An electrified process and plant for single distillation unit purification of bioethanol or similar compounds

Abstract

The present invention relates to a process of separating a target composition con- taining at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water optionally in admixture with water from a crude composition having been produced in a biocatalyzed process and containing the at least one oxygen containing organic compound as target compound, water and biomass, wherein the process comprises the steps of feeding the crude composition into a single distillation unit, distilling it therein and withdrawing from the single distillation unit an overhead composition as target composition, a bottom composition and option- ally a side composition, wherein a portion of the overhead composition is refluxed into the single distillation unit, wherein compressed vapor is injected into the single distillation unit, wherein the compressed vapor is produced by compressing vapor of a refrigerant having been obtained by evaporating the refrigerant by heating it with the overhead composition, wherein the refrigerant comprises, based on the total weight of the refrigerant, at least 70% by weight of water.

Description

[0001] Sulzer Management AG S13813P

[0002] An electrified process and plant for single distillation unit purification of bioethanol or similar compounds

[0003] The present invention relates to a process of separating a target composition containing at least one oxygen containing organic compound having a lower boiling point than water or forming a minimum boiling azeotrope with water, such as ethanol, as target compound optionally in admixture with water from a crude composition having been produced in a biocatalyzed process, such as a fermentation process, and containing the at least one oxygen containing organic compound as target compound, water and biomass. Furthermore, the present invention relates to a plant for conducting the process.

[0004] Biocatalyzed processes, i.e. processes making use of a biocatalyst or natural catalyst, respectively, for example enzymes or microorganism, such as yeast, gain more and more importance, since they allow to synthesize compounds more efficiently, selectively and environmentally friendly than traditional methods. Biocatalyzed processes are meanwhile used in various industries, such as for the synthesis of pharmaceuticals, agricultural products, food, beverage and biofuels. Prominent examples of biocatalyzed processes are the production of biodiesel from vegetable oils or waste fats using lipases, the production of bioplastics, such as polyhydroxyalkanoates or polylactic acid, from renewable sources using bacteria or fungi as biocatalyst and the production of oxygen containing organic compounds having a lower boiling point than water or forming a minimum boiling azeotrope with water, such as biomethanol, bioethanol or biopropanol, by fermentation.

[0005] For instance, ethanol is an important compound, which is for instance widely used as ingredient of alcoholic beverages, as raw material for chemical syntheses, as disinfection agent, as fuel and as solvent in a plurality of products. Ethanol is usually prepared by alcoholic fermentation from a natural, sugar or starch containing material, such as wheat, straw, potatoes or com. The crude composition obtained by the fermentation process must be purified, in order to separate the ethanol from the other ingredients of the crude mixture, such as proteins, yeast, other alcohols, carboxylic acids, aldehydes and other impurities. However, the known processes for producing pure alcohol are energy and device intensive processes.

[0006] In order to achieve an efficient separation of ethanol from the other compounds being included in the crude composition obtained by the fermentation process, the crude composition is often subjected to several distillation steps. For instance, a process of producing ethanol with the purity grade of extra neutral alcohol - which typically has an ethanol content of more than 95% by volume - comprises six distillation steps, wherein one of these is an extractive distillation step. More specifically, in a typical process of producing pure ethanol from a fermentation broth the crude composition obtained after the fermentation is distilled in a first distillation column called beer column so as to separate an ethanol containing stream from the biomass contained in the crude composition, before the ethanol containing stream is distilled in a second distillation column called rectifier column so as to remove therefrom light components, such as aldehydes. The ethanol containing stream obtained in the second distillation step is distilled in a third extractive distillation column using water as extractive agent so as to remove high boiling components from the ethanol containing stream, which is thereafter subjected to three further distillation steps in order to separate water, methanol, diacetyl and other impurities from the ethanol. But even processes of producing ethanol with a lower purity comprise at least two distillation steps, namely at least one first distillation step being performed in a beer column in order to remove the solids and at least one second distillation step being performed in a rectifier column in order to reduce the water content. However, these distillation based processes are energy intensive and thus characterized by high operational expenditures (OPEX) as well as by high capital expenditures (CAPEX). Furthermore, the plants for operating these processes require a certain size or plot area, respectively, due to the number and size of required distillation columns. The same is valid for processes for producing other oxygen containing organic compounds having a lower boiling point than water or forming a minimum boiling azeotrope with water, such as methanol, propanol or butanol from crude compositions having been produced in a biocatalyzed process.

[0007] In view of this, the object underlying the present invention is to provide a process of separating a target composition containing at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water optionally in admixture with water from a crude composition having been produced in a biocatalyzed process and containing the at least one oxygen containing organic compound as target compound, water and biomass, such as of a target composition containing ethanol optionally in admixture with water, which is characterized by low OPEX and by low CAPEX and which requires comparably little plot area for the plant.

[0008] In accordance with the present invention, this object is satisfied by providing a process of separating a target composition containing at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water optionally in admixture with water from a crude composition having been produced in a biocatalyzed process and containing the at least one oxygen containing organic compound as target compound, water and biomass, wherein the process comprises the steps of feeding the crude composition into a single distillation unit , distilling it therein and withdrawing from the single distillation unit an overhead composition as target composition, a bottom composition and optionally a side composition, wherein a portion of the overhead composition is refluxed into the single distillation unit, wherein compressed vapor is injected into the single distillation unit, wherein the compressed vapor is produced by compressing vapor of a refrigerant having been obtained by evaporating a refrigerant by heating it with the overhead composition, wherein the refrigerant comprises, based on the total weight of the refrigerant, at least 70% by weight of water.

[0009] This solution bases on the finding that by injecting compressed vapor having been produced by compressing vapor of a refrigerant, which has been obtained by evaporating the refrigerant by heating it with the overhead composition of the single distillation unit, into the single distillation unit, wherein the refrigerant comprises, based on the total weight of the refrigerant, at least 70% by weight of water, an efficient separation of an oxygen containing organic compound having a lower boiling point than water or forming a minimum boiling azeotrope with water, such as ethanol, from a crude composition having been produced in a biocatalyzed process and containing the oxygen containing organic compound, water and biomass is possible, even if only a single distillation unit is used, since the energy included in the overhead vapor stream of the single distillation unit is not lost, but exploited in the process to heat the refrigerant to vapor, which is then compressed and injected into the single distillation unit. Thus, the separation effect of a beer distillation column and of a rectifier distillation column may be combined in one single distillation unit by making use of compressed vapor, i.e. by using mechanical vapor recompression (MVR) technology meaning converting electrical and mechanical energy into an increment of the vapor dew point or, in other words, by using an electrified process, thereby reducing the CAPEX and OPEX as well as the required plot area of the plant operating the process. Without injecting the compressed vapor into the single distillation unit and hence by using the compressed vapor for heating and evaporating the bottom composition in the single distillation unit , the separation of the oxygen containing organic compound from the crude composition in a single distillation unit would require so much energy that the process would be commercially not convenient on a large scale, but suitable only for small plants and pilot units. In addition, the use of a single distillation unit in the process allows to use reflux and in particular reflux with a comparable high reflux ratio of the overhead composition into the single distillation unit, thereby improving the separation efficiency achieved in the single distillation unit. In contrast thereto, in traditional processes the beer column is operated without any reflux of overhead composition into the beer column. A further advantage of using compressed vapor is that the single distillation unit may be operated under vacuum even without using any vacuum unit, because the one or more compressors generating the compressed vapor may generate vacuum conditions in the single distillation unit. If the unit needs to operate at a deeper vacuum than the one achievable solely with the MVR, a vacuum unit can be also included.

[0010] In preferable embodiments the single distillation unit can have a dividing wall in a lower part of the single distillation unit separating said lower part into a first section and a second section, such that a first bottom composition can be withdrawn from the first section, and a second bottom composition can be withdrawn from the second section.

[0011] Furthermore, the single distillation unit is enhanced by the inclusion of the dividing wall located in a lower part of the distillation column. The dividing wall preferably extends vertically from a position proximate to the feed inlet, for instance from a position within two meters above or below the feed inlet and continues down to the bottom of the single distillation unit, in preferable embodiments of the column. The dividing wall can extend upwards from the bottom of the single distillation unit. The dividing wall hence can be a mechanical device partitioning the lower part of the single distillation unit (in particular column), including both the distillation internals (such as trays or packing) and a liquid sump, into two distinct sections: the first section, herein also referred to as the "section with solids", and the second section, herein also referred to as the "section without solids". The primary objective of the dividing wall is to physically segregate the liquid and solid phases within the lower part of the column, thereby preventing the migration of biomass and other solids from the section with solids to the section without solids. This segregation ensures that the solids-laden stream is handled separately from the cleaner, sol- ids-free water stream.

[0012] As a direct result of this partitioning, two different bottom liquid compositions can be simultaneously present in and withdrawn from the respective sumps of the two sections. The first bottom composition, herein also referred to as "stillage", is withdrawn from the sump of the section with solids. The stillage is primarily composed of water and the biomass solids from the crude composition, along with traces of ethanol and other organic components. A second bottom composition, herein referred to as "stripped water", is withdrawn from the sump of the section without solids. The stripped water consists mainly of water with only trace amounts of organic components, having been effectively stripped of both solids and the target compound. Each section can be serviced by its own pump; a stillage pump for removing the stillage, and a stripped-water pump for removing the stripped water.

[0013] In one arrangement according to the invention, the heating of the column bottom is achieved using two separate reboilers: a first reboiler for the first bottom composition also referred to as stillage reboiler and a second reboiler for the second bottom composition also referred to as stripped-water reboiler. The stillage pump directs a portion of the stillage to the stillage reboiler, where it is partially vaporized before being recycled into the base of the section with solids. The stripped-water pump similarly directs a portion of the stripped water to the stripped-water reboiler for partial vaporization, with the resulting vapor being recycled into the base of the section without solids. To provide the necessary heat, the compressed vapor exiting the main compressor is split, with a first portion being directed to the stillage reboiler and a second portion to the stripped-water reboiler. After transferring its heat and condensing, the liquid condensate from both reboilers is collected and combined, for instance in a common vessel, before being processed further. In another alternative or additional arrangement, heat may be supplied to the base of the column sections via direct injection of the compressed vapor. In this configuration, the compressed vapor stream from a compressor can be split into multiple streams. For instance, the compressed vapor may be split into four streams: a first stream to the stillage reboiler, a second to the stripped-water reboiler, a third for direct injection into the section with solids, and a fourth for direct injection into the section without solids. Alternatively, the reboilers may be bypassed entirely, and the compressed vapor can be split into two streams for direct injection into the base of the section with solids and the section without solids, respectively. A notable aspect of direct injection is that the vapor used for this purpose is not recovered as liquid condensate within the main process loop, as it mixes directly with the column contents.

[0014] The terms “overhead composition”, “side composition” and “bottom composition” refer to the gas and liquid fractions, respectively, being withdrawn from the overhead, side and bottom of the distillation unit. Since distillation is a continuous process, the terms “overhead composition”, “side composition” and “bottom composition” are equivalent with terms “overhead stream”, “side stream” and “bottom stream”.

[0015] In accordance with the present invention, compressed vapor is injected into the single distillation unit. Good results are in particular obtained, when the compressed vapor is injected into the bottom portion of the single distillation unit. Bottom portion of the single distillation unit means herein the bottom portion of any of the distillation columns being included in the single distillation unit extending, seen from the bottom to the top of the respective distillation column, from the lowest point to a point being located at 50% of the distance from the bottom to the top of the distillation column. In other words, if the single distillation unit comprises only one distillation column, the bottom portion is that portion of the distillation column, which extends, seen from the bottom to the top of the distillation column, from the lowest point to a point being located at 50% of the distance from the bottom to the top of the distillation column. If the single distillation unit comprises two or more distillation columns, as described further below, the bottom portion is that portion of one of the two or more distillation columns, which extends, seen from the bottom to the top of the respective distillation column, from the lowest point to a point being located at 50% of the distance from the bottom to the top of the distillation column. More preferably, the bottom portion of the single distillation unit extends, seen from the bottom to the top of the respective distillation column, from the lowest point to a point being located at 30% of the distance from the bottom to the top of the distillation column or even more preferably from a point being located at 5% to a point being located at 20% of the distance from the bottom to the top of the distillation column. Most preferably, the upper boundary of the bottom portion of the single distillation unit ends below the lowermost internal, such as tray, structured packing and random packing, in the respective distillation column.

[0016] In accordance with the present invention, a target composition containing at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water optionally in admixture with water is separated from a crude composition having been produced in a biocatalyzed process and containing the at least one oxygen containing organic compound as target compound, water and biomass. Minimum boiling azeotropes are those mixtures that boil at a lower temperature than the boiling point of the single pure components. The present invention is not particularly limited concerning the content of the at least one oxygen containing organic compound having a lower boiling point than water or forming a minimum boiling azeotrope with water in the crude composition and / or the chemical nature of the at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water. Good results are in particular obtained, when the crude composition comprises, based on 100% by weight of the crude composition, 0.5 to 40% by weight and preferably 3 to 20% by weight of at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water. Suitable examples for the at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water are compounds being selected from group consisting of methanol, ethanol, propanol, butanol, acetaldehyde, ethyl acetate, acetone and mixtures of two or more thereof. Particularly preferably, the oxygen containing organic compound is ethanol.

[0017] Since the crude composition has been produced in a biocatalyzed process, the crude composition contains in addition to the at least oxygen containing organic compound as target compound biomass, water and impurities. For instance, the crude composition comprises, based on 100% by weight of the crude composition, 50 to 99% by weight and preferably 60 to 95% by weight of water, 0 to 30% by weight and preferably 3 to 15% by weight of solids and 0 to 25% by weight and preferably 1 to 10% by weight of liquid compounds having a higher boiling point than water. The contained solids comprise biomass, i.e. the biocatalyst, such as one or more enzymes, proteins, microorganism, e.g. yeast, bacteria, fungi, algae or the like, and may in addition comprise dissolved solids, such as one or more salts, sugars, oligomers etc. Examples for the liquid compounds having a higher boiling point than water are carboxylic acids, organic acids, heavy alcohols and glycols.

[0018] The process in accordance with the present invention is in particular suitable to produce pure ethanol from a crude aqueous ethanol composition being obtained by fermentation of a mash derived from a natural feedstock, sugar or starch containing material, such as wheat, straw, potatoes, com, sugar beet, sugar cane, energy crops or wood, using yeast as biocatalyst. In this embodiment, the crude aqueous ethanol composition may comprise one or more of: up to 1 ,000 ppm, such as 5 to 100 ppm, of aldehydes, and / or up to 30,000 ppm, such as 100 to 5,000 ppm, of carboxylic acids, and / or up to 1 ,000 ppm, such as 5 to 100 ppm, of methanol, and / or up to 1 ,000 ppm, such as 50 to 500 ppm, of C3-alcohols, and / or up to 10,000 ppm, such as 200 to 4,000 ppm, of C4+-alcohols, and / or up to 1 ,000 ppm, such as 10 to 200 ppm, of esters.

[0019] In accordance with the present invention, the refrigerant comprises, based on the total weight of the refrigerant, at least 70% by weight of water. Refrigerant means in accordance with the present invention a fluid that is used to cool and / or condense the overhead composition in the heat exchanger or any other heat transfer device, as a consequence of which the refrigerant is heated up and / or evaporated during the heat exchange. From a viewpoint of separation efficiency, it is preferred that the refrigerant is pure water, which comes close to the bottom composition, whereas from a viewpoint of economy efficiency it is preferred to use as refrigerant an aqueous process stream from a different part of the plant. In view of this, a refrigerant is used, which comprises, based on the total weight of the refrigerant, at least 70%, preferably at least 80% by weight, more preferably at least 90% by weight, yet more preferably at least 95% by weight, still more preferably at least 98% by weight and most preferably at least 99% by weight of water, wherein the remainder to 100% by weight may contain bio-based residues, such as cellulose, lignin or the like, and optionally air and / or other impurities, such as one or more inorganic salts.

[0020] In accordance with the present invention, the crude composition is fed into a single distillation unit and is distilled therein. The term single distillation unit means here one thermodynamic distillation column, which may be composed of one apparatus piece or, as set out in further detail below, of two or more apparatus pieces acting together as one thermodynamic distillation column, wherein any vapor and liquid streams between two or more apparatus pieces are not subjected to any phase change meaning evaporation or condensation so that in fact the apparatus pieces act thermodynamically as one distillation column.

[0021] In accordance with a first particularly preferred embodiment of the present invention, the single distillation unit comprises only one distillation column. This one distillation column combines the separate beer column and rectifier column as used in the prior art, i.e. the one distillation column acts as beer column as well as as rectifier column.

[0022] Good results are in particular obtained, when the distillation column of this embodiment comprises the dividing wall being arranged in a lower part of the only one distillation column separating said lower part into the first section and the second section, a feed inlet for the crude composition, an overhead outlet for the target composition, a first bottom outlet for the solids (i.e. the stillage), and a second bottom outlet for water (i.e. the stripped water) and high boiling point impurities and a side outlet for fusel oil, wherein the feed inlet is arranged, seen from the top to the bottom of the distillation column, between the side outlet and the bottom outlets. Moreover, the distillation column preferably comprises internals for increasing the separation efficiency, such as trays, structured packings and / or random packings. It is particularly preferred in this embodiment of the present invention that the distillation column comprises, seen from the top to the bottom of the distillation column, between the overhead outlet and the side outlet at least one bed of structured packing or random packing and that the distillation column comprises between the side outlet and the feed inlet one or more trays. While the provision of at least one bed of structured packing or random packing between the overhead outlet and the side outlet of the at least of the distillation column minimizes the pressure drop of the distillation column, namely by 3 to 20 times in com- parision of using trays instead of using structured packings or random packings, such as from a pressure drop of 10 kPa in case of using of trays to a pressure drop of 3.3 to 0.5 kPa in case of using structured packings or random packings, the provision of one or more trays between the side outlet and the feed inlet allows an efficient withdrawal of fusel oil via the side outlet. Furthermore, it is preferred that the distillation column comprises between the feed inlet and the bottom outlets either one or more trays or at least one bed of structured packing or random packing. More specifically, the distillation column preferably comprises between the feed inlet and the bottom outlets one or more trays, if the crude composition contains solids with a high dso-particle size of 2 mm or more. However, if the crude composition contains solids with a low dso-particle size of less than 2 mm, the distillation column preferably comprises between the feed inlet and the bottom outlets at least one bed of structured packing or random packing.

[0023] In a further development of the idea of the present invention, it is preferred that the distillation is performed in the distillation column of this embodiment at a temperature of 20 to 120°C and at an absolute pressure of 5 to 450 kPa and more preferably at a temperature of 40 to 80°C and at an absolute pressure of 20 to 120 kPa. These distillation conditions are in particular suitable, if the crude composition contains as target compound ethanol.

[0024] In addition, it is preferred that the compressed vapor is injected in this embodiment into the bottom portion of the distillation column below the lowermost of the trays, of the at least one bed of structured packing and of the at least one bed of random packing.

[0025] In accordance with an alternative, second preferred embodiment of the present invention, the single distillation unit comprises one thermodynamic distillation column comprising two or more apparatus pieces. In other words, the single distillation unit of this embodiment of the present invention comprises two or more distillation columns, which are connected with each other so that each distillation column is connected with an adjacent distillation column by at least two connection lines. For instance, the single distillation unit comprises a first distillation column and a second distillation column, wherein one connection line leads from the overhead outlet of the first distillation column to an inlet in the lower portion of the adjacent second distillation column so that vapor overhead composition of the first distillation column is led to the lower portion of the adjacent second distillation column without condensation of the vapor overhead composition, whereas the other connection line leads from the bottom outlet of the second distillation column to an inlet in the upper portion of the adjacent first distillation column so that liquid bottom composition of the second distillation column is led to the upper portion of the adjacent first distillation column without evaporation of the liquid bottom composition. In other words, the vapor and liquid streams between the distillation columns in the single distillation unit are not subjected to any phase change meaning evaporation or condensation, so that in fact the distillation columns act thermodynamically as one distillation column. In difference thereto, in thermodynamic separate distillation columns, i) at least a portion of the vapor overhead composition obtained in an upstream distillation column is condensed, before at least a portion thereof is refluxed into the same distillation column and at least a portion of the remaining overhead composition is led into a downstream distillation column and / or within a liquid stream and / or ii) the liquid bottom composition obtained in a downstream distillation column is at least partially evaporated, before at least a portion thereof is introduced into the same distillation column and at least a portion of the remaining bottom composition is led into an upstream distillation column and / or withdrawn as a liquid stream.

[0026] Preferably, the single distillation unit of this second preferred embodiment of the present invention comprises (exactly) two distillation columns, wherein the two distillation columns are connected with each other by a liquid connection line through which bottom composition of a second distillation column flows - preferably from the bottom outlet of the second distillation column - without intermediate evaporation into preferably the upper portion of a first distillation column and are connected with each other by a vapor connection line through which overhead composition of the first distillation column flows - preferably from the overhead outlet of the first distillation column - without intermediate condensation into preferably the lower portion of the second distillation column. Upper portion of a distillation column means the top portion extending from the top of the distillation column downwardly along 50% of the length of the distillation column, whereas lower portion of a distillation column means the bottom portion extending from the bottom of the distillation column upwardly along 50% of the length of the distillation column. In other words, between the adjacent distillation columns no heat exchanger for a phase change, namely neither a condenser nor a reboiler, is arranged. However, it is preferred that one or both of the vapor connection line and the liquid connection line comprise a pressure increase device, such as a pump and / or a compressor or a similar equipment, which transports the liquid or vapor, respectively between both distillation columns.

[0027] In a further development of the idea of the present invention, it is proposed that the two distillation columns of this second embodiment of the present invention are arranged one above the other so as to form the single distillation unit.

[0028] Moreover, it is preferred in this second embodiment of the present invention that the crude composition is fed into the upper portion of the first distillation column, the dividing wall being arranged in a lower part of the first distillation column separating said lower part into the first section and the second section, the first bottom composition of the first distillation column is withdrawn as first bottom composition of the single distillation unit, the second bottom composition of the first distillation column is withdrawn as second bottom composition of the single distillation unit, the overhead composition of the second distillation column is withdrawn as overhead composition of the single distillation unit and optionally a side composition of the second distillation column is withdrawn as side composition of the single distillation unit. Good results are in particular obtained, when the second distillation column comprises an overhead outlet, a bottom outlet and between the overhead outlet and the bottom outlet a side outlet, wherein the first distillation column comprises an overhead outlet, first and second bottom outlets and between the overhead outlet and the bottom outlets a feed inlet, wherein the second distillation column comprises between the overhead outlet and the side outlet at least one bed of structured packing or random packing and comprises between the side outlet and the bottom outlet one or more trays. Preferably, the feed inlet is arranged below the location and / or at the same location, at which the liquid connection line leads into the first distillation column. As in the first preferred embodiment of the present invention, the provision of at least one bed of structured packing or random packing between the overhead outlet and the side outlet of the second distillation column minimizes the pressure drop of the second distillation column, whereas the provision of one or more trays between the side outlet and the bottom outlet of the second distillation column allows an efficient withdrawal of fusel oil via the side outlet. Moreover, it is preferred that the first distillation column comprises between the feed inlet and the bottom outlet either one or more trays or at least one bed of structured packing or random packing. More specifically, the first distillation column preferably comprises between the feed inlet and the bottom outlets one or more trays, if the crude composition contains solids with a high dso-particle size of 2 mm or more. However, if the crude composition contains solids with a low dso-particle size of less than 2 mm, the first distillation column preferably comprises between the feed inlet and the bottom outlet at least one bed of structured packing or random packing.

[0029] Preferably, the two distillation columns are operated in this second preferred embodiment of the present invention at similar pressures, meaning that the pressures within both distillation columns do not vary by more than 80 kPa. However, it is also possible to operate both distillation columns with different pressures.

[0030] Good results are in particular obtained, when in this second preferred embodiment of the present invention the distillation is performed in the second distillation col- umn at a top temperature of 20 to 120°C and at an absolute pressure of 5 to 450 kPa and more preferably at a temperature of 40 to 80°C and at an absolute pressure of 20 to 120 kPa, whereas the distillation is performed in the first distillation column preferably at a top temperature of 40 to 140°C and at an absolute pressure of 7 to 470 kPa and more preferably at a temperature of 45 to 85°C and at an absolute pressure of 22 to 130 kPa. Top temperature means the temperature of the vapor composition being withdrawn from the distillation column as overhead composition.

[0031] In accordance with preferred embodiments of the present invention, the only one distillation column or the first distillation column (or lowest first distillation column) is a dividing wall column with a bottom dividing wall, i.e. the dividing wall is a (preferably vertically arranged) bottom dividing wall positioned in the bottom portion of the dividing wall column, with the first side being the first section and the second side being the second section. Unlike a dividing wall column with a top dividing wall, a dividing wall column with a bottom dividing wall has two independent stripping sections (i.e., on either side of the dividing wall) with a common rectifying section (i.e., the top section above the dividing wall).

[0032] In addition, it is preferred that the compressed vapor is injected in this embodiment into the bottom portion of the first distillation column below the lowermost of the trays, of the at least one bed of structured packing and of the at least one bed of random packing.

[0033] In accordance with the present invention, a first and I or second bottom composition is withdrawn from the single distillation unit. If the single distillation unit comprises (only) one distillation column, the first and I or second bottom composition of the single distillation unit is the first and I or second bottom composition of the one distillation column. However, if the single distillation unit comprises two distillation columns, the first and / or second bottom composition of the single distillation unit is the first and I or second bottom composition of the first distillation column, whereas, if the single distillation unit comprises more than two distillation columns, the first and I or second bottom composition of the single distillation unit is the first and I or second bottom composition of the most upstream distillation column, i.e. the distillation column comprising the stream with the highest solids content.

[0034] In addition, a portion of the overhead composition of the single distillation unit is refluxed in accordance with the present invention into the single distillation unit. If the single distillation unit comprises (only) one distillation column, the overhead composition of the single distillation unit is the overhead composition of the one distillation column. However, if the single distillation unit comprises two distillation columns, the overhead composition of the single distillation unit is the overhead composition of the second distillation column, whereas, if the single distillation unit comprises more than two distillation columns, the overhead composition of the single distillation unit is the overhead composition of the most downstream distillation column. Preferably, the refluxed overhead composition is condensed, before it is refluxed into the single distillation unit. Good results are in particular obtained, when the reflux ratio of the overhead composition being refluxed into the single distillation unit is 0.5 to 8 and more preferably 1 .3 to 6. Preferably, the refluxed overhead composition is led into the upper portion of the distillation column of the single distillation unit and, if the single distillation unit comprises two or more distillation columns, into the upper portion of the most downstream distillation column. The reflux ratio is defined herein as the ratio of the mass flowrate of the overhead composition being recirculated into the single distillation unit, after compression, condensation, separation of the desuperheating stream, divided by the mass flowrate of the overhead composition being removed as product from the single distillation unit, which is leaving the unit.

[0035] In accordance with another preferred embodiment of the present invention, the overhead composition of the single distillation unit contains, based on 100% by weight of the overhead composition of the single distillation unit, 55 to 100% by weight and more preferably 75 to 95% by weight of the at least oxygen containing organic compound, 40 to 0% by weight and more preferably 25 to 5% by weight of water and remainder to 100% by weight impurities, such as in particular oxygen containing organic compounds having a lower boiling point than water or forming a minimum boiling azeotrope with water.

[0036] The preferred side composition obtained in the single distillation unit, called fusel oil, consists of a mixture of water, ethanol, higher alcohols and other organic compounds, such as Cs-alcohols, C4+-alcohols etc. , i.e. the side composition contains, based on 100% by weight of the side composition of the single distillation unit, 2 to 40% by weight of other organic compounds, whereas the bottom composition obtained in the single distillation unit contains water, solids, heavy boilers, i.e. compounds having the same or a higher boiling point than water, and traces of light boilers.

[0037] In accordance with the present invention, compressed vapor is injected into the single distillation unit, wherein the compressed vapor is produced by compressing vapor of a refrigerant having been obtained by evaporating the refrigerant by heating it with the overhead composition. For instance, one or more compressors may be used for compressing the vapor. The present invention is not particularly restricted concerning the kind of compressor used for the compression of vapor. For instance, suitable examples of compressors are centrifugal compressors, radial turbocompressors, turbofans, turboblowers, lobe blowers, screw compressors, piston compressors and reciprocating compressors. It is also possible to use a combination of two or more of the aforementioned compressors. Good results are in particular obtained, when one to three centrifugal compressor stages in series, one to three radial turbocompressor stages in series, three to seven turbofan stages in series, three to seven turboblower stages in series or two to five lobe blower stages in series are used for compressing the vapor. If the vapor volume to be compressed is too high for a single compressor, two or more compressors may be used in parallel to each other.

[0038] In accordance with the present invention, compressed vapor of a refrigerant, which has been obtained by evaporating liquid refrigerant by heating it with the overhead composition, is injected into the single distillation unit. Preferably at least 50%, more preferably at least 80% and most preferably all of the overhead composition is / are led through a heat exchanger so as to heat and at least partially evaporate therein liquid refrigerant to vapor, before the vapor of the refrigerant is then compressed, for instance in one or more compressors, to compressed vapor, which is partially or completely injected into the single distillation unit, where it comes into contact with the bottom composition to thereby heat and evaporate the bottom compositions of the single distillation unit. For instance, at least a portion, preferably at least 50%, more preferably at least 80% and most preferably all of the compressed vapor is / are injected into the single distillation unit and preferably into the bottom portion of the single distillation unit. Preferably, the liquid refrigerant is continuously fed into the heat exchanger through an inlet line for refrigerant.

[0039] Concerning the kind of heat exchanger used in this embodiment, the present invention is not particularly restricted. For example, the heat exchanger may be a kettle reboiler. Other suitable examples for heat exchangers being suitable for this embodiment of the present invention are shell and tube heat exchangers, plate heat exchanger reboilers, falling film reboilers, forced circulation reboilers and internal reboilers.

[0040] As mentioned above, preferably the heat exchanger comprises an inlet line for refrigerant to compensate for the compressed vapor of refrigerant being injected into the single distillation unit through a line leading from the heat exchanger into the single distillation column. The heat exchanger comprises a refrigerant line, through which the refrigerant flows, and an overhead line, through which the over- head outlet line of the distillation column flows. The refrigerant line leads to and through the compressor and from the compressor into the single distillation unit. According to one embodiment, a recirculation line splits off from the line leading from the compressor into the single distillation unit, wherein the recirculation line leads back into the heat exchanger or the main body thereof, respectively. The inlet line for refrigerant may lead directly into the main body of the heat exchanger or into the recirculation line. Hence, compressed vapor of refrigerant is continuously injected out of the heat exchanger or the recirculation system of the heat exchanger into the single distillation unit, which is compensated by fresh liquid refrigerant which is continuously fed into the main body of the heat exchanger or into a recirculation line of the heat exchanger.

[0041] In accordance with one particular preferred embodiment of the present invention, all of the compressed vapor is injected into the single distillation unit and preferably into the bottom portion of the single distillation unit. In this embodiment, the single distillation unit may comprise a bottom reboiler, but preferably does not comprise any bottom reboiler. Bottom reboiler means a reboiler, through which a portion of the bottom composition being withdrawn from the single distillation unit is led and evaporated, before the evaporated bottom composition is recycled into the single distillation unit.

[0042] In accordance with an alternative, particular preferred embodiment of the present invention, not all of the compressed vapor, but only a portion thereof is injected into the single distillation unit and preferably into the bottom portion of the single distillation unit. In this embodiment, the single distillation unit preferably comprises a bottom reboiler. Preferably, a portion of the bottom composition of the single distillation unit is withdrawn from the single distillation unit, evaporated in the reboiler and recycled into the single distillation unit, wherein 50 to 99% and preferably 70 to 95% of the compressed vapor are injected into the bottom portion of the single distillation unit, wherein the remainder to 100% of the compressed vapor is led through the reboiler and is condensed after leaving the reboiler, preferably in a trim condenser, before the condensed refrigerant is led back to the aforementioned heat exchanger. Trim condenser means in accordance with the present invention a heat exchanger used to further condense the vapors exiting from the previous equipment, for instance, from another heat exchanger or vessel. Furthermore, it is preferred in this embodiment that 2 to 90% by weight and more preferably 8 to 30% by weight of the bottom composition (first and I or second bottom composition), based on 100% by weight of the bottom composition being withdrawn from the single distillation unit, are evaporated in the reboiler and recycled into the single distillation unit.

[0043] In a further development of the idea of the present invention, it is proposed that a portion of the liquid refrigerant is led as desuperheating liquid into the compressor. The temperature of the desuperheating liquid can be lower, equal or higher than the temperature of the liquid refrigerant. The desuperheating liquid is injected into the vapor of the refrigerant entering the compressor, into the vapor of the refrigerant within the compressor or into the compressed vapor of the refrigerant exiting the compressor. Desuperheating liquid means in accordance with the present inventions any liquid that is mixed with a vapor, resulting in a vapor stream with a lower temperature than the one before liquid injection, for instance, liquid is spread into the vapor so that liquid droplets are finely dispersed in the vapor. Because the two streams, i.e. desuperheating liquid and vapor, are mixed, the mass flowrate after the desuper-heating is equal to the mass of the to-be-compressed vapor plus desuperheating liquid. Without injecting the desuperheating liquid, the vapors are compressed and a part of the mechanical work will be converted in temperature increase of the vapor, which leads to high outlet temperature. In turn, injecting the desuperheating liquid into the overhead composition upstream of the compressor, onto the rotor within the compressor or into the compressed vapor downstream of the compressor, the mechanical work is converted to evaporation enthalpy of this liquid without increasing a lot the temperature. Comparing to compression without desuperheating, desuperheating increases the overall efficiency by 2 to 20 % and helps to keep the temperature low. Furthermore, it allows to use a simpler material of construction and design temperature to be used. It is preferred in this embodiment that a multi-stage compression train is used, wherein a heat exchanger is installed between two compressors in series. More specifically, the multi-stage compression train comprises two or more compressors arranged in series to each other, wherein adjacent compressors are connected to each other each by a connection line, wherein the most upstream compressor is further connected with an inlet line and the most downstream compressor is further connected with an outlet line, wherein vapor being generated in the respective compressors flow through the connection and outlet lines. Preferably, at least one of the connection lines and / or the outlet line is equipped with at least one heat exchanger which is operated with cooling water or any other cooling liquid, wherein compressed vapor coming from an upstream compressor is cooled down by the heat exchanger and then flows into the adjacent downstream compressor. For example, the multi-stage compression train comprises four compressors being arranged in series to each and in total three connection lines, each of which connecting two adjacent compressors, wherein the most upstream compressor is further connected with an inlet line and the most downstream compressor is further connected with an outlet line. Preferably, at least one heat exchanger is arranged in any of the three connection lines and / or in the outlet line. For instance, in each of the three connection lines and in the outlet line each one heat exchanger may be arranged. Alternatively, in each of the connection lines and in the outlet line each two or more heat exchangers may be arranged. Still alternatively, in only three or in only two of the three connection lines and the outlet line each one or more heat exchangers may be arranged. Yet alternatively, in only one of the three connection lines and the outlet line one or more heat exchangers may be arranged. Again, each heat exchanger is operated with cooling water or with another cooling liquid on the utility side, which cools down the vapors after compression on the process side, wherein the (cooled) vapors are flowing through the connections lines and the outlet line. Utility side means here the part of the heat exchanger, through which the cooling water or another cooling liquid flows, whereas process side means the part of the heat exchanger, through which the vapors to-be-cooled flow.

[0044] Good results are in particular obtained, when the refrigerant is compressed with a compression ratio of 1 .3 to 7 to the compressed vapor, wherein the compressed vapor has a temperature of 30 to 160°C and preferably of 60 to 120°C.

[0045] The overhead composition partially condenses in the aforementioned heat exchanger and the mixture of condensed overhead composition and vapor of overhead composition is then preferably further condensed after leaving the heat exchanger, before a portion of the condensed overhead composition is refluxed into the single distillation unit. Preferably, the condensation is performed for instance in a trim condenser.

[0046] The target composition may, if required, be further purified. For example, the further purification of the target composition may comprise one or more distillation steps and / or the removal of water from the target composition in a dehydration unit. The dehydration unit preferably comprises one or more membranes, one or more pressure swing adsorption columns, one or more adsorption columns, one or more mol sieves, one or more azeotropic distillation columns and / or one or more extractive distillation columns. For instance, the purified target composition comprises, based on 100% by weight of the target composition, at least 80% by weight and more preferably at least 98% by weight of the at least one oxygen containing organic compound as target compound as well as at most 20% by weight and more preferably at most 2% by weight of water. For instance, if the oxygen containing organic compound is ethanol, the purified target composition preferably comprises, based on 100% by weight of the target composition, at least 98% by weight and more preferably at least 99.8% by weight of ethanol as well as at most 2% by weight and more preferably at most 0.2% by weight of water. All of the aforementioned distillation steps are preferably performed as continuous distillation steps.

[0047] In accordance with another aspect, the present invention relates to a plant for separating a target composition containing at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water optionally in admixture with water from a crude composition having been produced in a biocatalyzed process and containing the at least one oxygen containing organic compound as target compound, water and biomass, in particular for performing a process as described above, wherein the plant comprises a single distillation unit, which comprises a feed inlet for crude composition, an overhead outlet for target composition, a bottom outlet and at least one internal being selected from structured packings, random packings, trays and combinations thereof, wherein the plant further comprises a heat exchanger comprising an inlet line for refrigerant, a reflux line and at least one compressor, wherein the at least one compressor is connected with a line leading from the heat exchanger into the single distillation unit, wherein the heat exchanger is further connected with a line leading from the overhead outlet of the single distillation unit to the heat exchanger, wherein this line is connected downstream of the heat exchanger with a target composition withdrawal line and with the reflux line.

[0048] In preferable embodiments, a dividing wall can be provided in a lower part of the single distillation unit separating said lower part into a first section and a second section, a first bottom outlet associated with the first section, a second bottom outlet associated with the second section.

[0049] The aforementioned inlet line for refrigerant has the function to compensate for the compressed vapor of refrigerant being injected into the single distillation unit through the line leading from the heat exchanger into the single distillation column. The heat exchanger comprises a refrigerant line, through which the refrigerant flows, and an overhead line, through which the overhead outlet line of the distillation column flows. The refrigerant line leads to and through the compressor and from the compressor into the single distillation unit. According to one embodiment, a recirculation line splits off from the line leading from the compressor into the single distillation unit, wherein the recirculation line leads back into the heat exchanger or the main body thereof, respectively. The inlet line for refrigerant may lead directly into the main body of the heat exchanger or into the recirculation line.

[0050] Preferably, the aforementioned line leads from the heat exchanger into the bottom portion of the single distillation unit. Again, bottom portion of the single distillation unit means the bottom portion of any of the distillation columns being included in the single distillation unit extending, seen from the bottom to the top of the respective distillation column, from the lowest point to a point being located at 50% of the distance from the bottom to the top of the distillation column.

[0051] In a further development of the idea of the present invention it is proposed that the plant further comprises a line for liquid refrigerant as desuperheating liquid, which leads from the heat exchanger into the compressor or before or after the compressor into the line leading from the heat exchanger into the bottom portion of the single distillation unit.

[0052] According to a first particularly preferred embodiment of this aspect of the present invention, the single distillation unit comprises only one distillation column, which comprises the dividing wall being arranged in a lower part of the only one distillation column separating said lower part into the first section and the second section, a feed inlet, an overhead outlet, a first and second bottom outlet and a side outlet, wherein the feed inlet is arranged, seen from the top to the bottom of the distillation column, between the side outlet and the bottom outlets, wherein the distillation column comprises between the overhead outlet and the side outlet at least one bed of structured packing or random packing, comprises between the side outlet and the feed inlet one or more trays and comprises between the feed inlet and the bottom outlets either one or more trays or at least one bed of structured packing or random packing.

[0053] Preferably, the overhead outlet line of the distillation column of this embodiment leads through the heat exchanger and then into a vessel, which is connected via a line with a vacuum unit, wherein the vessel comprises an outlet line, which splits into the target composition withdrawal line and into the reflux line, and wherein the reflux line is connected with an inlet of the distillation column being arranged, seen from the top to the bottom of the distillation column, above the uppermost bed of structured packing or random packing.

[0054] According to another variant of this first particularly preferred embodiment of this aspect of the present invention, the plant comprises a first vessel with the heat exchanger, wherein the first vessel comprises an inlet line for liquid refrigerant as well as an outlet line for vapor of a refrigerant being connected with the at least one compressor, wherein an outlet line of the compressor leads into the distillation column and preferably into the bottom portion of the distillation column.

[0055] Preferably, the vessel with the heat exchanger further comprises a liquid outlet for desuperheating liquid, which leads into the at least one compressor.

[0056] Moreover, in the aforementioned embodiment the plant may further comprise a bottom reboiler (which in accordance with the disclosure might refer to respective reboilers associated with the first section and I or second section), which is connected with a recirculation line leading from the first bottom outlet and I or second bottom outlet through the reboiler back into a further inlet of the distillation column (in particular a first reboiler being connected with a first recirculation line leading from the first bottom outlet through the first reboiler and / or a second reboiler being connected with a second recirculation line leading from the second bottom outlet through the second reboiler), wherein the inlet is preferably arranged in the bottom portion of the distillation column. It is preferred in this embodiment that from the line leading from the heat exchanger into the distillation column a further line splits off downstream of the at least one compressor, which leads through the reboiler(s) and from the reboiler to the heat exchanger. More specifically, the further line preferably leads through the reboiler and downstream thereof through a condenser, such as a trim condenser, and then to an inlet of the first vessel, wherein a further line leads from the overhead outlet of the distillation column through the heat exchanger and then into a second vessel, which is connected via a line with a vacuum unit, and wherein the second vessel comprises an outlet line, which splits into the target composition withdrawal line and into the reflux line, wherein the reflux line is connected with an inlet of the distillation column being arranged, seen from the top to the bottom of the distillation column, above the uppermost bed of structured packing or random packing.

[0057] In accordance with a second particularly preferred embodiment of this aspect of the present invention, the single distillation unit comprises two distillation columns, wherein a second distillation column comprises an overhead outlet, a side outlet and a bottom outlet and a first distillation column comprises the dividing wall being arranged in a lower part of the first distillation column separating said lower part into the first section and the second section, an overhead outlet, a feed inlet, a first bottom outlet and a second a bottom outlet, wherein the overhead outlet of the first distillation column is connected with an inlet of the second distillation column being arranged, seen from the top to the bottom of the second distillation column, between the side outlet and the bottom outlet, wherein the bottom outlet of the second distillation column is connected via a line with an inlet of the first distillation column, wherein the second distillation column comprises between the overhead outlet and the side outlet at least one bed of structured packing or random packing and comprises between the side outlet and the bottom outlet one or more trays, and wherein the first distillation column comprises between the feed inlet and the bottom outlets either one or more trays or at least one bed of structured packing or random packing. The line, which connects the bottom outlet of the second distillation column with the inlet of the first distillation column, may be arranged, seen from the top to the bottom of the first distillation column, between the overhead outlet and the feed inlet, or at the same height as the feed inlet or swapped.

[0058] Preferably, the plant comprises a first vessel with the heat exchanger, wherein the first vessel comprises an inlet line for liquid refrigerant as well as an outlet line for vapor of a refrigerant being connected with the at least one compressor, wherein an outlet line of the compressor leads into the first distillation column and preferably into the bottom portion of the first distillation column.

[0059] Good results are in particular obtained, when the vessel with the heat exchanger further comprises a liquid outlet for desuperheating liquid, which leads into the at least one compressor.

[0060] According to another variant of this second particularly preferred embodiment of this aspect of the present invention, the overhead outlet line of the second distillation column of this embodiment leads through the heat exchanger and then into a second vessel, which is connected via a line with a vacuum unit, wherein the second vessel comprises an outlet line, which splits into the target composition withdrawal line and into the reflux line, and wherein the reflux line is connected with an inlet of the distillation column being arranged, seen from the top to the bottom of the distillation column, above the uppermost bed of structured packing or random packing.

[0061] Moreover, in the aforementioned embodiment the plant may further comprise a bottom reboiler, which is connected with a recirculation line leading from the bottom outlet through the reboiler back into a further inlet of the first distillation col- umn, wherein the inlet is preferably arranged in the bottom portion of the first distillation column. It is preferred in this embodiment that from the line leading from the heat exchanger into the first distillation column a further line splits off downstream of the at least one compressor, which leads through the reboiler and from the reboiler to the heat exchanger. More specifically, the further line preferably leads through the reboiler and downstream thereof through a condenser, such as a trim condenser, and then to an inlet of the first vessel, wherein a further line leads from the overhead outlet of the distillation column through the heat exchanger and then into a second vessel, which is connected via a line with a vacuum unit, and wherein the second vessel comprises an outlet line, which splits into the target composition withdrawal line and into the reflux line, wherein the reflux line is connected with an inlet of the distillation column being arranged, seen from the top to the bottom of the distillation column, above the uppermost bed of structured packing or random packing.

[0062] Subsequently, the present invention is described by means of an illustrative, but not limiting figure, in which:

[0063] Fig. 1 is a schematic view of a plant for producing ethanol as target composition from a crude aqueous ethanol composition in accordance with one embodiment of the present invention.

[0064] Fig. 2 is a schematic view of a plant for producing ethanol as target composition from a crude aqueous ethanol composition in accordance with another embodiment of the present invention.

[0065] Fig. 3 is a schematic view of a plant for producing ethanol as target composition from a crude aqueous ethanol composition in accordance with another embodiment of the present invention. The plant 10 for producing pure ethanol as target composition from a crude aqueous ethanol composition shown in figure 1 comprises a single distillation unit 12, which comprises (only) one distillation column 14. The distillation column 14 comprises a dividing wall 23, an inlet being connected with a feed inlet line 16, an overhead outlet being connected with an overhead outlet line 18, a first bottom outlet being connected with a first bottom outlet line 20’ being provided with a stillage pump 2T, a second bottom outlet being connected with a second bottom outlet line 20 being provided with a stripped-water pump 21 , a side outlet being connected with a side outlet line 22 and a side outlet being connected with a side outlet line 22 and an optional steam inlet line 25, wherein the feed inlet is arranged, seen from the top to the bottom of the distillation column 14, between the side outlet and the bottom outlets. Furthermore, the distillation column 14 comprises, seen from the top to the bottom of the distillation column 14, between the overhead outlet and the side outlet several beds 24 of structured packings, comprises between the side outlet and the feed inlet several trays 26 and comprises between the feed inlet and the bottom outlets several trays 26’. In addition, the plant 10 comprises a first recirculation line 28’, a second recirculation line 28 and a shell and tube reboilers 30, 30’, wherein the recirculation lines 28, 28’ split off from the bottom outlet lines 20, 20’, lead through the tube side of the reboilers 30, 30’ and then back into the lower portion of the distillation column 14. The dividing wall 23 is arranged in a lower part of the column 14 separating said lower part into a first section and a second section. Stripped-water from the first section is pumped by the stripped-water pump 21 and is split into two streams. Part of it is sent out of plant 10 as stripped-water via line 31 and the other part is recirculated to the stripped-water reboiler 30 through the recirculation line 28. Moreover, a bottom withdrawal line 32 splits off from the bottom outlet line 20’. In addition, the plant comprises a preheater 34, wherein the bottom withdrawal line 32 leads through the shell side and the feed inlet line 16 leads through the tube side of the preheater 34. The reboilers 30, 30’ are connected with a refrigerant unit 62, which comprises a compressor 36 as well as a kettle reboiler 64 with a tube bundle 66, wherein the kettle reboiler 64 comprises an outlet line 68 for vapor of the refrigerant, which leads into the compressor 36. While the kettle reboiler 64 comprises an inlet line 80 for refrigerant, the compressor 36 comprises an outlet line 76 for compressed vapor of the refrigerant, which splits into a line 78 leading into the bottom portion of the distillation column 14 as well as into a recirculation line 70 leading through the shell side of the reboilers 30, 30’, then through a trim condenser 42 and then back into the kettle reboiler 64. Furthermore, the kettle reboiler 64 comprises a line 52, through which liquid refrigerant is led as desuperheating liquid into the compressor 36, wherein the line 52 is connected with a pump 72. The overhead outlet line 18 of the distillation column 14 leads through the tube bundle 66 and then to a vessel 38. In turn, the vessel 38 comprises a vapor outlet line 40 being connected with a vacuum unit 74 and comprises a liquid outlet line 44 being provided with a pump 46. The liquid outlet line 44 splits into a target composition withdrawal line 48 as well as into a reflux line 51 leading back into the upper portion of the distillation column 14.

[0066] During the operation of the plant 10, a crude composition is fed via the feed inlet line 16 into the distillation column 14 and is distilled therein into an overhead composition comprising ethanol and minor amounts of water, into a side composition of fusel oil and into a bottom compositions containing solids, water and oxygen containing organic compounds with a higher boiling point than water (i.e. into stillage and stripped-water). While the side composition is withdrawn via the side outlet line 22 from the plant 10 and the bottom compositions are withdrawn from the distillation column 14 via the bottom outlet lines 20, 20’, the overhead composition is withdrawn from the distillation column 14 via the overhead outlet line 18. While refrigerant is fed into the kettle reboiler 64 via the inlet line 80, the overhead composition of the distillation column 14 heats in the tube bundle 66 the liquid refrigerant being contained in the kettle reboiler 64, thereby evaporating a portion of the liquid refrigerant, wherein the refrigerant vapor flows via the outlet line 68 into the compressor 36, which also receives via the line 52 refrigerant as desuper- heating liquid. A portion of the compressed refrigerant generated in the compressor 36 is split into four streams and then led through the outlet line 76 and the line 78 into the bottom portions of the distillation column 14, whereas the remaining portions of the compressed refrigerant is led through the recirculation line 70 and then through the shell side of the reboilers 30, 30’, in which it heats and evaporates the liquid bottom compositions being recirculated via the recirculation lines 28, 28’ into the lower portion of the distillation column 14. Thus, in fact the refrigerant unit 62 acts as indirect heat pump. Downstream of the tube bundle 66, where the overhead composition is partially condensed, the overhead composition is led into the vessel 38, in which it is further condensed. The portion of the bottom compositions, which is not recirculated via recirculation lines 28, 28’ and reboilers 30, 30’ back into the bottom portion of the distillation column 14, is withdrawn from the plant via the bottom withdrawal line 32 and a stripped-water withdrawal line 31 . In turn, a portion of the condensed overhead composition is withdrawn from the plant 10 via the target composition withdrawal line 48, whereas the remaining portion of the condensed overhead composition is led through the reflux line 51 into the upper portion of the distillation column 14.

[0067] The plant 10 for producing pure ethanol as target composition from a crude aqueous ethanol composition shown in figure 2 corresponds to that shown in figure 1 , except that the plant 10 does not comprise a recirculation line 28, 28’, a reboiler 30, 30’, a trim condenser 42 and a recirculation line 70. During the operation of the plant 10, all of the compressed vapor of refrigerant being produced by the compressor 36 is split into two streams and injected through line 78 into the bottom portions of the distillation column 14.

[0068] The plant 10 for producing pure ethanol as target composition from a crude aqueous ethanol composition shown in figure 3 corresponds to that shown in figure 1 , except that the single distillation unit 12 of the plant 10 shown in figure 3 comprises two distillation columns 54, 55 being connected with each other, namely a first distillation column 54 and a second distillation column 55. The second distillation column 55 comprises, seen from the top to the bottom of the distillation column 55, an overhead outlet being connected with the overhead outlet line 18, a bottom outlet being connected with a liquid connection line 56 being provided with a pump 58 and a side outlet being connected with a side outlet line 22, wherein between the overhead outlet and the side outlet several beds 24 of structured packings and between the side outlet and the bottom outlet several trays 26 are arranged. The liquid connection line 56 of the second distillation column 55 leads into the upper portion of the first distillation column 54, which comprises an overhead outlet being connected with a vapor connection line 60, which leads into the lower portion of the second distillation column 55. Moreover, the first distillation column 54 comprises a dividing wall 23, an inlet being arranged below the location, at which the liquid connection line 56 leads into the first distillation column 54 and being connected with a feed inlet line 16, and further comprises a first bottom outlet being connected with a bottom outlet line 20’ and a second bottom outlet being connected with a second bottom outlet line 20. Between the inlet being connected with the feed inlet line 16 and the bottom outlets, several trays 26’ are arranged.

[0069] The plant 10 shown in figure 3 is operated like that shown in figure 1 except that during the operation bottom liquid of the second distillation column 55 is pumped via the pump 58 through the liquid connection line 56 into the upper portion of the first distillation column 54 and that vapor of overhead composition of the first distillation column 54 flows upwardly through the vapor connection line 60 into the lower portion of the second distillation column 55. There is no phase change in the two connection lines 56, 58, i.e. the liquid bottom composition of the second distillation column 55 is not evaporated in the liquid connection line 56 and the vapor overhead composition of the first distillation column 55 is not condensed in the vapor connection line 60. Thus, in fact both distillation columns 54, 55 act thermodynamically as one distillation column. Reference numerals

[0070] 10 Plant for producing ethanol

[0071] 12 Single distillation unit

[0072] 14 Distillation column

[0073] 16 Feed inlet line

[0074] 18 Overhead outlet line

[0075] 20, 20’ Bottom outlet line

[0076] 21 , 2T Pump

[0077] 22 Side outlet line

[0078] 23 Dividing wall

[0079] 24 Bed of structured packing

[0080] 25 Steam inlet line

[0081] 26, 26’ T rays

[0082] 28, 28’ Recirculation line

[0083] 30, 30’ Shell and tube reboiler

[0084] 31 Stripped-water withdrawal line

[0085] 32 Bottom withdrawal line

[0086] 34 Preheater

[0087] 36 Compressor

[0088] 38 Vessel

[0089] 40 Vapor outlet line

[0090] 42 Trim condenser

[0091] 44 Liquid outlet line

[0092] 46 Pump

[0093] 48 Target composition withdrawal line

[0094] 51 Reflux line

[0095] 52 Line for desuperheating liquid 54 First distillation column

[0096] 55 Second distillation column

[0097] 56 Liquid connection line

[0098] 58 Pump 60 Vapor connection line

[0099] 62 Refrigerant unit

[0100] 64 Kettle reboiler

[0101] 66 Tube bundle

[0102] 68 Outlet line for refrigerant vapor 70 Recirculation line

[0103] 72 Pump

[0104] 74 Vacuum unit

[0105] 76 Outlet line for compressed vapor of the refrigerant

[0106] 78 Line leading into the bottom portion of the distillation column 80 Inlet line for refrigerant.

Claims

Claims:1 . A process of separating a target composition containing at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water optionally in admixture with water from a crude composition having been produced in a biocatalyzed process and containing the at least one oxygen containing organic compound as target compound, water and biomass, wherein the process comprises the steps of feeding the crude composition into a single distillation unit, distilling it therein and withdrawing from the single distillation unit an overhead composition as target composition, a bottom composition and optionally a side composition, wherein a portion of the overhead composition is refluxed into the single distillation unit, wherein compressed vapor is injected into the single distillation unit, wherein the compressed vapor is produced by compressing vapor of a refrigerant having been obtained by evaporating the refrigerant by heating it with the overhead composition, wherein the refrigerant comprises, based on the total weight of the refrigerant, at least 70% by weight of water.

2. The process in accordance with any of the preceding claims, wherein the single distillation unit comprises only one distillation column, wherein the distillation column comprises a dividing wall being arranged in a lower part of the only one distillation column separating said lower part into a first section and a second section, a feed inlet, an overhead outlet, a first bottom outlet, a second bottom outlet and a side outlet, wherein, seen from the top to the bottom of the distillation column, the feed inlet is arranged between the side outlet and the bottom outlets, wherein the distillation column comprises between the overhead outlet and the side outlet at least one bed of structured packing or random packing, comprises between the side outlet and the feed inlet one or more trays and comprises between the feed inletand the bottom outlets either one or more trays or at least one bed of structured packing or random packing, wherein the compressed vapor is injected into the bottom portion of the distillation column below the lowermost of the trays, of the at least one bed of structured packing and of the at least one bed of random packing.

3. The process in accordance with claim 1 or 3, wherein the compressed vapor is injected into the bottom portion of the single distillation unit, wherein the bottom portion of the single distillation unit is the bottom portion of any of the distillation columns being included in the single distillation unit extending, seen from the bottom to the top of the respective distillation column, from the lowest point to a point being located at 50% of the distance from the bottom to the top of the distillation column.

4. The process in accordance with claim 1 to 3, wherein the crude composition comprises, based on 100% by weight of the crude composition, 0.5 to 40% by weight and preferably 3 to 20% by weight of at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water and being preferably selected from group consisting of methanol, ethanol, propanol, butanol, acetaldehyde, ethyl acetate, acetone and mixtures of two or more thereof, and further comprises 50 to 99% by weight and preferably 60 to 95% by weight of water, 0 to 30% by weight and preferably 3 to 15% by weight of solids and 0 to 25% by weight and preferably 1 to 10% by weight of liquid compounds having a higher boiling point than water.

5. The process in accordance with any of the preceding claims, wherein the refrigerant comprises at least 70% by weight, more preferably at least 80% by weight, more preferably at least 90% by weight, yet more preferably at least 95% by weight, still more preferably at least 98% by weight and mostpreferably at least 99% by weight of water, wherein the remainder to 100% by weight contains bio-based residues and optionally air and other impurities.

6. The process in accordance with any of claims 1 , or 3 to 5, wherein the single distillation unit comprises two distillation columns, wherein the two distillation columns are connected with each other by a connection vapor line through which overhead composition of the first distillation column flows without intermediate condensation into the lower portion of the second distillation column and are connected with each other by a liquid connection line through which bottom composition of the second distillation column flows without intermediate evaporation into the first distillation column, wherein the crude composition is fed into the upper portion of the first distillation column, the dividing wall being arranged in a lower part of the first distillation column separating said lower part into the first section and the second section, the first bottom composition of the first distillation column is withdrawn as first bottom composition of the single distillation unit, the second bottom composition of the first distillation column is withdrawn as second bottom composition of the single distillation unit, the overhead composition of the second distillation column is withdrawn as overhead composition of the single distillation unit and optionally a side composition of the second distillation column is withdrawn as side composition of the single distillation unit, wherein the second distillation column comprises an overhead outlet, a bottom outlet and, seen from the top to the bottom of the second distillation column, between the overhead outlet and the bottom outlet a side outlet, wherein the first distillation column comprises an overhead outlet, a first bottom outlet, a second bottom outlet and, seen from the top to the bottom of the first distillation column, between the overhead outlet and the bottom outlets a feed inlet, wherein the second distillation column comprises between the overhead outlet and the side outlet at least one bed of structured pack-ing or random packing and comprises between the side outlet and the bottom outlet one or more trays, and wherein the first distillation column comprises between the feed inlet and the bottom outlets either one or more trays or at least one bed of structured packing or random packing, wherein the compressed vapor is injected into the bottom portion of the first distillation column below the lowermost of the trays, of the at least one bed of structured packing or of the at least one bed of random packing.

7. The process in accordance with any of the preceding claims, wherein at least a portion of the overhead composition is condensed, before it is refluxed into the single distillation unit, wherein the reflux ratio of the overhead composition being refluxed into the single distillation unit is 0.5 to 8.0 and preferably 1 .3 to 6.0.

8. The process in accordance with any of the preceding claims, wherein at least 50%, preferably at least 80% and more preferably all of the overhead composition is / are led through a heat exchanger so as to heat and at least partially evaporate therein refrigerant to vapor of the refrigerant, wherein the vapor of the refrigerant is then compressed to the compressed vapor, wherein at least a portion, preferably at least 50%, more preferably at least 80% and most preferably all of the compressed vapor is / are injected preferably into the bottom portion of the single distillation unit, wherein preferably liquid refrigerant is continuously fed through an inlet line for refrigerant into the main body of the heat exchanger or into a recirculation line leading from the main body of the heat exchanger via the compressor back to the main body of the heat exchanger.

9. The process in accordance with any of the preceding claims, wherein the compressed vapor is produced by compressing vapor of the refrigerant in a compressor, wherein a portion of liquid refrigerant is led as desuperheatingliquid into the vapor of the refrigerant upstream of the compressor, in which the vapor of the refrigerant is compressed, onto the rotor within the compressor or into the compressed vapor of the refrigerant downstream of the compressor.

10. The process in accordance with claim 8, wherein a portion of the bottom composition of the single distillation unit is withdrawn from the single distillation unit, is evaporated in a reboiler and recycled into the single distillation unit, and wherein 50 to 99% and preferably 70 to 95% of the compressed vapor are injected into the bottom portion of the single distillation unit, wherein the remainder to 100% of the compressed vapor is led through the reboiler and is condensed after leaving the reboiler, preferably in a trim condenser, before the condensed refrigerant is led back to the heat exchanger.11 . The process in accordance with any of the preceding claims, wherein the refrigerant is compressed with a compression ratio of 1 .3 to 7.0 to the compressed vapor, wherein the compressed vapor has a temperature of 30 to 160°C and preferably of 60 to 120°C.

12. A plant for separating a target composition containing at least one oxygen containing organic compound as target compound having a lower boiling point than water or forming a minimum boiling azeotrope with water optionally in admixture with water from a crude composition having been produced in a biocatalyzed process and containing the at least one oxygen containing organic compound as target compound, water and biomass, in particular for performing a process in accordance with any of the preceding claims, wherein the plant comprises a single distillation unit, which comprises a feed inlet for crude composition, an overhead outlet for target composition, a bottom outlet and at least one internal being selected from structuredpackings, random packings, trays and combinations thereof, wherein the plant further comprises a heat exchanger comprising an inlet line for refrigerant, a reflux line and at least one compressor, wherein the at least one compressor is connected with a line leading from the heat exchanger into the single distillation unit, wherein the heat exchanger is further connected with a line leading from the overhead outlet of the single distillation unit to the heat exchanger, wherein this line is connected downstream of the heat exchanger with a target composition withdrawal line and with the reflux line, wherein the inlet line for refrigerant leads directly into the main body of the heat exchanger or into a recirculation line leading from the main body of the heat exchanger via the compressor back to the main body of the heat exchanger.

13. The plant in accordance with claim 12, wherein the line leads from the heat exchanger into the bottom portion of the single distillation unit, wherein the bottom portion of the single distillation unit is the bottom portion of any of the distillation columns being included in the single distillation unit extending, seen from the bottom to the top of the respective distillation column, from the lowest point to a point being located at 50% of the distance from the bottom to the top of the distillation column, wherein the plant preferably further comprises a line for liquid refrigerant as desuperheating liquid, which leads from the heat exchanger into the compressor or before or after the compressor into the line leading from the heat exchanger into the bottom portion of the single distillation unit.

14. The plant in accordance with claim 12 or 13, wherein the single distillation unit comprises only one distillation column, which comprises a dividing wall being arranged in a lower part of the only one distillation column separating said lower part into a first section and a second section, a feed inlet, an overhead outlet, a first bottom outlet, a second bottom outlet and a side out-let, wherein the feed inlet is arranged, seen from the top to the bottom of the distillation column, between the side outlet and the bottom outlets, wherein the distillation column comprises between the overhead outlet and the side outlet at least one bed of structured packing or random packing, comprises between the side outlet and the feed inlet one or more trays and comprises between the feed inlet and the bottom outlets either one or more trays or at least one bed of structured packing or random packing, wherein optionally the plant further comprises a reboiler being connected with a recirculation line leading from the first bottom outlet and I or the second bottom outlet through the reboiler back into a further inlet of the distillation column, wherein from the line leading from the heat exchanger into the distillation column a further line splits off downstream of the at least one compressor, which leads through the reboiler and from the reboiler to the heat exchanger.

15. The plant in accordance with claim 12 or 13, wherein the single distillation unit comprises two distillation columns, wherein a first distillation column comprises the dividing wall being arranged in a lower part of the first distillation column separating said lower part into a first section and a second section, an overhead outlet, a feed inlet, a first bottom outlet and a second bottom outlet and a second distillation column comprises an overhead outlet, a side outlet and a bottom outlet, wherein the overhead outlet of the first distillation column is connected with an inlet of the second distillation column being arranged, seen from the top to the bottom of the second distillation column, between the side outlet and the bottom outlet, wherein the bottom outlet of the second distillation column is connected via a line with an inlet of the first distillation column, wherein the second distillation column comprises between the overhead outlet and the side outlet at least one bed of structured packing or random packing and comprises between the side outlet and the bottom outlet one or more trays, and wherein the first distillation column comprises between the feed inlet and the bottom outlets either oneor more trays or at least one bed of structured packing or random packing, wherein optionally the plant further comprises a reboiler being connected with a recirculation line leading from the first bottom outlet and I or second bottom outlet through the reboiler back into a further inlet of the first distilla- tion column, wherein from the line leading from the heat exchanger into the first distillation column a further line splits off, which leads through the reboiler and from the reboiler to the heat exchanger.

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