Study On The Co-pyrolysis Of Polypropylene And Biomass To Produce High-quality Pyrolysis Oil

With the development of society,people’s demand for energy is increasing,so it is urgent to find renewable resources to replace fossil energy.Biomass has become a research hotspot due to its abundance,carbon neutrality and renewability,and is a good substitute for fossil fuels.Pyrolysis is a promising technology for converting biomass into three valuable products:pyrolysis oil,char and gas.However,the high acidity,high viscosity,high oxygen and water content and low heating value of bio-oil limit its further industrial application.Polypropylene is rich in hydrocarbons,and co-pyrolysis of hydrogen-rich polypropylene and oxygen-rich biomass is a potential strategy to improve the yield and quality of bio-oil.In this paper,different biomass and biomass/polypropylene were pyrolyzed by tubular furnace,and their pyrolytic characteristics were explored to provide theoretical basis and data support for the comprehensive utilization of polypropylene and biomass resources.In this article,three kinds of barks（Raw pine bark,Pine bark and Douglas-Fir bark）were pyrolyzed separately.Mass and energy yield analysis,elemental analysis,molecular weight analysis,³¹P and ¹³C nuclear magnetic resonance analysis were used to evaluate the pyrolysis products.It was found that most of the elements in the pyrolysis oil prepared from different pine barks were carbon and oxygen,with the proportion of carbon～60wt%and oxygen～30wt%;the higher heating values of the pyrolysis oils are 24.54MJ/kg～26.70MJ/kg;the weight average molecular weight of pyrolysis oil is 389～489,and the number average molecular weight is250～294;the pyrolysis oils are rich in aliphatic OH,catechol,guaiacol and p-hydroxy-phenyl OH,while C₅ substituted guaiacyl phenolic OH and acid-OH are less.In order to improve the quality of bio-oil,the co-pyrolysis of different biomass and polypropylene was used to explore the synergistic effect of the product yield.Then,taking the co-pyrolysis of corn stover and polypropylene as an example,the effects of the mixing ratio of raw materials,reaction temperature,catalyst addition and reaction atmosphere on the yield of co-pyrolysis products and the physical and chemical properties of pyrolysis oil were studied.The research results show that when biomass and polypropylene are co-pyrolysis,the experimental yield of pyrolysis oil is higher than the theoretical yield,and the experimental yield of char and gas is lower than the theoretical yield.When corn stover:polypropylene=1:3,the yield of pyrolysis oil was as high as 52.1wt%,which was 4.5wt%higher than the theoretical value.With the increase of pyrolysis temperature,the yield of pyrolysis oil increased first and then decreased,and reached the optimal yield at 550°C.The addition of catalyst（HZSM-5）reduced the proportion of oxygenates and promoted the generation of aromatic hydrocarbons.CO₂ has a certain oxidation effect on the components of pyrolysis oil,which promoted the increase of oxygen-containing aromatics and the reduction of deoxy-aromatic hydrocarbons.Finally,biomass model compounds were used to replace single raw material to further study the synergistic mechanism of co-pyrolysis between biomass and polypropylene.Thermogravimetric analysis and synergistic analysis of product yield showed that there are some interactions between biomass and polypropylene during co-pyrolysis.¹H and ¹³C nuclear magnetic resonance analysis showed that the synergistic reactions between biomass and polypropylene during co-pyrolysis were as follows:（1）The olefin produced by polypropylene and the furan produced by cellulose and hemicellulose undergo dehydration reaction and Diels-Alder reaction to produce aromatic compounds;（2）The hydroxyl radicals produced by cellulose and hemicellulose combine with the resulting phenyl radicals to form phenolic substances;（3）Hydrogen radicals produced by polypropylene combine with phenoxy groups produced by lignin to form phenols;（4）Alkyl and olefin groups produced by polypropylene combine with the benzene ring to replace the hydrogen atoms on the benzene ring.