Method for pretreating straw through combination of ionic liquid and steam explosion

Abstract

The invention relates to the technical field of straw resource utilization, in particular to a method for pretreating straw through combination of ionic liquid and steam explosion. According to the method, straw is pretreated by adopting an ionic liquid and steam explosion combined method, [Bmim] [PF6] is adopted as the ionic liquid, straw powder is impregnated through the ionic liquid, the ionic liquid can permeate into a cellulose, hemicellulose and lignin cross-linked space structure in the impregnation process, and then the cellulose, hemicellulose and lignin cross-linked space structure is formed in a steam explosion mode; under the condition of instantaneous pressure loss, on one hand, a three-element cross-linked space structure can be destroyed, and on the other hand, the ionic liquid soaked in the straw can degrade hemicellulose, so that the three-element cross-linked space structure is destroyed more thoroughly, and the efficiency of the pretreated straw powder during subsequent treatment is improved. The method is simple in process, effective separation of the three elements in the straw can be achieved, and the method plays a positive role in subsequent high-valued conversion of the straw.

Description

Technical Field

[0001] The invention relates to the technical field of straw resource utilization, and in particular to a method for pretreating straw by using ionic liquid combined with steam explosion. Background Art

[0002] Straw is a general term for the stems and leaves (ears) of mature crops, usually referring to the remaining parts of wheat straw, corn stalks, sorghum stalks, rice straw, bean stalks and other crops after the seeds are harvested; straw is a lignocellulosic biomass, mainly composed of three parts: cellulose, hemicellulose and lignin; cellulose and hemicellulose are high-molecular polymers of hexose and pentose monomers, and lignin is a high-molecular polymer with aromatic compounds as the skeleton structure. The three components are combined together by strong hydrogen bonds, have a complex structure, and are difficult to separate. Efficient separation of the three components plays an important role in promoting the high-value conversion and utilization of straw.

[0003] Straw pretreatment is an important preliminary step in converting crop straw into energy or other high-value products. Pretreatment can effectively improve the efficiency and economy of the subsequent conversion process. By changing the physical and chemical properties of straw, the energy consumption of the subsequent conversion process can be effectively reduced, the conversion rate can be improved, and the amount of enzymes or other chemicals required can be reduced, thereby reducing the overall production cost. Straw pretreatment can not only effectively utilize agricultural waste and reduce environmental pollution, but also help promote rural economic development and provide important support for the development of renewable energy. It is one of the key technologies to achieve sustainable development goals.

[0004] Room temperature ionic liquids are salts that are liquid at room temperature and are composed of anions and cations. Compared with traditional organic solvents, they have the characteristics of non-volatility, low melting point, high stability, non-flammability, good electrical and thermal conductivity, selectivity, and solvency, and are called "green solvents". Pretreatment of straw with room temperature ionic liquids can destroy the cross-linked spatial structure of cellulose, hemicellulose, and lignin, thereby improving the efficiency and economy of the subsequent conversion process. In the existing methods, the spatial structure of the three elements in the straw is mainly destroyed by the dissolution of cellulose by ionic liquids, but on the one hand, the amount of ionic liquid used is large, and the energy consumption for recycling is high. On the other hand, it also causes the loss of part of the cellulose, which is not convenient for actual production application. Therefore, the present invention proposes a straw pretreatment method based on ionic liquids, adopts a pretreatment method of ionic liquid combined with steam explosion, and uses a small amount of ionic liquid to achieve pretreatment of straw. While the treatment effect is good, the energy consumption of ionic liquid recovery is reduced, which is convenient for use in actual production. Summary of the invention

[0005] The purpose of the present invention is to provide a method for pretreating straw by ionic liquid combined with steam explosion, so as to solve the problem that when pretreating straw by ionic liquid, the amount of ionic liquid is large, the recovery energy consumption is high, and it is not conducive to use in actual production.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for pretreating straw by ionic liquid combined with steam explosion, comprising the following steps:

[0007] S1, crushing the straw raw material to obtain straw powder, and storing the obtained straw powder for later use;

[0008] S2, adding the straw powder obtained in S1 into a reactor, and adding ionic liquid into the reactor to impregnate the straw powder;

[0009] S3. After the impregnation treatment is completed, the straw powder in the reactor is subjected to steam explosion treatment to achieve pretreatment of the straw.

[0010] Furthermore, in the above-mentioned S1, the straw raw material is crushed after removing impurities, and the particle size of the obtained straw powder is 1 to 3 mm.

[0011] Furthermore, in the S2, the ionic liquid includes [Bmim][PF6].

[0012] Furthermore, the ionic liquid is a mixture of [Bmim][PF6] and [Bmim][OAc].

[0013] Furthermore, in the S2, the ratio of [Bmim][OAc] to [Bmim][PF6] in the ionic liquid is 1:2-5.

[0014] Furthermore, the solid-liquid ratio of the straw powder to the ionic liquid is 1:1-2.

[0015] Furthermore, after the ionic liquid is added, water is continuously added to the reactor, the ratio of water to ionic liquid is 1:3-9, and the solid-liquid ratio of straw powder to liquid material is 1:1-2.

[0016] Furthermore, the immersion treatment is carried out at a temperature of 80 to 120° C., for a time of 1 to 3 hours, and at a stirring intensity of 60 to 120 r / min.

[0017] Furthermore, in the S3, the pressure of the steam explosion is 2-4 MPa, and the processing time is 1-2 min.

[0018] Furthermore, in the S3, water is used to clean the straw powder after steam explosion treatment in the reactor, the solid-liquid ratio of added water to the straw powder is 1:3-5, the number of cleanings is 1-3 times, the stirring intensity during the cleaning process is 60-120 r / min, and the time for a single cleaning is 15-30 min.

[0019] Beneficial effects of the present invention:

[0020] 1. The crushed straw is treated by the impregnation method. In the process, a large amount of ionic liquid is not required, and the amount of ionic liquid is less, which helps to reduce the use cost and subsequent recycling cost;

[0021] 2. [Bmim][PF6] in the method of the present invention is insoluble in water, and is easy to separate and reuse after use, which can effectively reduce the cost of recycling. At the same time, during the recycling process, the cellulose is dissolved to saturation, and no regeneration treatment is required, which can also effectively avoid the loss of cellulose;

[0022] 3. By adding [Bmim][OAc] and water to [Bmim][PF6], the efficiency of impregnation can be effectively improved, which has a positive effect on reducing the impregnation time and improving production efficiency, and also improves the effect of pretreatment;

[0023] 4. The method of the present invention uses ionic liquid combined with steam explosion. The steam explosion destroys the spatial structure of the three-element cross-linking, and the ionic liquid degrades the hemicellulose in the three-element while destroying the spatial structure. The combination of the two makes the spatial structure of the three-element cross-linking looser, realizes the separation of the three-element, and facilitates the subsequent resource utilization. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0025] Example 1

[0026] Corn stalks were taken and tested, wherein the cellulose content was 36.4%, the hemicellulose content was 21.6%, and the lignin content was 18.3%.

[0027] The corn stalks are removed of impurities and then crushed for later use. The particle size of the corn stalks after crushing is 1 to 3 mm.

[0028] Take 100 kg of the above-mentioned crushed residual straw and place it in a reactor, add ionic liquid [Bmim][PF6] (Bmim is 1-butyl-3-methylimidazole) into the reactor, the addition amount of [Bmim][PF6] is 150 L (the solid-liquid ratio involved in the technical solution of the present invention is the ratio of solid mass to liquid volume), soak for 2 hours at 110°C and 80 r / min, at which time the straw powder is in an infiltrated state.

[0029] The impregnated material is subjected to steam explosion at a pressure of 3 MPa and a stabilization time of 90 seconds. After the stabilization time is over, the pressure is instantly reduced to normal pressure to complete the steam explosion process.

[0030] The pretreated straw powder can be obtained by washing the material after steam explosion treatment.

[0031] The obtained straw powder is dried. After drying, the straw powder has a loose appearance and is in the form of fine fibers. After testing, the hemicellulose content is reduced to 6.1%, and the hemicellulose removal rate is more than 76%.

[0032] Cellulase was added to the pre-treated and cleaned straw powder for enzymolysis, with a solid-liquid ratio of 1:3, an amount of 50 kg of cellulase added, the enzymolysis temperature controlled at 53°C, a pH of 5, and an enzymolysis time of 72 h.

[0033] After the enzymolysis was completed, the solid and liquid were separated to obtain 294 L of enzymolysis solution. After testing, the content of cellulose glucose in the enzymolysis solution was 112.1 g / L, and the yield of cellulose glucose relative to cellulose in the straw raw material could reach more than 90%.

[0034] Example 2

[0035] In this embodiment, the ionic liquid is a mixture of [Bmim][PF6] and [Bmim][OAc] (OAc is acetate), wherein the ratio of [Bmim][PF6] to [Bmim][OAc] is 4:1.

[0036] 125 L of the mixed ionic liquid was added to the reactor, followed by 25 L of water. The rest was the same as in Example 1.

[0037] The pretreated straw powder was sampled and dried. The straw powder was loose in appearance and in the form of fine fibers. After testing, the hemicellulose content was reduced to 3.8%, and the hemicellulose removal rate was more than 85%.

[0038] Under the same conditions, enzymolysis was carried out to obtain 295 L of enzymolysis solution. After testing, the content of cellulose glucose in the enzymolysis solution was 117.6 g / L, and the yield of cellulose glucose relative to cellulose in the straw raw material could reach more than 95%.

[0039] Example 3

[0040] In this embodiment, the immersion conditions are 90° C. and 80 r / min for 1 hour, and the rest are the same as in Embodiment 2.

[0041] The pretreated straw powder was sampled and dried. The straw powder was loose in appearance and in the form of fine fibers. After testing, the hemicellulose content was reduced to 4.5%, and the hemicellulose removal rate was more than 82%.

[0042] Under the same conditions, enzymolysis was carried out to obtain 295 L of enzymolysis solution. After testing, the content of cellulose glucose in the enzymolysis solution was 116.2 g / L, and the yield of cellulose glucose relative to cellulose in the straw raw material could reach more than 94%.

[0043] It can be seen from Examples 1-3 that the use of ionic liquid [Bmim][PF6] alone for impregnation and steam explosion has a good effect after pretreatment, and the yield of cellulose glucose can reach more than 90% relative to the straw raw material; while the combination of [Bmim][PF6] and [Bmim][OAc] and the addition of a small amount of water can significantly improve the yield of cellulose glucose relative to the straw raw material to more than 95%, and at the same time can also shorten the time required for impregnation, and achieve good results at lower temperature and time.

[0044] Comparative Example 1

[0045] In this comparative example, the ionic liquid used was [Bmim][PF6], 125 L of the ionic liquid was added to the reactor, and then 25 L of water was added, and the rest was the same as in Example 1.

[0046] The pretreated straw powder was sampled and dried. The straw powder was loose in appearance and in the form of fine fibers. After testing, the hemicellulose content was reduced to 6.3%, and the hemicellulose removal was more than 75%.

[0047] In contrast, the use of ionic liquid [Bmim][PF6] and the addition of only water during the impregnation process did not significantly improve the removal of hemicellulose.

[0048] Comparative Example 2

[0049] In this comparative example, the amount of liquid used for impregnation was changed. In this comparative example, the ionic liquids used were [Bmim][PF6] and [Bmim][OAc]. During the impregnation process, 75 L of the mixed ionic liquid was added to the reactor, and then 15 L of water was added. The rest was the same as Example 2.

[0050] The straw powder after pretreatment was sampled and dried. The straw powder after drying had a loose appearance and was in the form of fine fibers. After testing, the hemicellulose content was reduced to 11.4%, and the hemicellulose removal rate was only 53%.

[0051] In contrast, too little impregnation liquid has a significant effect on the removal of hemicellulose, indicating that the amount of liquid is too little, the impregnation is incomplete, and the ionic liquid has not fully penetrated into the space of the three-element cross-linking. Although steam explosion can break a certain spatial structure, it lacks a combined effect with the ionic liquid, and the final treatment effect is not as good as the effect of complete impregnation in the embodiment.

[0052] Comparative Example 3

[0053] In this comparative example, the amount of liquid used for impregnation was changed. In this comparative example, the ionic liquids used were [Bmim][PF6] and [Bmim][OAc]. During the impregnation process, 300 L of the mixed ionic liquid was added to the reactor, and then 60 L of water was added. The rest was the same as Example 2.

[0054] The straw powder after pretreatment was sampled and dried. The appearance of the straw powder did not change significantly after drying. Then it was tested and found that the hemicellulose content was still 19.7% and the removal rate of hemicellulose was only 10%.

[0055] In contrast, too much impregnation liquid has a significant effect on the removal of hemicellulose, indicating that there is too much liquid and there is excess liquid in the reactor. At this time, the material is completely immersed in the liquid, which completely affects the subsequent steam explosion process. The removal of hemicellulose is only the removal amount of ionic liquid, and the removal effect is not good.

[0056] In this comparative example, the excess liquid was drained and then the steam explosion was repeated under the same conditions as in Example 1.

[0057] Finally, the pretreated straw powder was sampled and dried. After drying, the straw powder had a loose appearance and was in the form of fine fibers. After testing, the hemicellulose content was reduced to 3.3%, and the hemicellulose removal rate was more than 87%.

[0058] Enzymolysis was carried out under the same conditions as in Example 1 to obtain 294 L of enzymolysis solution. After testing, the content of cellulose glucose in the enzymolysis solution was 118.2 g / L, and the yield of cellulose glucose relative to cellulose in the straw raw material could reach more than 95%.

[0059] In contrast, the removal rate of hemicellulose will be improved to a certain extent after the steam explosion after the excess liquid is discharged, but the improvement effect is not obvious. At the same time, the final yield of cellulose glucose is not significantly improved. Therefore, in actual production, in order to save costs, choosing an appropriate amount of liquid for impregnation can not only ensure the removal effect of hemicellulose and the yield of cellulose glucose, but also reduce the use of raw materials and simplify the processing process.

[0060] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for pretreating straw by combining ionic liquid with steam explosion, It is characterized in that The following steps are involved: S1, crushing the straw raw material to obtain straw powder, and storing the obtained straw powder for later use; S2, adding the straw powder obtained in S1 into a reactor, and adding ionic liquid into the reactor to impregnate the straw powder; S3. After the impregnation treatment is completed, the straw powder in the reactor is subjected to steam explosion treatment to achieve pretreatment of the straw.

2. The method for pretreating straw by using ionic liquid combined with steam explosion according to claim 1, Features: In the above-mentioned S1, the straw raw material is cleaned from impurities and then crushed, and the particle size of the obtained straw powder is 1 to 3 mm.

3. The method for pretreating straw by combining ionic liquid with steam explosion according to claim 1, Features: In the S2, the ionic liquid includes [Bmim] [PF 6 ].

4. The method for pretreating straw by using ionic liquid combined with steam explosion according to claim 3, Features: The ionic liquid is [Bmim] [PF 6 ] and [Bmim][OAc].

5. The method for pretreating straw by using ionic liquid combined with steam explosion according to claim 4, Features: In the above-mentioned S2, [Bmim][OAc] and [Bmim][PF 6 ] content ratio is 1:2~5.

6. The method for pretreating straw by using ionic liquid combined with steam explosion according to claim 3, Features: The solid-liquid ratio of the straw powder to the ionic liquid is 1:1-2.

7. The method for pretreating straw by using ionic liquid combined with steam explosion according to claim 5, Features: After the ionic liquid is added, water is continuously added to the reaction kettle, the ratio of water to ionic liquid is 1:3-9, and the solid-liquid ratio of straw powder to liquid material is 1:1-2.

8. A method for pretreating straw using ionic liquid combined with steam explosion according to any one of claims 6 to 7, Features: The immersion treatment is carried out at a temperature of 80 to 120° C., for a time of 1 to 3 hours, and with a stirring intensity of 60 to 120 r / min.

9. The method for pretreating straw by using ionic liquid combined with steam explosion according to claim 1, Features: In the above-mentioned S3, the pressure of the steam explosion is 2-4 MPa, and the processing time is 1-2 min.

10. The method for pretreating straw by using ionic liquid combined with steam explosion according to claim 1, Features: In the S3, water is used to clean the straw powder after steam explosion treatment in the reactor, the solid-liquid ratio of added water to the straw powder is 1:3-5, the number of cleanings is 1-3 times, the stirring intensity during the cleaning process is 60-120r / min, and the time for a single cleaning is 15-30min.