Properties, Microstructures Of Ultrafine Straw Powder And Hydrogen Production From It By Photosynthetic Bacteria

ABSTRACT: This study was supported by National Natural Science Foundation“Reseach on metabolic heat and continuous photohydrogen production from straw biomass ultrafine powder”(NO. 50976029).Lignocellulosic biomass has some advantages, such as being rich in resources , renewable, and being converted to solid fuel, liquid fuel and gas fuel .But efficiency of enzymatic hydrolysis is relatively low because Cellulose, hemicellulose and lignin in lignocellulosic biomass has very complex structure. Pretreatment must be conducted in order to get high efficiency of enzymatic hydrolysis. There are 4 pretrantments including physical ,physico-chemical, chemical and biological processes. Although the researchers has made many achievements in pretreatment research, the prementment with high efficiency, low cost and being applied to production practice had never been found untill today. At the same time, factors affecting the hydrolysis has no unanimous conclusion at the present, so the new pretrament process and the mechanism of hydrolysis will be extremely necessary to study.Ultrafine gringding technology has made remarkable achievements in treatment chinese herbal medicines. The results showed that the technology of ultrafine grinding can increase the dissolution of the active ingredients of Chinese herbal medicines and the gastrointestinal absorption of active ingredients. Straw like the chinese herbal also belong to the lignocellulosic biomass and the matter being dissolving from straw were also be used by origanism during the process of photohydrogen production, so this reasearch applied the technology of ultrafine grinding to the pretreatment of straw and made the ultrafine straw powder hydrolysed hy enzyme for photohydrogen production. This research focused on physical and chemical properties of straw and the determination and observation of microstructure of straw smashed by ulfine gringding technology in order to find the particle size influencing regularities of hydrolysis. Effects of particle size on enzymatic hydrolysis and the process of photohydrogen production using the ultrafine straw powder were also studied. Conclusions came from these researchs were laid out below:(1) Specific surface area increases with reducing of the particle size, but no linear relationship were found between them because of the flaw and agglomeration. Apparent density increases with reducing of the particle size, but this increases slowed down while the reducing of particle size were beyond the certain value. The phenomenon that straw powder were close to sphere was possible cause. Water extract in 45℃and the recuding sugar incrseases with the reducing of the particle size under the condition of the same smashing way. This phenomenon was not only related with the particle but also with the smashing way.(2) SEM analysis for sorghum straw with different size showed that vascular structure and cell wall were destroied by ultrafine grinding and agglomeration happened. FTIR analysis showed that the molecular structure changed in benzene ring structure, cellulose hydroxyl and carbonyl on side chain of lignin. X-diffraction analysis showed that crystallinity index of cellulose decreased with the size reduction. Degree of polymerization also decreased and the number of molecular chain which were breaked became more and more according to the average viscosity determination.(3) Enzymatic hydrolysis of sorghum straw illustrated that cellulose accessibility increased for enzyme with the reducing of particle size. The phnomenon that active site for enzyme became more was found through SEM analysis for straw hydrolysed. This phnomenon perhaps can explain the increasing rate of enzymatic hydrolysis. Crystallinity index increased according to X-diffraction analysis for straw hydrolysed , maybe that amorphous parts of cellulose were hydrolysed and recrystallization happened cause this phnomenon. The reaction mechanism of ultrafine straw powder was different with other 3 samples according to the FTIR analysis for straw hydrolysis, bacause the absorption peak became sharp at 1604cm-1wavelength and this phnomenon disappeared for other 3 samples.(4) Enzymatic hydrolysis using sorghun straw milled for different times showed that enzymatic hydrolysis could be divided into two stages. The first stage was the initial 36h , about 70% reducing surgar were relased during this stage and the longer milling of straw the high rate of hydrolysis. The process of enzymatic hydrolysis showed the logarithmic fashion in the light of the fitting result using origin8.0. Mechaelis-Menten equation was most widely used to sescribe enzymatic kinetics, the Lineweaver-Burk plots were enployed to calculate the parameters of Vmax and Km in the test. The result exhibited that milling resluted in greater Vmax and also had influenced on Km but no regular patten were observed. In addition, the optimum condition of hydrolysis using ultrafine straw powder were obtained through response surface anaysis .(5) Researches on photohydrogen production using enzymatic hydrolysates of the ultrafine straw powder were carried out. The results showed that NaOH as reagent was better than KOH for enzymatic hydrolysates to be used for photohydrogen production, bacause more Na+ would make photosynthetic bacteria cation poisoned and leading to low efficiency of hydrogen production. Enzymatic hydrolysates after being centrifuged got more biohydrogen than that without centrifugal treatment, because it was been found that enzymatic hydrolysis continued through determation of the reducing suga. Within the experimental design level,the longer period of high hydrogen production were maintained under the condition of high substrate concentration, but the peak of hydrogen production lagged behined comparing with the low substrate concentration. 20% of the inoculation amount and 48h of cultivation period for the seed culture were more suitable for photosynthetic bacteria. Within 1000~3000Lx light intensity, the light conversion efficiency reached the most high.