Catalytic Pyrolysis Of Biomass For The Production Of Phenolic Compounds And Complexation Precipitation Extraction Of Phenols From Bio-Oil With The Study Of Complexation Reaction Mechanism

Biomass is the only renewable resource that can be transformed into liquid fuels.Fast pyrolysis technology has been extensively investigated because it can convert the wastes from agricultural and forestry industry into the liquid fuels called bio-oil.A lot of valuable chemicals can be separated from bio-oil as there are many different components in it.Specifically,the content of phenols in bio-oil is more than 20%,and these phenols which are more environmentally friendly,have the potential to replace the phenolic compounds from the petroleum industry.However,the extraction of phenolic components from bio-oil is very difficult because of more than 300 kinds of phenolic compounds contained in bio-oil.Therefore,the content and sorts of oxygenated chemicals in bio-oil need to be consolidated to make the extraction of phenolic compounds easier.Several kinds of catalysts?including montmorillonoid,?-Fe₂O₃,?-Fe₂O₃,ZnO,SiO₂,HZSM-5?Si:Al = 25:1?,HZSM-5?Si:Al = 50:1?and nano-HZSM-5?Si:Al = 50:1??have been screened,and HZSM-5,which has the proper pore size and acid sites,is found to be most suitable for transforming these oxygenated compounds into aromatic hydrocarbons while keeping phenols intact.For example,when pine sawdust was pyrolyzed at 550 ? with 20%HZSM-5 added as catalyst and the reactor was closed for 10 min,the yield of bio-oil was 32%.And the content of oxygenated compounds?except phenolic components?could be reduced from 22.1%to only 4.68%while the aromatic hydrocarbons increased from 2.44%to 64%;What's more,the content of phenols was kept at 27.83%.Thus,the main components of upgraded bio-oil were aromatic hydrocarbons and phenols,which makes the extraction of phenolic compounds easier compared to that from crude bio-oil.Many researchers have found that Ca²⁺ could coordinate with phenolic compounds in an alkaline environment to form complex precipitation that precipitates out of the aqueous solution.Based on this characteristic,Ca?OH?₂ was used as complexation agent to extraction phenolic components from bio-oil.On the study of guaiacol extraction from the modeled bio-oil,4 mol/L of ammonia solution,40 ? of reaction temperature,and 20 min of reaction time were found to be the best.For 40 g of the crude bio-oil used for the complexation extraction,about 2.9 g of phenolic compounds were obtained,with the purity of 93.07%.The whole extraction process did not discharge any pollutants into the environment and the calcium hydroxide can be recycled.What's more,the residual bio-oil has the potential to producing the deicer of CMA.The reaction mechanism of the complexation precipitation extraction was further studied.For the reaction between guaiacol and Ca?OH?₂,three sequential reaction phases were revealed.The first phase was the acid-base reaction,1 mol guaiacol reacted with 1 mol Ca?OH?₂ to produce 1 mol water and 1 mol Ca?GO?OH.The second phase included both the acid-base reaction and coordination reaction,that is,1 mol guaiacol reacted with 1 mol Ca?GO?OH,and the 1 mol guaiacol was neutralized by 1 mol OH-ionized from Ca?GO?OH to produce water and guaiacol ion;then the guaiacol ion coordinated with Ca²⁺ through the oxygen atom of hydroxyl group,in which the product with the molecular formula of Ca?Go??GO?was formed.The third phase was the coordination reaction between hydrogen?Ha and Hc2?atom of guaiacol molecule and Ca²⁺,in which 1,2,3-substituted guaiacol was yielded.The molecular formula of the final complex was Ca[?G_H?₂?Go?]?GO?.Based on the study of reaction mechanism,a pioneering phenolic extraction technology was proposed and researched in this work.The intermediate product Ca[GO]?GO?was considered to be the recyclable precipitation agent for guaiacol extraction.1 mole Ca[GO]?GO?reacted with 2 mole guaiacol to form 1 mole solid precipitation Ca[?G_H?₂?GO?]?GO?.And 2 mole guaiacol were released and collected when the precipitation was heated to 200 ?;at the same time,the circulating precipitation agent Ca[GO]?GO?was regenerated.The guaiacol extraction rate reached 96.63%when pH of the guaiacol solution was not adjusted,and a relatively high value of 93,16-96.63%was maintained when the pH of guaiacol solution was kept 5-10.Furthermore,guaiacol extraction rate was decreased with the increasing OH' or H+concentration in the guaiacol solution.Because Ca[GO]?GO?can be dissociated by H+,thus reactant guaiacol can be neutralized by OH'.The guaiacol extraction rate begins to decrease when the reaction temperature was increased to above 20 ?.Because the decomposition temperature of bond Ca²⁺-?HA/Hc2?was so low?134 ??that high temperature prevented the generation of coordination bond.10 s extraction time was enough for the complexation reaction.Such a short reaction time for the complexation reaction is beneficial for the industrial application of this technology.