Method for producing porous carbon from lignocellulosic biomass

Abstract

This invention provides an industrial method for producing porous carbon from lignocellulosic biomass. [Solution] A method for producing porous carbon, comprising: a saccharification step of saccharifying or saccharifying and fermenting lignocellulosic biomass; an impregnation step of impregnating the residue obtained from the saccharification step with an alkali metal carbonate aqueous solution; a thermal decomposition step of heating the residue impregnated with the alkali metal carbonate aqueous solution in an oxygen-free state until the temperature is raised to 600°C to produce a liquid substance and a carbonaceous substance, and removing the produced liquid substance from the carbonaceous substance; and a carbonization step of heating the carbonaceous substance obtained from the thermal decomposition step at a temperature of 700°C to 1200°C to obtain porous carbon.

Description

Technical Field

[0001] The present invention relates to a method for industrially producing porous carbon from lignocellulosic biomass.

Background Art

[0002] From the perspective of effective utilization of resources, utilization of non-edible plant biomass as a raw material for chemical industrial products is expected. In particular, processes for obtaining a liquid product from a mixture containing ethanol and the like by saccharifying or saccharifying and fermenting cellulose and hemicellulose contained in lignocellulosic biomass have attracted attention. Furthermore, studies have been conducted to heat the residue after obtaining the liquid product, and produce raw materials for resins such as phenolic resins and epoxy resins, which are used for electronic substrates, semiconductor components, automotive parts and the like, from the lignin contained therein, as well as to produce carbon materials that can be used as active coke for desulfurization, activated carbon and the like.

[0003] Ethanol production using lignocellulosic biomass as a raw material usually consists of a pretreatment step of thermochemically pretreating the biomass raw material, a saccharification step of enzymatically treating the pretreated biomass to produce a saccharified solution, a fermentation step of adding a microbial culture solution to the saccharified solution obtained in the saccharification step to perform ethanol fermentation, and a purification step of separating ethanol from the fermentation broth obtained in the fermentation step by distillation or the like. In this saccharification and fermentation step, lignin remains as a solid, which poses a problem of generating a large amount of residue. This residue is generally treated in boilers of affiliated factories, by methane fermentation or the like, and is currently not effectively utilized as a carbon resource.

[0004] Patent Document 1 discloses that a residue obtained by saccharifying a woody material, or a residue obtained by saccharifying and fermenting a woody material, is heated under pressure in the presence of phenols and a hydrogen-donating solvent to remove low-boiling components, thereby obtaining a woody pitch having a softening point of 170 to 230°C.

[0005] Patent Document 2 discloses a lignin degradation product solution or a method for producing lignin degradation products, which includes a step of further hydrothermally treating the enzymatic saccharification residue generated when biomass is enzymatically saccharified by autoclaving at a processing temperature of 170°C to 210°C, obtaining a solid from solid-liquid separation of the treated material, and a step of dissolving the solid obtained from solid-liquid separation in an organic solvent.

[0006] Patent Document 3 discloses a method for producing activated carbon by preheating lignin or its derivatives at a temperature of 150°C or higher, adding an alkali such as sodium hydroxide, and then heating at a temperature of 300°C to 900°C.

[0007] Patent Document 4 discloses an adsorbent for lower alcohols, which includes activated carbon produced by a method for producing activated carbon that includes an impregnation step of impregnating lignins with alkali metal carbonates and a carbonization step of carbonizing the lignins impregnated with alkali metal carbonates by heating them in an inert gas at a temperature of 700°C to 1200°C. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 5747488 (Claims, Examples, etc.) [Patent Document 2] Japanese Patent Publication No. 6349518 (Claims, Examples, etc.) [Patent Document 3] Japanese Patent Publication No. 6-183715 (Claims, Examples, etc.) [Patent Document 4] Japanese Patent Publication No. 5495208 (Claims, Examples, etc.) [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] By saccharifying or saccharifying and fermenting cellulose and hemicellulose from lignocellulosic biomass, and then heating the solid residue obtained after removing the liquid from the resulting mixture at high temperatures to decompose the contained lignin, carbonized products and gases can be manufactured industrially. However, when heating the solid residue, the thermal decomposition of lignin produces a significant amount of viscous tar as a by-product, in addition to water-soluble substances such as water and lignin decomposition products. Because this by-product tar is viscous, it causes problems with the equipment, such as fouling inside the heating device, blockage of pipes, and clogged filters.

[0010] The object of this invention is to provide an industrial method for efficiently producing porous carbon from lignocellulosic biomass. Specifically, the object of the present invention is to suppress the formation of viscous tar associated with the thermal decomposition of lignin when producing porous carbon using residue discharged from the saccharification and fermentation process of lignocellulosic biomass. [Means for solving the problem]

[0011] The present invention relates to a method for producing porous carbon, comprising: a saccharification step of saccharifying or saccharifying and fermenting lignocellulosic biomass; an impregnation step of impregnating the residue obtained from the saccharification step with an alkali metal carbonate aqueous solution; a thermal decomposition step of heating the residue impregnated with the alkali metal carbonate aqueous solution in an oxygen-free state and raising the temperature to 600°C to produce a liquid substance and a carbonaceous substance, and removing the produced liquid substance from the carbonaceous substance; and a carbonization step of heating the carbonaceous substance obtained from the thermal decomposition step at a temperature of 700°C to 1200°C to obtain porous carbon.

[0012] Another aspect of the present invention is a method for producing porous carbon, further comprising: a washing step of washing the carbonaceous material obtained in the thermal decomposition step with water to obtain washing water containing alkali metal carbonate; and a recycling step of using part or all of the alkali metal carbonate aqueous solution used in the impregnation step with the washing water obtained in the washing step.

[0013] In this invention, the industrial production of carbonaceous materials can be carried out in two stages, reducing the operational burden: a thermal decomposition step in which lignin is thermally decomposed at a relatively low temperature to remove the liquid substance produced, and a carbonization step in which the carbonaceous material obtained therefrom is heated at a high temperature to obtain porous carbon. Such a technical concept does not exist in the prior art described above. [Effects of the Invention]

[0014] In this invention, the amount of viscous tar produced during the thermal decomposition process is small, and the liquid substance containing it is fluid, making it easy to remove. According to the present invention, when industrially producing porous carbon from residue discharged from a saccharification process or a saccharification and fermentation process of lignocellulosic biomass, it is possible to prevent contamination, blockage, or filter clogging inside the manufacturing equipment used.

[0015] <Lignocellulose biomass> Lignocellulosic biomass refers to natural resources containing lignocellulose, which is formed by the bonding of lignin and cellulose. In this invention, the lignocellulosic biomass used as a raw material can be at least one selected from the group consisting of herbaceous plants (also called herbaceous biomass), woody plants (also called woody biomass), their processed products, and their waste products.

[0016] Herbaceous plants include bamboo, palm oil; grasses such as rice, wheat, sugarcane, reeds, Japanese pampas grass, corn, sorghum, switchgrass, eryanthus, and napia grass; jatropha and cashews. Bagasse, the residue left after sugarcane juicing, is readily available and a useful source of lignocellulose. Crop residues such as rice straw and wheat straw, as well as food waste containing fiber-rich vegetables, can also be used. In this embodiment, herbaceous plants (herbaceous biomass) are preferred as the lignocellulosic biomass used as raw material, and grasses are more preferred.

[0017] In addition, barks, branches and stems, fruit clusters, fruit shells and the like of woody plants can also be used, and processed materials such as plywood, fiberboard and glulam made from woody plants can also be used. Members dismantled after being used in buildings can also be used. Further, processed products of lignocellulosic biomass such as paper and waste paper can also be mixed and used.

[0018] Examples of the woody plant include Cryptomeria japonica, Chamaecyparis obtusa, Larix kaempferi, pine, Douglas fir, western red cedar, western hemlock, poplar, birch, willow, eucalyptus, sawtooth oak, Quercus serrata, oak, Castanopsis, beech, acacia, bamboo, Sasa, oil palm, sago palm and the like. Thinned wood can also be used.

[0019] The lignocellulosic biomass may be used in a pulverized form, and is preferably in the shape of blocks, chips, powder or the like. In addition, a residue containing lignocellulose generated in the process of producing bioethanol, biobutanol, biochemicals or the like from cellulose and hemicellulose in the lignocellulosic biomass may also be used.

[0020] The lignocellulosic biomass is pretreated by, for example, a steaming method using steam, a method using an ionic liquid, a pulverization method using a mill, or the like. Among them, pretreatment by the steaming method is preferred. Further, in the pretreatment step, an acid or an alkali may be appropriately mixed as necessary. Examples of the acid include sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid, and these may be used alone or in combination.

[0021] <Saccharification Step> The lignocellulosic biomass is preferably subjected to an enzymatic saccharification step after pretreatment. In the saccharification step, the lignocellulosic biomass is subjected to saccharification treatment using an enzyme to produce a saccharified solution. Saccharification and fermentation may be performed in parallel. In the present invention, the case where the saccharification treatment is performed alone and the case where the saccharification treatment and the fermentation treatment are performed in parallel are collectively referred to as the saccharification step.

[0022] In the saccharification process, the enzymes used are preferably one or more selected from the group consisting of cellulase and hemicellulase, from the viewpoint of improving saccharification efficiency. More preferably, the enzymes are one or more selected from the group consisting of cellobiohydrolase, β-glucosidase, endoglucanase, and hemicellulase, and even more preferably, one or more selected from the group consisting of cellobiohydrolase and endoglucanase.

[0023] Here, cellulase refers to an enzyme that hydrolyzes the glycosidic bonds of β-1,4-glucan in cellulose, and is a general term for enzymes such as endoglucanase, exoglucanase, cellobiohydrolase, and β-glucosidase. The cellulase used in this invention includes commercially available cellulase preparations and those derived from animals, plants, and microorganisms.

[0024] In the saccharification process, the processing conditions when lignocellulosic biomass is saccharified with enzymes can be appropriately selected depending on the lignin content in the lignocellulosic raw material, the degree of crystallinity of cellulose type I, and the type of enzyme used. For example, saccharification can be performed by adding the enzyme to a buffer solution in which lignocellulosic biomass is suspended in water at a concentration of 0.5 to 20%, in an amount of 0.001 to 15% relative to the lignocellulosic biomass raw material. The concentration and amount ratio of lignocellulosic biomass are both based on dry weight.

[0025] The pH in the saccharification process can be adjusted by appropriately selecting a buffer solution depending on the type of enzyme used, and is preferably pH 2 to 10, more preferably pH 3 to 7, and even more preferably pH 4 to 6. The temperature of the processing solution in the saccharification process is preferably 45°C to 70°C, more preferably 45°C to 55°C, and particularly preferably 50°C. The processing time in the saccharification process is preferably 12 hours to 120 hours, more preferably 24 hours to 96 hours, and even more preferably 24 hours to 72 hours.

[0026] (Fermentation process) Lignocellulosic biomass can be subjected to fermentation treatment after saccharification treatment. Saccharification and fermentation may be carried out in parallel. In this invention, the process of performing only saccharification treatment and the process of performing both saccharification and fermentation treatments together are collectively referred to as the saccharification process.

[0027] In the fermentation process, yeast is preferably used. Examples of yeast include Saccharomyces yeasts such as Saccharomyces cerevisiae, Pichia yeasts such as Pichia stipitis, Candida yeasts such as Candida shihatae, Pachysolen yeasts such as Pachysolen tannophilus, and Issatchenkia yeasts such as Issatchenkia orientalis. Preferably, yeasts belonging to the genera Saccharomyces and Issatchenkia are used, and more preferably Saccharomyces cerevisiae and Issatchenkia orientalis.

[0028] The pH of the fermentation liquid in the fermentation tank is preferably in the range of 3 to 10, and more preferably maintained in the range of 4 to 8. The temperature of the fermentation liquid in the fermentation tank should be within the optimal temperature range for the yeast used in the fermentation process, specifically preferably in the range of 20 to 40°C, and more preferably in the range of 30 to 40°C.

[0029] (saccharification residue) A solid residue is obtained by solid-liquid separation of a mixture obtained after saccharification or saccharification and fermentation of a lignocellulose raw material. In this disclosure, the solid residue separated from the mixture after saccharification or saccharification and fermentation is referred to as saccharification residue, or simply residue.

[0030] Solid-liquid separation operations of saccharified mixtures are performed using solid-liquid separation methods such as filtration and centrifugation. The saccharification residue is preferably washed with water to remove water-soluble polysaccharides, and then subjected to the thermal decomposition process as a solid or slurry. Prior to the thermal decomposition process, the saccharification residue may be used in a wet or dried state, and then mechanically crushed into a powder.

[0031] <Impregnation process> In this invention, an impregnation step is performed in which an alkali metal carbonate aqueous solution is impregnated into the residue after saccharification treatment or saccharification and fermentation treatment.

[0032] Examples of alkali metal carbonates used in aqueous alkali metal carbonate solutions include lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium bicarbonate, and potassium bicarbonate. Among these, potassium carbonate is preferred because it is readily available. Mixtures containing alkali metal carbonates, such as wood ash, can also be used.

[0033] The alkali metal carbonate used in the alkali metal carbonate aqueous solution can be dissolved or dispersed in water and added to the residue. The alkali metal carbonate aqueous solution may contain components other than alkali metal carbonate in amounts that do not impede the present invention. The alkali metal carbonate is added in an amount of 0.05 to 1 weight, preferably 0.1 to 0.7 weight, and more preferably 0.2 to 0.5 weight, relative to the dry weight of the residue. The residue impregnated with the alkali metal carbonate aqueous solution is subjected to heat treatment. Prior to the heat treatment, some of the water may be removed from the residue impregnated with the alkali metal carbonate aqueous solution.

[0034] <Pyrolysis process> The thermal decomposition process involves heating a residue impregnated with an alkali metal carbonate aqueous solution in an oxygen-free environment to 600°C to generate a liquid substance and a carbonaceous substance, and then removing the generated liquid substance from the carbonaceous substance. In the thermal decomposition process, the residue decomposes, the generated gases and liquid substances are released out of the system, and the carbonaceous substance remains as a solid. The decomposition reaction of lignin contained in the residue and the repolymerization reaction of the decomposition products occur simultaneously upon heating, but in this invention, a mixture of a fluid, water-soluble liquid and tar components is obtained.

[0035] In the thermal decomposition process of the present invention, the action of alkali metal carbonate impregnated into the residue accelerates the cleavage of the β-ether bond of lignin, thereby promoting the decomposition of lignin. As a result, in the thermal decomposition process of the present invention, the lignin decomposition reaction can be carried out at a relatively low temperature, resulting in suppressed tar formation, and the resulting liquid substance is fluid. Therefore, it is easy to remove the resulting liquid substance from the carbonaceous material. In the present invention, by removing this liquid substance from the carbonaceous material, the formation of viscous tar components can be suppressed. In the thermal decomposition process of the present invention, the amount of viscous tar produced is small, and the liquid substance containing it is fluid, making it easy to remove.

[0036] The pyrolysis process can be carried out by raising the temperature of the residue impregnated with an alkali metal carbonate aqueous solution from room temperature to 600°C. If the time required to raise the temperature from room temperature to 600°C is shortened to 10 minutes, gases and liquid substances are more easily generated, and the amount of tar produced also increases. If the time required to raise the temperature from room temperature to 600°C is extended to 6 hours, gases and liquid substances are reduced, and the amount of tar decreases, but it takes longer. Considering the equipment capacity and the time required, the time required to raise the temperature from room temperature to 600°C is preferably 20 minutes to 4 hours, and more preferably 40 minutes to 2 hours. It is also permissible to maintain a constant temperature for a while during the heating process, or to speed up or slow down the heating rate during the process. Here, room temperature refers to a temperature between 10°C and 50°C.

[0037] In the pyrolysis process of the present invention, the addition of alkali metal carbonates facilitates the pyrolysis of lignin contained in the residue at relatively low temperatures. In particular, the amount of viscous tar produced in the pyrolysis process is small, and the liquid substance containing it is fluid. Therefore, it is easy to remove the generated water-soluble substance from the heating container, and contamination of the inside of the apparatus including the heating container, blockage of piping, and clogging of filters can be prevented. By performing the thermal decomposition process of the present invention, in addition to the above advantages, the advantage of increasing the yield of porous carbon in the carbonization process can be obtained.

[0038] The pyrolysis process is usually carried out at atmospheric pressure in a heatable container, but it can also be carried out under pressure in a pressure-resistant heating container equipped with a heater and mixer. It can also be carried out in a burner-type electric furnace under an inert gas atmosphere. The pyrolysis process can be carried out in either a batch or flow-through manner. In the case of a flow-through manner, a rotary kiln with an incline can be used.

[0039] In the pyrolysis process, gases and volatile organic compounds are produced as by-products. The volatile organic compounds produced as by-products can be recovered by passing an inert gas through a heating container and guiding the resulting gas to a cooled trap. Alternatively, they can be recovered together with the gas released from the trap or used as fuel for the heating burner.

[0040] After heat treatment, the material is cooled, and the liquid substance containing the generated tar is separated from the porous carbon and removed from the heating container. In addition to standing, solid-liquid separation methods such as filtration and centrifugation can be used to separate the liquid substance from the porous carbon. Alternatively, the heating container may be tilted, and the liquid substance generated in the pyrolysis process may be discharged from an outlet at the bottom of the heating container. In the pyrolysis process of the present invention, the generated tar is fluid. Therefore, in the pyrolysis process, it is preferable to remove the liquid substance containing the tar generated by the heat treatment from an outlet at the bottom of the heating container. In this case, it is preferable to use a tilted tubular furnace as the heating container. The pyrolysis process yields a carbonaceous substance, which is a solid material generated by the modification of the residue due to the heat treatment.

[0041] The liquid substance obtained in the thermal decomposition process of the present invention is a fluid liquid containing a water-soluble substance and tar. The water-soluble substance mainly contains low molecular weight lignin, including lignin decomposition products and lignin oligomers. From the low molecular weight lignin, phenol compounds containing guaiacol derivatives can be obtained. The phenol compounds can be used as raw materials for chemical industrial products such as resin raw materials, composite materials, and surfactants.

[0042] <Carbonization Process> The carbonization process is carried out by heating the carbonaceous material, which is a modified residue obtained by removing the liquid substance generated in the thermal decomposition process, at a high temperature in an oxygen-free environment. The heating temperature in the carbonization process is in the range of 700°C to 1200°C, preferably 750°C to 1100°C, and more preferably 800°C to 1000°C. The heating time is 10 minutes to 5 hours, preferably 20 minutes to 2 hours, and more preferably 30 minutes to 90 minutes. The carbonization process can also be carried out in an inert gas atmosphere using the electric furnace used in the pyrolysis process. The processing method may be batch or flow-through. In the case of flow-through, a rotary kiln with an incline can be used. The pressure is carried out at atmospheric pressure, but it may also be carried out under pressurized conditions in a pressure-resistant heating vessel equipped with a heating device and a mixer.

[0043] The porous carbon obtained through the carbonization process retains alkali metal oxides, which are formed when carbon dioxide is removed from alkali metal carbonates. Therefore, it is advisable to wash the material with water to remove the alkali metal oxides. The porous carbon obtained through the carbonization process can be used as activated coke for desulfurization, activated coke for denitrification, and the like.

[0044] <Water washing process> The carbonaceous material obtained in the pyrolysis step contains alkali metal carbonates. In the present invention, in addition to the above step, it is also preferable to perform a washing step in which the porous carbon obtained in the thermal carbonization step is washed with water to obtain wash water containing alkali metal carbonates, and a recycling step in which part or all of the wash water obtained in the washing step is used in the pyrolysis step.

[0045] While it is possible to completely remove alkali metal carbonates from carbonaceous materials after the washing process, a small amount of alkali metal carbonates may remain in porous carbon depending on the degree of washing and the particle size of the carbonaceous material. It is also possible to heat-treat such porous carbon to produce activated carbon material. The resulting carbon material can be used as a solid fuel.

[0046] The process of washing the carbonaceous material obtained in the thermal decomposition process with water is called the water washing process. The amount of water used is 1 to 10 times the apparent volume of the carbonaceous material, preferably 2 to 5 times. The water used in the water washing process may be purified water, or it may be water containing components other than alkali metal carbonate in amounts that do not impede the present invention. The rinse water obtained by washing the carbonaceous material obtained in the thermal decomposition process contains alkali metal carbonates, and therefore can be reused as an aqueous solution of alkali metal carbonates to be added in the thermal decomposition process.

[0047] <Recycling Process> In this invention, the step of recovering the rinse water and using all or part of it as an alkali metal carbonate aqueous solution for use in the impregnation step is called the recycling step. All or part of the alkali metal carbonate aqueous solution used in the impregnation step can be obtained from the alkali metal carbonate aqueous solution recycled in the recycling step. Reusing the rinse water containing alkali metal carbonate reduces the amount of new alkali metal carbonate added in the thermal decomposition step and reduces the wastewater discharged from the rinse step. For this reason, a method for producing porous carbon that further adds a rinse step and a recycling step to the above-described method for producing porous carbon is a preferred embodiment for industrial implementation of this invention.

[0048] In other words, a preferred embodiment of the present invention is a method for producing porous carbon, comprising: a saccharification step of saccharifying or saccharifying and fermenting lignocellulosic biomass; an impregnation step of impregnating the residue obtained from the saccharification step with an alkali metal carbonate aqueous solution; a thermal decomposition step of heating the residue impregnated with the alkali metal carbonate aqueous solution in an oxygen-free state to raise the temperature to 600°C to produce a liquid substance and a carbonaceous substance, and removing the produced liquid substance from the carbonaceous substance; and a carbonization step of heating the carbonaceous substance obtained from the thermal decomposition step at a temperature of 700°C to 1200°C to obtain porous carbon; and further comprising a washing step of washing the carbonaceous substance obtained from the thermal decomposition step with water to obtain washing water containing alkali metal carbonate; and a recycling step of using part or all of the washing water obtained from the washing step as part of the alkali metal carbonate aqueous solution used in the impregnation step. [Examples]

[0049] Reference example 1 (Saccharification / fermentation residue) Sorghum, a herbaceous biomass, is used as the lignocellulosic biomass. Pretreatment involves grinding and steaming the sorghum, and to achieve a solid content of 5% by mass, an amount of acremonium cellulase is added as an enzyme resulting in a final concentration of 10 FPU / g-dried wood flour, and a final concentration of 1.0 × 10⁻⁶ is added. 7 A phosphate buffer (pH 5.0, 50 mmol / l) containing a yeast culture solution in an amount equivalent to cells / mL was added, and the mixture was maintained at 50°C for 50 hours to perform saccharification and fermentation. After saccharification and fermentation, the processed material was separated using a centrifuge, washed with distilled water, and dried in a hot air dryer to obtain a dried saccharification and fermentation residue.

[0050] Example 1 10.0g of the saccharification and fermentation residue obtained in Reference Example 1 was placed in a shallow quartz crucible. 31g of potassium carbonate solution (premium grade, manufactured by Wako Pure Chemical Industries, Ltd.) dissolved in 30g of pure water was added, and the mixture was kneaded thoroughly to impregnate the residue. After that, the residue impregnated with the potassium carbonate solution was placed back into the crucible and dried in an oven at 105°C, evaporating 21g of water. The heating device consisted of a coil-type heater furnace 45 cm long, a tubular furnace tilted at approximately 9 degrees from the horizontal, a thermocouple installed in the space inside the tubular furnace, and a cylindrical quartz furnace core tube 100 cm long inserted into the tubular furnace, so that the tubular furnace was centered within the furnace core tube. A nitrogen inlet pipe was installed at an opening at the upper end of the furnace core tube, and an outlet pipe was installed at an opening at the lower end of the furnace core tube. A collection trap cooled in an ice bath was connected to the outlet pipe.

[0051] The crucible containing the aforementioned residue was inserted into the core tube and positioned in the center of the tubular furnace of the heating device. Nitrogen was injected at a rate of 0.4 L / min from the nitrogen inlet tube on the upper side of the core tube while the central part of the core tube was heated in the tubular furnace, and the temperature was raised from room temperature to 600°C over approximately 50 minutes. During this time, the injected nitrogen was guided to a collection trap from the exhaust tube on the lower side of the core tube and then released into the atmosphere. After being held at 600°C for 5 minutes, the heating was stopped and the system was cooled. After 2 hours, when the temperature inside the reactor tube fell below 50°C, the introduction of nitrogen was stopped, liquid material was recovered from the collection trap, low-viscosity tar adhering to the lower end of the reactor tube that protruded from the tubular reactor was collected with a spatula, and carbonaceous material was recovered from the crucible in the center of the reactor tube.

[0052] The recovered carbonaceous material was washed with water on filter paper and then dried in an oven at 105°C. The carbonaceous material, after being washed and dried, was placed in the heating apparatus, and the central part of the furnace tube was heated in a tubular furnace while nitrogen was blown in at a rate of 0.4 L per minute. The temperature was then raised from room temperature to 1000°C over approximately 60 minutes, and the temperature was maintained at 1000°C for 1 hour to perform the carbonization process and recover porous carbon. Table 1 shows the amount of tar recovered after the pyrolysis process, the amount of carbonaceous material recovered, and the amount of carbonaceous material after washing and drying.

[0053] Example 2 The procedure was the same as in Example 1, except that 32 g of an aqueous potassium carbonate solution was added, which was prepared by dissolving 2 g of potassium carbonate in 30 g of pure water. Liquid material was collected from the collection trap, low-viscosity tar adhering from the lower end of the reactor tube was collected with a spatula, and carbonaceous material was collected from the crucible in the center of the reactor tube. The small amount of tar adhering to the crucible could be easily wiped off. The carbonization process was carried out in the same manner as in Example 1, and porous carbon was recovered. Table 1 shows the amount of tar and carbonaceous material recovered after the pyrolysis process.

[0054] Example 3 The procedure was the same as in Example 1, except that 32 g of a potassium carbonate aqueous solution was added, which was prepared by dissolving 3 g of potassium carbonate in 29 g of pure water. Liquid material was recovered from the collection trap, low-viscosity tar adhering from the lower end of the reactor core tube was collected with a spatula, and carbonaceous material was recovered from the crucible in the center of the reactor core tube. The small amount of tar adhering to the crucible could be easily wiped off. The carbonization process was carried out in the same manner as in Example 1, and porous carbon was recovered. Table 1 shows the amount of tar and carbonaceous material recovered after the pyrolysis process.

[0055] Comparative Example 1 The same procedure as in Example 1 was followed, except that potassium carbonate was not used and 32g of pure water was added. Liquid material was recovered from the collection trap. Viscous tar adhering to the lower end of the core tube just before the collection trap was collected with a spatula. The small amount of tar adhering to the crucible was viscous and somewhat difficult to wipe off. The carbonaceous material obtained was used to carry out a carbonization process similar to that in Example 1. No tar or liquid material was found in the crucible, the inside of the reactor tube, or the collection trap after the carbonization process. Table 1 shows the amount of tar collected after the pyrolysis process, the amount of carbonaceous material recovered, and the amount of carbonaceous material after washing the recovered carbonaceous material with water on filter paper and drying it in an oven at 105°C. The carbonization process was carried out in the same manner as in Example 1, and porous carbon was recovered. Table 1 shows the amount of tar collected, the amount of carbonaceous material recovered, and the amount after washing and drying.

[0056] As is clear from Table 1, in Examples 1 to 3, where potassium carbonate was used in the thermal decomposition process, the amount of tar adhering to the ends of the reactor tubes was small, whereas in Comparative Example 1, where heating equivalent to the thermal decomposition process was performed without using potassium carbonate, viscous tar adhered to the lower end inside the reactor tubes. In Examples 1-3, where potassium carbonate was used in the thermal decomposition process, the amount of carbonaceous material obtained increased. Although alkali metal carbonates were removed to some extent from the carbonaceous material by washing with water, a certain amount of those incorporated into the carbonaceous material remained.

[0057] [Table 1]

[0058] For the porous carbon finally obtained in each of the above examples and comparative examples, the weight was determined, and the BET specific surface area, pore volume, and nitrogen gas adsorption amount were measured as follows.

[0059] <Pore volume and nitrogen gas adsorption capacity> (Measurement conditions) • Measuring device A four-stage specific surface area and pore distribution analyzer (manufactured by Quantachrome, product name NOVA-TOUCH) was used. • Adsorbed gas and measurement temperature Nitrogen (N2) was used as the adsorption gas, and measurements were performed at liquid nitrogen temperature (77.35K). • Pretreatment (degassing) conditions The samples were degassed under vacuum at 110°C for 6 hours. • Measurement details and relative pressure range Obtain a nitrogen adsorption isotherm and calculate the relative pressure (P / P0) = 5 × 10⁻⁶ -3 Measurements were taken within the range of ~0.99.

[0060] (Analysis method) ·Adsorption isotherm The adsorption isotherm is measurement data obtained by plotting relative pressure (P / P0) on the horizontal axis and the amount of adsorbed gas on the vertical axis. ·Specific surface area (BET method) The specific surface area was calculated using the BET method (Brunauer-Emmett-Teller method). Specifically, isotherm data for relative pressures of 0.05 to 0.10 were used, and the linear region of the BET plot was appropriately selected to determine the specific surface area S. BET They sought it.

[0061] • Pore distribution (BJH method) Pore ​​size distribution was calculated using the BJH method (Barrett-Joyner-Halenda method). Desorption branches were used for the analysis, primarily focusing on mesopores (approximately 2-50 nm). • Total pore volume and average pore diameter (1) Total pore volume (V total The total pore volume was determined using the so-called single-point method, based on the amount of adsorption at the point of maximum P / P0 (0.99 in this example), assuming that the pores were filled with liquid nitrogen. (2) Average pore diameter (D ave ) was calculated using Equation 1 below, based on the geometric assumption that the pores are cylindrical in shape.

number

[0062] Here, D ave V is the average pore diameter. total represents the total pore volume, and S represents the BET specific surface area.

[0063] The measurement results are shown in Table 2. As is clear from Table 2, the porous carbon obtained in Examples 1-3 showed a large BET specific surface area, pore volume, and nitrogen gas adsorption capacity.

[0064] [Table 2]

[0065] The manufacturing method of the present invention made it possible to obtain porous carbon with suitable physical properties without causing contamination or blockage inside the manufacturing equipment used, or without filter clogging. [Industrial applicability]

[0066] The present invention can be used in industrial processes to produce porous carbon from biomass raw materials that can be used as activated coke for desulfurization, activated coke for denitrification, etc.

Claims

1. A method for producing porous carbon, comprising: a saccharification step of saccharifying or saccharifying and fermenting lignocellulosic biomass; an impregnation step of impregnating the residue obtained from the saccharification step with an alkali metal carbonate aqueous solution; a thermal decomposition step of heating the residue impregnated with the alkali metal carbonate aqueous solution in an oxygen-free state until the temperature is raised to 600°C to produce a liquid substance and a carbonaceous substance, and removing the produced liquid substance from the carbonaceous substance; and a carbonization step of heating the carbonaceous substance obtained from the thermal decomposition step at a temperature of 700°C to 1200°C to obtain porous carbon.

2. The method for producing porous carbon according to claim 1, wherein in the thermal decomposition step, the amount of alkali metal carbonate added to the residue is 0.05 to 1 times the weight of the dried residue.

3. A method for producing porous carbon according to claim 1, wherein the alkali metal carbonate is potassium carbonate.

4. A method for producing porous carbon according to claim 1, further comprising: a washing step of washing the carbonaceous material obtained in the thermal decomposition step with water to obtain washing water containing alkali metal carbonate; and a recycling step of using part or all of the alkali metal carbonate aqueous solution used in the impregnation step with the washing step.

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