Patent Publication Number: US-2017356015-A1

Title: Method for pretreating wood dust and method for manufacturing bioalcohol

Description:
RELATED APPLICATIONS 
     This application claims priority to Taiwan Application Serial Number 105118433, filed Jun. 13, 2016, which is herein incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a pretreatment method and a method for manufacturing bioalcohol. More particularly, the present disclosure relates to a method for pretreating wood dust and method for manufacturing bioalcohol using the same. 
     Description of Related Art 
     With industrialization, the dependence of human beings on energy is growing. However, the reserves of non-renewable energy sources, such as petroleum, coal and natural gas, are depleting. Using bioalcohols, such as ethanol, glycerol and butanol, as alternative energy sources is one of the strategies for reducing the dependence on non-renewable energy sources. 
     Nowadays, the biomass for manufacturing bioalcohol mainly includes sugar, starch and lignocellulose. The biomass which provides the sugar is mainly sugarcane. The biomass which provides the starch includes corn, cassava and grain. The biomass which provides the lignocellulose includes wheat straw, rice straw, corn cobs and bagasse. Techniques for manufacturing bioalcohol with the sugar and starch are well developed. However, manufacturing bioalcohol with the sugar and starch tends to compete with food resources and results in a higher food price. Furthermore, there is limited land suitable for cultivation of crops for producing sugar and starch on earth. Accordingly, manufacturing bioalcohol with the lignocellulose has become the focus of development. 
     The lignocellulose is mainly composed of cellulose, hemicellulose and lignin. The cellulose is a polysaccharide consisting of glucose units, and the hemicellulose is a polysaccharide consisting of various monomer units, such as glucose, xylose, galactose, arabinose and mannose. The monosaccharides of the cellulose and the hemicellulose can be converted into alcohols. However, a pretreatment is required for the lignocellulose to remove a portion of the lignin, so that the cellulose and the hemicellulose can be favorably hydrolyzed into monosaccharides, such as glucose, xylose, and the conversion of the monosaccharides into bioalcohol can be improved, too. 
     The pretreatment technique is critical to the saccharification rate of biomass. A high saccharification rate can help to reduce the cost and achieve mass production. However, different biomass has a different composition ratio of the cellulose, hemicellulose and lignin. Accordingly, the existing pretreatment techniques cannot be directly applied to new biomass. The known biomass which provides the lignocellulose includes wheat straw, rice straw, corn cobs and bagasse. The common features of the aforementioned biomass are having a lower content of lignin (all lower than 25 wt %) and a looser structure, so that the lignin thereof can be removed easily. However, as for a biomass with a higher content of lignin and a denser structure, there still lacks of a pretreatment method to effectively remove the lignin thereof. Take the wood for example, the wood contains about 39.6 wt % of cellulose and 11.7 wt % of hemicellulose, which indicates that the wood is a potential candidate for manufacturing bioalcohol. However, the wood has the content of the lignin up to 39 wt % and a dense structure. It is difficult to spoil the fiber structure of the wood so as to remove the lignin. Multiple attempts have been made, but none can successfully use the wood to manufacture the bioalcohol. Therefore, how to provide an effective method for pretreating the biomass with a higher content of lignin and a denser structure so as to improve the development of the bioalcohol has become an important goal of relevant academia and industry. 
     SUMMARY 
     According to one aspect of the present disclosure, a method for pretreating a wood dust includes steps as follows. A structurally damaged step is conducted, wherein the wood dust is disposed in a supercritical carbon dioxide (scCO 2 ) atmosphere with a pressure of 2600 psi to 3400 psi at a temperature of 40° C. to 120° C. for a predetermined time, and then the pressure is adjusted to drop to an atmospheric pressure in a sudden manner to obtain a structurally damaged wood dust. An alkali treatment step is conducted, wherein the structurally damaged wood dust is immersed in an alkaline hydrogen peroxide (H 2 O 2 ) solution at a temperature of 50° C. to 70° C., a concentration of H 2 O 2  in the alkaline H 2 O 2  solution is in a range of 0.1 wt % to 2.1 wt %, and a pH value of the alkaline H 2 O 2  solution is in a range of 10.5 to 12. Thus a treated wood dust is obtained. 
     According to another aspect of the present disclosure, a method for manufacturing a bioalcohol includes steps as follows. A pretreatment step, a hydrolysis step and a fermentation step are conducted. The pretreatment step includes steps as follows. A structurally damaged step is conducted, wherein the wood dust is disposed in a scCO 2  atmosphere with a pressure of 2600 psi to 3400 psi at a temperature of 40° C. to 120° C. for a predetermined time, and then the pressure is adjusted to drop to an atmospheric pressure in a sudden manner to obtain a structurally damaged wood dust. An alkali treatment step is conducted, wherein the structurally damaged wood dust is immersed in an alkaline H 2 O 2  solution at a temperature of 50° C. to 70° C., a concentration of H 2 O 2  in the alkaline H 2 O 2  solution is in a range of 0.1 wt % to 2.1 wt %, and a pH value of the alkaline H 2 O 2  solution is in a range of 10.5 to 12. Thus a treated wood dust is obtained. In the hydrolysis step, a polysaccharide of the treated wood dust is hydrolyzed into monosaccharides. In the fermentation step, the monosaccharides are converted into an alcohol. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
         FIG. 1  is a flow diagram showing a method for pretreating a wood dust according to one embodiment of the present disclosure; 
         FIG. 2  is a flow diagram showing a method for pretreating a wood dust according to another embodiment of the present disclosure; 
         FIG. 3  is a flow diagram showing a method for manufacturing a bioalcohol according to yet another embodiment of the present disclosure; 
         FIG. 4  is a flow diagram showing Step  310  in  FIG. 3 ; 
         FIG. 5  is a flow diagram showing Step  310  according to further another embodiment of the present disclosure; 
         FIG. 6  are scanning electron microscope (SEM) results of the comparative example (Com Ex.) 1 to Com Ex. 3 and example (Ex.) 1; and 
         FIG. 7  shows relationships of glucose recovery and time of Ex. 1 to Ex. 4 and Com Ex. 1 to Com Ex. 6. 
     
    
    
     DETAILED DESCRIPTION 
     Method for Pretreating Wood Dust 
       FIG. 1  is a flow diagram showing a method for pretreating a wood dust  100  according to one embodiment of the present disclosure. In  FIG. 1 , the method for pretreating the wood dust  100  includes Step  110  and Step  130 . 
     In Step  110 , a structurally damaged step is conducted. The wood dust is disposed in a scCO 2  atmosphere with a pressure of 2600 psi to 3400 psi at a temperature of 40° C. to 120° C. for a predetermined time, and then the pressure is adjusted to drop to an atmospheric pressure in a sudden manner to obtain a structurally damaged wood dust. By Step  110 , it is favorable for the scCO 2  permeating into the fiber structure of the wood dust so as to spoil the fiber structure of the wood dust. Accordingly, the dissolving efficiency of the lignin in the following alkali treatment step can be enhanced. 
     The aforementioned “in a sudden manner” refers that the pressure can drop to the atmospheric pressure within 3 seconds. 
     In Step  130 , an alkali treatment step is conducted. The structurally damaged wood dust is immersed in an alkaline H 2 O 2  solution at a temperature of 50° C. to 70° C., a concentration of H 2 O 2  in the alkaline H 2 O 2  solution is in a range of 0.1 wt % to 2.1 wt %, and a pH value of the alkaline H 2 O 2  solution is in a range of 10.5 to 12, thus a treated wood dust is obtained. Therefore, a portion of the lignin in the wood dust can be removed, which is favorable for hydrolyzing the polysaccharide (i.e., the cellulose and the hemicellulose) bonded with the lignin into monosaccharides. 
     With the method for pretreating the wood dust  100 , the glucose recovery of the treated wood dust can be significantly enhanced, which makes it possible to apply the wood dust to manufacture bioalcohol in practical use. Furthermore, the operating temperature of the method for pretreating the wood dust  100  (40° C. to 120° C. and 50° C. to 70° C.) can avoid the degradation of hemicellulose and the formation of furfural. The degradation of hemicellulose will inhibit the hydrolysis rate in the subsequent hydrolysis step, and the formation of furfural will inhibit the fermentation rate in the fermentation step. 
     Specifically, in Step  110 , the wood dust can recycle waste wood dust or waste wood as raw material, which can reduce the burden of dealing with the waste wood dust and the waste wood, and can meet the environmental demands. Furthermore, a particle size of the wood dust can be in a range of 5 μm to 10 μm. Accordingly, the time required for the method for pretreating the wood dust  100  can be reduced. The wood and the wood dust with a larger particle size can be processed with equipment such as wood chipper or grinder, so that the desired particle size can be obtained. How to process the wood and the wood dust so as to obtain the desired particle size is conventional, and will not be repeated herein. 
     In Step  110 , the predetermined time can be 7.5 minutes to 37.5 minutes. Therefore, it is favorable for the scCO 2  permeating into the fiber structure of the wood dust, and then the pressure is adjusted to drop to the atmospheric pressure in a sudden manner. 
     In Step  130 , the alkaline H 2 O 2  solution is prepared by mixing H 2 O 2  and deionized water or distilled water, and then the pH value thereof is adjusted by adding NaOH. 
     Step  130  can be conducted at most 9 hours. Therefore, a desired amount of lignin can be removed. 
       FIG. 2  is a flow diagram showing a method for pretreating a wood dust  200  according to another embodiment of the present disclosure. In  FIG. 2 , the method for pretreating the wood dust  200  includes Step  210 , Step  220  and Step  230 . Comparing to the method for pretreating the wood dust  100  in  FIG. 1 , there is one more Step  220  in the method for pretreating the wood dust  200 . 
     In Step  220 , a heating step is conducted before conducting the alkali treatment step. The structurally damaged wood dust is heated with a temperature of 80° C. to 120° C. Moreover, Step  220  can be conducted for 15 minutes to 30 minutes. Therefore, the structurally damaged effect can be improved, and the glucose recovery can be further enhanced. 
     Step  210  can be the same as Step  110  in  FIG. 1 , and Step  230  can be the same as Step  130  in  FIG. 1 . Therefore, Step  210  and Step  230  will not be repeated herein. 
     Method for Manufacturing Bioalcohol 
       FIG. 3  is a flow diagram showing a method for manufacturing a bioalcohol  300  according to yet another embodiment of the present disclosure. In  FIG. 3 , the method for manufacturing the bioalcohol  300  includes Step  310 , Step  320  and Step  330 . 
     In Step  310 , a pretreatment step is conducted.  FIG. 4  is a flow diagram showing Step  310  in  FIG. 3 . As shown in  FIG. 4 , Step  310  includes Step  311  and Step  313 . In Step  311 , a structurally damaged step is conducted. In Step  313 , an alkali treatment step is conducted. Step  311  can be the same as Step  110  in  FIG. 1 , and Step  313  can be the same as Step  130  in  FIG. 1 . Therefore, Step  311  and Step  313  will not be repeated herein. By Step  310 , a treated wood dust is obtained. 
       FIG. 5  is a flow diagram showing Step  310  according to further another embodiment of the present disclosure. In  FIG. 5 , Step  310  includes Step  311 , Step  312  and Step  313 . Comparing to Step  310  of  FIG. 4 , there is one more Step  312  in  FIG. 5 . In Step  312 , a heating step is conducted. Step  312  can be the same as Step  220  in  FIG. 2 , and will not be repeated herein. 
     In Step  320 , a hydrolysis step is conducted, in which a polysaccharide of the treated wood dust is hydrolyzed into monosaccharides. 
     In Step  330 , a fermentation step is conducted, in which the monosaccharides are converted into an alcohol. 
     Specifically, Step  320  can be an acid hydrolysis step or an enzyme hydrolysis step. How to hydrolyze the polysaccharide into monosaccharides is conventional, and will not be repeated herein. 
     Specifically, the alcohol in Step  330  can be ethanol, glycerol or butanol. The kinds of enzyme in the fermentation step can be decided according to the desired kinds of the alcohol. 
     With the wood dust as the biomass, the method for manufacturing the bioalcohol  300  can broadened the source of biomass to the wood, which is featured with a higher content of lignin. Therefore, it is favorable to improve the development of the bioalcohol, and can reduce the dependence on the non-renewable energy sources. 
     EXAMPLES 
     Ex. 1: wood dust with a particle size in a range of 5 μm to 10 μm (5 g) is disposed in a reaction container. CO 2  is introduced into the reaction container and is heated to 80° C. and pressurized to 2800 psi, so that the wood dust is disposed in a scCO 2  atmosphere. After 15 minutes, the pressure is adjusted to drop to an atmospheric pressure in a sudden manner to obtain a structurally damaged wood dust. The atmospheric pressure is about 1 atm. The structurally damaged wood dust is immersed in an alkaline H 2 O 2  solution at a temperature of 60° C. for 9 hours. A concentration of H 2 O 2  in the alkaline H 2 O 2  solution is in a range of 1 wt % to 1.6 wt %, and a pH value of the alkaline H 2 O 2  solution is 11.5. Thus the treated wood dust of Ex. 1 is obtained. 
     Ex. 2: wood dust with a particle size in a range of 5 μm to 10 μm (5 g) is disposed in a reaction container. CO 2  is introduced into the reaction container and is heated to 80° C. and pressurized to 2800 psi, so that the wood dust is disposed in a scCO 2  atmosphere. After 15 minutes, the pressure is adjusted to drop to the atmospheric pressure in a sudden manner to obtain a structurally damaged wood dust. The structurally damaged wood dust is heated with a temperature of 80° C. under the atmospheric pressure for 15 minutes. The structurally damaged wood dust is then immersed in an alkaline H 2 O 2  solution at a temperature of 60° C. for 9 hours. A concentration of H 2 O 2  in the alkaline H 2 O 2  solution is in a range of 1 wt % to 1.6 wt %, and a pH value of the alkaline H 2 O 2  solution is 11.5. Thus the treated wood dust of Ex. 2 is obtained. 
     Ex. 3: the structurally damaged wood dust is heated with a temperature of 100° C. under the atmospheric pressure for 15 minutes, and other steps are the same as that of Ex. 2. Thus the treated wood dust of Ex. 3 is obtained. 
     Ex. 4: the structurally damaged wood dust is heated with a temperature of 120° C. under the atmospheric pressure for 15 minutes, and other steps are the same as that of Ex. 2. Thus the treated wood dust of Ex. 4 is obtained. 
     Ex. 5 to Ex. 35: the conditions of the structurally damaged step, the heating step and the alkali treatment step of Ex. 2 are changed as shown in Table 1, and other steps are the same as that of Ex. 2. Thus the treated wood dust of Ex. 5 to Ex. 35 are obtained. In Table 1, “T1” represents the temperature in the structurally damaged step, “P” represents the pressure in the structurally damaged step, “t1” represents the predetermined time in the structurally damaged step, “T2” represents the temperature in the heating step, “t2” represents the time for the heating step, “C” represents the concentration of H 2 O 2  in the alkaline H 2 O 2  solution, “t3” represents the time for the alkali treatment step and “T3” represents the temperature in the alkali treatment step. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                 structurally damaged  
                 heating  
                   
               
               
                   
                 step 
                 step 
                 alkali treatment step 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 T1 
                 P 
                 t1 
                 T2 
                 t2 
                 C 
                   
                 t3 
                 T3 
               
               
                 EX. 
                 (° C.) 
                 (psi) 
                 (min) 
                 (° C.) 
                 (min) 
                 (wt %) 
                 pH 
                 (hr) 
                 (° C.) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 5 
                 60 
                 2800 
                 15 
                 100 
                 15 
                 0.6 
                 11.5 
                 9 
                 60 
               
               
                 6 
                 100 
                 2800 
                 15 
                 100 
                 15 
                 0.6 
                 11.5 
                 9 
                 60 
               
               
                 7 
                 60 
                 3200 
                 15 
                 100 
                 15 
                 0.6 
                 11.5 
                 9 
                 60 
               
               
                 8 
                 100 
                 3200 
                 15 
                 100 
                 15 
                 0.6 
                 11.5 
                 9 
                 60 
               
               
                 9 
                 60 
                 2800 
                 30 
                 100 
                 15 
                 0.6 
                 11.5 
                 9 
                 60 
               
               
                 10 
                 100 
                 2800 
                 30 
                 100 
                 15 
                 0.6 
                 11.5 
                 9 
                 60 
               
               
                 11 
                 60 
                 3200 
                 30 
                 100 
                 15 
                 0.6 
                 11.5 
                 9 
                 60 
               
               
                 12 
                 100 
                 3200 
                 30 
                 100 
                 15 
                 0.6 
                 11.5 
                 9 
                 60 
               
               
                 13 
                 60 
                 2800 
                 15 
                 100 
                 15 
                 1.6 
                 11.5 
                 9 
                 60 
               
               
                 14 
                 100 
                 2800 
                 15 
                 100 
                 15 
                 1.6 
                 11.5 
                 9 
                 60 
               
               
                 15 
                 60 
                 3200 
                 15 
                 100 
                 15 
                 1.6 
                 11.5 
                 9 
                 60 
               
               
                 16 
                 100 
                 3200 
                 15 
                 100 
                 15 
                 1.6 
                 11.5 
                 9 
                 60 
               
               
                 17 
                 60 
                 2800 
                 30 
                 100 
                 15 
                 1.6 
                 11.5 
                 9 
                 60 
               
               
                 18 
                 100 
                 2800 
                 30 
                 100 
                 15 
                 1.6 
                 11.5 
                 9 
                 60 
               
               
                 19 
                 60 
                 3200 
                 30 
                 100 
                 15 
                 1.6 
                 11.5 
                 9 
                 60 
               
               
                 20 
                 100 
                 3200 
                 30 
                 100 
                 15 
                 1.6 
                 11.5 
                 9 
                 60 
               
               
                 21 
                 40 
                 3000 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 22 
                 120 
                 3000 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 23 
                 80 
                 2600 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 24 
                 80 
                 3400 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 25 
                 80 
                 3000 
                 7.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 26 
                 80 
                 3000 
                 37.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 27 
                 80 
                 3000 
                 22.5 
                 100 
                 15 
                 0.1 
                 11.5 
                 9 
                 60 
               
               
                 28 
                 80 
                 3000 
                 22.5 
                 100 
                 15 
                 2.1 
                 11.5 
                 9 
                 60 
               
               
                 29 
                 80 
                 3000 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 30 
                 80 
                 3000 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 31 
                 80 
                 3000 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 32 
                 80 
                 3000 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 33 
                 80 
                 3000 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 34 
                 80 
                 3000 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                 35 
                 80 
                 3000 
                 22.5 
                 100 
                 15 
                 1.1 
                 11.5 
                 9 
                 60 
               
               
                   
               
            
           
         
       
     
     Com Ex. 1: wood dust with a particle size in a range of 5 μm to 10 μm (5 g). That is, Com Ex. 1 is an untreated wood dust. 
     Com Ex. 2: wood dust with a particle size in a range of 5 μm to 10 μm (5 g) is immersed in an alkaline H 2 O 2  solution at a temperature of 60° C. for 9 hours. A concentration of H 2 O 2  in the alkaline H 2 O 2  solution is in a range of 1 wt % to 1.6 wt %, and a pH value of the alkaline H 2 O 2  solution is 11.5. Thus the treated wood dust of Com Ex. 2 is obtained. 
     Com Ex. 3: wood dust with a particle size in a range of 5 μm to 10 μm (5 g) is disposed in a reaction container. CO 2  is introduced into the reaction container and is heated to 80° C. and pressurized to 2800 psi, so that the wood dust is disposed in a scCO 2  atmosphere. After 15 minutes, the pressure is adjusted to drop to the atmospheric pressure in a sudden manner. Thus the treated wood dust of Com Ex. 3 is obtained. 
     Com Ex. 4: wood dust with a particle size in a range of 5 μm to 10 μm (5 g) is disposed in a reaction container. CO 2  is introduced into the reaction container and is heated to 80° C. and pressurized to 2800 psi, so that the wood dust is disposed in a scCO 2  atmosphere. After 15 minutes, the pressure is adjusted to drop to the atmospheric pressure in a sudden manner to obtain a structurally damaged wood dust. The structurally damaged wood dust is heated with a temperature of 80° C. under the atmospheric pressure for 15 minutes. Thus the treated wood dust of Com Ex. 4 is obtained. 
     Com Ex. 5: the structurally damaged wood dust is heated with a temperature of 100° C. under the atmospheric pressure for 15 minutes, and other steps are the same as that of Com Ex. 4. Thus the treated wood dust of Com Ex. 5 is obtained. 
     Com Ex. 6: the structurally damaged wood dust is heated with a temperature of 120° C. under the atmospheric pressure for 15 minutes, and other steps are the same as that of Com Ex. 4. Thus the treated wood dust of Com Ex. 6 is obtained. 
     Compositions and Delignification Rates of Examples and Comparative Examples 
     The compositions of Com Ex. 1, Com Exs. 3-6 and Exs. 1-35 are obtained by acid hydrolysis method as follows. Weigh 0.3 g of the wood dust (the untreated wood dust of Com Ex. 1 or the treated wood dust of Com Exs. 3-6 and Exs. 1-35) into a tared pressure tube and then add 3 mL of 72 wt % H 2 SO 4  solution therein to form a sample. Place the tared pressure tube in a water bath set at 30° C. and incubate the sample for 60 minutes. Use a stirring rod to stir the sample without removing the tared pressure tube from the water bath. Afterwards, dilute the sample to a 4 wt % concentration by adding 84 mL deionized water. Securely screw the tared pressure tube with a teflon cap, and then place the tared pressure tube in an autoclave at a temperature of 121° C. for 1 hour. Use the liquid fraction to determine glucose and xylose by HPLC (High Performance Liquid Chromatography) and convert to cellulose and hemicellulose. Use the solid fraction to determine the acid insoluble lignin. The delignification rate is calculated by the measured results. The compositions and delignification rates of Com Ex. 1, Com Exs. 3-6 and Exs. 1-35 are listed in Table 2. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Com Ex./ 
                 composition 
                 delignification 
               
            
           
           
               
               
               
               
               
            
               
                 Ex. 
                 cellulose (%) 
                 hemicellulose (%) 
                 lignin (%) 
                 rate (%) 
               
               
                   
               
               
                 Com Ex. 1 
                 39.6 
                 11.7 
                 39.4 
                 — 
               
               
                 Com Ex. 3 
                 41.4 
                 11.8 
                 39.2 
                 0.51 
               
               
                 Com Ex. 4 
                 41.3 
                 12.9 
                 39.3 
                 0.25 
               
               
                 Com Ex. 5 
                 41.8 
                 11.2 
                 39.2 
                 0.51 
               
               
                 Com Ex. 6 
                 41.9 
                 11.2 
                 39.2 
                 0.51 
               
               
                 Ex. 1 
                 50.8 
                 11.3 
                 33.8 
                 14.2 
               
               
                 Ex. 2 
                 51.8 
                 11.3 
                 31.9 
                 19.0 
               
               
                 Ex. 3 
                 51.9 
                 11.5 
                 31.2 
                 20.8 
               
               
                 Ex. 4 
                 52.0 
                 11.4 
                 31.1 
                 21.1 
               
               
                 Ex. 5 
                 50.5 
                 13.7 
                 33.5 
                 15.0 
               
               
                 Ex. 6 
                 50.7 
                 13.8 
                 33.6 
                 14.7 
               
               
                 Ex. 7 
                 49.2 
                 13.1 
                 33.6 
                 14.7 
               
               
                 Ex. 8 
                 49.1 
                 13.6 
                 33.7 
                 14.5 
               
               
                 Ex. 9 
                 53.1 
                 16.9 
                 33.9 
                 14.0 
               
               
                 Ex. 10 
                 52.1 
                 12.2 
                 32.4 
                 17.8 
               
               
                 Ex. 11 
                 52.1 
                 12.2 
                 32.6 
                 17.3 
               
               
                 Ex. 12 
                 51.8 
                 12.5 
                 32.0 
                 18.8 
               
               
                 Ex. 13 
                 56.2 
                 12.1 
                 33.8 
                 14.2 
               
               
                 Ex. 14 
                 54.6 
                 12.1 
                 31.8 
                 19.3 
               
               
                 Ex. 15 
                 54.6 
                 11.5 
                 34.1 
                 13.5 
               
               
                 Ex. 16 
                 53.2 
                 12.0 
                 31.7 
                 19.5 
               
               
                 Ex. 17 
                 57.1 
                 13.4 
                 35.7 
                 9.4 
               
               
                 Ex. 18 
                 56.8 
                 16.4 
                 32.8 
                 16.8 
               
               
                 Ex. 19 
                 55.5 
                 11.9 
                 34.7 
                 11.9 
               
               
                 Ex. 20 
                 56.5 
                 15.8 
                 31.8 
                 19.3 
               
               
                 Ex. 21 
                 52.2 
                 11.6 
                 33.9 
                 14.0 
               
               
                 Ex. 22 
                 51.3 
                 11.7 
                 33.7 
                 14.5 
               
               
                 Ex. 23 
                 53.1 
                 11.6 
                 33.5 
                 15.0 
               
               
                 Ex. 24 
                 51.3 
                 11.5 
                 33.8 
                 14.2 
               
               
                 Ex. 25 
                 53.9 
                 11.9 
                 34.1 
                 13.5 
               
               
                 Ex. 26 
                 52.2 
                 11.4 
                 33.8 
                 14.2 
               
               
                 Ex. 27 
                 50.7 
                 12.0 
                 34.3 
                 12.9 
               
               
                 Ex. 28 
                 54.7 
                 11.2 
                 31.8 
                 19.3 
               
               
                 Ex. 29 
                 51.9 
                 11.8 
                 31.7 
                 19.5 
               
               
                 Ex. 30 
                 52.8 
                 12.4 
                 33.1 
                 16.0 
               
               
                 Ex. 31 
                 54.9 
                 14.2 
                 32.5 
                 17.5 
               
               
                 Ex. 32 
                 52.9 
                 11.5 
                 32.6 
                 17.3 
               
               
                 Ex. 33 
                 53.5 
                 11.7 
                 32.8 
                 16.8 
               
               
                 Ex. 34 
                 55.8 
                 14.0 
                 31.8 
                 19.3 
               
               
                 Ex. 35 
                 52.9 
                 12.0 
                 32.4 
                 17.8 
               
               
                   
               
               
                 Note: 
               
               
                 delignification rate (%) = 100 × (1 − X/Y). 
               
               
                 X represents the composition ratio of the lignin of Com Exs. 3-6 and Ex. 1-35. 
               
               
                 Y represents the composition ratio of the lignin of Com Ex1. 
               
            
           
         
       
     
     As shown in Table 2, the method for pretreating the wood dust according to the present disclosure can enhance the delignification rate. Moreover, as shown in Exs. 1-4, when the other conditions are the same, adding the heating step can enhance the effect of delignification. 
     Specific Surface Area 
     The specific surface areas of Com Ex. 1, 2, 5 and Ex. 1 are obtained by a Brunauer-Emmett-Teller (BET) measurement with Autosorb-1 (purchased from Quantachrome Instrument), which can obtain the adsorption and desorption isotherm of nitrogen. Moreover, the pore volume and pore size are measured, too. The results are listed in Table 3. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Com Ex./ 
                 specific surface areas 
                 pore volume 
                 pore size 
               
               
                   
                 Ex. 
                 (m 2 /g) 
                 (cm 3 /g) 
                 (Å) 
               
               
                   
                   
               
             
            
               
                   
                 Com Ex. 1 
                 1.44 
                 0.006 
                 165 
               
               
                   
                 Com Ex. 2 
                 0.96 
                 0.004 
                 162 
               
               
                   
                 Com Ex. 5 
                 1.96 
                 0.007 
                 189 
               
               
                   
                 Ex. 1 
                 2.01 
                 0.008 
                 205 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 3, the method for pretreating the wood dust according to the present disclosure can enhance the specific surface area, pore volume and pore size, which is favorable to enhance the glucose recovery. 
     SEM Results 
     The untreated wood dust of Com Ex. 1 and the treated wood dust of Com Ex. 2-3 and Ex. 1 are observed by a SEM (JSM-5600, purchased from JEOL).  FIG. 6  are SEM results of Com Ex. 1-3 and Ex. 1, in which (A) is the SEM result of Com Ex. 1, (B) is the SEM result of Com Ex. 2, (C) is the SEM result of Com Ex. 3, and (D) is the SEM result of Ex. 1. As shown in  FIG. 6 , the method for pretreating the wood dust according to the present disclosure can effectively spoil the fiber structure of the wood dust. 
     Glucose Recovery 
     The glucose recovery at 24 hours, 48 hours and 72 hours of the untreated wood dust of Com Ex. 1 and the treated wood dust of Com Ex. 2-6 and Exs. 1-4 are measured as follows. Weigh 0.5 g of wood dust (the untreated wood dust of Com Ex. 1 or the treated wood dust of Com Exs. 2-6 and Exs. 1-4) into a 20 mL glass vial, and add 5.0 mL of sodium citrate buffer (0.1M, pH 4.8). Then add 0.1 mL of sodium azide solution (2 wt %) to prevent the growth of bacterial during the hydrolysis. Add 9.7 mL of deionized water and an appropriate volume of the CTec-2 enzyme (Novozym with 120 FPU (Filter Paper Unit)/mL) preparation to equal approximately 15 FPU/g cellulose. Close the glass vial tightly and place it in a vial rack suitable for the shaking oven. Set the temperature to 50° C. and incubate with shaking sufficiently to keep solids in constant suspension for a period of 72 hours. A 0.5 mL of an aliquot of the enzymatic hydrolysis liquid is removed at each 24 hours interval. The 0.5 mL of an aliquot of the enzymatic hydrolysis liquid is filtered through a 0.22 μm filter and subjected to glucose analysis using HPLC method. Glucose recovery (%, w/w)={(glucose in enzymatic hydrolysis liquid)/[(cellulose in the wood dust of comparative example or example)×0.9]}×100%.  FIG. 7  shows relationships of glucose recovery and time of Ex. 1 to Ex. 4 and Com Ex. 1 to Com Ex. 6. As shown in  FIG. 7 , the glucose recovery at 72 hours of the untreated wood dust of Com Ex. 1 is only 7.1%. When the wood dust is only treated with the alkali treatment step, such as Com Ex. 2, the glucose recovery at 72 hours thereof is 28.3%. When the wood dust is only treated with the structurally damaged step, such as Com Ex. 3, or when the wood dust only treated with the structurally damaged step and the heating step, such as Com Exs. 4-6, the glucose recovery at 72 hours of each of the Com Exs. 3-6 is in the range of 14.9%-15.8%. However, the treated wood dust obtained by the method for pretreating the wood dust according to the present disclosure, such as Exs. 1-4, the glucose recovery at 72 hours of each of Exs. 1-4 is in the range of 44.8%-45.0%. It is apparent that the method for pretreating the wood dust according to the present disclosure can significantly enhance the glucose recovery. In other words, the method for pretreating the wood dust according to the present disclosure can effectively spoil the fiber structure of the wood dust (i.e., can break the bond between the lignin and the cellulose/hemicellulose), so that the glucose recovery can be enhanced. 
     The glucose recovery at 72 hours of each of the treated wood dust of Ex. 5-35 is measured, and the results are listed in Table 4. 
                                 TABLE 4                       Ex.   glucose recovery                                                    5   44.4           6   44.5           7   50.7           8   44.5           9   41.2           10   69.0           11   78.5           12   56.0           13   78.1           14   78.6           15   68.8           16   86.7           17   63.9           18   77.9           19   71.5           20   77.8           21   77.8           22   73.9           23   78.2           24   86.3           25   82.8           26   83.0           27   80.6           28   80.1           29   74.1           30   64.4           31   74.7           32   78.4           33   70.9           34   79.2           35   82.9                        
As shown in Table 4, the glucose recovery at 72 hours of each of Exs. 5-35 is in the range of 41.2%-86.7%, which can further confirm that the method for pretreating the wood dust according to the present disclosure can significantly enhance the glucose recovery.
 
     According to the present disclosure, “saccharification” refers to the process that the polysaccharide, such as the cellulose and the hemicellulose, is hydrolyzed into monosaccharides. “Saccharification rate” refers to the ratio of the weight of the monosaccharides obtained by the hydrolysis and the weight of the polysaccharide before the hydrolysis. “Glucose recovery” refers to the process that the cellulose is hydrolyzed into the glucose. 
     Although the present disclosure has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims.