Research On The Production Of Monomeric Aromatics From Co-pyrolysis Of Lignin

For the special aromatic structure of lignin,it can be converted to high-valued products such as aromatics and phenols by fast pyrolysis process,which have a great application prospect in the future.However,High C content and low H content result in the low H/Ceff of lignin.The quality of pyrolysis oil of lignin is relatively low.The application of lignin co-pyrolysis technology can adjust the composition of pyrolysis products and further obtain higher yield of high-valued chemicals.Therefore,in this research,black-liquor lignin and its model compounds were used as raw materials to study the production of mono-aromatic compounds in fast co-pyrolysis process.The evolution method and co-pyrolysis mechanism were derived towards different solid and liquid blends.TG-FTIR and Py-GC/MS were used to detect the thermogravimetic characteristcs and distribution of monomeric aromatic products in fast pyrolysis process of lignin.The results showed that lignin has a wide weight loss temperature range(180 ℃-669 ℃)and the main gases produced in lignin pyrolysis process detected by FTIR included H20、CO、CO2 and CH4.G-and S-type compounds dominated in pyrolysis products when pyrolysis temperature was relatively low(500 ℃-600 ℃),while AH-and H-type compounds were the main products at higher temperature(700 ℃～900 ℃).At the pyrolysis condition of 700 ℃,different types of lignin pyrolysis products were uniformly distributed.Three types of plastic polymers(LDPE,PC and PS)were used as blends in lignin co-pyrolysis process in order to study the influence of blends type and blend ratio to the distribution of co-pyrolysis products.The results showed that the TG experimental curve of lignin/PC blends has great difference compared with theoretical one,for the reason that lignin can produce H2O in low temperature for its low thermal stability.H20 produced by lignin can participate the hydrolysis reaction of PC,resulting its lower initiation reaction temperature.The co-pyrolysis results of lignin with three types of plastic polymers showed that LDPE can restrain the production of most aromatics in co-pyrolysis process.PS promoted the production of aromatic hydrocarbons(especially for styrene).The promotion function was more obvious when blend ratio of lignin and PS was 4:1.PC promoted the production phenol type compounds.For the selection of liquid blends,the characters of four type of alcohols(CH3OH,CH3CH2OH,CH3CH2CH2OH and CH3CH3CHOH)were calculated through quantum chemical calculation method.It was found that methanol has the highest reactivity when attacked by free radicals,the most likely bond breakage for the production of H radical and the simplest structure of radical,so methanol is a suitable blend which can be used in lignin co-pyrolysis process.The results of co-pyrolysis process of BPE and PPE with methonal showed that methanol promoted the production of mono-aromatics and restrain the produciton of dimer and trimer aromatics.The promotion of monomeric aromatics in co-pyrolysis reaction increased as the increased content of methanol.The co-pyrolysis mechanism was infered by tracer experiements,in which methnal-d(CH3OD)was used as tracer material.It was found that the hydroxy’s D in CH3OD played an active role in co-pyrolysis process,which reflected on the participation of most monomeric aromatics’ formation.Almost all phenol products were labled with two D in co-pyrolysis of PPE with methonal-d.These results explained that the pyrolysis methanism of PPE was radical production mechanism while the concerted retro-ene mechanism did not exist in co-pyrolysis of PPE with methonal.