JPH1112971A - Acetic acid pulping of straws under atmospheric pressure and acetic acid pulping effectively utilizing waste liquors - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pulp obtained by effectively pulping straws under the atmosheric pressure, having strength characteristics equal to those of pulps prepared according to a conventional method and excellent in quality, by adding an aqueous solution of acetic acid containing a catalytic amount of a mineral acid added thereto to cut straws and heating the resultant mixture. SOLUTION: An aqueous solution of acetic acid containing a catalytic amount of a mineral acid such as hydrochloric acid or sulfuric acid added thereto is added to cut straws and the resultant mixture is then heated to carry out the pulping of the straws under atmospheric pressure. An unbleached pulp is preferably bleached with a hypo (a hypochlorite) and oxygen- chlorine dioxide-hydrogen peroxide, etc., to produce a bleached pulp and the straws are pulped with acetic acid under atmospheric pressure. The resultant digested liquor is separated into the pulp and a waste liquor. The mineral acid in the waste liquor is then neutralized with an alkali to distill the aqueous solution of the acetic acid for use in washing of the pulp. The pulp is subsequently washed with hot water and warm water is added to the solid matter in the waste liquor and separated into a water-soluble part and a water-insoluble part. Saccharides are recovered from the water-soluble part and acetic acid lignin is recovered from the water-insoluble part. The acetic acid contained in the hot water wash liquid of the pulp is recovered with an ion exchange membrane, etc., and the acetic acid wash liquid of the pulp is preferably reused as a solvent for the acetic acid pulping method under the atmospheric pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a pulping method for polluting straw, which is a low-quality plant resource, and a biomass for straw, which recovers valuable resources from waste liquid from the pulping method. Concerning the effective use method.

[0002]

2. Description of the Related Art Public missions such as the preservation and maintenance of the global environment require efficient separation and use of effective ingredients from low-quality plant resources. Particularly in Japan, where forest resources are scarce, low-quality It is desired to establish a method for efficiently using plant resources as pulp raw materials. By the way, in Japan, rice is a staple food, and rice straw generated during its production is treated as agricultural waste and is not effectively used. In China, three-quarters of paper is produced from straw. However, since the soda AQ method is currently used for the pulping of the straws, the black liquor generated in the pulping method has a high silica content, a low calorific value (low lignin content) and a high viscosity. Therefore, it is difficult to recover the chemicals from the black liquor, and the processing of the black liquor is an important problem. Therefore, development of a pollution-free pulping method for straws, that is, a pulping method that does not generate polluting substances by effectively utilizing waste liquid generated in the pulping step such as black liquor is desired. Recently, the atmospheric pressure acetic acid pulping method has attracted attention as a pollution-free, energy-saving, and resource-saving pulping method. It is suggested that, in addition to papermaking pulp, sugar and lignin can be recovered in high yield from pulp waste liquor by pulping the woody part.)

[0003]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a pulping method free of the pollution of straws and a valuable substance that can be efficiently recovered from waste liquids and the like generated in the pulping method. It is an object of the present invention to establish a technique of a pulping method capable of highly effectively utilizing biomass.

[0004]

The gist of the invention of claim 1 of the present application is that straws to be pulped by adding an aqueous acetic acid solution obtained by adding a catalytic amount of a mineral acid to the laid straws are heated. The gist of the invention of claim 2 is a method of producing pulp by bleaching unbleached pulp with hypo and oxygen-chlorine dioxide-hydrogen peroxide and the like to obtain pulp. The gist of the invention of item 3 is that an aqueous acetic acid solution containing a catalytic amount of a mineral acid is added to the cut straws, which is heated to convert the straws into acetic acid pulp at normal pressure, which is separated into pulp and waste liquid by a separator. Separate, neutralize the mineral acid in the waste liquid with alkali, distill the acetic acid aqueous solution in the waste liquid and use it for washing pulp, wash the pulp with hot water, add warm water to the solid content of the waste liquid, and add water-soluble And lignin acetate from the water-insoluble part. A method characterized in that the acetic acid contained in the hot water wash pulp was recovered by ion-exchange membrane, re-using acetic acid washing liquid of the pulp in a solvent normal 圧酢 acid pulping.

[0005] When the atmospheric pressure acetic acid pulping method is applied to straws, it is a problem of the conventional pulping method despite that it is a pulp raw material having a high silica content.
Due to the high silica content, low calorific value (low lignin content) and high viscosity, there is no difficulty in recovering chemicals from the pulp waste liquid, and the waste liquid discharged in the pulping process is very easy to handle. The present invention has been made based on the knowledge. The reason why the waste liquid is easy to handle is that 50% of the silica component in the rice straw remains in the pulp, or conversely, the extraction of silica into the waste liquid is small.

Accordingly, since the amount of silica contained in lignin recovered from waste pulp liquor is small, it can be used as a raw material for producing carbon fibers by carbonizing the fibers. It has been found that it is preferable from the viewpoint of improving the utilization of rice straw biomass components. The pulp has a strength comparable to that obtained by a conventional pulping method even after bleaching, and thus is useful as a pulping means.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail. Examples of the straws that can be used in the present invention include rice straw, wheat straw, bacas, and the like, and rice straw is particularly preferred.
When pulping these straws, they are usually cut to about 3 cm. As the mineral acid used as a catalyst, hydrochloric acid and sulfuric acid are preferred, and at least one of these mineral acids is added to a 70 to 90% aqueous acetic acid solution. The relationship between the ratio of acetic acid solution to rice straw (liquid ratio) and the yield of pulp and cake and the kappa number is shown in FIG. FIG. 2 shows the relationship between the acetic acid concentration, the pulp / cake yield, and the kappa number. As the ratio of the mineral acid to be added, sulfuric acid 0.26 to 0.32%, hydrochloric acid 0.1
0%. At the time of pulping, a mineral acid-containing aqueous acetic acid solution is added to the straw at a ratio of 10 to 12 and heated. FIG. 3 shows the relationship between the sulfuric acid concentration, the yield of pulp and cake, and the kappa number. The heating condition is the boiling temperature (about 105 ° C),
The pulping is finished after about 3 hours. FIG. 4 shows the relationship between the pulping time and the yield of pulp and cake and the kappa number. After the pulping is completed, the pulp is separated into pulp and waste liquid, and the separated waste liquid is sent to a process of recovering valuable resources from chemicals and straws. The pulp is washed with an acetic acid solution and water recovered from the waste liquid, and a part of the acetic acid cleaning liquid is returned to the pulping step as a pulping solution, and the water cleaning liquid is sent to a step of recovering valuable resources from the waste liquid. The coarse pulp is separated into fine pulp and lees by a conventional method such as screening to be selected pulp.
Fine pulp can be used as a raw material for alcohol fermentation,
Silica of fine pulp can be used as a pulp pigment or the like.
To recover valuable substances from organic solvents and straws from waste liquid and washing liquid, concentrate these liquids by distillation under reduced pressure, etc., collect acetic acid water from the distillate, and add water to this concentrate. Separate into a water-soluble part and a water-insoluble part, and recover saccharides from the water-soluble part and lignin acetate from the water-insoluble part.

[0008] As described above, in the acetic acid pulping of straws at normal pressure, it is easy to recover organic solvents and valuables of straws from the waste liquid discharged in the pulping step, and thus, it is possible to remove polluting substances. It is an excellent pulping method with low emissions and low energy consumption. FIG. 5 shows an overall image of the process under batch conditions.

[0009]

EXAMPLES The present invention will be described more specifically based on examples. Normal pressure acetic acid pulping method of rice straw. Rice straw is cut into a length of 3 cm, and the rice straw is put into a pulping tank so that the liquid ratio becomes 10 to 12. The acetic acid aqueous solution containing a small amount of mineral acid (90% containing 0.1% hydrochloric acid) is added thereto. Acetic acid aqueous solution or 80% acetic acid aqueous solution containing 0.32% sulfuric acid)
, Refluxed for 3 to 4 hours, and treated with acetic acid at normal pressure. Separate into crude pulp and pulp waste liquid. The crude pulp is washed with hot acetic acid aqueous solution recovered from the waste liquid and warm water. A part of the acetic acid aqueous solution recovered from the waste liquid is returned to the pulping tank as a pulping solvent. Pulp waste liquor is neutralized with a part of the acetic acid washing liquid after neutralizing the mineral acid contained therein with alkali, and then concentrated under reduced pressure to solidify. Pulp washing water is added to the solidified product to precipitate lignin acetate as a water-insoluble portion, which is collected, and saccharides are recovered from the water-soluble portion. Fine fibers (passing through 200 mesh) and debris were removed from the crude pulp by a flat screen to obtain a selected pulp in high yield. The selected pulp is 44.8 based on 100 rice straw raw materials, and the selected pulp contains 17.3% ash. The silica content in lignin acetate is:
It was as low as 5%. Table 1 shows the material balance by the acetic acid pulping method. The reason why the sum of the material balances does not reach 100% is due to the fact that some components have been removed from the system at the time of pulp selective operation or the like.

[0010]

[Table 1]

[0011] The selected pulp is made of hypo (NaClO)
And bleached with oxygen-chlorine dioxide-hydrogen peroxide. The saponification treatment of the pulp is performed before or during the oxygen treatment. As shown in Table 2, the obtained bleached pulp was confirmed to have strength properties comparable to conventional pulp.

[0012]

[Table 2]

[0013]

The atmospheric pressure acetic acid pulping method of straw not only has a strength property comparable to that of the pulp obtained by the conventional method, but also a valuable resource from waste liquor generated by the pulping method. Is easy to recover, furthermore, it has become possible to leave much of the silica of straw in the pulp,
It is useful in that highly efficient utilization of straw biomass is possible and emission of polluting substances and waste pulp is reduced.

[Brief description of the drawings]

FIG. 1 shows the relationship between the ratio of acetic acid solution to rice straw (liquid ratio) and pulp / cake yield and kappa number.

FIG. 2 shows the relationship between acetic acid concentration and pulp / cake yield and kappa number.

FIG. 3 shows the relationship between sulfuric acid concentration and pulp / cake yield and kappa number.

FIG. 4 shows the relationship between pulping time, pulp / cake yield, and kappa number.

FIG. 5 is a process chart of acetic acid pulping under normal pressure.

Claims (3)

[Claims] An acetic acid aqueous pulping method for straws, comprising adding an aqueous acetic acid solution obtained by adding a catalytic amount of a mineral acid to the cut straws, and heating and pulping the straws. 2. The method according to claim 1, wherein the bleached unbleached pulp is bleached with hypo and oxygen-chlorine dioxide-hydrogen peroxide to produce bleached pulp. 3. An aqueous acetic acid solution containing a catalytic amount of a mineral acid is added to the cut straws, and the straws are heated to convert the straws into acetic acid pulp at normal pressure, which is separated into pulp and waste liquid by a separator. The mineral acid in the waste liquid is neutralized with alkali and the aqueous acetic acid solution in the waste liquid is distilled and used for washing the pulp.The pulp is washed with hot water, and warm water is added to the solid content of the waste liquid to dissolve the water-soluble part in water. Pulp is recovered from the water-soluble portion, lignin acetate is recovered from the water-insoluble portion, acetic acid contained in the pulp hot water washing solution is recovered using an ion-exchange membrane, etc. The method according to claim 1, wherein the solvent is reused as a solvent in the acetic acid pulping method.