Study On The Preparation Of Fermentable Sugar From Bamboo Via NaOH/Urea Pretreatment And Oxalic Acid Hydrolysis

Environmental pollution and energy shortage are global crises at present,which makes it imperative to develop renewable and clean energy.Bamboo is considered to be an ideal raw material for bioethanol due to its large reserves,wide distribution,short production cycle,strong viability and high cellulose content.In addition,bamboo has the advantages of not being restricted by season and not easy to corrupt.In order to explore a suitable and cost-effective approach for saccharification of bamboo materials,NaOH/Urea pretreatment and oxalic acid hydrolysis of bamboo were systematically studied in the present work.Firstly,bamboo powder was pretreated with NaOH/Urea,and the effects of temperature,time,NaOH concentration and Urea concentration on the main chemical composition of bamboo were investigated.The efficiency of pretreatment was evaluated by sugar content in dilute acid(H₂SO₄)hydrolysate of the pretreated-bamboo powder.Combined with the change of components contents in bamboo and sugar contents in dilute acid hydrolysate,the optimal pretreatment conditions were determined as follows:6 wt%NaOH,12 wt%Urea,1:10 g/m L,40?,4 h.The corresponding contents of main components in bamboo were 60.56%cellulose,14.40%hemicellulose and 20.79%lignin.The minimum glucose content of 5.23g/L and xylose content of 18.80g/L were obtained from pretreated-bamboo after hydrolysis for 24 h.In addition,SEM,FT-IR and XRD analysis results showed that the surface of bamboo powder became rough,more holes were found accompanied by removal of hemicellulose and lignin after pretreatment,and the crystal type of partial cellulose was transformed from?into?.Subsequently,the mechanism of NaOH/Urea pretreatment on bamboo powder was explored through various determination,including water retention value,Zeta potential,intrinsic viscosity,degree of polymerization and thermal stability.It could be speculated that the pretreatment mechanism was demonstrated as follows:the ester bond in bamboo was saponified by OH^-of ionized NaOH,which resulted in the removal of partial hemicellulose and lignin.The negatively charged–COOH and–OH groups on the surface of bamboo were neutralized by Na⁺of ionized NaOH,which leaded to the increase of surface charge of bamboo.Moreover,the hydrogen bond between cellulose chains was also destroyed by Na⁺,leading to the decrease of polymerization degree and intrinsic viscosity after breaking the cellulose chain segment.On the other hand,urea played an important role in pretreatment,such as destroying the binding force and capillary cavity between the cell walls of biomass,forming a protection layer on the surface of broken cellulose,and preventing cellulose from re-polymerization.The pretreated-bamboo powder was hydrolyzed by oxalic acid under different oxalic acid concentration,reaction temperature and solid-liquid ratio,and the contents of glucose and xylose in the hydrolysate were used to evaluate hydrolysis saccharification efficiency.The results showed that the optimal conditions could be defined as follows:10 wt%oxalic acid,105?and 1:10 g/m L.Meanwhile,the highest content of glucose(0.85 g/L)and xylose(4.88 g/L)in hydrolysate could be received at the optimal conditions.Additionally,the hydrolysate also included other substances belonging to cellulose,hemicellulose and lignin,which were proved by UV-vis and FT-IR analysis.According to SEM,FT-IR and XRD analysis,it could be found that the particle size of pretreated bamboo became smaller than that of raw bamboo material,and the vascular bundle structure was greatly destroyed.However,the typical cellulose structure was maintained after oxalic acid hydrolysis.Typically,the molecular structure and crystal structure of bamboo were not changed significantly before and after hydrolysis.In conclusion,NaOH/Urea pretreatment was an effective approach,which could not only assist in removing part of hemicellulose and lignin in bamboo powder,but also contribute to destroying the surface of bamboo,promoting the subsequent hydrolysis process.Oxalic acid was confirmed to be an effective catalyst in the hydrolysis of lignocellulose as well.The structure of pretreated-bamboo powder could be further destroyed during oxalic acid hydrolysis.Meanwhile,the cellulose and hemicellulose can be converted to glucose and xylose via oxalic acid hydrolysis.However,the further study was still necessary for the complete hydrolysis of cellulose after pretreatment.