Treatment of alcohol compositions

Abstract

Process for reducing the water and carboxylic acid content of an alcohol composition containing at least one C.sub.1-4 alcohol, water and at least one C.sub.1-4 carboxylic acid by (a) forming a vapor phase alcohol composition A and a liquid phase alcohol composition B, (b) separating a second vapor phase alcohol composition C and an aqueous phase D from the liquid phase alcohol composition B, the aqueous phase D containing the majority of the carboxylic acid that was present in the liquid phase alcohol composition B; (c) passing the vapor phase alcohol composition A to a drying unit, (d) passing the vapor phase alcohol composition C to a drying unit; and (e) recovering an alcohol composition from the drying units of steps (c) and (d). The recovered alcohol composition of step (e) has a reduced water and carboxylic acid content.

Claims

1. A process for reducing the water and carboxylic acid content of an alcohol composition comprising at least one alcohol having from one to four carbon atoms, water and at least one carboxylic acid having from one to four carbon atoms, wherein said process comprises: (a) forming a vapour phase alcohol composition A and a liquid phase alcohol composition B from the alcohol composition; (b) separating a second vapour phase alcohol composition C and an aqueous phase D from the liquid phase alcohol composition B in a distillation column, wherein the aqueous phase D contains the majority of the carboxylic acid that was present in the liquid phase alcohol composition B; (c) passing the vapour phase alcohol composition A to a drying unit comprising a desiccant; (d) passing the vapour phase alcohol composition C to a drying unit comprising a desiccant; and (e) recovering an alcohol composition from the drying unit of step (c) and the drying unit of step (d); wherein the recovered alcohol composition of step (e) has a reduced water and carboxylic acid content.

2. A process as claimed in claim 1, wherein the vapour phase alcohol composition A and the liquid phase alcohol composition B are formed by vaporisation of the alcohol composition.

3. A process as claimed in claim 1, wherein the vapour phase alcohol composition A and liquid phase alcohol composition B are formed by pre-dividing the alcohol composition into a first portion and a second portion, passing the first portion to a vaporisation unit so that substantially all of the first portion is vaporised in the vaporisation unit to form the vapour phase alcohol composition A, and passing the second portion to the distillation column as the liquid phase alcohol composition B.

4. A process as claimed in claim 1, wherein the vapour phase alcohol composition A and liquid phase alcohol composition B are formed by pre-dividing the alcohol composition into a first portion and a second portion, passing the first portion to a vaporisation unit so that the first portion is divided in the vaporisation unit into the vapour phase alcohol composition A and a third portion, and passing the second portion and the third portion to the distillation column as the liquid phase alcohol composition B.

5. A process as claimed in claim 1, wherein the vaporisation step does not result in a significant difference in the concentration of water present in the vapour phase alcohol composition A and the liquid phase alcohol composition B.

6. A process as claimed in claim 1, wherein the vapour phase alcohol composition A and the vapour phase alcohol composition C are passed to the same drying unit comprising a desiccant.

7. A process as claimed in claim 6, wherein the vapour phase alcohol composition A and the vapour phase alcohol composition C are combined prior to being passed to the drying unit comprising a desiccant.

8. A process as claimed in claim 1, wherein the alcohol composition comprises ethanol.

9. A process as claimed in claim 1, wherein the alcohol composition comprises acetic acid.

10. A process as claimed in claim 1, wherein the alcohol composition comprises at least one butanol.

11. A process as claimed in claim 1, wherein the alcohol composition comprises butyric acid.

12. A process as claimed in claim 1, wherein the alcohol composition has a water concentration in the range of from 0.05 wt % to 10 wt %.

13. A process as claimed in claim 1, wherein the alcohol composition has a carboxylic acid concentration in the range of 500 ppmw to 5 wt %.

14. A process as claimed in claim 1, further comprising using a portion of the alcohol composition having a reduced water and carboxylic acid content recovered in step (e) to regenerate the drying unit of step (c) and/or step (d), and optionally passing a portion of the resulting stream comprising alcohol and water to the distillation column.

15. A method of preparing a fuel alcohol composition from an alcohol composition comprising at least one alcohol having from one to four carbon atoms, water and at least one carboxylic acid having from one to four carbon atoms, wherein said method involves: (a) determining the concentration of water and carboxylic acid present in the alcohol composition; (b) if the alcohol composition comprises a concentration of water which is greater than the azeotropic concentration for the alcohol composition, passing the entire alcohol composition to a distillation column of step (c) as a liquid phase alcohol composition B; if the alcohol composition comprises a concentration of water which is equal to or lower than the azeotropic concentration for the alcohol composition, and the carboxylic acid concentration is equal to or lower than the maximum desired concentration of carboxylic acid in the fuel alcohol composition, vaporising the entire alcohol composition to form a vapour phase alcohol composition A; or if the alcohol composition comprises a concentration of water which is equal to or lower than the azeotropic concentration for the alcohol composition, and the carboxylic acid concentration is greater than the maximum desired concentration of carboxylic acid in the fuel alcohol composition, forming a vapour phase alcohol composition A and a liquid phase alcohol composition B from the alcohol composition; (c) separating a second vapour phase ethanol composition C and an aqueous phase D from the liquid phase ethanol composition B, if present, in a distillation column, wherein the aqueous phase D contains the majority of the carboxylic acid that was present in the liquid phase alcohol composition B; (d) passing the vapour phase alcohol composition A, if present, to a drying unit comprising a desiccant; (e) passing the vapour phase alcohol composition C, if present, to a drying unit comprising a desiccant; and (f) recovering a fuel alcohol composition from the drying unit of step (d), if present, and the drying unit of step (e), if present; wherein the recovered fuel alcohol composition has a reduced water content.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The regeneration of the desiccant bed, or beds, can be performed by any means known in the art for the regeneration of a desiccant material. Typically, the regeneration of the desiccant bed may be performed by contacting the desiccant bed with a carrier fluid containing essentially no water and either increasing the temperature of the desiccant to a temperature at which the water is desorbed from the desiccant bed into the carrier fluid or reducing the pressure to a pressure at which the water is desorbed from the desiccant bed into the carrier fluid; whilst the regeneration of the desiccant bed via means of increasing the temperature may be performed in both the liquid and the vapour phase, the regeneration of the desiccant bed via means of decreasing the pressure would be performed in the vapour phase only. A particularly convenient carrier fluid (either liquid phase or gas phase) which may be used for the regeneration of the desiccant bed is the dried alcohol which is effluent from the process of the present invention; alternative carrier fluids include other dry alcohols (either in the gas phase or liquid phase), dry alkanes (either in the gas phase or liquid phase), or gases which are inert in the desiccant bed, such as dry nitrogen and dry carbon dioxide.

(2) In a particular embodiment, the process of the present invention further comprises using a portion of the alcohol composition having reduced a water and carboxylic content recovered in step (e) to regenerate the drying unit of step (c) and/or step (d). Optionally in this embodiment, the process further comprises passing a portion of the resulting stream comprising alcohol and water to the distillation column for distillation, together with the liquid phase alcohol composition B, to form the second vapour phase alcohol composition C and the aqueous phase D.

(3) In one embodiment of the present invention, the, or each, drying unit comprises two or more parallel desiccant beds, wherein the vapour phase alcohol composition A and/or C is contacted with the desiccant bed in at least one of the desiccant beds (the active bed(s)) at the process temperature and pressure, whilst at least one of the other, parallel, desiccant beds is being regenerated (the regenerating bed(s)) by contacting a carrier fluid with the desiccant bed at an increased temperature relative to the active bed (temperature swing adsorption). In temperature swing adsorption systems operated in the gas phase, the pressure of both the active bed and the regenerating bed may be kept approximately constant. Advantageously, temperature swing adsorption systems may be operated entirely in the liquid phase. Operation of such systems would enable continuous regeneration of the desiccant beds through the use of systematic changing of the active and regenerating beds. Typical temperatures for regenerating the desiccant bed in temperature swing adsorption systems are temperatures having a minimum temperature of at least 180 C. and also being at least 10 C. greater than the process temperature; preferably, temperatures for regenerating the desiccant bed in temperature swing adsorption systems are temperatures having a minimum temperature of at least 200 C. and also being at least 15 C. greater than the process temperature; and, more preferably, temperatures for regenerating the desiccant bed in temperature swing adsorption systems are temperatures having a minimum temperature of at least at least 220 C. and also being at least 20 C. greater than the process temperature. By the term process temperature, it is meant the temperature at which the vapour phase alcohol composition A and/or C is contacted with the desiccant bed (e.g. the temperature of the active bed). The heating of the desiccant bed in the regenerating bed may be achieved by preheating the carrier fluid prior to contacting it with the desiccant bed.

(4) In one embodiment of the present invention, the, or each, drying unit comprises two or more parallel desiccant beds, wherein the vapour phase alcohol composition A and/or C is contacted with the desiccant bed in at least one of the desiccant beds (the active bed(s)) at the process temperature and pressure, whilst at least one of the other, parallel, desiccant beds is being regenerated (the regenerating bed(s)) by contacting a carrier gas with the desiccant bed at an decreased pressure relative to the active bed (pressure swing adsorption). In pressure swing adsorption systems, the temperature of both the active bed and the regenerating bed may be kept approximately constant. Operation of such systems would enable continuous regeneration of the desiccant beds through the use of systematic changing of the active and regenerating beds. Typical pressures for regenerating the desiccant bed in pressure swing adsorption systems are pressures having a maximum pressure of at most 0.2 MPa and also said pressure being at least 0.05 MPa lower than the process pressure; preferably, the pressures for regenerating the desiccant bed in pressure swing adsorption systems are pressures having a maximum pressure of at most 0.15 MPa and also said pressure being at least 0.075 MPa lower than the process pressure; and, more preferably, the pressures for regenerating the desiccant bed in pressure swing adsorption systems are pressures having a maximum pressure of at most 0.1 MPa and also said pressure being at least 0.1 MPa lower than the process pressure. By the term process pressure, it is meant the pressure at which the vapour phase alcohol composition A and/or C is contacted with the desiccant bed (e.g. the pressure of the active bed). Systems which employ a combination of temperature swing adsorption and pressure swing adsorption may also be used in the process of the present invention.

(5) The time required for the regeneration of the porous inorganic oxide material will be dependent upon the various factors, such as the amount of water adsorbed, the exact desiccant bed used, the temperature and/or pressure used during the regeneration cycle, the carrier fluid used during the regeneration cycle as well as the flow rate of the carrier fluid during the regeneration cycle. The time required for the regeneration of the desiccant bed can be readily determined through means known in the art, for example, it may be determined by monitoring the water content in the effluent carrier fluid during a regeneration cycle or by monitoring the temperature of the porous inorganic oxide material during a regeneration cycle.

(6) The effluent alcohol composition from the process of the present invention has a reduced content of water and carboxylic acid relative to the alcohol composition which is fed to the process of the present invention.

(7) In one aspect of the present invention, the alcohol composition which results from the process of the present invention has a water content and a carboxylic acid content which meets required specifications for fuel alcohol compositions. Thus, in one particular aspect of the present invention, the process of the present invention provides a method for reducing the water and carboxylic acid content of an alcohol composition which contains a water and/or carboxylic acid content which is greater than is permissible in a fuel alcohol specification, such that the water and/or carboxylic acid content of the alcohol composition is equal to or lower than the maximum water and/or carboxylic acid content required by the fuel alcohol specification.

(8) In another particular aspect of the present invention, the process of the present invention provides a method for reducing the water and acetic acid content of an ethanol composition comprising ethanol, water and acetic acid, wherein said process comprises:

(9) (a) forming a vapour phase ethanol composition A and a liquid phase ethanol composition B from the alcohol composition;

(10) (b) separating a second vapour phase ethanol composition C and an aqueous phase D from the liquid phase ethanol composition B in a distillation column, wherein the aqueous phase D contains the majority of the acetic acid that was present in the liquid phase ethanol composition B;

(11) (c) passing the vapour phase ethanol composition A to a drying unit comprising a desiccant;

(12) (d) passing the vapour phase ethanol composition C to a drying unit comprising a desiccant; and

(13) (e) recovering an ethanol composition from the drying unit of step (c) and the drying unit of step (d);

(14) wherein the recovered ethanol composition of step (e) has a reduced water and acetic acid content.

(15) In another particular aspect of the present invention, the process of the present invention provides a method for the preparation of a fuel ethanol composition suitable for use in ethanol-containing gasoline compositions from an ethanol composition comprising ethanol, water and acetic acid, wherein said process comprises:

(16) (a) forming a vapour phase ethanol composition A and a liquid phase ethanol composition B from the ethanol composition;

(17) (b) separating a second vapour phase ethanol composition C and an aqueous phase D from the liquid phase ethanol composition B in a distillation column, wherein the aqueous phase D contains the majority of the acetic acid that was present in the liquid phase ethanol composition B;

(18) (c) passing the vapour phase ethanol composition A to a drying unit comprising a desiccant;

(19) (d) passing the vapour phase ethanol composition C to a drying unit comprising a desiccant; and

(20) (e) recovering a fuel ethanol composition from the drying unit of step (c) and the drying unit of step (d);

(21) wherein the recovered fuel ethanol composition of step (e) has a reduced water and acetic acid content.

(22) In another particular aspect of the present invention, the process of the present invention provides a method for reducing the water and butyric acid content of a butanol composition comprising at least one butanol, water and butyric acid, wherein said process comprises:

(23) (a) forming a vapour phase butanol composition A and a liquid phase butanol composition B from the butanol composition;

(24) (b) separating a second vapour phase butanol composition C and an aqueous phase

(25) D from the liquid phase butanol composition B in a distillation column, wherein the aqueous phase D contains the majority of the butyric acid that was present in the liquid phase butanol composition B;

(26) (c) passing the vapour phase butanol composition A to a drying unit comprising a desiccant;

(27) (d) passing the vapour phase butanol composition C to a drying unit comprising a desiccant; and

(28) (e) recovering a butanol composition from the drying unit of step (c) and the drying unit of step (d);

(29) wherein the recovered butanol composition of step (e) has a reduced water and butyric acid content.

(30) In another particular aspect of the present invention, the process of the present invention provides a method for the preparation of a fuel butanol composition suitable for use in butanol-containing gasoline compositions from a butanol composition comprising at least one butanol, water and butyric acid, wherein said process comprises:

(31) (a) forming a vapour phase butanol composition A and a liquid phase butanol composition B from the butanol composition;

(32) (b) separating a second vapour phase butanol composition C and an aqueous phase D from the liquid phase butanol composition B in a distillation column, wherein the aqueous phase D contains the majority of the butyric acid that was present in the liquid phase butanol composition B;

(33) (c) passing the vapour phase butanol composition A to a drying unit comprising a desiccant;

(34) (d) passing the vapour phase butanol composition C to a drying unit comprising a desiccant; and

(35) (e) recovering a fuel butanol composition from the drying unit of step (c) and the drying unit of step (d);

(36) wherein the recovered fuel butanol composition has a reduced water and butyric acid content.

(37) In one specific aspect of the present invention, the alcohol composition which results from the process of the present invention is an ethanol composition having a water content and an acetic acid content which meets required specifications for fuel ethanol compositions.

(38) The present invention further provides a system for reducing the water and carboxylic acid content of an alcohol composition comprising at least one alcohol having from one to four carbon atoms, water and at least one carboxylic acid having from one to four carbon atoms, wherein said system comprises:

(39) (a) means to form a vapour phase alcohol composition A and a liquid phase alcohol composition B from the alcohol composition;

(40) (b) a distillation column configured to separate a second vapour phase alcohol composition C and an aqueous phase D from the liquid phase alcohol composition B, wherein the aqueous phase D contains the majority of the carboxylic acid that was present in the liquid phase alcohol composition;

(41) (c) a drying unit comprising a desiccant through which the vapour phase alcohol composition A is passed; and

(42) (d) a drying unit comprising a desiccant through which the vapour phase alcohol composition C is passed.

(43) The system of the present invention comprises means to form a vapour phase alcohol composition A and a liquid phase alcohol composition B from the alcohol composition. The means to form the vapour phase alcohol composition A and the liquid phase alcohol composition B may be any suitable means for forming a vapour phase and a liquid phase from the alcohol composition.

(44) In a first specific embodiment, the means to form the vapour phase alcohol composition A and the liquid phase alcohol composition B comprises a vaporisation unit configured to vaporise part of the alcohol composition to form the vapour phase alcohol composition A and the liquid phase alcohol composition B.

(45) In an alternative embodiment, the means to form the vapour phase alcohol composition A and the liquid phase alcohol composition B comprises means to pre-divide the alcohol composition into a first portion and a second portion, and a vaporisation unit configured to vaporise substantially all of the first portion.

(46) In a further alternative embodiment, the means to form the vapour phase alcohol composition A and the liquid phase alcohol composition B comprises means to pre-divide the alcohol composition into a first portion and a second portion, and a vaporisation unit configured to vaporise part of the first portion to form the vapour phase alcohol composition A and a third portion, the second portion and the third portion together forming liquid phase alcohol composition B. In this embodiment, the means to form the vapour phase alcohol composition A and the liquid phase alcohol composition B may further comprise means to pass the second portion and the third portion separately to the distillation column, or means to combine the second portion and the third portion before they are passed to the distillation column.

(47) In the embodiment of the system of the present invention comprising means to pre-divide the alcohol composition into a first portion and a second portion, the means may comprise any suitable means for dividing an alcohol composition into two portions, preferably the two portions having the same composition, but optionally having different sizes, such as by flow control.

(48) Vaporisation units suitable for use in the system of the present invention comprise any vaporisation units capable of fully vaporising and/or partially vaporising an alcohol composition comprising at least one alcohol having from one to four carbon atoms, water and at least one carboxylic acid having from one to four carbon atoms.

(49) Distillation columns suitable for use in systems according to the present invention comprise any distillation columns suitable to separate the liquid phase alcohol composition B into a second vapour phase alcohol composition C and an aqueous phase D.

(50) The system of the present invention comprises a drying unit comprising a desiccant through which the vapour phase alcohol composition A is passed, and a drying unit comprising a desiccant through which the vapour phase alcohol composition C is passed. These may be separate drying units; however, in a preferred embodiment, the drying unit through which the vapour phase alcohol composition C is passed is the same drying unit as the drying unit through which the vapour phase alcohol composition A is passed. In this embodiment, the system according to the present invention will comprise only a single drying unit.

(51) The, or each, drying unit forming part of the system according to the present invention may comprise a single or multiple desiccant beds.

(52) The present invention further comprises a method of preparing a fuel alcohol composition from an alcohol composition comprising at least one alcohol having from one to four carbon atoms, water and at least one carboxylic acid having from one to four carbon atoms, wherein said method involves:

(53) (a) determining the concentration of water and carboxylic acid present in the alcohol composition;

(54) (b) if the alcohol composition comprises a concentration of water which is greater than the azeotropic concentration for the alcohol composition, passing the entire alcohol composition to a distillation column of step (c) as a liquid phase alcohol composition B; if the alcohol composition comprises a concentration of water which is equal to or lower than the azeotropic concentration for the alcohol composition, and the carboxylic acid concentration is equal to or lower than the maximum desired concentration of carboxylic acid in the fuel alcohol composition, vaporising the entire alcohol composition to form a vapour phase alcohol composition A; or

(55) if the alcohol composition comprises a concentration of water which is equal to or lower than the azeotropic concentration for the alcohol composition, and the carboxylic acid concentration is greater than the maximum desired concentration of carboxylic acid in the fuel alcohol composition, forming a vapour phase alcohol composition A and a liquid phase alcohol composition B from the alcohol composition;

(56) (c) separating a second vapour phase ethanol composition C and an aqueous phase D from the liquid phase ethanol composition B, if present, in a distillation column, wherein the aqueous phase D contains the majority of the carboxylic acid that was present in the liquid phase alcohol composition B;

(57) (d) passing the vapour phase alcohol composition A, if present, to a drying unit comprising a desiccant;

(58) (e) passing the vapour phase alcohol composition C, if present, to a drying unit comprising a desiccant; and

(59) (f) recovering a fuel alcohol composition from the drying unit of step (d), if present, and the drying unit of step (e), if present;

(60) wherein the recovered fuel alcohol composition has a reduced water content.

(61) In the method of preparing a fuel alcohol composition of the present invention, the step of determining the concentration of water and carboxylic acid present in the alcohol composition may be carried out in any conventional way.

(62) The present invention will now be illustrated, without limiting the scope thereof, with reference to the following Examples and the accompanying Figures in which:

(63) FIG. 1 shows an embodiment of a process and apparatus of the present invention;

(64) FIG. 2 provides a plot of acid in product (mg/L) and total duty versus split fraction, corresponding to the embodiment of FIG. 1;

(65) FIG. 3 shows another embodiment of a process and apparatus of the present invention;

(66) FIG. 4 provides a plot of acid in product (mg/L) and total duty versus split fraction, corresponding to the embodiment of FIG. 3 operated with a 1% blowdown from vaporizer (140); and

(67) FIG. 5 provides a further plot of acid in product (mg/L) and total duty versus split fraction, corresponding to the embodiment of FIG. 3 operated with a 5% blowdown from vaporizer (140);

DETAILED DESCRIPTION OF THE INVENTION

(68) FIG. 1 shows an embodiment of a system and apparatus for reducing the water and carboxylic acid content of an alcohol composition in accordance with the present invention. The apparatus comprises a first splitter (20), a distillation column (30), a vaporiser (40), a mixer/heater (50), a drying unit (60) comprising a desiccant, for example molecular sieve 3A and/or molecular sieve 4A, a second splitter (70), a first cooler (80) and a second cooler (90).

(69) An alcohol composition (1), comprising at least one alcohol having from one to four carbon atoms, water and at least one carboxylic acid having from one to four carbon atoms enters the process and is separated in the first splitter (20) into a first portion (3) and a second portion (2). The relative sizes of the first portion (3) and the second portion (2) are controlled by adjusting the splitter, and, advantageously, may be selected so that the acid level in the final product meets the appropriate specification. The first portion (3) is passed to the vaporiser (40), where it is heated so that substantially all of the first portion is converted into a first vapour phase alcohol composition (6). The second portion removed from the divider (20) is passed to the distillation column (30), where it is separated by distillation into a second vapour phase alcohol composition (5) and an aqueous phase (4). Optionally, the distillation column (30) receives an additional alcohol and water feed stream (11) obtained by regenerating the drying unit (60), and optionally further comprising part of the effluent (8) from the drying unit (60). The aqueous phase (4) contains a majority of the carboxylic acid that was present in the liquid phase alcohol composition (2), and also the majority of the carboxylic acid that was present in the additional water and alcohol feed stream (11), if present.

(70) The first vapour phase alcohol composition (6) and the second vapour phase alcohol composition (5) are combined in the mixer/heater (50), and are heated therein, for example to 160 C., to form a combined vapour phase alcohol composition (7). The combined alcohol vapour phase (7) is passed to the drying unit (60), which comprises at least one desiccant bed, preferably comprising at least one porous inorganic oxide material containing Brnsted acid sites and/or neutralised Brnsted acid sites, such as molecular sieve 3A and/or molecular sieve 4A. Passing the combined vapour phase alcohol composition (7) through the dryer (60) removes a large portion of the water from the combined vapour phase alcohol composition, and an alcohol composition (8) having a reduced water and carboxylic acid content compared to the water and carboxylic acid content of the feed stream (1) is withdrawn from the drying unit (60).

(71) Optionally, the alcohol composition having a reduced water and carboxylic acid content (8) is divided into a first portion (10) and a second portion (12) in the second splitter (70). The first portion (10) and the second portion (12) will have substantially the same compositions, but the size of each portion may be adjusted by adjustment of the splitter (70). The relative size of the first portion (10) and the second portion (12) will be selected to provide a suitable composition for the additional feed (11) to the distillation column (30).

(72) Water removed from the combined vapour phase alcohol composition (7) in the drying unit (60) may be removed therefrom as a water stream (9), and this may be combined with the first portion (10) of the alcohol composition having a reduced water and carboxylic acid content (8) in the first cooler/condenser (80), where it is cooled to, for example, 50 C., to form an additional water and alcohol feed stream (11), which may be passed to the distillation column (30).

(73) Alternatively or additionally, the first portion (10) of the alcohol composition having a reduced water and carboxylic acid composition (8) obtained in the second splitter (70) may be used to regenerate a desiccant bed in the dryer (60), and this will produce a mixture of water and alcohol which may be fed to the distillation unit (30) as the additional water and ethanol feed stream (11).

(74) The second portion (12) of the alcohol composition having a reduced water and carboxylic acid content (8), which may represent substantially all of the alcohol composition having a reduced water and carboxylic acid content (8) recovered from the drying unit (60), may optionally be further cooled in second cooler (90), for example to 20 C., to form a cooled alcohol composition having a reduced water and carboxylic acid content (13). The cooled alcohol composition having a reduced water and carboxylic acid content (13) may be used as a fuel component or used for any other conventional use.

(75) The distillation column (30) has 11 theoretical stages with no condenser, stage 11 being equivalent to a reboiler. Second portion (2) of the alcohol composition (1) enters the distillation column (30) above stage 1. The additional water and ethanol feed stream (11) enters the distillation column (30) above stage 5.

(76) FIG. 3 shows another embodiment of a system and apparatus for reducing the water and carboxylic acid content of an alcohol composition in accordance with the present invention. The apparatus comprises a first splitter (120), a first distillation column (130), a second distillation column (140), a mixer/heater (150), a drying unit (160) comprising a desiccant, for example molecular sieve 3A and/or molecular sieve 4A, a second splitter (170), a first cooler (180) and a second cooler (190).

(77) An alcohol composition (101), comprising at least one alcohol having from one to four carbon atoms, water and at least one carboxylic acid having from one to four carbon atoms enters the process and is separated in the first splitter (120) into a first portion (103) and a second portion (102). The relative sizes of the first portion (103) and the second portion (102) are controlled by adjusting the splitter, and, advantageously, may be selected so that the acid level in the final product meets the appropriate specification. The first portion (103) is passed to the second distillation column (140), where it is separated by distillation so that substantially all of the first portion is separated into a first vapour phase alcohol composition (106) and a liquid base composition (106a). The second portion removed from the splitter (120) and the liquid base composition (106a) are passed to the first distillation column (130), where they are separated by distillation into a second vapour phase alcohol composition (105) and an aqueous phase (104). Optionally, the first distillation column (130) receives an additional alcohol and water feed stream (111) obtained by regenerating the drying unit (160), and optionally further comprising part of the effluent (108) from the drying unit (160). The aqueous phase (104) contains a majority of the carboxylic acid that was present in the liquid phase alcohol composition (102), and also the majority of the carboxylic acid that was present in the additional water and alcohol feed stream (111), if present.

(78) The first vapour phase alcohol composition (106) and the second vapour phase alcohol composition (105) are combined in the mixer/heater (150), and are heated therein, for example to 160 C., to form a combined vapour phase alcohol composition (107). The combined alcohol vapour phase (107) is passed to the drying unit (160), which comprises at least one desiccant bed, preferably comprising at least one porous inorganic oxide material containing Brnsted acid sites and/or neutralised Brnsted acid sites, such as molecular sieve 3A and/or molecular sieve 4A. Passing the combined vapour phase alcohol composition (107) through the dryer (160) removes a large portion of the water from the combined vapour phase alcohol composition, and an alcohol composition (108) having a reduced water and carboxylic acid content compared to the water and carboxylic acid content of the feed stream (101) is withdrawn from the drying unit (160).

(79) Optionally, the alcohol composition having a reduced water and carboxylic acid content (108) is divided into a first portion (110) and a second portion (112) in the second splitter (170). The first portion (110) and the second portion (112) will have substantially the same compositions, but the size of each portion may be adjusted by adjustment of the splitter (170). The relative size of the first portion (110) and the second portion (112) will be selected to provide a suitable composition for the additional feed (111) to the distillation column (130).

(80) Water removed from the combined vapour phase alcohol composition (107) in the drying unit (160) may be removed therefrom as a water stream (109), and this may be combined with the first portion (110) of the alcohol composition having a reduced water and carboxylic acid content (108) in the first cooler/condenser (180), where it is cooled to, for example, 50 C., to form an additional water and alcohol feed stream (111), which may be passed to the distillation column (130).

(81) Alternatively or additionally, the first portion (110) of the alcohol composition having a reduced water and carboxylic acid composition (108) obtained in the second splitter (170) may be used to regenerate a desiccant bed in the dryer (160), and this will produce a mixture of water and alcohol which may be fed to the distillation unit (130) as the additional water and ethanol feed stream (111).

(82) The second portion (112) of the alcohol composition having a reduced water and carboxylic acid content (108), which may represent substantially all of the alcohol composition having a reduced water and carboxylic acid content (108) recovered from the drying unit (160), may optionally be further cooled in second cooler (190), for example to 20 C., to form a cooled alcohol composition having a reduced water and carboxylic acid content (113). The cooled alcohol composition having a reduced water and carboxylic acid content (113) may be used as a fuel component or used for any other conventional use.

(83) The first distillation column (130) has 11 theoretical stages with no condenser, stage 11 being equivalent to a reboiler. Second portion (102) of the alcohol composition (101) enters the first distillation column (130) above stage 1. The additional water and ethanol feed stream (111) enters the first distillation column (130) above stage 5.

EXAMPLES

Example 1

(84) An ethanol feedstock comprising 2% wt % water and 150 ppmw acetic acid (1.6 vol % water and 121 mg/L acetic acid) was used as the feed stream to a system as illustrated in FIG. 1. A process according to the present invention was carried out a number of times, with the feed stream being split into first and second portions of different sizes, as illustrated in Table 1, in different runs. Table 1 also lists reboiler duty of the distillation column (30), and heating duty of the vaporiser (40), plus total duty. The table also lists the amount of water in the product (as volume %), water removal and the acid remaining in the product (in mg/L).

(85) The results in Table 1 for acid in product and total duty versus split fraction to the distillation column are shown graphically in FIG. 2.

(86) TABLE-US-00001 TABLE 1 Split to Column Evaporator Water in Acid in Split to Evaporator Reboiler Duty Total Duty product Water product Colum 30 40 Duty (kW) (kW) (kW) (vol %) removal (mg/L) 0.000 1.000 0.461 15.307 15.768 0.80 0.596 120 0.100 0.900 2.739 13.776 16.515 0.80 0.743 108 0.200 0.800 4.736 12.245 16.981 0.80 0.790 96 0.300 0.700 6.670 10.715 17.385 0.80 0.818 84 0.400 0.600 8.584 9.184 17.768 0.80 0.839 73 0.500 0.500 10.486 7.653 18.140 0.80 0.854 62 0.550 0.450 11.440 6.888 18.328 0.80 0.861 56 0.600 0.400 12.389 6.123 18.512 0.80 0.867 51 0.700 0.300 14.273 4.592 18.865 0.80 0.877 40 0.800 0.200 16.164 3.061 19.225 0.80 0.886 29 0.900 0.100 18.048 1.531 19.579 0.80 0.893 18 1.000 0.000 19.932 0.000 19.932 0.80 0.899 8

(87) As illustrated in FIG. 2, increasing the proportion of the feed stream divided to the distillation column increases the total energy duty for running the process, but results in a decrease in the amount of acid in the final product. Thus, selecting the proportion of the feed divided to the distillation column, and the portion divided to the vaporisation unit, allows one to minimise the total duty of the system for a given acid content in the final product; i.e., it is possible to minimise the power required for a given acid level required to satisfy a particular alcohol fuel specification.

(88) The compositions of the feed stream and the various streams produced in the process when the feed stream was split to feed 55% to the distillation column (30) and 45% to the evaporator (40) are shown in Table 2, using numbering corresponding to that employed in FIG. 1.

(89) TABLE-US-00002 TABLE 2 STREAM 1 2 3 4 5 6 MASS FLOW Acetic acid, 7.5 4.1 3.4 4.1 0.3 3.4 kg/hr Water, kg/hr 1000.0 550.0 450.0 509.4 3311.8 450.0 Ethanol, kg/hr 48992.5 26945.9 22046.6 0.3 30216.8 22046.6 VOL. FRAC. (LIQUID) Water, vol % 1.6% 1.6% 1.6% 99.1% Ethanol, vol % 98.4% 98.4% 98.4% 0.1% MASS CONC. (LIQUID) Acetic acid, 121 121 121 6790 mg/L STREAM 7 8 9 10 11 12 MASS FLOW Acetic acid, 3.7 3.7 0.0 0.2 0.2 3.4 kg/hr Water, kg/hr 3761.8 523.3 3238.5 32.8 3271.2 490.6 Ethanol, kg/hr 52263.5 52263.5 0.0 3271.2 3271.2 48992.3 VOL. FRAC. (LIQUID) Water, vol % 44.8% Ethanol, vol % 55.6% MASS CONC. (LIQUID) Acetic acid, 31 mg/L STREAM 13 MASS FLOW Acetic acid, 3.4 kg/hr Water, kg/hr 490.6 Ethanol, kg/hr 48992.3 VOL. FRAC. (LIQUID) Water, vol % 0.8% Ethanol, vol % 99.2% MASS CONC. (LIQUID) Acetic acid, 56 mg/L

(90) The water content of the final product is 0.8 volume %, and the acetic acid composition is 56 mg/L, both of which satisfy various specifications for denatured fuel ethanol, such as China Specification GB 18350-2001.

Example 2

(91) An ethanol feedstock comprising 2% wt % water and 150 ppmw acetic acid (1.6 vol % water and 121 mg/L acetic acid) was used as the feed stream to a system as illustrated in FIG. 3. A process according to the present invention was carried out a number of times, with the feed stream being split into first and second portions of different sizes, as illustrated in Tables 3-4, in different runs. Tables 3 and 4 also list reboiler duty of the first distillation column (130), and heating duty of the vaporiser (140), plus total duty. The tables also list the amount of water in the product (as volume %), water removal and the acid remaining in the product (in mg/L). Table 3 corresponds to a 1% blowdown from vaporizer (140) and Table 4 corresponds to a 5% blowdown from vaporizer (140).

(92) The results in Tables 3 and 4 for acid in product and total duty versus split fraction to the distillation column are shown graphically in FIGS. 4 and 5 respectively.

(93) TABLE-US-00003 TABLE 3 Split to Column 130 Evaporator Water in Acid in Split to Evaporator Reboiler 140 Duty Total Duty product Water product Column 130 140 Duty (kW) (kW) (kW) (vol %) removal (mg/L) 0.000 1.000 0.793 15.197 15.990 0.80 0.573 110 0.100 0.900 2.963 13.677 16.640 0.80 0.758 98 0.200 0.800 4.926 12.158 17.084 0.80 0.798 87 0.300 0.700 6.834 10.638 17.472 0.80 0.823 77 0.400 0.600 8.726 9.118 17.844 0.80 0.842 66 0.500 0.500 10.609 7.598 18.207 0.80 0.857 56 0.600 0.400 12.474 6.079 18.552 0.80 0.868 46 0.700 0.300 14.340 4.559 18.899 0.80 0.878 37 0.800 0.200 16.208 3.039 19.247 0.80 0.886 27 0.900 0.100 18.071 1.520 19.591 0.80 0.893 17 1.000 0.000 19.932 0.000 19.932 0.80 0.899 8

(94) TABLE-US-00004 TABLE 4 Split to Column 130 Evaporator Water in Acid in Split to Evaporator Reboiler 140 Duty Total Duty product Water product Column 130 140 Duty (kW) (kW) (kW) (vol %) removal (mg/L) 0.000 1.000 2.050 14.758 16.808 0.80 0.774 78 0.100 0.900 3.908 13.282 17.191 0.80 0.806 71 0.200 0.800 5.715 11.806 17.522 0.80 0.826 63 0.300 0.700 7.510 10.331 17.841 0.80 0.842 56 0.400 0.600 9.289 8.855 18.143 0.80 0.854 49 0.500 0.500 11.066 7.379 18.445 0.80 0.865 42 0.600 0.400 12.840 5.903 18.743 0.80 0.874 35 0.700 0.300 14.616 4.427 19.044 0.80 0.881 28 0.800 0.200 16.390 2.952 19.341 0.80 0.888 21 0.900 0.100 18.161 1.476 19.637 0.80 0.894 14 1.000 0.000 19.932 0.000 19.932 0.80 0.899 8

(95) As illustrated in FIGS. 4-5, increasing the proportion of the feed stream divided to the distillation column increases the total energy duty for running the process, but results in a decrease in the amount of acid in the final product. Thus, selecting the proportion of the feed divided to the distillation column, and the portion divided to the vaporisation unit, allows one to minimise the total duty of the system for a given acid content in the final product; i.e., it is possible to minimise the power required for a given acid level required to satisfy a particular alcohol fuel specification.

(96) The compositions of the feed stream and the various streams produced in the process corresponding to FIG. 3 and Table 3, when the feed stream was split to feed 50% to the first distillation column (130) and 50% to the second distillation column (140) are shown in Table 5, using numbering corresponding to that employed in FIG. 3. Commensurately, the compositions of the feed stream and the various streams produced in the process corresponding to FIG. 3 and Table 4, when the feed stream was split to feed 30% to the first distillation column (130) and 70% to the second distillation column (140) are shown in Table 6, also using numbering corresponding to that employed in FIG. 3.

(97) TABLE-US-00005 TABLE 5 STREAM 101 102 103 104 105 106 MASS FLOW Acetic acid, kg/hr 7.5 3.8 3.8 4.0 0.3 0.3 Water, kg/hr 1000.0 500.0 500.0 509.5 3147.3 5.0 Ethanol, kg/hr 48992.5 24496.3 24496.3 0.3 27892.8 244.9 VOL. FRAC. (LIQUID) Water, vol % 1.6% 1.6% 1.6% 99.1% 1.5% Ethanol, vol % 98.4% 98.4% 98.4% 0.1% 98.4% MASS CONC. (LIQUID) Acetic acid, mg/L 121 121 121 6758 910 STREAM 106a 107 108 109 110 111 MASS FLOW Acetic acid, kg/hr 3.4 3.7 3.7 0.0 0.2 0.2 Water, kg/hr 495.0 3642.4 522.1 3120.3 31.6 3151.9 Ethanol, kg/hr 24251.4 52144.2 52144.2 0.0 3151.8 3151.9 VOL. FRAC. (LIQUID) Water, vol % 44.8% Ethanol, vol % 55.6% MASS CONC. (LIQUID) Acetic acid, mg/L 32 STREAM 112 113 MASS FLOW Acetic acid, kg/hr 3.5 3.5 Water, kg/hr 490.5 490.5 Ethanol, kg/hr 48992.3 48992.3 VOL. FRAC. (LIQUID) Water, vol % 0.8% Ethanol, vol % 99.2% MASS CONC. (LIQUID) Acetic acid, mg/L 56

(98) TABLE-US-00006 TABLE 6 STREAM 101 102 103 104 105 106 MASS FLOW Acetic acid, kg/hr 7.5 2.3 5.3 4.1 0.2 1.8 Water, kg/hr 1000.0 300.0 700.0 509.8 2613.8 34.7 Ethanol, kg/hr 48992.5 14697.8 34294.8 0.3 19200.8 1714.4 VOL. FRAC. (LIQUID) Water, vol % 1.6% 1.6% 1.6% 99.1% 1.5% Ethanol, vol % 98.4% 98.4% 98.4% 0.1% 98.5% MASS CONC. (LIQUID) Acetic acid, mg/L 121 121 121 6795 687 STREAM 106a 107 108 109 110 111 MASS FLOW Acetic acid, kg/hr 3.5 3.6 3.6 0.0 0.2 0.2 Water, kg/hr 665.3 3279.2 518.4 2760.7 27.9 2788.9 Ethanol, kg/hr 32580.4 51781.2 51781.2 0.0 2788.7 2788.9 VOL. FRAC. (LIQUID) Water, vol % 44.8% Ethanol, vol % 55.6% MASS CONC. (LIQUID) Acetic acid, mg/L 31 STREAM 112 113 MASS FLOW Acetic acid, kg/hr 3.4 3.4 Water, kg/hr 490.5 490.5 Ethanol, kg/hr 48992.5 48992.5 VOL. FRAC. (LIQUID) Water, vol % 0.8% Ethanol, vol % 99.2% MASS CONC. (LIQUID) Acetic acid, mg/L 56

(99) The water content of the final product in both cases is 0.8 volume %, and the acetic acid composition is 56 mg/L, both of which satisfy various specifications for denatured fuel ethanol, such as China Specification GB 18350-2001.