Study On Producing Bio-oil By Biomass Vacuum Pyrolysis Liquation And Activated Carbon By Biomass Vacuum Chemical Activation

Biomass energy is a very important part of the renewable energy. The biomass resources are very abundant,inexhaustible and sustainable in the world.The exploitation and utilization of the biomass energy is an effective method for relieving the pressure of the shortage of conventional energy resources and environment pollution in China. Thermochemical conversion is the major way for high efficient utilization of biomass and a hot point of research both in China and abroad.Biomass pyrolysis technology has been paid great attention through which low-quality biomass can be converted to higher quality liquid fuel or high add-value products.Pyrolysis process is the most essential content in a variety of thermochemical conversion processes of biomass.From the study of the changing rules and influence factors during the biomass pyrolysis process,it provides scientific basis and help to achieve efficient biomass thermal conversion technology.In this study,TGA and self-made vacuum pyrolysis apparatus were used to detect the characteristics of biomass pyrolysis liquation and the rules of preparation of activated carbon under vacuum.The seven kinds of common agricultural and forestry waste biomass were from Yiyang. The main contents studied are as follows:(1) TGA was used to detect the influence of biomass species and heating rate on the pyrolysis reaction.The results show that the vacuum pyrolysis laws of seven kinds of biomass are almost the same.There are three stages mainly:free hydrolysis adsorption and precipitation extraction stage,rapid weight loss stage of pyrolysis,and slow decomposition stage of residue.The order of total weight loss rate of biomass under the same condition is as follows:fir sawdust＞corn stalk＞pine sawdust＞erythrina sawdust＞bean stalk＞rice husk＞peanut shell.The maximum peak temperature,thermal decomposition rate,the initial decomposition temperature and thermal stability of forestry biomass are higher than that of agricultural biomass.Vacuum pyrolysis reaction almostly complete when the temperature is 500℃.As the heating rate increased,the TG curves shift to right,peak temperature shift to high temperature,the temperature range of main reaction widen. The pyrolysis of fir sawdust under vacuum keeps the first order reaction rules approximately.(2) Fir sawdust was taken as raw material to study the biomass vacuum pyrolysis liquation.The influence of process parameters on the pyrolysis products was researched.The results show that the optimum conditions of pyrolysis as follows:pyrolysis temperature is 500℃,the system pressure is 20kPa,and holding time is 60min.Compared with fast pyrolysis,vacuum pyrolysis of fir sawdust can also get a higher yield of bio-oil with a lower heating rate.The pyrolysis product is mainly bio-oil and the yield of bio-oil can reach to above 67%under better preparation condition.There are larger differences of the main chemical composition and its relative content when the pyrolysis parameters are different.We can get bio-oil with higher additional value by choosing appropriate pyrolysis parameters.The vacuum pyrolysis carbon already has an initial pore structure,and the pores are mainly micropores,which can be excellent raw materials for activated carbon preparation.(3) Seven kinds of biomass were taken as raw material to prepare bio-oils.The effects of biomass species on the yield of the pyrolysis product and the physical and chemical properties of bio-oil were studied. The main product of pyrolysis is bio-oil,and the yield of which is all above 55%.The bio-oil yields of forest biomass are higher than that of agriculture biomass,and for fir sawdust the highest yield is 67.25%and for corn straw the lowest yield is 55.46%.The pH value of bio-oil is 1.82～3.24,and the pH value of the forest bio-oils are less than that of agriculture bio-oil.The density is 1.0163～1.1670,and the density of the forest bio-oils are more than that of agriculture bio-oil.The viscosity is 2.29～7.36,which is small,and the viscosity of the forest bio-oils are more than that of agriculture bio-oil.The types of compounds contained in the bio-oil were similar,but there are some difference in the specific chemical composition and its relative content.For example,the furan derivatives content of the rice husk bio-oil is the highest(22.8%),and that of the fir sawdust is the lowest(0.99%).While relative content of phenol and its derivatives in fir sawdust bio-oil can up to 72.81%,but which in bean stalk bio-oil is only 23.97%.Only fir sawdust bio-oil has eugenol which has antibacterial,stomachic,anesthesia,lowing blood pressure and other pharmacological effects.(4) The vacuum pyrolysis mechanism of biomass was studied according to the chemical composition and molecular structure of raw material and the structure of bio-oil components.The formation mechanism of the main components of bio-oil was obtained.(5) Activated carbon was prepared from biomass under vacuum by zinc chloride activation.Activated carbons prepared by fir sawdust under atmosphere and vacuum were compared.Effects of system pressure,activation condition and other process parameters on the properties of activated carbon were studied.Results show that the yield of activated carbon is about 40%.Fir sawdust is the most appropriate precursor for activated carbon preparation.The best system pressure of preparing activated carbon from fir sawdust is 20.5kPa.We can get activated carbon with excellent properties and bio-oil with high additional value under better preparation conditions.The mainly structure of activated carbon is microspore.The surface area of prepared activated carbon is 1070.59m~2/g,microspore volume is 0.5581cm~3/g, average pore diameter is 2.085nm,iodine adsorption value and methylene blue adsorption values are 1142.92mg/g and 131.24mg/g respectively.The nitrogen adsorption isotherms of activated carbon prepared from fir sawdust under vacuum are all belong to typeⅠadsorption isotherm,they are can be described by the Langmiur equation。With the system pressure dropped,the nitrogen adsorption equilibrium constant of the activated carbon increased.The pore structure characteristic and adsorption performance of activated carbon prepared under vacuum are better than that of the one prepared under atmosphere.