fed as extracting agent into the distillation column used in step c), and wherein another portion of the first liquid composition is fed as extracting agent into the liquid-liquid extraction column used in step b). Good results are in particular obtained, when 10 to 90% by weight and more preferably 15 to 45% by weight of the first liquid composition are fed as extracting agent into the distillation column used in step c), whereas the remainder to 100% by weight of the first liquid composition is fed as extracting agent into the liquid-liquid extraction column used in step b).

Preferably, the bottom composition obtained in the distillation column used in step c) contains, based on 100% by weigh of the bottom composition, 90 to 100% by weight and preferably 98 to 99.99% by weight of phenol.

In order to reduce the content of acetone in the single process compositions, it is suggested in a further development of the idea of the present invention that the process further comprises a stripping step for removing acetone from a composition, wherein the stripping step is performed with one or more of the following compositions: i) the overhead composition obtained in step a), before the remaining composition, from which acetone has been at least partially stripped off, is led to the liquid-liquid extraction column of step b), preferably with the portion of the condensed overhead composition which remains, after the overhead composition obtained in step a) has been condensed in a condenser and a portion of the condensed overhead composition has been removed and recycled into the dividing-wall distillation column, ii) the raffinate composition obtained in step b), iii) the extract composition obtained in step b), before the remaining composition, from which acetone has been at least partially stripped off, is led to the distillation column of step c), iv) the overhead composition obtained in step c), preferably with the portion of the condensed overhead composition which remains, after the overhead composition obtained in step c) has been condensed in a condenser and a portion of the condensed overhead composition has been removed and recycled into the distillation column, and v) the crude composition, before it is fed into the dividing-wall distillation column of step a).

Stripping may be a step of contacting any of the aforementioned compositions i) to v) preferably in counter-current direction with a gas, such as nitrogen, air or steam, so as to desorb the acetone from the respective composition into the gas. Other stripping methods as used in the prior art may be also used.

In accordance with a further aspect, the present invention relates to a plant for removing water from a crude composition containing water, phenol and bisphenol A, wherein the plant comprises: a) a dividing-wall distillation column comprising an inlet line for the crude composition, an outlet line for an overhead composition, an outlet line for a side composition and an outlet line for a bottom composition, b) a liquid-liquid extraction column comprising an inlet line being directly or indirectly connected with the outlet line for overhead composition of the dividing-wall distillation column, an inlet line for extracting agent, an outlet line for extract and an outlet line for raffinate and c) a distillation column comprising an inlet line being directly or indirectly connected with the outlet line for extract of the liquid-liquid extraction column, an inlet line being connected with the outlet line for a side composition of the dividing-wall distillation column, an inlet line for extracting agent, an outlet line for an overhead composition and an outlet line for a bottom composition.

In accordance with a particularly preferred embodiment of the present invention, the plant further comprises a liquid-liquid separator comprising an inlet line, a first outlet line and a second outlet line, wherein the inlet line of the liquid-liquid separator is directly or indirectly connected with the outlet line for an overhead composition of the distillation column, and wherein the first outlet line of the liquid-liquid separator is connected with the inlet line for extracting agent of the liquid-liquid extraction column as well as with the inlet line for extracting agent of the distillation column. In turn, the second outlet line of the liquid-liquid separator is for the removal of water from the plant. It is preferred that the inlet line of the liquid-liquid separator is indirectly connected with the outlet line for an overhead composition of the distillation column, namely that a condenser is located between the outlet line for an overhead composition of the distillation column and the inlet line of the liquid-liquid separator, wherein the condenser comprises an outlet line, which leads into the inlet line of the liquid-liquid separator.

Good results are in particular obtained, when the dividing-wall distillation column is a middle dividing-wall distillation column, which comprises a dividing wall extending from a point being located below the top of the distillation column at least essentially vertically downwards to a point being located above the bottom of the dividing-wall distillation column. Thereby, the dividing-wall distillation column is subdivided into a top section being located above the dividing-wall, into a bottom section being located below the dividing-wall and into a middle section comprising a first middle subsection being located on one side of the dividing wall and a second middle subsection being located on the opposite side of the dividing wall.

Good results are in particular obtained, when the dividing wall extends, seen from the bottom to the top of the dividing-wall distillation column, from a point being located at 10 to 45% of the distance from the bottom to the top of the dividing-wall distillation column to a point being located at 50 to 90% of the distance from the bottom to the top of the dividing-wall distillation column and preferably from a point being located at 25 to 40% of the distance from the bottom to the top of the dividing-wall distillation column to a point being located at 60 to 80% of the distance from the bottom to the top of the dividing-wall distillation column.

In a further development of the idea of the present invention, it is proposed that the dividing wall extends, seen from the bottom to the top of the dividing-wall distillation column, over 5 to 90%, preferably over 20 to 80% and more preferably over 30 to 70% of the distance from the bottom to the top of the dividing-wall distillation column.

Preferably, one of the first and second middle subsections covers at least 30%, more preferably at least 40%, yet more preferably at least 45% and most preferably 50% of the total area of the cross-section of the middle section of the middle dividing-wall column, whereas the other of the first and second middle subsections covers the remainder to 100% of the total area of the cross-section of the middle section of the dividing-wall column.

In accordance with a further preferred embodiment of the present invention, the liquid-liquid extraction column is an agitated extraction column and preferably an agitated countercurrent extraction column. Good results are in particular obtained, when the agitated extraction column comprises at least one and preferably a plurality, such as 2 to 80 and more preferably 5 to 40, agitated internals being disposed within the liquid-liquid extraction column. For instance, each of the agitated internals comprises one or more rotating shafts, each of which being connected with one or more agitators being preferably selected from the group consisting of discs, blades, paddles, turbine impellers, fins and arbitrary combinations of two or more of the aforementioned agitators. In addition thereto, the agitated extraction column preferably comprises an inlet line for extracting agent, an inlet line for the overhead composition obtained in the dividing-wall distillation column of step a), an outlet line for extract and an outlet line for raffinate. Preferably, the inlet line for extracting agent and the inlet line for the overhead composition obtained in the dividing-wall distillation column of step a) are arranged on opposite ends of the liquid-liquid extraction column. Likewise, it is preferred that the outlet line for extract and the outlet line for raffinate are arranged on opposite ends of the liquidliquid extraction column, preferably with the outlet line for extract and the inlet line for the overhead composition obtained in the dividing-wall distillation column of step a) being arranged on the same end of the liquid-liquid extraction column and with the outlet line for raffinate and the inlet line for extracting agent being arranged on the same opposite end of the liquid-liquid extraction column.

Good results are in particular obtained, when the agitated extraction column comprises two or more compartments, which are separated from each other by static partition plates, wherein at least some and preferably all of the compartments comprise a rotating shaft comprising one or more agitators being preferably selected from the group consisting of discs, blades, paddles, turbine impellers, fins and arbitrary combinations of two or more of the aforementioned agitators. For instance, the liquid-liquid extraction column, in which the agitated liquid-liquid extraction is performed, may be embodied as a Kuhni column and the like.

It is preferred that the inlet line of the liquid-liquid extraction column is indirectly connected with the outlet line for an overhead composition of the dividing-wall distillation column, namely that a condenser is located between the outlet line for an overhead composition of the dividing-wall distillation column and the inlet line of the liquid-liquid extraction column, wherein the condenser comprises an outlet line, which splits into a recycle line leading to the dividing-wall distillation column and into the inlet line of the liquid-liquid extraction column.

In accordance with a further particularly preferred embodiment of the present invention, the plant further comprises at least one stripping column for removing acetone, wherein the at least one stripping column is arranged at any of the following locations: i) in the line connecting the outlet line for overhead composition of the dividing-wall distillation column with the inlet line of the liquid-liquid extraction column, preferably downstream of a condenser being located in the line connecting the outlet line for overhead composition of the dividing-wall distillation column and the inlet line of the liquid-liquid extraction column, wherein the condenser comprises an outlet line which splits into a recycle line for refluxing a portion of the condensed liquid into the divided-wall distillation column and into the line leading into the at least one stripping column, the liquid outlet of which being connected with the inlet line of the liquidliquid extraction column, ii) in the outlet line for raffinate of the liquid-liquid extraction column, iii) in the line connecting the outlet line for extract of the liquid-liquid extraction column with the inlet line of the distillation column, iv) in a second outlet line of a liquid-liquid separator being connected with the outlet line for an overhead composition of the distillation column, wherein the liquid-liquid separator is preferably arranged downstream of a condenser being located in the line connecting the outlet line for overhead composition of the distillation column and the inlet line of the liquid-liquid separator, and v) upstream of the inlet line for the crude composition of the dividing-wall distillation column.

Subsequently, the present invention is described by means of an illustrative, but not limiting figure, in which:

Fig. 1 is a schematic view of a plant for removing water from a crude composition containing water, phenol and bisphenol A in accordance with one embodiment of the present invention. Fig. 2a and 2b are schematic length-sectional views of a part of the liquid-liquid extraction column of the plant shown in figure 1.

The plant 10 for removing water from a crude composition containing water, phenol and bisphenol A comprises a dividing-wall distillation column 12, a liquid-liquid extraction column 14, a distillation column 16 and a liquid-liquid separator 18. The dividing-wall distillation column 12 is a middle dividing-wall distillation column 12, which comprises a dividing wall 20 extending from a point being located below the top of the distillation column 12 vertically downwards to a point being located above the bottom of the dividing-wall distillation column 12. Thereby, the dividingwall distillation column 12 is subdivided into a top section being located above the dividing-wall 20, into a bottom section being located below the dividing-wall 20 and into a middle section comprising a first middle subsection being located on the left side of the dividing wall 20 and a second middle subsection being located on the right side of the dividing wall 20. The dividing-wall distillation column 12 further comprises an inlet line 22 for crude composition, an outlet line 24 for an overhead composition, an outlet line 26 for a side composition and an outlet line 28 for a bottom composition. The outlet line 24 for the overhead composition is connected with a condenser (not shown) and splits into to recycle line 30 leading back to the dividing-wall distillation column 12 and into a connection line 32. In turn, the liquidliquid extraction column 14 comprises an inlet line 34 being connected with the connection line 32, an inlet line 36 for extracting agent, an outlet line 38 for extract and an outlet line 40 for raffinate. The distillation column 16 comprises an inlet line 42 being connected with the outlet line 38 for extract of the liquid-liquid extraction column 14, an inlet line 44 being connected with the outlet line 26 for a side composition of the dividing-wall distillation column 12, an inlet line 46 for extracting agent, an outlet line 48 for an overhead composition and an outlet line 50 for a bottom composition. Finally, the liquid-liquid separator 18 comprises an inlet line 52, a separation wall 53, a first outlet line 54 and a second outlet line 56. While the inlet line 52 of the liquid-liquid separator 18 is connected with the outlet line 48 for the overhead composition of the distillation column 16, the first outlet line 54 of the liquid-liquid separator 18 is connected with the inlet line 36 for extracting agent of the liquid-liquid extraction column 14 as well as with the inlet line 46 for extracting agentof the distillation column 16. The second outlet line 56 is a removal line.

During the operation of the plant 10, crude composition containing bisphenol A, acetone, water and phenol is fed via inlet line 22 into the dividing-wall distillation column 12, in which the crude composition is distilled into an overhead composition being enriched in water and further comprising acetone and phenol residues, into a side composition being enriched in phenol and into bottom composition, which is the dewatered bisphenol A composition. The overhead composition is then condensed, wherein a portion of the condensed overhead composition is recycled via the recycle line 30 into the dividing-wall distillation column 12, whereas the other portion of the overhead composition is led via lines 24, 32, 34 into the upper section of the liquid-liquid extraction column 14. Via inlet line 36 extracting agent, namely ethylbenzene, is fed into the lower section of the liquid-liquid extraction column 14, which extracts phenol from the overhead composition into the extract composition, which is withdrawn from the upper section of the liquid-liquid extraction column 14 via the outlet line 38. In turn, the phenol depleted, water rich raffinate composition is withdrawn from the lower section of the liquid-liquid extraction column 14 via the outlet line 40. The extract composition containing mainly ethylbenzene, phenol and minor amounts of water and acetone is led via lines 38, 42 into the distillation column 16, whereas via lines 26, 44 the phenol enriched side composition being withdrawn from the dividing-wall distillation column 12 is led into the distillation column 16 and via inlet line 46 ethylbenzene as extracting agent is led into the distillation column 16. Both compositions are distilled in the distillation column 16 so that a phenol rich bottom composition being withdrawn from the distillation column 16 via outlet line 50 and an ethylbenzene rich and water containing overhead composition being withdrawn from the distillation column 16 via outlet line 48 are obtained. The ethylbenzene rich and water containing overhead composition is led into the liquid-liquid separator 18, in which the overhead composition is separated by gravity into a first liquid composition consisting mainly of ethylbenzene and into a second liquid composition consisting mainly of water. While the second liquid composition is withdrawn from the plant 10, the first liquid composition is partially recycled via lines 54, 46 as extracting agent into the distillation column 16, whereas the remaining portion of the first liquid composition is recycled via lines 54, 36 as extracting agent into the liquidliquid extraction column 14.

Figures 2a and 2b show schematically length-sectional views of a part of the liquid-liquid extraction column 14 of the plant 10 shown in figure 1. The liquid-liquid extraction column 14 is margined by a wall 58 and comprises a plurality of compartments 60, 60’, 60”, from which three are shown in figure 2a and one is shown in figure 2b. Each of the compartments 60, 60’, 60” is separated from adjacent compartments 60, 60’, 60” by means of a static partition plate 62, 62’, 62”, 62’”. Each of the static partition plates 62, 62’, 62”, 62’” is perforated (not shown), i.e. comprises several holes allowing liquid to pass from one side of the partition plate 62, 62’, 62”, 62’” to the other. Furthermore, the liquid-liquid extraction column 14 comprises a rotating shaft 64 extending through each of the compartments 60, 60’, 60” and being arranged, seen in the length section, in the center of the compartments 60, 60’, 60”. The rotating shaft 64 comprises several turbine impellers as agitators 66, wherein each compartment 60, 60’, 60” comprises two agitators 66.

As shown in more detail in figure 2b, which shows the section of the liquid-liquid extraction column 14 highlighted in the box 68 of figure 2a, during the operation of the liquid-liquid extraction column 14 extracting agent flows in the direction of arrows 70, 72’ through the liquid-liquid extraction column 14, whereas the overhead composition obtained in the dividing-wall distillation column 12 flows in the counter-direction as indicated by the arrows 72, 70’. The mixture of the overhead composition and of the extracting agent is agitated through the rotating agitators 66, wherein a rapid flow in the length direction is restricted by the perforated partition plates 62, 62’, 62”, so that, seen in the length-section, an oval flow pattern as shown by the arrows 74, 74’ is generated. Thereby an intimate contact between the overhead composition and the extracting agent is achieved leading to a particular efficient extraction of phenol from the composition into the extracting agent.

Reference numerals

10 Plant

12 Dividing-wall distillation column

14 Liquid-liquid extraction column

16 Distillation column

18 Liquid-liquid separator

20 Dividing wall

22 Inlet line for crude composition of the dividing-wall distillation column

24 Outlet line for overhead composition of the dividing-wall distillation column

26 Outlet line for side composition of the dividing-wall distillation column

28 Outlet line for bottom composition of the dividing-wall distillation column

30 Recycle line

32 Connection line

34 Inlet line of the liquid-liquid extraction column

36 Inlet line for extracting agent of the liquid-liquid extraction column

38 Outlet line for extract of the liquid-liquid extraction column

40 Outlet line for raffinate of the liquid-liquid extraction column

42 Inlet line of the distillation column

44 Inlet line of the distillation column

46 Inlet line for extracting agent of the distillation column

48 Outlet line for an overhead composition of the distillation col- umn 50 Outlet line for a bottom composition of the distillation column

52 Inlet line of the liquid-liquid separator

53 Separation wall

54 First outlet line of the liquid-liquid separator 56 Second outlet line of the liquid-liquid separator

58 Wall of liquid-liquid extraction column

60, 60’, 60” Compartments of liquid-liquid extraction column

62, 62’, 62”, 62’” Static partition plate

64 Rotating shaft 66 Agitators

68 Part of the liquid-liquid extraction column shown in figure 2b

70, 72’ Arrow showing the flow direction of the extracting agent

72, 70’ Arrow showing the flow direction of the overhead composition

74, 74’ Arrow showing flow pattern in the compartment

Claims

Claims:

1 . A process for removing water from a crude composition containing water, phenol and bisphenol A, wherein the process comprises the steps of: a) feeding the crude composition into a dividing-wall distillation column and distilling it therein so as to obtain an overhead composition, a side composition and a bottom composition, wherein the bottom composition is a dewatered bisphenol A composition, b) subjecting the overhead composition obtained in step a) to a liquidliquid extraction with an extracting agent in an extraction column so as to obtain a raffinate composition being enriched in water and an extract composition being enriched in phenol, and c) feeding the extract composition obtained in step b), the side composition obtained in step a) and an extracting agent being the same as that used in step b) separately from each other into a distillation column and distilling these therein so as to obtain an overhead composition containing the extracting agent and water as well as a bottom composition containing phenol.

2. The process in accordance with claim 1 , wherein the crude composition contains, based on 100% by weight of the crude composition, 15 to 35% by weight of bisphenol A, 1 to 5% by weight of water, 0.5 to 5% by weight of acetone and 60 to 80% by weight of phenol and preferably 20 to 30% by weight of bisphenol A, 1 .5 to 2.0% by weight of water, 0.8 to 2.9% by weight of acetone and 65 to 75% by weight of phenol.

3. The process in accordance with claim 1 or 2, wherein the crude composition is fed in step a) into a middle dividing-wall distillation column, which comprises a dividing wall extending from a point being located below the top of the distillation column at least essentially vertically downwards to a point being located above the bottom of the dividing-wall distillation column so as to subdivide the dividing-wall distillation column into a top section being located above the dividing-wall, into a bottom section being located below the dividing-wall and into a middle section comprising a first middle subsection being located on one side of the dividing wall and a second middle subsection being located on the opposite side of the dividing wall.

4. The process in accordance with any of the preceding claims, wherein the dewatered bisphenol A composition contains, based on 100% by weight of the dewatered bisphenol A composition, 20 to 40% by weight of bisphenol A, 60 to 80% by weight of phenol, up to 0.1% by weight of water and up to 0.1% by weight of acetone.

5. The process in accordance with any of the preceding claims, wherein the extracting agent used in steps b) and c) is selected from the group consisting of methyl isobutyl ketone, diisopropyl ether, ethylbenzene, toluene, hexane, octane, benzene, heptane, cyclohexane, hexadecance and arbitrary combinations of two or more of the aforementioned compounds.

6. The process in accordance with any of the preceding claims, wherein the liquid-liquid extraction in step b) is performed in an agitated extraction column and preferably in an agitated countercurrent extraction column, wherein the agitated extraction column comprises one or more rotating shafts, each of which comprising one or more agitators being preferably selected from the group consisting of discs, blades, paddles, turbine impellers, fins and arbitrary combinations of two or more of the aforementioned agitators.

7. The process in accordance with claim 6, wherein the agitated extraction column comprises two or more compartments, which are separated from each other by static partition plates, wherein at least some and preferably all of the compartments comprise a rotating shaft comprising one or more agitators being preferably selected from the group consisting of discs, blades, paddles, turbine impellers, fins and arbitrary combinations of two or more of the aforementioned agitators.

8. The process in accordance with any of the preceding claims, wherein the raffinate composition obtained in step b) contains, based on 100% by weight of the raffinate composition, 90 to 99.99% by weight and preferably 95 to 99.99% by weight of water and 0 to 1% by weight and preferably 0.01 to 0.1% by weight of phenol.

9. The process in accordance with any of the preceding claims, wherein in step c) the extracting agent is fed into the distillation column at a location being above the location at which the extract composition obtained in step b) is fed into the distillation column, wherein the location at which the extract composition obtained in step b) is fed into the distillation column is above the location at which the side composition obtained in step a) is fed into the distillation column.

10. The process in accordance with any of the preceding claims, wherein the overhead composition obtained in step c) is led into a liquid-liquid separator, in which the overhead composition is separated into a first liquid composition and into a second liquid composition, wherein the first liquid composition is enriched in the extracting agent and has a lower density than the second liquid composition being enriched in water, and wherein the first liquid composition is at least partially fed as extracting agent into the distillation column used in step c), wherein a portion of the first liquid composition is fed as extracting agent into the distillation column used in step c), and wherein another portion of the first liquid composition is fed as extracting agent into the liquid-liquid extraction column used in step b).

11 . The process in accordance with any of the preceding claims, which further comprises a stripping step for removing acetone, wherein the stripping step is performed with one or more of the following compositions: i) the overhead composition obtained in step a), before the remaining composition, from which acetone has been at least partially stripped off, is led to the liquid-liquid extraction column in step b), ii) the raffinate composition obtained in step b), iii) the extract composition obtained in step b), before the remaining composition, from which acetone has been at least partially stripped off, is led to the distillation column of step c), iv) the overhead composition obtained in step c) and v) the crude composition, before it is fed into the dividing-wall distillation column of step a).

12. A plant for removing water from a crude composition containing water, phenol and bisphenol A, wherein the plant comprises: a) a dividing-wall distillation column comprising an inlet line for the crude composition, an outlet line for an overhead composition, an outlet line for a side composition and an outlet line for a bottom composition, b) a liquid-liquid extraction column comprising an inlet line being directly or indirectly connected with the outlet line for overhead composition of the dividing-wall distillation column, an inlet line for extracting agent, an outlet line for extract and an outlet line for raffinate and c) a distillation column comprising an inlet line being directly or indirectly connected with the outlet line for extract of the liquid-liquid extraction column, an inlet line being connected with the outlet line for a side composition of the dividing-wall distillation column, an inlet line for ex- tracting agent, an outlet line for an overhead composition and an outlet line for a bottom composition.

13. The plant in accordance with claim 12, which further comprises a liquidliquid separator comprising an inlet line, a first outlet line and a second outlet line, wherein the inlet line of the liquid-liquid separator is directly or indirectly connected with the outlet line for an overhead composition of the distillation column, and wherein the first outlet line of the liquid-liquid separator is connected with the inlet line for extracting agent of the liquid-liquid extraction column as well as with the inlet line for extracting agent of the distillation column.

14. The plant in accordance with claim 12 or 13, wherein the dividing-wall distillation column is a middle dividing-wall distillation column, which comprises a dividing wall extending from a point being located below the top of the distillation column at least essentially vertically downwards to a point being located above the bottom of the dividing-wall distillation column so as to subdivide the dividing-wall distillation column into a top section being located above the dividing-wall, into a bottom section being located below the dividing-wall and into a middle section comprising a first middle subsection being located on one side of the dividing wall and a second middle subsection being located on the opposite side of the dividing wall.

15. The plant in accordance with any of claims 12 to 14, which further comprises at least one stripping column for removing acetone, wherein the at least one stripping column is arranged at any of the following locations: i) in the line connecting the outlet line for overhead composition of the dividing-wall distillation column with the inlet line of the liquid-liquid extraction column, preferably downstream of a condenser being located in the line connecting the outlet line for overhead composition of the dividing-wall distillation column and the inlet line of the liquid-liquid extraction column, wherein the condenser comprises an outlet line which splits into a recycle line for refluxing a portion of the condensed liquid into the divided-wall distillation column and into the line leading into the at least one stripping column, the liquid outlet of which being connected with the inlet line of the liquid-liquid extraction column, ii) in the outlet line for raffinate of the liquid-liquid extraction column, iii) in the line connecting the outlet line for extract of the liquid-liquid extraction column with the inlet line of the distillation column, iv) in a second outlet line of a liquid-liquid separator being connected with the outlet line for an overhead composition of the distillation column, wherein the liquid-liquid separator is preferably arranged downstream of a condenser being located in the line connecting the outlet line for overhead composition of the distillation column and the inlet line of the liquid-liquid separator, and v) upstream of the inlet line for the crude composition of the dividing-wall distillation column.