JPS5858077B2 - Pretreatment method for enzymatic hydrolysis of cellulosic materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pretreatment method for enzymatic hydrolysis of cellulosic materials.

Conventionally, as a method to decompose cellulose into glucose,
There are acid hydrolysis and enzymatic hydrolysis.

Among these, the enzymatic hydrolysis method has the advantage that the reaction proceeds under mild pressure and temperature conditions, is specific, and does not cause secondary decomposition.

However, wood, rice straw, wheat straw, corn stalks,
Cellulose contained in leaves, bagasse, paper, etc. is generally highly crystalline, and because it is mixed with lignin, ash, etc., it exhibits strong resistance to enzymatic hydrolysis, the reaction rate is slow, and the decomposition rate is low. There is a drawback.

In order to eliminate this drawback, prior to enzymatic hydrolysis, physical pretreatments such as mechanical pulverization using a ball mill, high-temperature heating pulverization, destruction by γ-ray irradiation, etc. that increase the quality of cellulose and the reaction surface area, and H3PO4 , H2SO4゜ZrC1□, cadoxene, NaOH, and other reagents are used to destroy the crystalline structure of cellulose and perform chemical pretreatment to remove lignin, changing the natural cellulosic material into a structure that is easy to be broken down by hydrolytic enzymes. things are being done.

However, if conventional pretreatment methods are expected to be sufficiently effective, they require long-time operation, high concentration, high temperature, and high pressure, resulting in high energy consumption.

The present invention improves the drawbacks of the prior art, and provides a pretreatment method that requires mild conditions and less energy, and provides a fast reaction rate and high decomposition rate for the enzymatic hydrolysis reaction of cellulosic materials. This is what we provide.

That is, the present invention facilitates alkaline aqueous solution treatment by irradiating electron beams or gamma rays at 10'rad or more and L08rad or less as a pretreatment for enzymatic hydrolysis.

As a pretreatment method, treatment of highly crystalline and lignin-containing cellulosic materials with radiation can (1) decrease the degree of polymerization of cellulose, (2) decrease the amount of crystals, (3) produce reducing sugars, and (4) mechanical It is known that it has the effect of deteriorating the
), the effect of (3) becomes especially noticeable when
When the irradiation dose is 108 rad or more, it requires a large amount of energy and is difficult to perform as a pretreatment for enzymatic hydrolysis.

The effect of (4) is obvious even with an irradiation dose of about 106 rad, but in order to dramatically increase the rate and decomposition rate of the enzymatic hydrolysis reaction, it is necessary to make the powder into a fine powder of about 30μ, so electron beam or The energy required for irradiation and crushing with gamma rays is quite large.

In addition, it is known that the synergistic effect of irradiation and heating increases the rate and decomposition rate of enzymatic hydrolysis reactions, but this requires considerably high temperature conditions, so it is difficult to expect a sufficient effect. Requires large energy consumption.

However, according to the method of the present invention, the amount of irradiation of electron beams or gamma rays may be between 06 rad and 108 rad, and the alkaline aqueous solution treatment conditions are sufficient at room temperature for a short time, resulting in low energy consumption. Pretreatment can provide fast reaction rates and high decomposition rates.

Electron beam or γ of 106 rad or more L 08 rad or less
When a highly crystalline, lignin-containing cellulosic material that has been irradiated with radiation is treated with an alkaline aqueous solution under milder conditions than those in which all the lignin contained in the cellulosic material is solubilized, if the irradiation dose becomes large, Indeed, the recovery rate of the cellulosic material after treatment decreases and the soluble content increases.

The amount of Klason lignin in cellulose material is 106 rad.
It has been reported that the amount of Klason lignin is slightly reduced by irradiation with electron beams or γ-rays, but the reduction in Klason lignin content is
Lignin contained in cellulosic materials is exposed to electron beams or γ
This shows that irradiation with radiation increases its reactivity.

The present invention utilizes this improvement in the reactivity of lignin by irradiation with electron beams or gamma rays.

Lignin contained in a cellulosic material irradiated with electron beams or gamma rays at 106 rad or more and 108 rad or less becomes easily reduced in molecular weight and becomes solubilized by treatment with an alkaline aqueous solution.

As a result, even if conditions such as alkali concentration, treatment temperature, and treatment time are relaxed, the fine bonds between cellulose and lignin can be easily separated, and cellulose hydrolase can be easily separated from the cellulose and lignin. It can now reach the cellulose layer of the cell wall without being inhibited by lignin.
Saccharification rate and decomposition rate are improved.

The insoluble matter of the cellulosic material treated with aqueous alkali solution may be separated from P and used as a substrate for enzymatic hydrolysis reaction, but the degree of polymerization of cellulose will decrease due to irradiation with electron beams or gamma rays, and the treatment conditions may be In some cases, some cellulose content becomes solubilized during alkaline aqueous treatment, so in order to fully utilize the cellulose in the cellulosic material, it is necessary to add acetic acid or phosphoric acid to the sap, in addition to the enzymatic hydrolysis of the insoluble content. Either use it as a buffer solution, add cellulose hydrolase to perform enzymatic hydrolysis, or do not send the treated solution to each house.
It is preferable to add acetic acid or phosphoric acid to adjust the pH, add cellulose hydrolase to form a saccharification solution, and perform enzymatic hydrolysis.

The degree of polymerization of solubilized cellulose is low, and the rate at which glucose is produced by cellulose hydrolase is high.

Furthermore, unlike solid lignin, solubilized lignin does not adsorb cellulose hydrolase and lose its activity, and does not significantly inhibit enzymatic hydrolysis.

Examples will be described in detail below, but it goes without saying that the present invention is not limited only to these practical examples.

Actual Example ■ Rice straw (cellulose content: 31%) was crushed using a hammer mill as a cellulosic material. A sample of 42 to 80 meshes was irradiated with an electron beam accelerator and kept at various temperatures. The mixture was stirred for 5 minutes in twice the volume of 1N aqueous sodium hydroxide solution, washed separately with water and acetic acid aqueous solution, and dried to determine the recovery rate, and the lignin removal rate was calculated.

Table 1 shows the lignin removal rate when samples with various irradiation doses were treated at various temperatures.

As shown in this table, it was found that the removal rate of lignin was improved by irradiation, and the effect of irradiation was particularly remarkable in treatment near room temperature.

Example 2 As a cellulosic material, rice straw (cellulose content: 31φ) was irradiated with an electron beam accelerator and pulverized with a hammer mill. Of these, the material that passed through a 511L7IL round hole screen was used, resulting in a treatment concentration of 7 man Add 0.25N aqueous sodium hydroxide solution and stir at 30°C for 915 minutes.

Add IOφ acetic acid aqueous solution and water to adjust pH to 4.9 and substrate concentration to 5%, and add cellulose hydrolase (trade name: Cellulase Onozu Chikara, manufactured by Kinki Yakult ■) to 0.2 part of the total amount. and enzymatic hydrolysis.

Figure 1 shows the hydrolysis time versus cellulose decomposition rate by enzymatic hydrolysis.

The lignin removal rate of the samples that had been irradiated in advance was improved, and the effect of irradiation was remarkable.

Similar results have been obtained when an alkaline aqueous solution such as a potassium hydroxide aqueous solution or an ammonia aqueous solution is used.

[Brief explanation of drawings]

FIG. 1 shows the hydrolysis time versus cellulose degradation rate by enzymatic hydrolysis.

Claims (1)

[Claims] 1. A pretreatment method for enzymatic hydrolysis of cellulosic material, which comprises irradiating the cellulosic material with electron beams or gamma rays at 106 rad or more and 108 rad or less before delignifying the cellulosic material with an alkaline aqueous solution. .