JP2016131549A - Method and apparatus for synthesizing ethanol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove a hydrocarbon compound such as benzene, toluene and xylene efficiently from raw material gas such as syngas, and efficiently produce ethanol.SOLUTION: Raw material gas 2a is brought into contact with absorbent 3a containing ethanol in an absorption part 23 in the previous step of ethanol synthetic part 10 to make a hydrocarbon compound in raw material gas 2a be absorbed into absorbent 3a. Raw material gas 2b after absorption is introduced into a culture tank 11 of the ethanol synthetic part 10 to synthesize ethanol. In a separation and regeneration part 42, hydrocarbon compound is isolated from absorbent 3c after absorption.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and apparatus for synthesizing ethanol from a source gas such as syngas, and more particularly to an ethanol synthesis method and apparatus suitable for performing ethanol synthesis after removing a hydrocarbon compound such as benzene in the source gas. .

  Plants for producing ethanol from a raw material gas such as syngas are known (see Patent Documents 1 and 2, etc.). This kind of plant often requires a process for removing aromatic compounds such as BETX (benzene, ethylbenzene, toluene, xylene) and other hydrocarbon compounds in the syngas. For example, when ethanol is purified by the fermenting action of anaerobic microorganisms, it is considered that BETX or the like adversely affects the activity of the anaerobic microorganisms (see Patent Document 3, etc.).

As a method for removing BETX from the syngas, a PSA (pressure-swing adsorption) method or a water absorption method can be considered.
In the PSA system, BETX in a syngas is absorbed by a solid absorbent such as zeolite. Thereafter, the solid absorbent is regenerated by desorbing BETX from the solid absorbent by evacuation.
In the water absorption method, water is absorbed by BETX. The absorbed water is diffused into the atmosphere to evaporate BETX.

JP 2004-504058 A JP 2012-217886 A JP 2014-050406 A ([0096], [0102])

The PSA method has the following problems.
(1) Since the solid absorbent is easily damaged by sulfur in the syngas, it is necessary to replace the solid absorbent regularly.
(2) Since the solid absorbent absorbs not only BETX but also water, it is essential to remove moisture from the syngas.
(3) Power consumption for driving a vacuum pump or the like to regenerate the solid absorbent or heating for removing moisture is large.
(4) Since the solid absorbent also absorbs raw material components such as CO and H ₂ , ethanol production efficiency decreases.

The water system has the following problems.
(1) Since the solubility of water in BETX is low, a large amount of water is required.
(2) When releasing into the atmosphere for water regeneration, BETX is released into the environment and mixed with a large amount of air. It is almost impossible to collect and process this BETX.

  In view of the above circumstances, the present invention efficiently removes aromatic compounds such as BEXT (benzene, ethylbenzene, toluene, xylene) and other hydrocarbon compounds from a raw material gas such as syngas, and efficiently produces ethanol. The purpose is to do.

In order to solve the above problems, the method of the present invention is an ethanol synthesis method for synthesizing ethanol from a raw material gas such as syngas.
An absorption step in which the raw material gas before the ethanol synthesis step is brought into contact with an absorption liquid containing ethanol to absorb the hydrocarbon compound contained in the raw material gas into the absorption liquid;
A separation and regeneration step for separating the hydrocarbon compound from the absorption liquid after the absorption step and reusing the absorption liquid;
It is provided with.

  Examples of the hydrocarbon compound include BETX, that is, aromatic compounds such as benzene, ethylbenzene, toluene, and xylene. Ethanol has a higher absorption capacity for these hydrocarbon compounds than water. Therefore, the hydrocarbon compound can be efficiently removed from the raw material gas by using the absorption liquid containing ethanol. As a result, the quality of the raw material gas can be improved, and ethanol for synthesis can be efficiently produced. Further, the required flow rate of the absorbing liquid can be reduced, and the enlargement of the equipment can be avoided. Furthermore, the separation and regeneration step can recover (regenerate) the absorption capacity of the absorption liquid with respect to the hydrocarbon compound, and the absorption liquid can be circulated and reused.

In the ethanol synthesis step, the raw material gas after the absorption step is introduced into the culture solution, ethanol is synthesized from the raw material gas by fermentation of anaerobic microorganisms in the culture solution,
Furthermore, a purification step for purifying ethanol from the culture solution after the ethanol synthesis step is provided,
It is preferable that at least a part of the purification step also serves as the separation and regeneration step by sending the absorption liquid after the absorption step to the purification step.
Thereby, the separation / regeneration step dedicated to the absorbent after the absorption step can be omitted, and the treatment process can be simplified. By making the absorbing substance that absorbs the hydrocarbon compound and the target substance to be synthesized the same substance (ethanol), it becomes more advantageous in terms of man-hours and equipment costs than using different substances.
On the other hand, when an absorption part using ethanol is used in a plant that synthesizes a substance other than ethanol (for example, butanol), the ethanol is removed from the system or recovered by heating or cooling after the absorption process. It is necessary to do so, and additional equipment is increased, resulting in an increase in cost. In addition, if a hydrocarbon compound is absorbed by a substance other than ethanol (for example, butanol) in a plant that synthesizes ethanol, the substance other than ethanol is removed from the system or recovered by heating or cooling after the absorption step. It is necessary to do so, and additional equipment is increased, resulting in an increase in cost.

Furthermore, the storage step of storing the absorption liquid after the absorption step in the post-absorption liquid tank,
It is preferable that the absorption liquid in the post-absorption liquid tank is subjected to the separation and regeneration step.
Even if the hydrocarbon compound concentration in the absorption liquid after the absorption process fluctuates due to fluctuations in the partial pressure of the hydrocarbon compound in the raw material gas, the absorption liquid after this absorption process is stored in the liquid tank after absorption. The hydrocarbon compound concentration can be averaged and stabilized at a concentration sufficiently lower than the peak concentration. By supplying the absorption liquid of this low hydrocarbon compound concentration to the separation and regeneration process, it is possible to avoid exceeding the processing capacity of the separation and regeneration, and the equipment is enlarged to cope with the peak of the hydrocarbon compound concentration. There is no need to

The ethanol synthesizer according to the present invention is an ethanol synthesizer having an ethanol synthesizer that synthesizes ethanol from a raw material gas such as syngas.
An absorption part for bringing the raw material gas before introduction into the ethanol synthesis part into contact with an absorption liquid containing ethanol and absorbing the hydrocarbon compound contained in the raw material gas into the absorption liquid;
A separation / regeneration unit that separates the hydrocarbon compound from the absorbed liquid after the absorption so that the absorbent can be reused;
It is provided with.
Thereby, the hydrocarbon compound can be efficiently removed from the raw material gas, the quality of the raw material gas can be improved, and ethanol for synthesis can be efficiently produced. Further, the required flow rate of the absorbing liquid can be reduced, and the enlargement of the equipment can be avoided. Further, in the separation / regeneration unit, the absorption capacity of the absorption liquid with respect to the hydrocarbon compound can be recovered (regeneration), and the absorption liquid can be recycled and reused by returning it to the absorption section.

The ethanol synthesis unit has a culture tank for culturing anaerobic microorganisms that synthesize ethanol from the source gas by fermentation in a culture solution,
Furthermore, a gas path after absorption for sending the raw material gas after absorption to the culture tank;
A purification unit for purifying ethanol from the culture solution after the ethanol synthesis;
A regeneration outbound path for sending the absorbed liquid after the absorption to the purification section,
It is preferable that at least a part of the purification unit is provided as the separation / regeneration unit.
As a result, it is possible to omit a separation / regeneration unit dedicated to the absorbent after absorption. In the ethanol synthesis system using this kind of anaerobic microorganism, since a purification unit for purifying ethanol from a culture solution after ethanol synthesis is usually installed (see Patent Document 1, etc.), using this existing purification unit, The absorption liquid can be regenerated. Therefore, it is possible to prevent the facility from becoming large and to avoid an increase in facility cost.

The purification unit comprises a plurality of distillation columns connected in sequence,
The culture tank is connected to the first distillation column in the first stage;
The regeneration forward path is connected to a second distillation column connected to a subsequent stage of the first distillation column;
Furthermore, it is preferable to provide a regeneration return path for returning a part of the bottoms of the second distillation column to the absorption part as the absorption liquid.
By distilling the culture solution after the ethanol synthesis in the first distillation column, a relatively high concentration ethanol distillate can be obtained. The ethanol distillate is introduced into the second distillation column, and the absorbed liquid after the absorption is introduced into the second distillation column. These two liquids are preferably mixed with each other and then introduced into the second distillation column, but may be separately introduced into the second distillation column and mixed in the second distillation column. By distilling this mixed liquid in the second distillation column, the hydrocarbon compound derived from the absorbing liquid after the absorption is separated and removed.
By connecting the regeneration path to the second distillation column instead of the first distillation column, the ethanol concentration of the absorption solution after absorption is reduced by mixing with the culture solution before distillation in the first distillation column. Can be prevented. Therefore, the burden of distillation or separation / regeneration in the second distillation column can be reduced, and purification efficiency or separation efficiency can be ensured. Then, by returning a part of the bottomed liquid of the second distillation column from the regeneration return path to the absorbing part, the part of the bottomed liquid can be reused as the absorbing liquid.

Furthermore, it comprises a post-absorption liquid tank that stores the absorption liquid after absorption,
It is preferable that the regeneration outward path extends from the post-absorption liquid tank to the purification unit.
Even if the hydrocarbon compound concentration in the absorption liquid after absorption changes due to fluctuations in the partial pressure of the hydrocarbon compound in the raw material gas, the absorption liquid after absorption is stored in the post-absorption liquid tank, thereby carbonizing. The hydrogen compound concentration can be averaged and stabilized at a concentration sufficiently lower than the peak concentration. Therefore, it is not necessary to match the processing capacity of the purification section, that is, the separation / regeneration section, at the peak time, and an increase in the size of the equipment can be avoided.

It is preferable that the absorption liquid is a mixture of ethanol and water.
Separation rate of ethanol and hydrocarbon compounds at the azeotropic point with a solution in which a hydrocarbon compound such as benzene is absorbed in a mixture of ethanol and water, rather than a solution in which a hydrocarbon compound such as benzene is absorbed in 100% ethanol Can be high. Therefore, the separation efficiency of the hydrocarbon compound in the separation / regeneration step (separation / regeneration unit) can be increased. The ratio of ethanol and water in the mixture is desirably set so that a desired absorption efficiency can be secured and a desired separation efficiency can be secured. If the ethanol content of the mixture is too low (the water content is too high), the absorption efficiency of the hydrocarbon compound in the collecting part is lowered. When the ethanol content of the mixture is too high (when the water content is too small), the separation efficiency of the hydrocarbon compound in the separation and regeneration section is lowered.

  According to the present invention, a hydrocarbon compound can be efficiently removed from a raw material gas, and ethanol can be produced efficiently.

FIG. 1 is a circuit configuration diagram showing an ethanol synthesizer according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the ethanol synthesis apparatus 1 includes a syngas generation unit 2 (raw material gas generation unit), an ethanol synthesis unit 10, a pretreatment unit 20, and an ethanol purification unit 40. Although detailed illustration is omitted, the syngas generation unit 2 is configured in a waste treatment facility for treating industrial waste and the like. In other words, the ethanol synthesizer 1 is incorporated in a waste treatment system. The syngas generation unit 2 is equipped with a gasification furnace, in which the waste is burned with high-concentration oxygen gas and decomposed to a low molecular level, and finally the syngas 2a (raw material gas) and Become. The syngas 2a contains carbon dioxide (CO ₂ ) and nitrogen (N ₂ ) as main components in addition to carbon monoxide (CO) and hydrogen (H ₂ ). Furthermore, the syngas 2a at the time of production (before the absorption step) is a trace amount or a small amount (mol-ppm order to several mol% order) of hydrogen sulfide (H ₂ S), oxygen (O ₂ ), and BETX (benzene, ethylbenzene). , Toluene, xylene) and other hydrocarbon compounds.

The ethanol synthesis unit 10 includes a culture tank 11 and a culture stock solution supply unit 12. A culture solution 8 is stored in the culture tank 11. An anaerobic microorganism 19 is cultured in the culture solution 8. As the anaerobic microorganism 19, anaerobic bacteria disclosed in, for example, the above-mentioned Patent Documents 1 and 3 (Japanese Patent Laid-Open Nos. 2004-504058 and 2014-050406) can be used. The anaerobic microorganism 19 synthesizes ethanol (C ₂ H ₅ OH) or the like from carbon monoxide (CO), hydrogen (H ₂ ), or the like by its fermentation action.

  A culture stock supply unit 12 is connected to the culture tank 11. The culture stock supply unit 12 supplies the stock solution of the culture solution 8 before the anaerobic microorganism 19 is added to the culture tank 11. The stock solution of the culture solution 8 contains water as a main component, and various nutrient components for the anaerobic microorganism 19 are dissolved in the water.

A pretreatment unit 20 is provided between the syngas generation unit 2 and the ethanol synthesis unit 10. The pretreatment unit 20 includes a desulfurization unit 21, a deoxygenation unit 22, and a BETX absorption unit 23. The desulfurization unit 21, the deoxygenation unit 22, and the BETX absorption unit 23 are connected in series from the syngas generation unit 2 side (upstream side). Desulfurization unit 21 includes a desulfurizing agent such as _Fe 2 _{O 3.} The deoxidation part 22 contains a transition metal catalyst such as Cu.

  The BETX absorption unit 23 includes an absorber 30, a pre-absorption liquid tank 31, and a post-absorption liquid tank 32. The pre-absorption liquid tank 31 stores an absorption liquid 3a before the absorption process described later.

  The absorber 30 is a cylindrical container extending vertically (up and down). A sprayer 33 is disposed at the upper end in the absorber 30. A pre-absorption liquid path 34 extends from the pre-absorption liquid tank 31 and is connected to the sprayer 33. A temporarily stored absorbent 3b after the absorption step is stored at the bottom of the absorber 30.

  A pre-absorption gas path 24 extends from the deoxygenation unit 22 and is connected to the bottom of the absorber 3. The connection portion of the absorber 30 with the pre-absorption gas path 24 is preferably disposed above the liquid level of the temporarily stored absorbent 3b. Further, a gas passage 25 after absorption extends from the upper side of the absorber 30 and is connected to the bottom of the culture tank 11.

The temperature in the absorber 30 is preferably normal temperature (for example, about 10 ° C. to 40 ° C.). The lower the temperature, the more easily BEXT is absorbed.
The internal pressure of the absorber 30 is preferably higher than atmospheric pressure, more preferably 5 atmospheres (gauge pressure) or more, more preferably 10 atmospheres or more, but is not limited thereto, and may be atmospheric pressure or less than atmospheric pressure. .

A post-absorption liquid passage 35 extends from the bottom of the absorber 30 and is connected to the post-absorption liquid tank 32. The post-absorption liquid tank 32 stores post-absorption storage liquid 3c (absorption liquid after the absorption process). The internal volume of the absorbing solution after tank 32 depends on the processing capacity of ethanol synthesizer 1, for example ^{1 m} 3 through 10m ³ mm, preferably 2m ³ approximately.

The absorbing liquids 3a, 3b, 3c are mixed liquids containing ethanol (C ₂ H ₅ OH) and water (H ₂ O). The ethanol concentration of the absorbing liquids 3a, 3b, 3c is, for example, about 50 wt% to 95 wt%. Most of the components other than ethanol in the absorbing liquids 3a, 3b, and 3c are occupied by water. If the ethanol content of the absorbent 3a is too low (too much water), the absorption efficiency of BETX will decrease. If the ethanol content of the absorption liquid 3c is too high (the amount of water is too small), the BETX separation efficiency in the separation and regeneration step described later is lowered.

Further, the absorbing liquids 3b and 3c contain BETX. The BETX concentration of the temporarily stored absorbent 3b varies greatly, for example, in the order of ppm order to several percent order. The BETX concentration of the post-absorption storage liquid 3c is stable at a concentration sufficiently lower than the peak value of the BETX concentration of the temporary storage absorption liquid 3b.
In addition, the absorption liquid 3a before absorption can contain a very small amount of BETX. The allowable BETX concentration of the absorption liquid 3a is sufficiently smaller than the BETX concentration of the post-absorption storage liquid 3c, for example, several tens mol-ppm or less is desirable.

An ethanol purification unit 40 is disposed after the ethanol synthesis unit 10.
The ethanol purification section 40 includes a plurality of distillation columns 41, 42... (Only two stages are shown in FIG. 1). These distillation columns 41, 42, ... are successively connected in series. Each distillation column 41, 42 ... extends vertically.

  A post-culture liquid channel 14 is drawn out from the culture solution 8 in the culture tank 11, and the post-culture liquid channel 14 is connected to the middle part of the first distillation column 41 in the first stage. A first reboiler 44 is provided at the lower end of the first distillation column 41, and a water treatment unit 4 (waste water treatment) is connected thereto.

  A first condenser 43 is provided at the upper end of the first distillation column 41. A primary condensate channel 47 extends from the first condenser 43 and is connected to an intermediate portion of the second distillation column 42 in the second stage (the latter stage).

  On the other hand, the regeneration outward path 36 is drawn from the post-absorption liquid tank 32 and extends to the purification unit 40. The regeneration outward path 36 joins the primary condensate path 47 at the junction 47c. Therefore, the regeneration forward path 36 is connected to the second distillation column 42 via the primary condensate path 47 downstream from the junction 47c.

  A second condenser 45 is provided at the upper end of the second distillation column 42. A secondary condensate passage 49 extends from the second condenser 45.

  A second reboiler 46 is provided at the lower end of the second distillation column 42. In addition, a secondary bottom discharge channel 48 extends from the lower end of the second distillation column 42 and is connected to a third-stage distillation column (not shown). A regeneration return path 37 branches from the secondary can discharge liquid path 48. The regeneration return path 37 extends to the absorption unit 23 and is connected to the pre-absorption liquid tank 31.

A method for synthesizing ethanol by the ethanol synthesizer 1 will be described.
<Raw gas generation process>
In the syngas generator 2, the waste is burned to generate the syngas 2a. The BETX concentration in the syngas 2a at the time of generation (before the absorption process) varies greatly depending on the waste component of the raw material.

<Pretreatment process>
Prior to introducing the syngas 2 a into the culture tank 11, it is subjected to a pretreatment process by the pretreatment unit 20. The pretreatment process includes a desulfurization process, a deoxygenation process, and a BETX absorption process.
<Desulfurization process>
Specifically, first, in the desulfurization section 21, H ₂ S in the syngas 2a is absorbed by a desulfurization agent such as Fe ₂ O ₃ and removed.
<Deoxygenation process>
Next, in the deoxygenation unit 22, using a transition metal catalyst such as Cu, O ₂ in the syngas 2a is removed by reacting with other gases (CO, H _2, etc.) in the syngas 2a. By removing H ₂ S in advance in the desulfurization section 21, it is possible to prevent the Cu catalyst in the deoxygenation section 22 from being damaged.

<Absorption process>
Next, in the BETX absorption part 23, BETX in the syngas 2a is absorbed by ethanol and removed.
Specifically, the syngas 2 a from the deoxygenation unit 22 is introduced into the absorber 30 through the pre-absorption gas path 24 and rises in the absorber 30.
In addition, the absorbent 3 a in the pre-absorption liquid tank 31 is introduced into the sprayer 33 via the pre-absorption liquid path 34, and is sprayed into the absorber 30 from the sprayer 33 and falls.
Thereby, in the absorber 30, the syngas 2a and the absorbing liquid 3a come into contact with each other while constituting a counter flow, and BETX in the syngas 2a is absorbed by the absorbing liquid 3a.
Since the absorption capacity of ethanol with respect to BETX is more than 1,000 times that of water, the required flow rate of the absorbent 3a can be significantly reduced as compared with the case where 100% of water is used as the absorbent of BETX. By making the inside of the absorber 30 high, the BETX partial pressure of the syngas 2a can be increased, and the BETX absorption rate of the absorbent 3a can be increased.
Prior to this absorption step, O ₂ is removed in advance in the deoxygenation unit 22 to prevent the ethanol in the absorption liquid 3a from reacting with O ₂ and generating unnecessary components such as formic acid.

The BETX concentration of the post-absorption syngas 2b in the upper part of the absorber 30 is lower than the BETX concentration of the pre-absorption syngas 2a. Moreover, in the absorber 30, a part of ethanol in the absorption liquid 3a is vaporized. For this reason, the absorbed syngas 2b contains ethanol.
The initial temperature of the syngas 2a (temperature at the time of introduction into the absorber 30) is higher than room temperature, for example, about 30 ° C. to 50 ° C., and preferably about 40 ° C. By depriving the heat of vaporization of ethanol from the syngas 2a, the temperature in the absorber 30 is maintained at substantially normal temperature (for example, about 25 ° C.).

At the bottom of the absorber 30, temporarily stored absorbent 3b that has absorbed BETX is temporarily stored. The BETX concentration of the temporarily stored absorbent 3 b is approximately balanced with the BETX partial pressure of the syngas 2 a at the bottom of the absorber 30.
Since the BETX partial pressure of the syngas 2a is likely to fluctuate according to the waste components combusted in the syngas generator 2, the BETX concentration of the temporarily stored absorbent 3b is also likely to fluctuate.

<Storage process>
The temporarily stored absorption liquid 3b is sent to the post-absorption liquid tank 32 via the post-absorption liquid path 35 and stored in the post-absorption liquid tank 32 as the post-absorption storage liquid 3c.
Even if the BETX concentration of the temporarily stored absorbent 3b varies with the variation of the BETX partial pressure of the syngas 2a, the BETX concentration can be averaged by storing in the post-absorption liquid tank 32. Thus, the BETX concentration of the post-absorption storage liquid 3c can be stabilized at a concentration sufficiently lower than the peak value of the BETX concentration of the temporary storage absorption liquid 3b. Therefore, in the separation / regeneration process described later, when separating the betx from the post-absorption stored liquid 3c and regenerating the absorption liquid 3a, it is not necessary to match the separation / regeneration processing capability of the separation / regeneration unit 42 to the peak value, and the separation / regeneration unit The burden of 42 can be reduced and the enlargement of equipment can be avoided.
The post-absorption liquid tank 32 may be provided with a stirrer to stir the post-absorption storage liquid 3c, thereby promoting uniformization of the BETX concentration of the post-absorption storage liquid 3c.

<Synthesis process>
The syngas 2b after the absorption step is introduced into the culture tank 11 via the post-absorption gas path 25 and is dissolved in the culture solution 8. The anaerobic microorganisms 19 in the culture liquid 8, by performing the fermentation, synthesizing ethanol from CO and H ₂ and the like in the syngas 2b. By introducing the syngas 2b that has undergone BETX absorption and removal into the culture tank 11, it is possible to prevent the anaerobic microorganism 19 from being adversely affected, and to ensure that ethanol is fermented.

  At this time, ethanol in the syngas 2b is also dissolved in the culture solution 8. That is, even if ethanol is vaporized from the absorbing solution 3 a in the absorption step, the ethanol can be combined with ethanol generated by the ethanol synthesis unit 10. And ethanol can be collect | recovered by the refinement | purification process mentioned later. Therefore, waste of ethanol can be suppressed. Moreover, it can prevent that the fermentation activity of the anaerobic microorganism 19 declines by suppressing the vaporization flow rate of ethanol in the said absorption process to about 1/10 of the ethanol production flow rate by the anaerobic microorganism 19.

<Gas release process>
The gas in the culture tank 11 is discharged from the gas discharge path 13. The released gas components are mainly unreacted CO and H ₂ , CO ₂ , and N ₂ , and may further contain a trace amount of ethanol, BETX, and the like. This released gas may be recovered and reused, or may be released after detoxification as appropriate.

<Culture medium derivation process>
A part 8a of the culture solution 8 in the culture tank 11 is led out to the post-culture liquid channel 14 at a predetermined flow rate. The derived culture solution 8a is a mixed solution of ethanol and water. Further, the derived culture solution 8a contains a living body of the anaerobic microorganism 19 or biomass such as a carcass and other solid components (suspended solids). The solid component is preferably captured and collected by a filter (not shown) and returned to the culture tank 11 or decomposed.

<Purification process>
The derivation culture solution 8a is sent to the ethanol purification unit 40 after removal of the solid components, and is supplied to the purification step.
Specifically, the lead-out culture solution 8a is first introduced into the first distillation column 41 and distilled, and is separated into a lower primary distillate 8b and an upper primary distillate vapor 9a. Most of the primary bottom liquid 8b is water (H ₂ O). A part of the primary effluent 8b is sent to the first reboiler 44, heated, and returned to the first distillation column 41 as steam. The remaining portion of the primary bottom liquid 8b is sent to the water treatment unit 4 and subjected to aerobic treatment or the like. The treated primary effluent 8b may be discarded or returned to the culture tank 11.

The primary distillate vapor 9a includes a relatively high concentration of ethanol gas and water that cannot be separated in the first distillation column 41, that is, water vapor (H ₂ O). This primary distillate vapor 9a is sent from the upper end of the first distillation column 41 to the first condenser 43, where it is cooled and condensed to become the primary condensate 9b. A part of the primary condensate 9b is returned to the first distillation column 41. The remainder of the primary condensate 9b is sent to the second distillation column 42 via the primary condensate channel 47.

<Merging process>
At the same time, the stored liquid 3c after absorption at a constant flow rate is sent out from the liquid tank 32 after absorption, and is mixed with the primary condensate 9b in the junction 47c via the regeneration forward path 36. As a result, a pre-secondary distillation liquid 9c made of a mixed liquid of the post-absorption storage liquid 3c and the primary condensate 9b is formed. The pre-secondary distillation liquid 9c contains a relatively high concentration of ethanol and water, and further contains BETX derived from the post-absorption storage liquid 3c. The ethanol concentration of the mixed solution 9c can be kept high by mixing the post-absorption storage solution 3c with a high ethanol concentration with the primary condensate 9b with a high ethanol concentration instead of mixing with the culture solution 8a with a low ethanol concentration. Therefore, the burden of the refinement | purification part 40 can be reduced and refinement | purification efficiency can be ensured. Specifically, the required heat supply amount of the reboiler 46 can be reduced.

<Separation and regeneration process>
The pre-secondary distillation liquid 9c is introduced into the second distillation column 42 and distilled, and is separated into an upper secondary distillate 9d and a lower secondary bottom 9e. Secondary distillate vapor 9d contains low-boiling substances such as BETX gas derived from post-absorption storage liquid 3c and methanol gas derived from culture liquid 8a, in addition to ethanol gas and water vapor having a relatively low concentration. The secondary bottom liquid 9e is a mixed liquid of ethanol and water having a relatively high concentration, and hardly contains BETX derived from the post-absorption storage liquid 3c. In short, the second distillation column 42 of the ethanol purifying unit 40 can separate BETX from the ethanol in the stored liquid 3c after absorption, recover the absorption ability for BETX, and make it reusable as the absorbing liquid 3a. Therefore, at least a part of the ethanol purification unit 40 (second distillation column 42) is provided as a separation / regeneration unit that separates BETX from the post-absorption storage liquid 3c to regenerate the absorption liquid 3a. Further, at least a part of the purification process also serves as a separation and regeneration process. Therefore, it is not necessary to separately provide a separation / regeneration unit dedicated to the stored liquid 3c after absorption, and it is not necessary to perform the separation / regeneration step separately from the purification step. As a result, the facility can be prevented from becoming large, an increase in facility cost can be avoided, and the processing process can be simplified.

  Furthermore, since the pre-secondary distillation liquid 9c is a mixture of ethanol and water, and BETX is mixed into this mixture, ethanol at an azeotropic point is higher than that of a liquid in which BETX is mixed with 100% ethanol. And BETX separation rate can be increased. Therefore, the ethanol concentration of the secondary distillate vapor 9d can be further reduced, and the BETX concentration of the secondary bottoms 9e can be further reduced.

  The secondary distillate steam 9d is introduced into the second condenser 45 and cooled and condensed to become a secondary condensate 9f. A part of the secondary condensate 9f is returned to the second distillation column 42. The remaining portion of the secondary condensate 9f may be used for fuel or the like, and may be discarded after post-processing.

  A part of the secondary bottoms 9e is sent to the second reboiler 46, heated, and returned to the second distillation column 42 as steam.

<Rear purification process>
The other part of the secondary bottoms 9e is further purified by distillation by being sent to the third stage distillation tower (not shown) via the secondary bottoms 48. A high-concentration ethanol solution of 99 wt% or more can be obtained by distillation purification after the third stage.

<Reuse process>
The remaining part (part) of the secondary bottoms 9e is returned to the absorption part 23 by the regeneration return path 37 and stored in the pre-absorption liquid tank 31. Thereby, the remaining part (part) of the secondary bottoms 9e can be reused as the absorbent 3a.

According to this apparatus 1, by making the absorbing substance that absorbs BETX and the target substance to be synthesized the same substance (ethanol), it is more advantageous in terms of processing process and equipment costs than using different substances. Become.
On the other hand, when the BETX absorption part 23 made of ethanol is used in a plant that synthesizes a substance other than ethanol (for example, butanol), the ethanol is excluded from the system by heating or cooling after the absorption step or recovered. It is necessary to do so, and additional equipment is increased, resulting in an increase in cost. In addition, in a plant that synthesizes ethanol, when BETX is absorbed by a substance other than ethanol (for example, butanol), after the absorption step, the substance other than ethanol is excluded from the system by heating or cooling, or recovered. It is necessary to increase the number of additional facilities and the cost.

The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, an almost 100% ethanol solution may be used as the BETX absorption solution. In this case, BETX can be taken out as a mixture with ethanol by distilling the ethanol solution after absorption. The content ratio of BETX and ethanol in this mixture is about 1: 1 in terms of molar ratio.
The syngas generation unit 2 may be an iron mill or a coal combustion unit.
The source gas is not limited to the syngas 2a containing carbon monoxide and hydrogen, and may contain only one of carbon monoxide and hydrogen, or may contain carbon dioxide and hydrogen instead of carbon monoxide. Good (see Patent Document 2 etc.).
In the synthesis step, ethanol may be synthesized by bringing the raw material gas into contact with the catalyst (see Patent Document 2, etc.).
The hydrocarbon compound to be separated from the source gas is not limited to BETX (benzene, ethylbenzene, toluene, xylene), and may be other aromatic compounds such as naphthalene, or acetylene.
The circuit configuration of the ethanol synthesizer 1 can be modified as appropriate. For example, the regeneration outward path 36 may be directly connected to the second distillation column 42 without joining the primary condensate liquid path 47.

  The present invention can be applied to, for example, an ethanol synthesis system that synthesizes ethanol from syngas generated by incineration of industrial waste.

1 Ethanol synthesizer 2a Syngas before absorption (raw gas before absorption process (before absorption))
2b Syngas after absorption (source gas after absorption process (after absorption))
3a Pre-absorption liquid (absorption liquid before absorption process (before absorption))
3b Temporary storage liquid after absorption (absorption liquid after absorption process (after absorption))
3c Storage liquid after absorption (absorption liquid after absorption process (after absorption))
8 Culture solution 8a Derived culture solution (culture solution after ethanol synthesis)
9e Secondary bottoms (second bottom distillation bottoms)
19 Anaerobic microorganism 10 Ethanol synthesis part 11 Culture tank 23 BETX absorption part (absorption part)
25 Gas path after absorption 32 Liquid tank after absorption 36 Regeneration outbound path 37 Regeneration return path 40 Ethanol purification section (purification section)
41 First distillation column (distillation column)
42 Second distillation column (separation regeneration unit, distillation column)

Claims (9)

In an ethanol synthesis method for synthesizing ethanol from a raw material gas,
An absorption step in which the raw material gas before the ethanol synthesis step is brought into contact with an absorption liquid containing ethanol to absorb the hydrocarbon compound contained in the raw material gas into the absorption liquid;
A separation and regeneration step for separating the hydrocarbon compound from the absorption liquid after the absorption step and reusing the absorption liquid;
An ethanol synthesis method characterized by comprising: In the ethanol synthesis step, the raw material gas after the absorption step is introduced into the culture solution, ethanol is synthesized from the raw material gas by fermentation of anaerobic microorganisms in the culture solution,
Furthermore, a purification step for purifying ethanol from the culture solution after the ethanol synthesis step is provided,
The ethanol synthesis method according to claim 1, wherein at least a part of the purification step also serves as the separation and regeneration step by sending the absorption liquid after the absorption step to the purification step. Furthermore, the storage step of storing the absorption liquid after the absorption step in the post-absorption liquid tank,
The ethanol synthesis method according to claim 1 or 2, wherein the absorption liquid in the post-absorption liquid tank is subjected to the separation and regeneration step.   The ethanol synthesis method according to any one of claims 1 to 3, wherein the absorbing liquid is a mixture of ethanol and water. In an ethanol synthesizer having an ethanol synthesis unit that synthesizes ethanol from a raw material gas,
An absorption part for bringing the raw material gas before introduction into the ethanol synthesis part into contact with an absorption liquid containing ethanol and absorbing the hydrocarbon compound contained in the raw material gas into the absorption liquid;
A separation / regeneration unit that separates the hydrocarbon compound from the absorbed liquid after the absorption so that the absorbent can be reused;
An ethanol synthesizer characterized by comprising: The ethanol synthesis unit has a culture tank for culturing anaerobic microorganisms that synthesize ethanol from the source gas by fermentation in a culture solution,
Furthermore, a gas path after absorption for sending the raw material gas after absorption to the culture tank;
A purification unit for purifying ethanol from the culture solution after the ethanol synthesis;
A regeneration outbound path for sending the absorbed liquid after the absorption to the purification section,
The ethanol synthesis apparatus according to claim 5, wherein at least a part of the purification unit is provided as the separation and regeneration unit. The purification unit comprises a plurality of distillation columns connected in sequence,
The culture tank is connected to the first distillation column in the first stage;
The regeneration forward path is connected to a second distillation column connected to a subsequent stage of the first distillation column;
The ethanol synthesizer according to claim 6, further comprising a regeneration return path for returning a part of the bottomed liquid of the second distillation column to the absorption part as the absorption liquid. Furthermore, it comprises a post-absorption liquid tank that stores the absorption liquid after absorption,
The ethanol synthesis apparatus according to claim 6 or 7, wherein the regeneration outward path extends from the post-absorption liquid tank to the purification unit.   The ethanol synthesizer according to any one of claims 5 to 8, wherein the absorbing liquid is a mixture of ethanol and water.

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