KR20120094628A - A method for selective removal of sulfur compounds from syngas based on biomass using room temperature ionic liquids - Google Patents

Abstract

PURPOSE: A method for selectively eliminating sulfur components from biomass-based syngas using room temperature-based ionic liquid is provided to minimize the elimination of carbon dioxide and methane. CONSTITUTION: A method for selectively eliminating sulfur components from biomass-based syngas using room temperature-based ionic liquid includes the following: sulfide components are absorbed in room temperature-based ionic liquid by contacting syngas and the ionic liquid at 20-60 degrees Celsius; the sulfide component-absorbed ionic liquid is degassed at 100-180 degrees Celsius; the sulfide components are separated from the ionic liquid; and the ionic liquid is circulated to the absorbing process. The ionic liquid is salt with which organic cations and fluorine-containing hydrophobic anions are combined.

Description

A Method for Selective Removal of Sulfur Compounds from Syngas Based on Biomass Using Room Temperature Ionic Liquids

The present invention relates to a method for selectively removing sulfur components from syngas generated in the gasification step of biomass using room temperature ionic liquid as an absorption solvent.

As oil resource depletion and climate change have emerged as major obstacles to the realization of a sustainable growth society, the importance of renewable energy is emerging as a means to effectively cope with this, and the prospect of high oil prices will prevail. In addition to crude oil, many interests and researches are being made to manufacture fuels from alternative raw materials such as natural gas, coal, and biomass. In particular, transportation oils such as diesel and aviation oils produced from biomass are regarded as energy sources in which all carbon dioxide generated during the conversion process and the use of synthetic carbon energy sources are consumed in the production of biomass and ultimately do not emit carbon dioxide. In addition, since it can be directly applied to the transportation field has the advantage that the replacement effect of petroleum energy is very high.

In order to prepare a transport oil from biomass, first, a synthesis gas is prepared by the gasification step of biomass, and impurities such as sulfur components are contained in order to prepare hydrocarbons having a distribution of various carbon chains. After the Fischer-Tropsch synthesis, it is separated into an appropriate boiling range suitable for the transport oil. On the other hand, the catalyst applied to the Fischer Drops reaction for producing a hydrocarbon is composed of iron-based and cobalt-based catalysts generally known as a highly active component, since these catalysts are very sensitive to some impurities contained in the raw material, Proper purification is very important. In general, although there are differences depending on the type of biomass, carbon monoxide (CO) and hydrogen (H ₂ ), which are the main components in the gasification step of biomass, generate about 1: 1 (volume ratio), and carbon dioxide (CO ₂ ) and Methane (CH ₄ ) is produced in a volume ratio of 0.8 and 0.15, respectively, based on CO. Moreover, in the Fischerthrops reactor suitable for the fixed bed catalytic reactor to which the present invention is applied, the control of the heat of reaction is very important. In the case where carbon dioxide and methane, which are byproducts of the reaction, are introduced into the Fischerthrops reaction together with the main product, The heat of reaction can be controlled by the dilution effect without doing so.

On the other hand, the synthesis gas, in addition to the various impurities contained in the trace amount produced by the hot gasification reaction derived from biomass. Among these impurities, sulfur compounds such as hydrogen sulfide (H ₂ S) and carbonyl sulfide (COS) drastically lower the activity of the catalytic reaction by poisoning of the active site of the catalyst, and acidic by moisture generated during the Fischer Drops reaction. It can turn into a component and cause corrosion, which greatly affects the reaction, and needs to be removed below 1 ppm for the Fisher Drops reaction.

In this regard, looking at the purification techniques of conventionally known sulfur compounds are as follows.

Korean Patent Application No. 10-2005-0091215 discloses a technique for removing acid gas by spraying an aqueous solution of caustic soda (NaOH) or a catalyst solution to remove acid gas such as hydrogen sulfide contained in a high temperature and high pressure synthesis gas. According to this technology, it is very excellent in removing the components such as hydrogen sulfide contained in the synthesis gas generated from the gasifier, but there is a drawback of strong corrosion of the device by using an alkaline solution.

In addition, Korean Patent Application No. 10-1987-0001305 discloses a method of removing hydrogen sulfide from a contaminated gas using a cation exchange resin doped with a metal and regenerating a cation exchange resin using an oxidizing microorganism. and, in the case of water purified H ₂ S is HS ^- or S ^-, etc. Since the fugitive substance with an anion is determined to be the more preferable the use of an anion exchange resin than the cation exchange resin, and mainly acidic pH is about 1.5 ~ 8 Regeneration of the resin was carried out, and since H ₂ S is acidic in aqueous solution, it is considered that the removal efficiency of H ₂ S is higher than that of the anion exchange resin having a basic regeneration process.

Korean Patent Application No. 10-1994-0013701 discloses a partial oxidation method for producing a purified hot gas, which produces a synthesis gas composed mainly of H ₂ and CO under high temperature and high pressure, and contains H ₂ S and A technique for removing contaminants such as COS has been proposed, but according to this technique, the concentration of sulfur compound after purification is rather high, and thus it is judged that it is not suitable to use purified syngas as a chemical raw material.

On the other hand, Korean Patent Nos. 1998-0065216, 1999-0034665, 2000-0042374 and 2001-0098060 use a dry fluidized bed desulfurization method and apparatus under high temperature (400 ~ 700 ° C), high pressure (10 ~ 35 atm), or zinc-based desulfurization agent. A method of using is provided, but when oxygen is supplied at a temperature higher than the reaction temperature to regenerate the desulfurization catalyst, SO ₂ is generated and post-treatment is necessary, and additional energy is required because heating is required for catalyst regeneration. There is a problem that needs to be used.

Korean Patent Publication No. 2003-0040068 discloses a technique for purifying CO / H ₂ or N ₂ / H ₂ syngas that removes CO ₂ and possibly other impurities before undergoing a cryogenic process. A gas stream to be adsorbed is passed through a NaLSC-type zeolite to be adsorbed and then regenerated by desorption at elevated temperature (TSA) or reduced pressure (PSA or VSA). This purification method is applied when the gas concentration is extremely low. This is possible.

In addition, the selecol and rectisol processes are known as a representative physical absorption method for removing acidic gases such as hydrogen sulfide and carbon dioxide from the waste gas. It is used as a solvent. The above methods are the most widely used techniques for treating syngas produced by coal or heavy hydrocarbon gasification process. In the case of the rectisol process, the acid gas is relatively high pressure (2.76 ~) in the feed gas using methanol cooled to about -40 ° C. 6.89 MPa) is a method of dissolving acid gas from a solvent in which a large amount of acid gas is dissolved by reducing the pressure or heating with steam. However, this physical method operates under low temperature and high pressure by using a low boiling point solvent, and absorbs and removes most of carbon dioxide as well as acidic gas. Therefore, when the exotherm caused by Fisherthrops reaction occurs rapidly, the reaction heat is controlled. There is a problem in that special process control and device design have to be introduced.

Japanese Patent 1995-258665 is a representative method using a solvent capable of chemical reaction, a method of removing carbon dioxide and hydrogen sulfide by contacting an aqueous solution of an amine selected from lower alkylamino and lower alkanol with various gases including carbon dioxide and hydrogen sulfide. Known. The aqueous solution of the amine compound absorbs various gases through a compound bond in a gas containing carbon dioxide, so the absorption rate is high and the absorption is large.However, the amine compound is separated and recovered from the amine compound chemically bonded to the gas and regenerates the absorbent. In order to do this, a high temperature of thermal energy is required, and a part of the absorbent is thermally decomposed during this regeneration process, so that the function is lost, and the corrosion resistance of the absorbent is increased at a high temperature. In addition, there is a problem in that new amine compounds must be continuously replenished to compensate for the functions lost during the regeneration process.

In the Fischerthrops reaction using a fixed bed catalytic reactor for producing a hydrocarbon for transport from a synthesis gas obtained in the gasification step of biomass, the present inventors use fischerthrops of carbon dioxide and methane which are side reaction components in the synthesis gas for controlling the heat of reaction. By introducing together with the reaction, it is possible to easily control the heat of reaction, while selectively removing only the sulfur component which affects the Fischer Trops reaction in the pre-refining syngas, and the carbon dioxide and methane are the It is intended to provide a purification method.

According to the method of the present invention, when using a low boiling point solvent, which is a problem of the known physical method, the external exposure of the volatile organic solvent is inevitable, and since exothermic carbon dioxide as well as acid gas is mostly absorbed and removed, the exothermic due to the Fischer Drops reaction is eliminated. In case of rapid occurrence, it is possible to solve the problems of the existing process, which is very difficult to control the reaction heat. In addition, high temperature thermal energy is required to regenerate the absorbent, which is a problem in the use of the amine compound, which is a method of separating acid gases by chemical bonding, and during this regeneration process, some of the absorbent is thermally decomposed to lose its function. The corrosiveness of the absorbent is increased and it is possible to solve the problems of the existing prior art, which must continuously replenish the new amine compound to compensate for the loss of function in the regeneration process.

In order to achieve the above object, the present inventors pay attention to the fact that the ionic liquid shows a very high dissolution property at room temperature with respect to the sulfur component, but the solubility is very low with respect to the other syngas components obtained from the biomass, the sulfur component of more than 100ppm Using the ionic liquid which can selectively absorb only sulfur components at room temperature from the biomass-derived synthesis gas having a concentration, the method of the present invention has been completed.

Therefore, the present invention selectively lowers only the sulfur component from the syngas obtained in the gasification step from biomass to 1 ppm or less using a room temperature ionic liquid, and introduces hydrogen and carbon monoxide as the main components when introduced into the Fischer Drops reaction for producing hydrocarbons. The present invention relates to a method for selectively removing sulfur components from syngas derived from biomass, in which carbon dioxide and methane components are introduced together to control the exothermic control of the Fischer Drops reaction, and the present invention relates to a fischer using a fixed bed catalytic reactor. The synthesis gas containing the sulfur compound component obtained from the biomass, which is introduced into the Robs reaction, is contacted with a room temperature ionic liquid containing a hydrophobic anion containing an organic cation and fluorine.

Specifically, the method of the present invention comprises the following steps:

(1) absorbing the sulfur compound component into the room temperature ionic liquid by countercurrently contacting the biomass-derived synthesis gas with a room temperature ionic liquid at a temperature of 20 to 60 ° C;

(2) separating the sulfur compound component from the room temperature ionic liquid by degassing the room temperature ionic liquid in which the sulfur compound component is absorbed at a temperature of 100 to 180 ° C; And

(3) circulating the resultant room temperature ionic liquid to the absorption process of step (1).

The biomass-derived synthesis gas used in the step (1) of the present invention is a synthesis gas obtained through a gasification and a tar cracker step from the biomass, and the components differ slightly depending on the type of biomass. Although the main components CO and H ₂ are usually The amount of 1: 1 (volume ratio) is generated, and in addition, CO ₂ and CH ₄ generate volume ratios of 0.8 and 0.15, respectively, based on CO.

In the present invention, sulfur compounds to be selectively removed from the biomass-derived syngas are carbonyl sulfides, such as hydrogen sulfide and CS ₂ , and are generally included in a concentration of 100 to 200 ppm in the biogas-derived syngas. . The syngas obtained in the gasification step of the biomass has to remove sulfur components below 1 ppm in order to control the heat of reaction before being introduced into the Fischer Drops reaction step.

The ionic liquid used in the present invention is a salt-type substance in which an organic cation and an organic or inorganic anion are combined. The ionic liquid has a very low vapor pressure, has no volatility, has a high polarity, and exists as a liquid even at a relatively low temperature such as room temperature. Refers to. Ionic liquids generally have high ionic conductivity, excellent thermal stability, low toxicity, and almost no volatility and are easy to recover since they are reusable. In particular, the polarity can be easily controlled by changing the structure of the cationic and anionic groups used, and solubility in various organic and inorganic substances can be changed, thereby replacing the conventionally toxic organic solvents. It is emerging as an environmentally friendly solvent candidate. The chemical and physical properties of the ionic liquid are determined by the type and structure of the cation and anion constituting the ionic liquid, and the physical properties of the ionic liquid can be controlled by the combination of the cation and the anion. In particular, the ionic liquid present as a liquid at room temperature is called room temperature ionic liquid (RTIL). Such ionic liquids and room temperature ionic liquids have never been applied in the field of purification of conventional biomass-derived syngas, and the inventors found that only the sulfur component can be effectively and selectively removed when applied to biomass-derived syngas. It became.

In order to apply such an ionic liquid to selectively remove only sulfur compound components from the biomass-derived syngas as intended in the present invention, the main component of the synthesis gas is hydrogen, carbon monoxide, and side reactions, and controls the exotherm in the Fischer Drops reaction. It should be characterized by the selective removal of only sulfur components while minimizing the removal of carbon dioxide and methane.

That is, the ionic liquid is in the form of [cation] [anion], and the selective solubility of the sulfur compound contained in the synthesis gas should be very large. In order to satisfy the selective solubility condition for such sulfur compounds, the [cation] that can be used in the present invention is a C ₁ ~ C ₈ hydroxyalkyl group, C ₁ ~ C ₈ alkoxy group and C ₁ ~ C ₈ alkyl group Organic cations containing one or two or more substituents selected from the group consisting of ammonium, imidazolium, pyridium, pyridinium, pyrrolinium A pyrrolinium-based, phosphonium-based, morphorinium-based or tetramethylguanidinum-based cation may be used, and preferably an ammonium-based, imidazolium-based, or tetramethyl-based cation. It is preferable to use guanidinium-based cations. At this time, if the carbon number of the substituent exceeds 8 may have a high melting point at room temperature irrespective of the anion, it is preferable to have a carbon number within the above range, preferably using a room temperature ionic liquid which is liquid at room temperature .

[Anion] of the ionic liquid used in the present invention may be a form containing mainly fluorine groups in order to have temperature stability and stability to moisture, and the anion corresponding thereto is tetrafluoroborate (BF). ₄ ), hexafluorophosphate (PF ₆ ), bis (trifluoromethylsulfonyl) imide {bis (trifluoromethyl) sulfonylimide, Tf ₂ N}, trifluoromethanesulfonate (OTf) or tris (tri Fluoromethylsulfonyl) methanide (tris (trifluoromethylsulfonyl) methanide, CTf ₃ ) may be used.

The temperature in the absorption step of step (1) is applicable to the 20 ~ 60 ℃ range, preferably room temperature (20 ~ 25 ℃) is more appropriate because no separate heating and cooling is required. If the temperature range exceeds 60 ° C during the absorption step, it is difficult to remove sulfur compounds by less than 1ppm due to low absorption of gas at the time of absorption; do.

In addition, the operating temperature of the degassing step of step (2) is 100 ~ 180 ℃ range is applicable, preferably 120 ~ 150 ℃ can be used as appropriate. In the degassing step, it is difficult to remove the sulfur compound below a desired concentration (1 ppm) when it is out of the temperature range.

The present invention can not avoid the external exposure of the volatile organic solvent due to the use of a low boiling point solvent, which is a problem of the known method, and absorbs and removes carbon dioxide as well as acidic gas in the Fischer Drops reaction using a fixed bed catalytic reactor. In order to solve the problem that the control of exotherm is very difficult, it is possible to minimize the removal of carbon dioxide and methane and to selectively remove only sulfur compounds by using room temperature ionic liquid as an absorption solvent at room temperature. It is possible to easily control the heat generation during the used Fisthrops reaction to increase the stability of the process and to reduce the device cost.

Figure 1 schematically shows a method for the continuous separation of sulfur compounds using the ionic liquid according to the present invention.

Hereinafter, the present invention will be described in detail based on the following representative examples, which are only intended to illustrate embodiments of the present invention, and the present invention is not limited by the following examples.

Example  1-7 and Comparative example  1-4

The composition of the synthesis gas, which has undergone the biomass gasification step, is composed of CO, H _{2 ,} CO ₂ , and CH ₄ with 1.0: 1.0: 0.8: 0.15 (volume ratio), and contains a small amount of sulfur compounds (hydrogen sulfide and carbo). Neal sulfide form (hereinafter, 'sulfur gas component') contained about 200 ppm.

This synthesis gas is contacted in countercurrent with the ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([emim] [BF ₄ ]) to countercurrent. The component was absorbed off. At this time, the flow rate of the syngas was 100 cc / min, and the flow rate of the ionic liquid was 1 liter / min. Absorption is achieved by contact of the syngas with the ionic liquid at room temperature (20 ° C.), and only sulfur gas components are continuously absorbed. Then, the sulfur gas component was removed by degassing at a temperature of 150 ° C. from the ionic liquid containing the resulting sulfur gas component. The ionic liquid from which the sulfur gas component was removed was cooled again and recycled to an absorption process operated at room temperature.

The sulfur gas component discharged from the degassing process was analyzed by a sulfur analyzer (Gas chromatography (Younglin Acme 6000 equipped with a PFPD (Pulse Flame Photometry, OI Analytical 5380)), and the results are shown in Table 1.

The results of Examples 2 to 7 and Comparative Examples 1 to 4 performed in the same manner as in Example 1 by changing the type of the ionic liquid were also shown in Table 1 below.

division Ionic liquid Sulfur concentration after purification (ppm) Example 1 [emim] [BF ₄ ] 0.31 Example 2 [emmim] [BF ₄ ] 0.44 Example 3 [bmim] [PF ₆ ] 0.62 Example 4 [bmmim] [BF ₄ ] 0.66 Example 5 [p ₅ mim] [Tf ₂ N] 0.14 Example 6 [hmim] [BF ₄ ] 0.22 Example 7 [emim] [Tf ₂ N] 0.11 Comparative Example 1 [VBBI] [BF ₄ ] 2.31 Comparative Example 2 [omim] [BF ₄ ] 4.21 Comparative Example 3 [mabi] [PF ₆ ] 5.14 Comparative Example 4 [ap ₃ bim] [BF ₄ ] 3.51

[emim] [BF ₄ ]: 1-ethyl-3-methyl-imidazolium tetrafluoroborate

[emmim] [BF ₄ ]: 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate

[bmim] [PF ₆ ]: 1-butyl-3-methylimidazolium hexafluorophosphate

[bmmim] [BF ₄ ]: 1-butyl-2,3-dimethylimidazolium tetrafluoroborate

[p ₅ mim] [Tf ₂ N]: 1-pentyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide

[hmim] [BF ₄ ]: 1-hexyl-3-methylimidazolium tetrafluoroborate

[emim] [Tf ₂ N]: 1-ethyl-3-methyl-imidazolium bis (trifluoromethylsulfonyl) imide

[VBBI] [BF ₄ ]: 1- (p-vinylbenzyl) -3-butylimidazolium tetrafluoroborate

[omin] [BF ₄ ]: 1-octyl-3-methylimidazolium tetrafluoroborate

[mabi] [PF ₆ ]: 1- [2- (methacryloyloxy) ethyl] -3-butylimidazolium hexafluorophosphate

[ap ₃ bim] [BF ₄ ]: 3- (3-aminopropyl) -1-butylimidazolium tetrafluoroborate

Referring to Table 1 above, in the case of using the ionic liquid according to the present invention, the concentration of the sulfur component after purification is 1 ppm or less, whereas in the comparative examples using ionic liquids that do not correspond to the ionic liquid of the present invention after purification The concentration of sulfur component was as high as 1 ppm or more.

Example  8-11 and Comparative example  5 ~ 8

In the same manner as in Example 1, but was carried out by changing the temperature at the time of absorption and degassing, the results are shown in Table 2 below.

division Absorption Temperature (℃) Degassing temperature (℃) Sulfur concentration after purification (ppm) Example 8 30 150 0.41 Example 9 60 150 0.74 Example 10 20 100 0.52 Example 11 20 180 0.86 Comparative Example 5 -10 250 1.81 Comparative Example 6 -20 200 1.91 Comparative Example 7 80 150 7.14 Comparative Example 8 100 150 9.51

Referring to Table 2, in the case of the embodiments according to the temperature range at the time of absorption and degassing according to the present invention achieved a sulfur concentration of less than 1ppm after purification, when the absorption and degassing is carried out at a temperature outside the temperature range of the present invention Sulfur concentration was significantly higher after purification.

Claims (6)

A method for selectively removing sulfur compounds from syngas comprising sulfur compound components obtained from biomass, comprising the following steps:
(1) absorbing the sulfur compound component into the room temperature ionic liquid by countercurrent contacting the synthesis gas with a room temperature ionic liquid at a temperature of 20 ~ 60 ℃;
(2) separating the sulfur compound component from the room temperature ionic liquid by degassing the room temperature ionic liquid in which the sulfur compound component is absorbed at a temperature of 100 to 180 ° C; And
(3) circulating the resultant room temperature ionic liquid to the absorption process of step (1).
The method of claim 1, wherein the ionic liquid is a salt in which an organic cation and a fluorine-containing hydrophobic anion are combined.
The cation according to claim 2, wherein the cation is an ammonium cation, an imidazolium cation, a pyridium cation, a pyridinium cation, a pyrrolinium cation, a phosphonium cation, a morpholinium cation or a tetramethylguanidium. A method characterized in that the cation.
4. The method of claim 3 wherein the cation is an organic cation comprising a substituent of the C ₁ ~ C ₈ hydroxyalkyl group, C ₁ ~ C ₈ alkoxy group, and C ₁ ~ ₁ kind or two selected from the group of C ₈ species of Method characterized in that.
3. The hydrophobic anion according to claim 2, wherein the hydrophobic anion is tetrafluoroborate, hexafluorophosphate, bis (trifluoromethyl) sulfonylimide, trifluoromethanesulfonate or tris (trifluoromethylsulfonyl) methanide. How to.
The method according to any one of claims 1 to 5, wherein the method lowers the concentration of the sulfur compound component of the syngas to 1 ppm or less.

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