Method for pretreating corn straws by adopting steam explosion

Abstract

The invention discloses a method for pretreating corn straw by adopting steam explosion, and belongs to the technical field of straw raw material pretreatment. By adopting steam explosion pretreatment, the content of lignin, cellulose and hemicellulose in the corn straw can be effectively reduced, the removal effect of the lignin is particularly obvious, and the hemicellulose is degraded and converted into an available carbon source under high pressure. The result provides an important basis for optimization of a pretreatment process and improvement of subsequent microbial decomposition efficiency.

Description

Technical Field

[0001] This invention relates to a method for pretreating corn stalks using steam explosion, belonging to the field of straw raw material pretreatment technology. Background Technology

[0002] Straw is a renewable green biological resource with broad application prospects in biomass energy, papermaking, feed, and fertilizer. The main components of straw are fiber (primarily crude fiber), hemicellulose, lignin, soluble sugars, crude protein, crude fat, ash, and trace elements. Straw is both agricultural waste and an important agricultural resource. However, due to the heterogeneous and crystalline structure of lignocellulose biomass, its resource utilization is difficult and its efficiency is low. Large amounts of straw-derived lignocellulose are discarded or directly burned, causing not only resource waste but also environmental pollution. Therefore, lignocellulose conversion and utilization technologies have gradually become a research hotspot in this field. These technologies mainly include physical, chemical, physicochemical, and biological methods. Among them, biological treatment is an environmentally friendly technology that uses microorganisms to catalyze the degradation of lignocellulose, facilitating its further conversion.

[0003] If untreated corn stalks are directly introduced into a microbial degradation system, their highly crystalline fibrous structure, densely wrapped with lignin-hemicellulose, will severely hinder the effective contact between microorganisms and their extracellular enzymes and cellulose. This results in slow release of fermentable sugars, delayed degradation initiation, and acid inhibition due to depletion of soluble sugars. Therefore, corn stalks must be pretreated before microbial degradation to break down the "resistant structure," improve the accessibility of enzymes and microorganisms, shorten the reaction cycle, and increase product yield. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for pretreating corn stalks using steam explosion.

[0005] This invention is achieved through the following technical solution: The first objective of this invention is to provide a method for pretreating corn stalks using steam explosion, wherein the corn stalks are placed in a steam explosion machine and held at a pressure of 1.0-2.0 MPa for 60-420 seconds, and then the pressure is released instantaneously to obtain steam-exploded pretreated corn stalks.

[0006] In one embodiment of the present invention, the corn stalks are soaked in water before being placed in a steam blasting machine.

[0007] In one embodiment of the present invention, the amount of water added is 20%-40% of the mass of corn stalks.

[0008] In one embodiment of the present invention, the soaking time is 10-15 hours.

[0009] In one embodiment of the present invention, the steam explosion treatment pressure is preferably 1.2-1.8 MPa.

[0010] In one embodiment of the present invention, the steam explosion treatment time is preferably 120-300s.

[0011] In one embodiment of the present invention, the corn stalks are cut into 1-10cm before soaking.

[0012] In one embodiment of the present invention, the corn stalks are preferably cut to 2-3 cm.

[0013] A second objective of this invention is to provide a pretreated corn stalk prepared by the method described above.

[0014] A third objective of this invention is to provide a method for preparing fuel by fermentation using the aforementioned pretreated corn stalks.

[0015] The beneficial effects of this invention are: This invention utilizes steam explosion pretreatment to effectively reduce the content of lignin, cellulose, and hemicellulose in corn stalks, with particularly significant lignin removal. Furthermore, hemicellulose is degraded and converted into a usable carbon source under high pressure. These results provide important evidence for optimizing the pretreatment process and improving the efficiency of subsequent microbial decomposition. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 Comparison of morphological characteristics of straw pretreated by steam explosion; A1 is SEM of unexploded straw, A2 is SEM of straw pretreated by steam explosion; B1 is CLSM of unexploded straw, B2 is CLSM of straw pretreated by steam explosion; C1 is AFM of unexploded straw, C2 is AFM of straw pretreated by steam explosion. Figure 2 X-ray diffraction patterns of apple pomace before and after pretreatment; Figure 3 Optimize the pressure (A) and time (B) for pretreatment of straw steam explosion; Figure 4The changes in cellulose, hemicellulose and lignin in corn straw under different pretreatment pressures (A) and times (B) were investigated. Detailed Implementation

[0018] The present invention will be further illustrated below with specific examples. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0019] Detection methods Reducing sugars were detected using the DNS method; Soluble sugars were detected using the anthrone colorimetric method; Total sugar was determined by the DNS method after hydrolysis with dilute acid; Determination of cellulose, lignin, and hemicellulose content: (1) Place about 1g of straw sample in a 300ml iodine flask, add 100ml of neutral detergent, then place it in a boiling high-pressure steam autoclave, keep it warm for 1h, filter it with a No. 3 sand core funnel, wash the residue with water and acetone to obtain residue 1.

[0020] (2) Dry residue 1 at 60°C for 72 hours, weigh it, and calculate W1.

[0021] (3) Place residue 1 in a 300ml iodine flask, add 100ml 2M HCl solution, and then place it in a boiling high-pressure steam autoclave. Keep it at 100°C for 50min, then filter it with a No. 3 sand core funnel, and wash the residue with water until the pH is 6.5~7.0 to obtain residue 2.

[0022] (4) Dry residue 2 at 60°C for 72 hours, weigh it, and calculate W2.

[0023] (5) Wash residue 2 twice with acetone, dry at 60°C, then place it in a 300ml iodine flask, add 10ml of 72% H2SO4, hydrolyze at 20°C for 3h, then add 90ml of water, leave at room temperature overnight, filter with a weighed No. 3 sand core funnel the next day, wash the residue with water until pH=6.5, and obtain residue 3.

[0024] (6) Dry residue 3 at 60°C for 72 hours, weigh it, and calculate W3.

[0025] (7) Ash the residue 3 at 550°C to obtain ash, weigh it, and calculate W4.

[0026] Hemicellulose (%) = (W1 - W2) / sample weight × 100%; Cellulose (%) = (W2 - W3) / sample weight × 100%; Lignin (%) = (W3-W4) / sample weight × 100%.

[0027] The technical solution of the present invention will be described in detail below with reference to specific embodiments. In the following embodiments, unless otherwise specified, the reagents, materials and equipment used can be purchased commercially, prepared by conventional methods, or commonly used in the industry.

[0028] Example 1: A method for pretreating corn stalks using steam explosion includes the following steps: (1) Cut the corn stalks into 2-3cm lengths, add 30% water by weight and soak for 12 hours, then place them in a steam blasting machine; (2) Introduce steam to pressurize to 1.6 MPa, maintain for 180 s, and then release the pressure instantly to obtain steam-exploded pretreated corn stalks.

[0029] The surface morphology of corn stalks before and after steam explosion pretreatment was observed using scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown. Untreated raw corn stalks have a relatively smooth surface and dense structure ( Figure 1 After steam explosion pretreatment, its surface morphology changed significantly, becoming rough, loose, and uneven, with numerous obvious cracks and pores appearing. Figure 1 (A2). This change is mainly attributed to the softening and partial degradation of the lignocellulose components by high-temperature and high-pressure steam during pretreatment, as well as the powerful mechanical tearing effect generated by instantaneous pressure relief. The aforementioned structural damage significantly increases the specific surface area and surface roughness of the straw, thereby providing more accessible sites and interfaces for microbial attachment and enzyme activity, which is beneficial to the subsequent biodegradation process.

[0030] To further reveal the changes in surface structure at the nanoscale, the samples were characterized using atomic force microscopy (AFM), and the results are as follows: Figure 1 As shown. Untreated corn stalks have a relatively smooth surface, a relatively intact structure, and no obvious damage or sedimentation. Figure 1 (B1). After steam explosion pretreatment, its surface exhibits significant roughening, accompanied by numerous irregular protrusions and localized deposits (B1). Figure 1 (B2). AFM results clearly show that the thermo-mechanical synergy during pretreatment effectively disrupted the original dense surface of the straw, forming a rich nanoscale uneven and porous structure. This nanoscale structural change further confirms at the microscopic level the increase in specific surface area and the alteration of surface properties, which helps to enhance the contact and mass transfer efficiency between the substrate and enzymes or functional microorganisms.

[0031] Lignin, a key structural component of cell walls, directly affects the enzymatic accessibility of cellulose. Based on the autofluorescence properties of lignin in the visible to far-infrared range, confocal laser scanning microscopy (CLSM) was used to observe the distribution of lignin in the cell walls of corn stalks before and after pretreatment. The results are as follows: Figure 1 As shown. Before pretreatment, the sample exhibited a clear, complete, and interconnected fluorescent network structure, indicating that lignin was continuously distributed in the cell wall and tightly bound to cellulose and hemicellulose, forming a dense anti-degradation barrier. Figure 1 (C1). After steam explosion pretreatment, the continuous fluorescent network structure showed significant breakage and dispersion. Figure 1 The presence of C2 indicates that the complete distribution of lignin at the cellular and tissue levels was disrupted, and the cell wall structure became loose. This phenomenon suggests that pretreatment effectively disrupted the physical and chemical bonds between lignin and carbohydrates, leading to cell wall deconstruction and thus providing more attack sites for cellulase.

[0032] Characterization results from SEM, AFM, and CLSM indicate that steam explosion pretreatment profoundly alters the structure of corn stalks at multiple scales through the thermo-mechanical synergistic effect of high temperature, high pressure, and instantaneous depressurization. Macroscopically, it causes surface tearing and porosity; at the nanoscale, it creates rough protrusions and new surface features; and at the cell wall component level, it disrupts the continuous network structure of lignin, weakening its protective effect on cellulose. These multi-level structural disruptions collectively lead to a significant increase in the specific surface area of ​​the raw material, improved surface roughness, and a marked improvement in cellulose accessibility, thus creating favorable conditions for subsequent efficient enzymatic saccharification or microbial fermentation processes.

[0033] To analyze the effect of steam explosion pretreatment on the cellulose crystal structure in corn stalks, X-ray diffraction (XRD) was used to characterize the samples. The results are as follows: Figure 2 As shown, cellulose, as a polymer composed of crystalline and amorphous regions, exhibits crystallinity variations that reflect the degree of structural damage caused by pretreatment. XRD patterns revealed characteristic diffraction peaks at 16.5° and 21.8°, corresponding to the (101) and (002) crystal planes of cellulose, respectively. Calculations showed that the crystallinity of untreated corn stalks was 49.8%, while it decreased to 30.3% after steam explosion pretreatment. This significant decrease indicates that the pretreatment process effectively disrupted the hydrogen bond network between cellulose molecules, partially undermining the integrity of its crystal structure, resulting in a reduction in crystalline regions and a relative increase in the proportion of amorphous regions, thus improving the accessibility of subsequent enzymatic hydrolysis of cellulose.

[0034] Example 2: A method for pretreating corn stalks using steam explosion includes the following steps: (1) Cut the corn stalks into 2-3cm lengths, add 30% water by weight and soak for 12 hours, then place them in a steam blasting machine; (2) Introduce steam to pressurize to 1.0 MPa, maintain for 180 s, and then release the pressure instantly to obtain steam-exploded pretreated corn stalks.

[0035] Example 3: A method for pretreating corn stalks using steam explosion includes the following steps: (1) Cut the corn stalks into 2-3cm lengths, add 30% water by weight and soak for 12 hours, then place them in a steam blasting machine; (2) Introduce steam to increase the pressure to 1.3 MPa, maintain for 180 s, and then release the pressure instantly to obtain steam-exploded pretreated corn stalks.

[0036] Example 4: A method for pretreating corn stalks using steam explosion includes the following steps: (1) Cut the corn stalks into 2-3cm lengths, add 30% water by weight and soak for 12 hours, then place them in a steam blasting machine; (2) Introduce steam to pressurize to 1.9 MPa, maintain for 180 s, and then release the pressure instantly to obtain steam-exploded pretreated corn stalks.

[0037] Example 5: A method for pretreating corn stalks using steam explosion includes the following steps: (1) Cut the corn stalks into 2-3cm lengths, add 30% water by weight and soak for 12 hours, then place them in a steam blasting machine; (2) Introduce steam to pressurize to 1.6 MPa, maintain for 60 s, and then release the pressure instantly to obtain steam-exploded pretreated corn stalks.

[0038] Example 6: A method for pretreating corn stalks using steam explosion includes the following steps: (1) Cut the corn stalks into 2-3cm lengths, add 30% water by weight and soak for 12 hours, then place them in a steam blasting machine; (2) Introduce steam to pressurize to 1.6 MPa, maintain for 300 s, and then release the pressure instantly to obtain steam-exploded pretreated corn stalks.

[0039] Example 7: A method for pretreating corn stalks using steam explosion includes the following steps: (1) Cut the corn stalks into 2-3cm lengths, add 30% water by weight and soak for 12 hours, then place them in a steam blasting machine; (2) Introduce steam to pressurize to 1.6 MPa, maintain for 420 s, and then release the pressure instantly to obtain steam-exploded pretreated corn stalks.

[0040] The pretreated corn stalks obtained in Examples 1-7 were tested for reducing sugar, soluble sugar, and total sugar. The results are as follows: Figure 2 As shown, the results showed that when treated at 1.6 MPa for 180 s, the contents of reducing sugar, soluble sugar and total sugar were all at high levels.

[0041] The lignin, cellulose, and hemicellulose contents of the pretreated corn stalks obtained in Examples 1-7 were detected, and the results are as follows: Figure 3 As shown, the results indicate that steam explosion treatment effectively disrupts the straw structure and promotes the dissolution and transformation of major components. With increasing pretreatment pressure, the lignin content in corn straw showed a significant decreasing trend. The lignin content in the untreated raw material was 11.56%; after pretreatment at 1.6 MPa for 180 s, the content decreased to 5.18%; when the pressure was further increased to 1.9 MPa and maintained for the same time, the lignin content further decreased to 4.23%. This demonstrates that steam explosion treatment can significantly disrupt the lignin structure, which is beneficial to the subsequent decomposition process. Similarly, the contents of cellulose and hemicellulose also gradually decreased with increasing pretreatment pressure. The contents of cellulose and hemicellulose in the original sample were 36.98% and 21.16%, respectively; after pretreatment at 1.6 MPa for 180 s, their contents decreased to 33.75% and 11.26%, respectively; further increases in treatment pressure resulted in further reductions in both contents. Especially under higher pressure conditions, hemicellulose underwent significant degradation, transforming into soluble sugars, which are thus more easily utilized by microorganisms. In summary, steam explosion pretreatment effectively reduces the content of lignin, cellulose, and hemicellulose in corn stalks, with particularly significant lignin removal. Furthermore, hemicellulose is degraded and converted into a usable carbon source under high pressure. These results provide important evidence for optimizing the pretreatment process and improving the efficiency of subsequent microbial decomposition.

[0042] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for pretreating corn stalks using steam explosion, characterized in that, Corn stalks are placed in a steam explosion machine and held at a pressure of 1.0-2.0 MPa for 60-420 seconds, then the pressure is released instantly to obtain steam-exploded pretreated corn stalks.

2. The method according to claim 1, characterized in that, The corn stalks are soaked in water before being placed in the steam blasting machine.

3. The method according to claim 1, characterized in that, The amount of water added is 20%-40% of the weight of the corn stalks.

4. The method according to claim 1, characterized in that, Soaking time is 10-15 hours.

5. The method according to claim 1, characterized in that, The preferred steam explosion treatment pressure is 1.2-1.8 MPa.

6. The method according to claim 1, characterized in that, The preferred steam explosion treatment time is 120-300 seconds.

7. The method according to claim 1, characterized in that, Before soaking, cut the corn stalks into 1-10cm pieces.

8. The method according to claim 1, characterized in that, Corn stalks should ideally be cut to 2-3 cm.

9. A pretreated corn stalk prepared by the method according to any one of claims 1-8.

10. A method for preparing fuel by fermentation using the pretreated corn stalks as described in claim 9.

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