Tham khảo tài liệu 'progress in biomass and bioenergy production part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Combined Microwave - Acid Pretreatment of the Biomass 229 Biomass type Fig. 2. Pretreatment of the biomass with H2SO4 at 140 C Fig. 3. Pretreatment of the biomass with H2SO4 at 160 C In the case of the pretreatment with H2SO4 at 140 C an increase of the reaction pretreatment time has significant consequences only in the case of hemp sawdust when higher concentration of free sugars are obtained when the pretreatment time is 30 minutes instead of 15 minutes. For the hardwood oak and softwood fir sawdust an increase of the pretreatment time does not lead to a significant improvement of the free sugars yield. In the case of pretreatment with dilute acid at 160 C our previous studies showed that there is no difference between the results of the pretreatment process at 15 or 30 min. Taking into 230 Progress in Biomass and Bioenergy Production account that in the other pretreatment methods best results have been obtained when the pretreatment lasted 30 minutes the same period was chosen for the hydrolysis with H2SO4 at 160 C. All the presented results show that best results are obtained when pretreatment at 160 C is performed. The highest yields in free sugars are obtained for softwood and herbaceous sawdust respectively so it may be said that the softwood and herbaceous sawdust structure is more easily attacked than the hardwood sawdust structure during the acid hydrolysis. The same pretreatment method with dilute sulfuric acid combined with microwave irradiation was used for the same types of sawdust hardwood-oak softwood-fir herbaceous-hemp at three different temperatures. The experiments were carried out in the same conditions as mentioned before the only change being the different concentration of the acid. The aim of the study was to establish if an increase of the acid concentration leads to an increase of the amount of obtained sugars in the same temperatures conditions or as a result much of the already formed sugars will be degraded. The
