Microwave Pretreatment Of Biomass And Its Pyrolysis Characteristics

Biomass pretreatment is a processing step before pyrolysis,which will affect the characteristics of biomass,thus changing the pyrolysis process of biomass and the distribution and properties of its products.The microwave pretreatment for its rapid,uniform,energy-saving features of concern.High-efficiency pretreatment of crop stalks is a key prerequisite for further conversion to usable fuels,and it is also one of the methods for effectively controlling the characteristics of pyrolysis products.In this paper,on the basis of summarizing the pretreatment of biomass combined with microwave and chemical methods,the microwave pretreatment combined with deionized water and dilute ammonia solution was selected.The corn stalk was used as raw material for microwave pretreatment of straw.The study of its pyrolysis characteristics,in order to be able to make a certain contribution to the development of pretreatment technology to improve the quality and yield of biomass pyrolysis products.The corn stalk samples pretreated by microwave and ammonia pretreatment were compared with their original physicochemical characteristics.The results of SEM and BET show that microwave pretreatment at 180 ? for 30 minutes destroyed the overall structure of corn stalks,which can effectively increase the specific surface area of raw materials and enrich the pore structure of the samples.Elemental and compositional analysis showed that microwave pretreatment caused a decrease of O/C ratio and an increase of H/C ratio,increased the high caloric value of the original sample,increased the content of cellulose in corn stalks,and aggravated the effect of hemicellulose break down.The results of FTIR and XRD showed that the three pretreatment methods affected the functional groups and crystallinity of corn stalk,destroyed the chemical structure of the raw materials,and the destructive intensity order was MAS>AS>MW.The thermogravimetry coupled with thermogravimetry(FTIR)was used to analyze the pyrolysis behavior of corn stalks and pretreated corn stalks.Compared with the pyrolysis process of pretreatment samples,the final solid residue of pyrolysis of corn stalks was the highest,while the increase of maximum weight loss rate(DTGmax)also showed that the pretreatment was conducive to the degradation of corn stalk samples,and microwave pretreatment effect is better.Infrared absorption spectroscopy of corn stalks in the pyrolysis of volatile products in real-time monitoring found that the absorption peak in the spectrum more,indicating that in the pyrolysis process to obtain a large number of pyrolysis products,pre-treated samples pyrolysis-volatile compounds of the precipitation peak decreases and acetic acid and other substances decreased.In addition,we can get the same conclusions by the equal conversion method and the Malek's method to calculate the apparent activation energy,frequency factor and reaction mechanism function of pyrolysis of corn stalks before and after pretreatment.Microwave pretreatment reduces the activation energy of pyrolysis,making the reaction easier to occur.The pyrolysis products composition and product distribution of corn stalks before and after pretreatment were investigated by using pyrolysis chromatography mass spectrometry.The major volatile products of corn stalk pyrolysis can be roughly divided into acids,ketones,phenols,aldehydes,furans and esters.Phenols compounds are the most important chemical components of all samples,and ketone products are also abundant.The phenols content of the pretreated samples decreased.Pretreatment can promote the ring cutting of cellulose and hemicellulose to form light aldehyde and increase the aldehyde content.In addition,microwave pretreatment affected the interaction between hemicellulose and cellulose,and thus had a positive effect on the formation of furan.Pretreatment of corn stalk samples before pyrolysis led to a substantial decrease in acid content,especially acetic acid was completely removed after pretreatment with microwave ammonia,and the increase of ester content further indicates that microwave pretreatment can effectively improve the quality of bio-oil produced by biomass pyrolysis.