CN115786423B - Method for reducing enzyme amount for enzymolysis of cellulose by steam explosion grading utilization of straw - Google Patents

Abstract

The invention provides a method for reducing enzyme amount for cellulose enzymolysis by steam explosion grading utilization of straw, which comprises the following steps: (1) Carrying out refining treatment on the straws, carrying out rehydration treatment, and carrying out steam explosion treatment on the rehydrated straws to obtain steam exploded straws; (2) Soaking the steam exploded straw in water and stirring, and then grading long and short fibers in the raw materials by water flow screening to obtain short fibers; (3) And (3) carrying out high-solid enzymolysis treatment on the short fibers in the step (2). The method couples pretreatment and grading treatment, improves the uniformity of the straw raw materials, and effectively reduces the enzyme consumption in the high-solid enzymolysis process of the straw.

Description

A method for reducing the amount of enzymes used for enzymatic hydrolysis of cellulose by steam-explosion graded utilization of straw

technical field

The invention belongs to the field of straw application and relates to a method for enzymatic hydrolysis of straw, in particular to a method for reducing the amount of enzymes used for enzymatic hydrolysis of cellulose by steam explosion and graded utilization of straw.

Background technique

At present, grain carbon sources such as glucose, sucrose, and starch are still the main carbon sources used in the fermentation industry. However, the use of grain carbon sources inevitably has the problem of competing with others for grain, which is contrary to my country's current industrial policy. The use of cheap carbon sources such as straw sugar for production can effectively reduce the cost of the fermentation industry and solve the problem of carbon source supply in the fermentation industry. my country is a large agricultural country, and the output of straw is basically stable at about 800 million tons per year. Therefore, the use of straw to produce fermentable sugar has great potential.

Although straw fermentable sugar can effectively solve the problem of carbon source supply in the fermentation industry, it has not yet achieved large-scale industrialization. This is mainly due to the fact that the amount of cellulase used in the production of straw fermentable sugar is too high, which reduces its economic feasibility. The existing straw enzymatic hydrolysis process mainly uses the whole straw for enzymatic hydrolysis. Due to the strong heterogeneity of the straw itself, the anti-degradation barriers vary greatly among different tissues. The amount of enzyme reduces the economy of the high-value straw refining process. Existing studies have proved that graded utilization of straw raw materials can effectively reduce the amount of enzyme used for the preparation of straw fermentable sugars.

At present, the straw classification method mainly adopts the mechanical method. CN102261007A discloses a method for fractionating and separating the whole components of agricultural and forestry cellulose biomass and a method for preparing fuel alcohol and xylooligosaccharides by using the separated components. and other steps to achieve the classification of cellulose, hemicellulose and lignin in raw materials. However, this method is cumbersome, costly and produces a large amount of pollutants, which is difficult to apply to the treatment of lignocellulosic raw materials on an industrial scale. At the same time, it is difficult to classify lignocellulosic raw materials at the composition level, and the income is low, so it is difficult to achieve a stable industrial scale. CN109056400A provides a method for comprehensive utilization of straw, which uses a straw cutting machine system, a roller dust collector system, a water film dust removal system, a washing and sand removal device system, a continuous cooking system, a pressure relief receiving bin system, a screw squeezer system, and a ripening system. The tower system, high-consistency refiner system, and fiber classification system realize the classification of long and short fibers of straw raw materials, and apply enzymatic hydrolysis of straw short fibers. However, this method has many steps, low grading efficiency, and high grading cost, making it difficult to promote and use it on a large scale. At the same time, mechanical classification inevitably has the possibility of being crushed together with the outer skin, thereby reducing the separation efficiency. In addition, mechanical separation only involves physical effects and is difficult to affect the chemical composition and tissue structure of raw materials. Therefore, it still needs to be combined with other pretreatment methods, which increases the processing cost of raw materials.

CN102268833A discloses a method for preparing dissolving pulp by steam explosion pre-hydrolysis kraft method of crop stalks. Steam explosion and mechanical carding device are used to enrich long fibers for pulping and short fibers for biogas fermentation. However, the separation effect of this method is It is difficult to guarantee that after the steam explosion, the long fibers tightly wrap the short fibers and it is difficult to effectively separate the short fibers by mechanical carding. At the same time, the mechanical carding device provided by this patent has a low processing capacity and is difficult to apply to the preparation of industrial-grade raw materials. The lack of a detoxification step in the fractionation process and the high inhibitor concentration will have a great impact on the fermentation process.

Therefore, while achieving high-efficiency grading of straw materials and reducing the amount of enzymes used for fermentable sugar production, reducing the influence of inhibitors on subsequent fermentation has become an urgent problem to be solved.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a method for reducing the amount of enzymes used for enzymatic hydrolysis of cellulose by steam explosion grading of straws. The method couples pretreatment and grading treatment, improves the uniformity of straw raw materials, and effectively The amount of enzyme used in the high-solid enzymolysis process of straw is reduced.

For reaching above-mentioned purpose, the present invention adopts following technical scheme:

The invention provides a method for reducing the amount of enzymes used for enzymatic hydrolysis of cellulose by steam explosion classification of straw, the method comprising the following steps:

(1) Rehydration treatment is carried out after refining the straw, and steam explosion treatment is performed on the rehydrated straw to obtain steam explosion straw;

(2) Soak the steam-exploded straw in step (1) in water and stir, and then sieve through water flow to classify long and short fibers in the raw material to obtain short fibers;

(3) Perform high-solid enzymolysis treatment on the short fiber described in step (2).

As a preferred technical solution of the present invention, the straw in step (1) includes any one or a combination of at least two of corn straw, rice straw or wheat straw. Typical but non-limiting examples of the combination include: corn straw and A combination of rice straw, a combination of rice straw and wheat straw, a combination of wheat straw and corn straw, or a combination of corn straw, rice straw and wheat straw, etc.

In the present invention, the straw is rehydrated and steam-exploded, and the steam-exploded straw is soaked in excess water to remove inhibitors, which improves the utilization performance of the prepared fermentable sugar and reduces the inhibitory effect of inhibitors on bacterial growth. Stirring continuously during the soaking process can fully stretch the long fibers and fully release the adsorbed short fibers. Utilizing the volume difference of different tissues after steam explosion, the long fibers and short fibers are directly separated by sieving, and then the short fibers are subjected to high-solid enzymolysis, and the long fibers can be used for pulping and other ways. This method combines pretreatment with The coupling of graded treatment improves the uniformity of straw raw materials, reduces the difficulty of enzymatic hydrolysis, and effectively reduces the amount of enzyme used in the process of enzymatic hydrolysis of high-solid straw.

As a preferred technical solution of the present invention, the thinning treatment in step (1) includes cutting and/or crushing.

Preferably, the length of the thinned straw in step (1) is 3 to 5 cm, such as 3 cm, 3.2 cm, 3.5 cm, 3.8 cm, 4 cm, 4.2 cm, 4.5 cm, 4.8 cm or 5 cm etc., but not limited to the listed data, other unlisted values within this range are also applicable.

In the present invention, before the thinning treatment, the straw is cleaned to remove dust and other impurities on the surface.

As a preferred technical solution of the present invention, the water content of the stalk after the rehydration treatment in step (1) is 30~60wt%, such as 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt% wt% or 60 wt%, etc., but not limited to the listed data, other unlisted values within this range are also applicable.

As the preferred technical solution of the present invention, the pressure of the steam explosion treatment in step (1) is 0.5~1.0 Mpa, such as 0.5Mpa, 0.55 Mpa, 0.6 Mpa, 0.65 Mpa, 0.7 Mpa, 0.75 Mpa, 0.8 Mpa, 0.85 Mpa, 0.9 Mpa, 0.95Mpa or 1.0 Mpa, etc., but not limited to the listed data, other unlisted values within this range are also applicable.

Preferably, the pressure maintenance time of the steam explosion treatment is 5 to 10 min, such as 5 min, 6 min, 7 min, 8 min, 9 min or 10 min, etc., but not limited to the listed data, within this numerical range Other values not listed also apply.

As a preferred technical solution of the present invention, the amount of water used for soaking in step (2) is 3 to 5 times the volume of the steam-exploded straw, such as 3 times, 3.2 times, 3.5 times, 3.8 times, 4 times, 4.2 times, 4.5 times, 4.8 times or 5 times, etc., but not limited to the listed data, other unlisted values within the range of values are also applicable.

Preferably, the soaking water temperature in step (2) is 70-90°C, such as 70°C, 72°C, 75°C, 78°C, 80°C, 82°C, 85°C, 88°C or 90°C, etc., but not only Limited to the listed data, other unlisted values within the range of values are also applicable.

Preferably, the soaking time in step (2) is 30-120 min, such as 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min, etc., but It is not limited to the listed data, and other unlisted values within the numerical range are also applicable.

In the present invention, the role of the soaking is to remove the fermentation inhibitors produced by the pretreatment and fully stretch the long fibers to completely release the adsorbed short fibers.

In the present invention, the stirring device may be a common stirring device such as a ribbon stirrer, a paddle stirrer, or a turbine stirrer.

As a preferred technical solution of the present invention, the water flow sieving method in step (2) includes: sieving after soaking, long fibers on the sieve, and solid-liquid separation of the sieved liquid to obtain the first short fiber. fiber, the long fiber is washed to obtain a second length of fiber, and the first short fiber and the second short fiber are combined and dried.

In the present invention, in the sieving treatment, the long fibers are larger and retained, and the short fibers pass through the sieve along with the water flow. The sieve can be a 30-80 mesh sieve.

As a preferred technical solution of the present invention, the solid-liquid separation method includes any one or a combination of at least two of static sedimentation, centrifugation or filtration.

As a preferred technical solution of the present invention, the high-solid enzymolysis treatment in step (3) includes: placing the short fiber in a buffer solution, adjusting the solid content to 15-25 wt%, and adding cellulase for enzymolysis. Wherein, the solid content can be 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt% or 25wt% etc., but not limited to the listed data, other unlisted values within this range are also applicable.

In the present invention, the buffer solution can be a citric acid buffer solution (0.05 M, pH 4.8).

As a preferred technical solution of the present invention, the dosage of the cellulase is 5-20 FPU/g DM, such as 5 FPU/gDM, 6 FPU/g DM, 7 FPU/g DM, 8 FPU/g DM, 9 FPU/g DM g DM, 10 FPU/g DM, 11 FPU/g DM, 12 FPU/g DM, 13 FPU/g DM, 14 FPU/g DM, 15 FPU/g DM, 16 FPU/g DM, 17 FPU/g DM, 18 FPU/gDM, 19 FPU/g DM or 20 FPU/g DM, etc., but not limited to the listed data, other unlisted values within this range are also applicable.

In the present invention, the enzymolysis reactor can be static, shaker, stirring tank and other commonly used devices for enzymolysis reactions.

Compared with the prior art solutions, the present invention has at least the following beneficial effects:

The invention provides a method for reducing the amount of enzymes used for enzymatic hydrolysis of cellulose by steam explosion grading of straw. The method couples pretreatment and grading treatment, improves the uniformity of straw raw materials, changes the difficulty of enzymatic hydrolysis of raw materials, and effectively reduces The amount of enzyme used in the high-solid enzymatic hydrolysis process of straw can be reduced, and the amount of cellulase used can be saved by 75%. In addition, soaking treatment can effectively remove fermentation inhibitors in raw materials and improve the utilization efficiency of fermentable sugars.

Description of drawings

Figure 1 is a schematic diagram of the difference between long and short fibers D50 (the corresponding particle size when the cumulative particle size distribution percentage reaches 50%) after classification;

Figure 2 is a 40-fold magnified schematic diagram of long and short fibers before and after classification (wherein 1 and 2 are straw skins before steam explosion, 3 and 4 are straw cores before steam explosion, 5 and 6 are long fibers after steam explosion, and 7 and 8 are steam explosion post-short fiber);

Figure 3 is a schematic diagram of the difference in crystallinity between long and short fibers;

Figure 4 is a schematic diagram of the distribution of pools during the enzymatic hydrolysis of steam-exploded straw long and short fibers;

Fig. 5 is embodiment 1, embodiment 2, embodiment 3 and comparative example 1 sugar concentration change after enzymolysis 12 hours;

Figure 6 shows the changes in sugar concentration after 36 hours of enzymatic hydrolysis in Example 1, Example 2, Example 3 and Comparative Example 1.

The present invention will be further described in detail below. However, the following examples are only simple examples of the present invention, and do not represent or limit the protection scope of the present invention, and the protection scope of the present invention shall be determined by the claims.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and through specific implementation methods.

For better illustrating the present invention, facilitate understanding technical scheme of the present invention, typical but non-limiting embodiment of the present invention is as follows:

Example 1

This embodiment provides a method for reducing the amount of enzymes used for enzymatic hydrolysis of cellulose by steam explosion classification of straw, the method comprising the following steps:

(1) After cleaning the dust and other impurities on the surface of corn stalks, crush them into small pieces of 3-5 cm, rehydrate the cut corn stalks, adjust the water content of the straws to 50 wt%, and put the rehydrated straws in Enter in the steam explosion reaction device, carry out steam explosion treatment, the pressure of described steam explosion treatment is 1.0 Mpa, and the time is 5 min, obtains steam explosion stalk;

(2) Soak the steam-exploded straw in step (1) in 5 times the volume of hot water with a temperature of 80°C and stir continuously during the soaking process to fully stretch the long fibers and release the wrapped short fibers completely, and mix clean water and The steam-exploded straws pass through the 30-mesh sieve together, in which the long fibers are larger and are retained, and the short fibers pass through the sieve with the water flow, and the clear water containing the short fibers is left to settle to collect the short fibers, and the long fibers are rinsed again with clean water to make them The short fibers are punched out, repeated 3 times, and the dried short fibers are used for standby, and the treated long fibers can be used for pulping and other ways;

(3) Add citric acid buffer solution (0.05 M, pH 4.8) to the short fibers described in step (2) to adjust the solids content to 20%, and add cellulase (15 FPU/g DM) at the same time The enzymatic hydrolysis reactor performs enzymatic hydrolysis.

Example 2

This example provides a method for reducing the amount of enzymes used for enzymatic hydrolysis of cellulose by steam explosion classification of straw. The method is the same as that of Example 1 except that the added amount of cellulase is 10 FPU/g DM.

Example 3

This example provides a method for reducing the amount of enzymes used for enzymatic hydrolysis of cellulose by steam explosion classification of straw. The method is the same as that of Example 1 except that the added amount of cellulase is 5 FPU/g DM.

Example 4

This embodiment provides a method for reducing the amount of enzymes used for enzymatic hydrolysis of cellulose by steam explosion classification of straw, the method comprising the following steps:

(1) After cleaning the dust and other impurities on the surface of the rice straw, crush it into small pieces of 3-5 cm, rehydrate the cut corn straw, adjust the water content of the straw to 30 wt%, put the rehydrated straw in Enter in the steam explosion reaction device, carry out steam explosion treatment, the pressure of described steam explosion treatment is 0.5 Mpa, and the time is 10 min, obtains steam explosion stalk;

(2) Soak the steam-exploded straw in step (1) in 3 times the volume of hot water with a temperature of 90°C and stir continuously during the soaking process to fully stretch the long fibers and release the wrapped short fibers completely, and mix clean water and The steam-exploded straws pass through the 30-mesh sieve together, in which the long fibers are larger and are retained, and the short fibers pass through the sieve with the water flow, and the clear water containing the short fibers is left to settle to collect the short fibers, and the long fibers are rinsed again with clean water to make them The short fibers are punched out, repeated 3 times, and the dried short fibers are used for standby, and the treated long fibers can be used for pulping and other ways;

(3) Add citric acid buffer solution (0.05 M, pH 4.8) to the short fiber described in step (2) to adjust the solid content to 15%, and add cellulase (5 FPU/g DM) at the same time, mix well and place in The enzymatic hydrolysis reactor performs enzymatic hydrolysis. Using this method to classify straw can save the amount of cellulase.

Example 5

This embodiment provides a method for reducing the amount of enzymes used for enzymatic hydrolysis of cellulose by steam explosion classification of straw, the method comprising the following steps:

(1) After cleaning the dust and other impurities on the surface of the rice straw, crush it into small pieces of 3-5 cm, rehydrate the cut corn straw, adjust the water content of the straw to 30 wt%, put the rehydrated straw in Enter in the steam explosion reaction device, carry out steam explosion treatment, the pressure of described steam explosion treatment is 0.8 Mpa, and the time is 8 min, obtains steam explosion stalk;

(2) Soak the steam-exploded straw in step (1) in 4 times the volume of hot water with a temperature of 70°C and stir continuously during the soaking process to fully stretch the long fibers and completely release the wrapped short fibers. The steam-exploded straws pass through a 50-mesh sieve together, in which the long fibers are larger and retained, and the short fibers pass through the sieve with the water flow, and the clear water containing the short fibers is left to settle to collect the short fibers, and the long fibers are rinsed again with clean water to make them The short fibers are punched out, repeated 3 times, and the dried short fibers are used for standby, and the treated long fibers can be used for pulping and other ways;

(3) Add citric acid buffer solution (0.05 M, pH 4.8) to the short fibers described in step (2) to adjust the solids content to 25%, and add cellulase (15 FPU/g DM) at the same time, mix well and place in The enzymatic hydrolysis reactor performs enzymatic hydrolysis. Using this method to classify straw can save the amount of cellulase.

Comparative example 1

This comparative example provides a method for reducing the amount of enzymes used for cellulose enzymatic hydrolysis by steam explosion classification of straw, said method comprising the following steps:

(1) After cleaning the dust and other impurities on the surface of corn stalks, crush them into small pieces of 3-5 cm, rehydrate the cut corn stalks, adjust the water content of the straws to 50 wt%, and put the rehydrated straws in Enter in the steam explosion reaction device, carry out steam explosion treatment, the pressure of described steam explosion treatment is 1.0 Mpa, and the time is 5 min, obtains steam explosion stalk;

(2) Soak the steam-exploded straw in step (1) in 5 times the volume of hot water with a temperature of 80°C and stir continuously during the soaking process to fully stretch the long fibers and release the wrapped short fibers completely, and mix clean water and The steam-exploded straws pass through a 30-mesh sieve together, in which the long fibers are larger and are retained, and the short fibers pass through the sieve with the water flow, and the long fibers are dried for later use;

(3) Add citric acid buffer solution (0.05 M, pH 4.8) to the long fibers described in step (2) to adjust the solids content to 20%, and at the same time add cellulase (15 FPU/g DM) and mix well before placing The enzymatic hydrolysis reactor was carried out for 12 h.

The test results of the mechanical properties of the corn stalks used in the implementation are shown in Table 1.

Table 1

The hardness, adhesiveness and chewiness of the cortex were 25.59 times, 19.34 times and 19.72 times that of the core, respectively, which indicated that the cortex had higher mechanical strength and resistance to external forces. The difference in mechanical strength of different tissues makes the skin and pith different states after steam explosion.

Figure 1 is a schematic diagram of the difference between long and short fibers D50 (the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%) after classification. The particle size of the short fibers obtained after classification is smaller, which shows that the lower mechanical strength of the pith core is more serious tearing during the steam explosion process, and the particle size drop is more obvious. It also shows that the classification method can effectively realize the pretreatment of straw raw materials.

Figure 2 is a 40-fold magnified schematic diagram of long and short fibers before and after classification (wherein 1 and 2 are straw skins before steam explosion, 3 and 4 are straw cores before steam explosion, 5 and 6 are long fibers after steam explosion, and 7 and 8 are steam explosion post-short fibers). It can be seen from the figure that the short fibers after classification and the core tissue before steam explosion are mainly parenchyma cells, and the long fibers after classification and the skin tissue before steam explosion are mainly fibroblasts, which shows that this method effectively realizes straw The grading of different tissues is more thorough than mechanical grading.

Figure 3 is a schematic diagram of the difference in crystallinity between long and short fibers. After classification, the crystallinity of long fibers is 58.27%, and after classification, the crystallinity of short fibers is 51.94%. The difference in crystallinity between long and short fibers is also an important reason for the difference in enzymatic hydrolysis efficiency.

Figure 4 is a schematic diagram of the distribution of water pools during the enzymatic hydrolysis of long and short fibers of steam-exploded straw. In Figure 4, compared with the initial state, the peak height of the main water pool increased by 39.1% to 55.6% during the long fiber enzymatic hydrolysis process, and the short fiber increased by 90.6% to 112.7%. This shows that this method effectively realizes the pretreatment of straw raw materials and improves the mass transfer efficiency in the process of high-solid enzymolysis.

The sugar concentration in the enzymolysis process of Examples 1-3 and Comparative Example 1 was tested, and the results are shown in Figure 5 and Figure 6 .

It can be seen from Figure 5 and Figure 6 that when the enzyme amount of 5 FPU/g DM is used for short fibers after classification, it can reach the similar level of 20 FPU/g DM for long fibers. Save around 75%.

The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of selected components in the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention. These simple modifications All belong to the protection scope of the present invention.

In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way if there is no contradiction. The combination method will not be described separately.

In addition, various combinations of different embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the idea of the present invention, they should also be regarded as the disclosed content of the present invention.

Claims (8)

1. A method for stalk steam explosion grading to reduce the amount of enzyme used for cellulose enzymolysis, characterized in that, the method comprises the following steps: (1) Rehydration treatment is carried out after refining the straw, and steam explosion treatment is performed on the rehydrated straw to obtain steam explosion straw; (2) Soak the steam-exploded straw in step (1) in water and stir, and then sieve through water flow to classify long and short fibers in the raw material to obtain short fibers; The amount of water used for soaking is 3 to 5 times the volume of the steam-exploded straw, the water temperature for soaking is 70-90°C, and the time is 30-120 min; The method of water flow sieving includes: performing sieving treatment after soaking, long fibers on the sieve, performing solid-liquid separation on the sieved liquid to obtain first short fibers, and rinsing the long fibers to obtain second short fibers. a segment of fiber, combining the first staple fiber with the second staple fiber and drying; (3) Perform high-solid enzymolysis treatment on the short fiber described in step (2). 2. The method according to claim 1, characterized in that the straw in step (1) includes any one or a combination of at least two of corn straw, rice straw or wheat straw. 3. The method according to claim 1, characterized in that the thinning treatment in step (1) includes cutting and/or crushing; The length of the thinned straw in step (1) is 3-5 cm. 4. The method according to claim 1, characterized in that the moisture content of the straw after the rehydration treatment in step (1) is 30-60 wt%. 5. The method according to claim 1, characterized in that the pressure of the steam explosion treatment in step (1) is 0.5~1.0Mpa; The pressure maintenance time of the steam explosion treatment is 5-10 min. 6. The method according to claim 1, characterized in that, the method for solid-liquid separation comprises any one or a combination of at least two of static sedimentation, centrifugation or filtration. 7. The method according to claim 1, wherein the high-solid enzymolysis treatment in step (3) comprises: placing the short fiber in a buffer solution, adjusting the solid content to 15-25 wt%, adding Cellulase for enzymatic hydrolysis. 8. method according to claim 1, is characterized in that, described cellulase consumption is 5～20 FPU/g DM.

Images