Apparatus for and method of heteroazeotropic extractive distillation

Abstract

A heteroazeotropic extractive distillation method is performed using two-stage heteroazeotropic extractive distillation within at least one distillation column (100, 102). A first stage (10) comprising distilling a first mixture (104) of water, at least acetic acid and formic acid and entrainer inside a temperature range difference 5°C to 20°C for separating water from the first mixture (104), which has a first percentage of said entrainer and a first percentage of water. A second stage (12) receives a bottom product of water, at least acetic acid and formic acid and said entrainer from a bottom section (108) of the first stage (10). The second stage (12) has a second percentage of said entrainer and a second percentage of water, wherein the second percentage of said entrainer being greater than the first percentage of said entrainer, and / or the first percentage of water being greater than the second percentage of water. At least a part of overhead vapor of at least one of the first stage (10) and the second stage (12) is pressurized by vapor recompression. At least a part of the first mixture (104) is circulated back to the first stage (10), and heat of the overhead vapor to first mixture (104) is circulated to the first stage (10).

Description

[0001] Apparatus for and method of heteroazeotropic extractive distillation

[0002] Field

[0003] The invention relates to an apparatus for and a method of heteroazeotropic extractive distillation.

[0004] Background

[0005] A heteroazeotropic extractive distillation process that can be used as a part of biorefinery is used to separate and recover water, at least one organic acid, and entrainer, which is often furfural. Furfural may have a double role both as an azeotrope forming component and an extractant.

[0006] The distillation process uses a column for separating the organic acids and water to different streams. The separation requires a lot of energy because water is a lighter component than common acids and it needs to be evaporated. The energy consumption can be lowered by the entrainer that increases the relative volatility between water and acids. Easier separation results in lower ratio. Still, the energy consumption is high and there is a need to improve the process.

[0007] Brief description

[0008] The present invention seeks to provide an improvement in the process.

[0009] The invention is defined by the independent claims. Embodiments are defined in the dependent claims.

[0010] If one or more of the embodiments is considered not to fall under the scope of the independent claims, such an embodiment is or such embodiments are still useful for understanding features of the invention.

[0011] List of drawings

[0012] Example embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which Figures 1 to 6 illustrate various examples of an apparatus for a heteroazeotropic extractive distillation process with one or more vapor recompression devices increases pressure of at least a part of overhead vapor of at least one of a first and or second column and transfers heat of the vapor to the first mixture of the first column;

[0013] Figure 7 illustrates an example of the apparatus with a data processing unit;

[0014] Figure 8 illustrates an example of the data processing unit; and

[0015] Figure 9 illustrates of an example of a flow chart of a heteroazeotropic extractive distillation method.

[0016] Description of embodiments

[0017] The following embodiments are only examples. Although the specification may refer to "an" embodiment in several locations, this does not necessarily mean that each such reference is to the same embodiment's), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, words "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may also contain features / structures that have not been specifically mentioned. All combinations of the embodiments are considered possible if their combination does not lead to structural or logical contradiction.

[0018] It should be noted that while Figures illustrate various embodiments, they are simplified diagrams that only show some structures and / or functional entities. It is apparent to a person skilled in the art that the described apparatus may also comprise other functions and structures than those described in Figures and text. It should be appreciated that details of some functions, structures, and the signalling used for a measurement and / or control are irrelevant to the actual invention. Therefore, they need not be discussed in more detail here.

[0019] The expression "azeotrope" refers to a mixture of substances wherein vapour and liquid compositions are identical in a phase equilibrium. The azeotrope corresponds to an extreme point (minimum, maximum or saddle point) in a boiling temperature isobar or in a vapour pressure isotherm.

[0020] The expression "extractive distillation" refers to distillation wherein entrainer boiling at a relatively high temperature is added to a distillation column above the actual feed flow. Entrainer increases the relative volatility of the components and enhances separation of components, which is the main target of distillation.

[0021] Extraction, per se, refers to a process wherein a desired substance in a mixture dissolves in a solvent while the rest of the substances are insoluble in said solvent. In the mixture, the substances are completely mixed up with one another and the mixture, perse, may contain end products of chemical reactions.

[0022] The expression "heteroazeotrope" refers to an azeotrope having, in addition to the vapour phase, two liquid phases present.

[0023] The expression "heteroazeotropic distillation" refers to either distillation of heteroazeotropic mixtures or distillation wherein a heteroazeotrope forming component ("entrainer") is added to a process.

[0024] The expression "heteroazeotropic extractive distillation" refers to a combination of heteroazeotropic distillation and extractive distillation. The component to be added, boiling at a relatively high temperature, changes relative volatilies of components to be separated and boiling at a lower temperature, and it forms a low boiling azeotrope with any one of the remaining components. A person skilled in the art is familiar with these terms and definitions, perse.

[0025] The heteroazeotropic extractive distillation may be a part of a biorefining process where bio-mass fractions are vaporized and / or dried. Such a process provides a flow of bio-mass component, organic acid(s) and furfural, which is vaporized and / or dried.

[0026] A column is a tubular, often upright construction wherein substances fed thereto become completely mixed up together. Such a column may be used for separating different fluids from each other based on the properties of the substances in various processing conditions. A typical field of application is chemical industry. The column, perse, is known to those skilled in the art. Referring to Fig. 1, heteroazeotropic extractive distillation apparatus performs a two-stage heteroazeotropic extractive distillation. The two separate stages may also be understood to be two phases of the process. The apparatus comprises at least one column 100, 102 of heteroazeotropic extractive distillation. In the example of Fig. 1, two stages 10, 12 of the process are included in the column 100. A first stage 10 of the heteroazeotropic extractive distillation receives distillation feed that has a ratio of water and entrainer, the ratio of the water and entrainer being high. Then the first stage 10 processes a first mixture 104 of water, at least acetic acid and formic acid and entrainer for separating water from the first mixture 104 through distillation. The distillation may also be considered to include vaporization and / or evaporation. The entrainer acts as a former of a minimum boiling azeotrope and an extractant in the first mixture 104. The first mixture 104 has a first percentage of said entrainer and a first percentage of water.

[0027] A second stage 12 of the heteroazeotropic extractive distillation receives a bottom product including water, at least acetic acid and formic acid and said entrainer from a bottom section 14 of the first stage 10. The second stage 12 processes a second mixture 106 that has a second percentage of said entrainer and a second percentage of water, wherein the second percentage of water of the second stage 12 is smaller than the first percentage of water of the first stage 10. The second percentage of water is at least partially based on the bottom product received from the bottom section 108 of the first stage 10. In an embodiment, the second percentage of said entrainer of the second stage 12 may be greater than that of the first stage 10.

[0028] A mechanical vapor recompression means 112A, 112B, 112C that may comprise mechanical vapor recompression means and / or thermal vapor recompression means or the like pressurizes overhead vapor of the at least one column 100, 102. The pressurizing means that pressure of the overhead vapor of the first stage 10 is increased. The increase of pressure also increases the dewpoint temperature of the overhead vapor. The apparatus performs at least one the following: circulates at least a part of the first mixture 104 of the first stage 10 back to the first stage 10, and transfers heat of the overhead vapor to first mixture 104 circulated back to the first stage 10.

[0029] Process conditions relating to the first stage 10 are: temperature in a range about 60°C to about 120°C and pressure about 0.2 bar to about 1.5 bar. The temperature difference between an upper section 114 and the bottom section 14 of the first stage 10 being about 5°C to about 20°C. The acid concentration within the first column 100 is about 10% to about 40%, for example. In Fig. 1, the second column 102 is optional.

[0030] Fig. 2 shows an example of an apparatus for a heteroazeotropic extractive distillation process where the two stages 10 and 12 are structurally separated in two columns 100, 102, respectively. Process features explained to relate to the first and second columns 100, 102 apply also to the first and second stages 10, 12. The first column 100 receives distillation feed that has a ratio of water and entrainer, the ratio of the water and entrainer being high. The first column 100 processes a first mixture 104 of water, at least acetic acid and formic acid and entrainer, the first mixture 104 being formed from the distillation feed, for separating water, entrainer and the acids of the first mixture 104 through vaporization. The entrainer is a former of azeotrope and it may also act as an extractant in the first mixture 104. The first mixture 104 has a first percentage of said entrainer and a first percentage of water, the first percentages having nonzero values. A lot of energy requiring process to separate / distil most of water out from feed mainly is performed in column 100, where MVR is possible to utilize efficiently thanks to low temperature difference between bottom and top of column 100. The second column 102 may have a lower water percentage than the first column 100.

[0031] Process conditions within the first column 100 are: temperature range about 60°C to about 120°C and pressure about 0.2 bar to about 1.5 bar. The temperature difference between the upper section 114 and a bottom section 108 of the first column 100 being about 5°C to about 20°C. If the bottom section 108 has temperature about 120°C then the upper section 114 has temperature in a range about 100°C to 115°C. The temperature range of the first column 100 depends on the pressure within the first column 100 such both are high simultaneously or both are low simultaneously. The acid concentration of feed to the first column 100 may be about 10% to about 40%, for example.

[0032] Note that the mixture of water and entrainer boils at a lower temperature than the entrainer alone. As a rule of thumb it may be defined, the higher the entrainer percentage, the higher the boiling temperature. That is also a reason why the bottom section temperature is higher than that of the upper section. Additionally, the difference in temperatures between the bottom section 14 or 108 and the upper section 114 may depend or be defined based on the boiling points of entrainer and the mixture of water and entrainer.

[0033] A second column 102 of the heteroazeotropic extractive distillation receives a bottom product including water, at least acetic acid and formic acid and said entrainer from the bottom section 108 of the first column 100. The column 102 may be similar to the first column 100 when it comes to internal types and / or material. The material should tolerate acetic and formic acids in the process conditions. Acid concentration of the bottom product from the first column 100 is in a range about 50% to about 80%, for example. The second column 102 processes a second mixture 106 that has a second percentage of said entrainer and a second percentage of water. The second percentages also have non-zero values. The second mixture 106 includes the bottom product from the first column 100. The second percentage of said entrainer of the second column 102 is greater than the first percentage of said entrainer of the first column 100, and / or the second percentage of water of the second column 100 is smaller than the first percentage of water of the first column 102. The second percentages of water and said entrainer are at least partially based on the bottom product received from the bottom section 108 of the first column means 100. Process conditions within the second column 102 are: temperature about 60°C to about 170°C and pressure about 0.2 bar to about 1.5 bar.

[0034] The percentage of the entrainer is greater in the stream that is output from the bottom section 108 of the first column because the first column 100 vaporizes water or a stream that includes mainly water which then decreases the percentage of water in the bottom section 108 of the first column 100. The first column 100 also removes vaporized water, which may also include a fraction of entrainer, from the upper section 114 of the first column 100. The vaporization and removal of water from the first column 100 lowers the percentage of water of the bottom product that is fed to the second column 102, which in turn causes the second percentage of water to be smaller and / or the second percentage of entrainer to be greater than corresponding percentages in the first mixture 104 of the first column 100.

[0035] In an embodiment, a vapor recompression arrangement 112A, i.e. mechanical vapor recompression means and / or thermal vapor recompression means, may pressurize at least a part of the overhead vapor output from the top section 114 of the first stage 10 to higher pressure and to utilize the latent heat of the overhead vapor for heating the first mixture 104 and to reduce external energy consumption. In Fig. 2, the process of the first stage 10 is performed in the first column 100. The bottom product is output from the bottom section 108 of the first section 10. The first stage 10 is above the second stage 12 as drawn in Fig. 1. In Fig. 2, the bottom section 108 is below a middle point M of the first column 100 that is in an erected position. The erected position means that a longitudinal axis of the first column 100 is substantially vertical. Also, the second column 102 is in an erected position such that a top section 116 of the second column 102 is higher than a bottom section 118 of the second column 102.

[0036] Both the first column 100 and the second column 102 may output vaporized water that includes entrainer from the top sections 114, 116. The top section 114, 116 is in general an opposite section to the bottom section 108, 118. The vaporized water that includes entrainer is condensed to a liquid phase, and the stream of a liquid phase may be fed, in an embodiment, to a decanter 200 which separates said entrainer-rich stream and water-rich stream from each other. The separated water-rich and entrainer may be processed further and / or recycled in the process. In the example of Figs 1 and 2, a compressor 112(1) of the vapor recompression arrangement 112A that may be a mechanical vapor recompression means and / or thermal vapor recompression means or the like receives the stream from the top section 114 of the first column 100 and feeds it to a heat exchanger 112(2) of the vapor recompression arrangement 112A that transfers the heat to the first mixture 104 in the first column 100. From the heat exchanger 112(2) the stream may continue to a decanter 200 for water and entrainer separation.

[0037] In examples of Figs 1 and 2, the pressure and temperature are increased by the compressor 112(1), and the heat is transferred to the column 100 by the heat exchanger 112(2). The increased pressure elevates dew point of the vapor stream above boiling point of the boiling liquid in the heat exchanger 112(2). This enables latent heat recovery of the vapor stream to the boiling liquid.

[0038] Fig. 3 also shows another example of the apparatus for a heteroazeotropic extractive distillation process. In this example, the second column 102 removes vaporized water, which may also include some entrainer, from a top section 116 of the second column 102. In this embodiment, a vapor recompression arrangement 112B may heat the first mixture 104 of the first column 100 by heat of at least a part of overhead vapors of the second column 102 for saving heating energy. The process in the first column 100 decreases water contents and increasing acids contents of the bottom product of the first column 100 with respect to those of the first mixture 104.

[0039] In the example of Fig. 3, the compressor 112(3) of the vapor recompression arrangement 112B receives the stream from the top section 116 of the second column 102 and feeds it to a heat exchanger 112(4) of the vapor recompression arrangement 112B, i.e. mechanical vapor recompression means and / or thermal vapor recompression means or the like, that transfers the heat to the first mixture 104 of the first column 100. From the heat exchanger 112(4) the stream may continue to flow to the decanter 200 for water and entrainer separation.

[0040] In an example of Fig. 3, the pressure and temperature are elevated by a compressor 112(3) of the vapor recompression arrangement 112B, and the heat is transferred to the first mixture 104 of the first column 100 by the heat exchanger 112(4) of the vapor recompression arrangement 112B.

[0041] Fig. 4 shows still another embodiment of the apparatus for a heteroazeotropic extractive distillation process where a vapor recompression device 112C, i.e. mechanical vapor recompression means and / or thermal vapor recompression means or the like, may transfer heat to the first mixture 104 of the first column 100 from heat of at least a part of pressurized overhead vapors of the first column 100 and the second column 102 for saving heating energy. The pressure and temperature are elevated by compressors 112(6) and 112(7), and the heat is transferred to the first mixture 104 of the column 100 by the heat exchanger 112(8).

[0042] In general, the vapor recompression arrangement 112A, 112B, 112C transfers heat that is received from at least a part of pressurized overhead vapors of at least one of the first column 100 and the second column 102 to the first mixture 104 of the first column 100 for saving heating energy.

[0043] This kind of process system efficiently separates water from organic acids. The entrainer, water and / or the acids may also be efficiently recycled in the process. Because latent heat of water is high, even a low reflux ratio requires reboiling of water and relatively high heat consumption. The process system described in this document reduces energy consumption in the heteroazeotropic extractive distillation column (s). Examine next more examples of the process system.

[0044] In an embodiment, the vapor recompression arrangement 112A, 112B, 112C comprises at least one heat pump. In an embodiment, any of the vapor recompression arrangements 112A, 112B, 112C may include at least two operational heat pump units coupled in series. In an embodiment, three to six vapor recompression arrangements may be coupled in series, for example. A person skilled in the art is familiar with coupling such arrangements together, per se. Overhead vapor of the column 100, 102 may be compressed with multistage compressors / fans for achieving a desired pressure and a boiling point temperature in the column 100. The vapor recompression arrangements 112A, 112B, 112C may be arranged in a form that utilizes direct vapor recompression like in Figs 1 and 2, steam eject, and / or an auxiliary circuit.

[0045] Fig. 5 illustrates an example of utilization of steam eject based on a stream ejector 202. The stream injector 202 receives the stream from the top section 114 of the first column 100 and feeds it to the heat exchanger 112(8) that transfers the heat to the first mixture 104 of the first column 100. From the heat exchanger 112(8) the stream may continue to the decanter 200 for water and entrainer separation.

[0046] Fig. 6 illustrates an example of an auxiliary circuit for heating arrangement. The heat exchanger 112(10) connected with the top section 114 of the first column 100 receives a stream from the top section 114 of the first column 100 and feeds it through a compressor 112(9) to another heat exchanger 112(12) that transfers the heat to a section below the middle point M of the first column 100. A power plant producing pressurized stream may be used as a control in a process start-up and / or shut-down situations as well as balancing reboiling and condencing duty differences.

[0047] In general as can be understood based on Figs 1, 2, 3 and 4, the one or more vapor recompression arrangements 112A, 112B, 112C transfer heat to the first mixture 104 of the first column 100 from heat of at least a part of overhead vapors of at least one of the first column 100 and the second column 102 for saving energy and thus also protecting the environment. In that manner, the ratio pe / pwof percentages of entrainer and water is larger in the second column 102 than in the first column 100, where peis the percentage of entrainer and pwis the percentage of water.

[0048] Each ofthe vapor recompression arrangements 112A, 112B, 112C may comprise a compressor 112(1), 112(3), 112(7), 112(9) and a heat exchanger 112(2), 112(4), 112(6), 112(8), 112(10), 112(12), which together may mean a heat pump system, for example. The compressor 112(1), 112(3), 112(7), 112(9) increases both pressure and temperature of the overhead vapor, and the heat exchanger 112(2), 112(4), 112(6), 112(8), 112(10), 112(12) transfers the heat thus formed to the first mixture 104 that is circulated between the first column 100 and the heat exchanger 112(2), 112(4), 112(6), 112(8), 112(10), 112(12). The circulated mixture 104 may be output from the bottom section 106 of the first column 100 to the heat exchanger 112(2), 112(4), 112(6), 112(8), 112(10), 112(12), and the heat exchanger 112(2), 112(4), 112(6), 112(8), 112(10), 112(12) then feeds the heated mixture 104 back to the first column 100. The heat exchanger 112(2), 112(4), 112(6), 112(8), 112(10), 112(12) may feed the heated mixture 104 to the bottom section 106 of the first column 100. In an embodiment, the heated mixture 104 may be fed to the first column 100 at a point that is below the middle point M.

[0049] In this kind of process, the first column 100 is split in a way that part of water or most part of water is removed from the feed, but still the difference between the top and bottom temperature of the first column 100 is relatively low. This kind of unsharp separation enables the use of the vapor recompression technology in an energy efficient manner. This kind of processing saves energy, and it can be seen as steam consumption reduction in heating. Steam consumption in general is larger than the consumption of electric energy, and thus the reduced steam consumption results in a real saving of energy instead of a mere change of a form of energy from steam to electricity. The COP (Coefficient Of Performance) can high, about 11 to about 14, for example. Additionally, heat energy recycling is performed technically in a simple and effective manner.

[0050] In an embodiment, the entrainer may include furfural. In an embodiment, the entrainer may at least almost solely be furfural. In an embodiment, the entrainer may include acetone, benzene, cyclohexane, cyclohexanone, heptane, hexane, hexanol and pentane to name a few.

[0051] In an embodiment, at least one heat pump of the vapor recompression arrangements 112A, 112B, 112C may receive at least a part of said overhead vapors from the first column 100 and / or the second column 102 and increase pressure of said overhead vapors for causing an increase of temperature of said overhead vapors, and at least one heat exchanger transferring heat from said overhead vapors to the first mixture 104 within the first column 100. In an embodiment, the second column 102 may receive a third mixture 110 of water, at least acetic acid and formic acid and entrainer that may have a smaller water / entrainer ratio than that of the distillation feed to the first column 100. A third percentage of said entrainer of the third mixture 110 is thus greater than the first percentage of said entrainer of the first column 100, and / or a third percentage of water of third mixture 110 is smaller than the first percentage of water of the first column 100.

[0052] In an embodiment, the vapor compression arrangement 112A, 112B, 112C may cause the COP of the apparatus to be 10 or greater, and / or the vapor compression arrangement 112A, 112B, 112C may enable a temperature difference that is equal to or less than 10°C within the first column 100, i.e. between the top and bottom of the first column 100.

[0053] In a double-effect distillation of the prior art, two columns are also used in series such that one of the double-effect columns has a low pressure (0.3 bar, for example) and another of the double-effect columns has a high pressure and temperature (3 bar and 200°C). A technical problem in the double-effect columns is that in high temperatures, the entrainer may change its physical properties and it thus loses its desired effect for the process. Furfural is an example of entrainer, and it may polymerize and become sticky that is an undesired feature. Entrainer may be any substance or any mixture of substances that forms minimum boiling azeotrope with water and works as an extractant for acids. Other entrainers such as acetone, benzene, cyclohexane, cyclohexanone, heptane, hexane, pentane, hexanol, an ester of hexanol, and / or 2-methylpentanol may be used alone or as a mixture, the mixture comprising two or more of said entrainers. In this connection, hexanol also refers to n-hexanol. Any of these entrainers alone or in some combination may also react correspondingly negatively in a high temperature. Additionally, the vapor recompression arrangements 112A, 112B, 112C are not suitable for high temperatures and / or high temperature differences within the column. That is, heat pumps can be used to moderately increase the temperature by compression of gas, the temperature increase being about 5°C to about 20°C, for example. As a result, heat energy consumption of the double-effect distillation consumption is undesirable high which affect substances within the mixture negatively, but at least a part of the problems can be avoided using the new manner described in this document.

[0054] In an embodiment, liquid phase formed from overhead vapors of the first distilling column 100 may be fed to the decanter 200, the overhead vapors including water and entrainer caused by the process of the first distilling column 100, and water and entrainer are separated at least partly from each other to different streams by the decanter 200. The liquid phase may be formed by condensation of the overhead vapors. The different streams from the decanter 200 include water-rich stream and entrainer-rich stream. The water-rich stream means a stream that has mainly water and the entrainer-rich stream means a stream that has mainly entrainer as a person skilled in the art well understands. The entrainerrich stream and / or the water-rich stream may be at least partly fed back to the column 100.

[0055] The process system described in this document allows production of pure and concentrated acids with a small reflux ratio and good energy efficiency.

[0056] Fig. 7 illustrates an example based on Fig. 2 where data processing unit 600 receives information on pressure, temperature, composition of streams and contents of the mixtures and / or flow of streams from at least one sensor 602 (not all possible sensors are drawn in Fig. 7). The at least one sensor 602 may measure the mixture within the column 100 and / or the column 102, potentially streams from the column 100 and / or contents of the decanter 200. Additionally, the data processing unit 600 may receive information on pressure and / or temperature before and / or after one or more compressors 112(1), 112(3), 112(5), 112(7). There may also be other sensors for providing the data processing unit 600 with information on other process conditions and / or substances. The data processing unit 600 may adjust the processing conditions in at least one of the columns 100, 102 based on the measurement results. For example, if water percentage of the output fed from the first column 100 to the second column 102 is above a predetermined threshold percentage, the data processing unit 600 may alter temperature and / or a temperature difference in the first column 100. In an embodiment, the temperature and / or the temperature difference may be increased. In an embodiment, the temperature may be increased but the temperature difference may be decreased. The adjustment of the temperature and / or the temperature difference may be performed by the at least one vapor recompression arrangement 112A, 112B, 112C based on a command from the data processing unit 600. The rotation speed of the compressors may be controlled based on the information from the at least one sensor 602, for example.

[0057] If the water percentage of the output fed from the first column 100 to the second column 102 is below a predetermined threshold percentage, the temperature and / or the temperature difference may be decreased in an embodiment. In an embodiment, the temperature may be decreased but the temperature difference may be increased, kept unchanged or decreased if the water percentage of the output fed from the first column 100 to the second column 102 is below a predetermined threshold percentage. The adjustment of the temperature and / or the temperature difference may also in this case be performed by the at least one vapor recompression arrangement 112A, 112B, 112C based on a command from the data processing unit 600.

[0058] Fig. 8 illustrates an example of the data processing unit 600 that can be considered a computer comprises one or more processors 700 and one or more memories 702. The one or more memories include a computer program code. The one or more processors 700, one or more memories 702 and the computer program code are configured to cause the apparatus for heteroazeotropic extractive distillation at least to control the process. The data processing unit 600 includes or is connected with a user interface 604.

[0059] The term "computer" includes a computational device that performs logical and arithmetic operations. For example, a "computer" may comprise an electronic computational device, such as an integrated circuit, a microprocessor, a mobile computing device, a laptop computer, a tablet computer, a personal computer, or a mainframe computer. A "computer" may comprise a central processing unit, an ALU (arithmetic logic unit), a memory unit, and a control unit that controls actions of other components of the computer so that steps of a computer program are executed in a desired sequence. A "computer" may also include at least one peripheral unit that may include an auxiliary memory (such as a disk drive or flash memory), and / or may include data processing circuitry.

[0060] The user interface 604 means an input / output device and / or unit. Nonlimiting examples of a user interface include a touch screen, other electronic display screen, keyboard, mouse, microphone, handheld electronic controller, digital stylus, display screen, speaker, and / or projector for projecting a visual display. The user may input commands and / or computer code to the data processing unit 700 and / or the one or more memories 702. The user interface 604 may present data on the processing conditions to the user.

[0061] Fig.9 is a flow chart of the distillation method. The extractive distillation is performed in two stages. The first stage comprises step 800 where a first mixture 104 of water, at least acetic acid and formic acid and entrainer are distilled in a first stage 10 of heteroazeotropic extractive distillation for separating water from the first mixture 104 through distillation, the entrainer being a former of azeotrope and an extractant in the first mixture 104, and the first mixture 104 having a first percentage of said entrainer and a first percentage of water.

[0062] The second stage comprises step 802 where a bottom product including water, at least acetic acid and formic acid and said entrainer is received from a bottom section 108 of the first stage 10 of heteroazeotropic extractive distillation, the second stage 12 including a second mixture 106 having a second percentage of said entrainer and a second percentage of water, wherein the first percentage of water of the first column 100 being greater than the second percentage of water of the second column 102, the second percentages of water being at least partially based on the bottom product received from the bottom section 108 of the first stage 10.

[0063] In step 804, at least a part of overhead vapor of at least one of the first stage 10 and the second stage 12 is pressurized by vapor recompression. In step 806, at least one the following circulation and transfer of heat is performed: circulating at least a part of the first mixture 104 of the first stage 10 back to the first stage 10, and transferring heat of the overhead vapor to first mixture 104 circulated to the first stage 10.

[0064] It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the example embodiments described above but may vary within the scope of the claims.

Claims

What is claimed is:

1. A heteroazeotropic extractive distillation method, c h a r a c t e r i z e d by performing a two stage heteroazeotropic extractive distillation within at least one distillation column (100, 102), a first stage (10) of the heteroazeotropic extractive distillation comprising distilling (800) a first mixture (104) of water, at least acetic acid and formic acid and entrainer inside a temperature range difference 5°C to 20°C within the first stage for separating water from the first mixture (104) through distillation, the entrainer being a former of a minimum boiling azeotrope and an extractant in the first mixture (104), and the first mixture (104) having a first percentage of said entrainer and a first percentage of water; a second stage (12) of the heteroazeotropic extractive distillation, the second stage (12) being separate from the first stage (10), receiving (802) a bottom product of water, at least acetic acid and formic acid and said entrainer from a bottom section (108) of the first stage (10), the second stage (12) including a second mixture (106) having a second percentage of said entrainer and a second percentage of water, wherein the second percentage of said entrainer of the second stage (12) being greater than the first percentage of said entrainer of the first stage (10), and / or the first percentage of water of the first stage (10) being greater than the second percentage of water of the second stage (12), the second percentages of water and said entrainer being at least partially based on the bottom product received from the first stage (10); pressurizing (804) at least a part of overhead vapor of at least one of the first stage (10) and the second stage (12) by vapor recompression; and circulating (806) at least a part of the first mixture (104) of the first stage (10) back to the first stage (10), and transferring heat of the overhead vapor to first mixture (104) circulated to the first stage (10).

2. The method of claim 1, c h a r a c t e r i z e d by performing the first stage of said heteroazeotropic extractive distillation within a first distillation column (100), a second distillation column (102) of heteroazeotropic extractivedistillation receiving the bottom product from a bottom section (108) of the first distillation column (100), and performing the second stage of said heteroazeotropic extractive distillation within the second distillation column (102), the product from the bottom of the first distillation column (100) including water, at least acetic acid and formic acid and said entrainer, where the second percentages of water and said entrainer being at least partially based on the product received from the bottom section (108) of the first column (100); and pressurizing (804) at least a part of the overhead vapor of at least one of the first column (100) and the second column (102), and transferring heat of the overhead vapor that is pressurized to the first mixture (104) of the first column (100).

3. The method of claim 1, characterized by the entrainer including furfural.

4. The method of claim 1, characterized by pressurizing (804) including heating the first mixture (104) of the first column (100) such that at least one compressor (112(1), 112(3), 112(5), 112(7), 112(9)) receives the at least a part of the overhead vapor from the first column (100) and / or the second column (102) and increases pressure of said overhead vapor for causing an increase of temperature of said overhead vapor, and transferring heat through heat exchange from said overhead vapor to the first mixture (104) within the first column (100).

5. The method of claim 4, characterized by performing pressurizing by at least two heat pumps in series.

6. The method of claim 1, characterized by feeding a third mixture (110) of water, at least acetic acid and formic acid and the entrainer to the second stage (12), a third percentage of said entrainer of the third mixture (110) being greater than the first percentage of said entrainer of the first stage (10), and / or a third percentage of water of third mixture (110) is smaller than the first percentage of water of the first stage (10).

7. The method of claim 1, c h a r a c t e r i z e d by causing a coefficient of performance (COP) to be 10 or greater based on said pressurizing by vapor recompression of said overhead vapors, and / or enabling a temperature difference that is inside a range 5°C to 20°C within the first stage (10) based on said pressurizing with the vapor recompression of said overhead vapors.

8. The method of claim 1, c h a r a c t e r i z e d by feeding said overhead vapors of the first stage (10) in a condensed form to a decanter (200), the overhead vapors including water and entrainer caused by the process of the first stage (10), and separating water-rich liquid and entrainer-rich liquid from each other to different streams by the decanter (200).

9. An apparatus for heteroazeotropic extractive distillation, c h a r a c t e r i z e d in that the apparatus is configured to perform a two stage heteroazeotropic extractive distillation, the apparatus comprising at least one column means (100, 102) of heteroazeotropic extractive distillation that is configured to process a first mixture (104) of water, at least acetic acid and formic acid and entrainer in a first stage (10) of the heteroazeotropic extractive distillation for separating water from the first mixture (104) through distillation, the entrainer being a former of azeotrope and an extractant in the first mixture (104), and the first mixture (104) having a first percentage of said entrainer and a first percentage of water; a second stage (12) of the heteroazeotropic extractive distillation that is separate from the first stage (10) and is configured to receive a bottom product including water, at least acetic acid and formic acid and said entrainer from a bottom section (108) of the first stage (10), and process a second mixture (106) that has a second percentage of said entrainer and a second percentage of water, wherein the second percentage of water of the second stage (12) is smaller than the first percentage of water of the first stage (10), the second percentages of water and said entrainer being at least partially based on the bottom product received from the bottom section (108) of the first stage (10);a vapor recompression means (112A, 112B, 112C) that is configured to pressurize overhead vapor of the first stage (10); and the apparatus is configured to circulate at least a part of the first mixture (104) of the first stage (10) back to the first stage (10), and transfer heat of the overhead vapor to first mixture (104) circulated back to the first stage (10).

10. The apparatus of claim 9, characterized in that the entrainer includes furfural.

11. The apparatus of claim 9, characterized in that at least one heat pump of the vapor recompression means (112A, 112B, 112C) is configured to receive at least a part of said overhead vapors from the first stage (10) and / or the second stage (12) and increase pressure of said overhead vapors for causing an increase of temperature of said overhead vapors, and at least one heat exchanger (112(2), 112(4), 112(6), 112(8), 112(10), 112(12)) configured to transfer heat from said overhead vapors to the first mixture (104) of the first stage (10).

12. The apparatus of claim 11, characterized in that the vapor recompression means (112A, 112B, 112C) comprises at least two heat pumps in series.

13. The apparatus of claim 9, characterized that the second stage (12) is configured to receive a third mixture (110) of water, at least acetic acid and formic acid and the entrainer, a third percentage of said entrainer of the third mixture (110) being greater than the first percentage of said entrainer of the first stage (10), and / or a third percentage of water of third mixture (110) is smaller than the first percentage of water of the first stage (10).

14. The apparatus of claim 9, characterized in that the vapor compression means (112A, 112B, 112C) is configured to cause a coefficient of performance (COP) of the apparatus to be 10 or greater, and / or the vapor compression means (112A, 112B, 112C) is configured to enable a temperature difference that is inside a range 5°C to 20°C within the first stage (10).

15. The apparatus of claim 9, characterized that the apparatus is configured to feed said overhead vapors of the first stage (10) in a condensed form to a decanter (200), the overhead vapors including water and entrainer caused by the process of the first stage (100), and the decanter (200) is configured to separate water-rich liquid and entrainer-rich liquids from each other to different streams.

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