Study On The Pyrolysis Of Polyolefin Waste Plastics For Food Packaging Catalyzed By The Composite Of Nanofiber Carbon And HZSM-5

Large amounts of cellulose waste can be produced in the process of processing agricultural products.In addition,a lot of plastic waste can be produced in the process of food packaging and sales.Both the cellulose and plastic waste is extremely hostile to the environment.Associated with its excellent specific surface area and porous structure,nanocarbon materials can be used as catalysts after certain treatments.Based on that,turning nanocellulose into nanocellulose-based carbon catalyst is becoming a new application filed.For the plastic waste,turning it into bio-oil through pyrolysis is currently the mostly promising method to repay the fossil fuel industry.In this paper,we studied the preparation of nanocellulose and the preparation process of nanocellulose-based carbon composite catalyst.By using this catalyst,the mechanism and optimal preparation of high aromatic bio-oil by pyrolysis of food packaging plastic waste were studied and discussed.1.Preparation of nanocellulose by hydrolysis of celluloseIn this chapter,we developed a magnetic carbon-based solid acid,MBC-SA,by using Fe₃O₄and straw as raw materials.Two types of magnetic carbon-based solid acids,MBC-SA1 and MBC-SA2,were prepared by changing the sequence of sulfonation and carbonization.We further characterized the crystal structure,acidity,distribution of functional groups,and channel information of MBC-SA1 and MBC-SA2.In addition,we explored a process for hydrolyzing cellulose into nanocellulose using magnetic solid acids as catalyst.It was found that when MBC-SA1 was used to hydrolyze cellulose,93.75%of the nanocellulose size was less than 100 nm.When MBC-SA2 was used,74.72%of the nanocellulose size was less than 100 nm.The distribution of nanocellulose obtained by MBC-SA1 hydrolysis was concentrated at 21-60 nm.The relative nanocellulose size from the MBC-SA2 hydrolysis was larger,which was concentrated at 30-90 nm.The mechanism of hydrolysis of cellulose by carbon-based solid acid was deduced by the particle size distribution of the hydrolysates.2.Optimization for processing nanocellulose by hydrolysis of celluloseTo convert the cellulose into nanocellulose as much as possible,we further increased the yield of nanocellulose from 57.68%to 87.12%by further utilizing the advantages of enzymatic hydrolysis.Cellulase has strong activity in the pH range of4.5-6 and the pH range created by carbon-based solid acid was the same as the optimal pH of cellulase.Therefore,the addition of MBC-SA not only does not affect the activity of cellulase,but also provides the best weak acid environment for cellulase.This chapter studies the effect of the amount and order of adding cellulase and solid acid on the yield and size of the product.The results demonstrated that the addition of solid acid was beneficial to the hydrolysis of cellulose by cellulase and the increase of cellulase content also contributed to the hydrolysis of cellulose.By comparative analysis of the structure of residual cellulose and the size distribution of nanocellulose,it was found that the crystallinity of cellulose hydrolyzed by MBC-SA1 was higher and more difficult to be hydrolyzed by cellulase.On the contrary,the crystallinity of cellulose hydrolyzed by MBC-SA2 was lower and easier to be hydrolyzed by cellulase.When both the MBC-SA hydrolyzing the cellulose at the same time,MBC-SA2 showed a higher yield of nanocellulose of 84.63%.By analyzing the size distribution of nanocellulose and the structure of carbon-based solid acid,the related mechanism of cellulase hydrolysis of cellulose was deduced.3.Preparation of carbon-based nano cellulose catalyst and its catalytic pyrolysis of waste food packaging plasticsNano carbon-based catalyst（NCBC）was prepared by fast microwave-assisted pyrolysis of nano cellulose.The structure and properties of nano cellulose carbon-based catalysts were studied by BET,temperature programmed desorption（NH₃-TPD）,Fourier transform infrared（FT-IR）,transmission electron microscope（TEM）,scanning electron microscope（SEM）,X-ray diffraction（XRD）,thermogravimetric analysis（TGA）and other modern scientific techniques.After comparing the NCBC with metal supported carbon-based catalysts and structural analysis,it was found that NCBC had not only high specific surface area and abundant acidic sites,but also structures full of macro-porous,mesoporous,and microporous.These characteristics fully meet the requirements of pyrolysis catalysts.Results showed that the yield of liquid fuel increased and then decreased with the increase of catalytic pyrolysis temperature.The yield reached the highest（78.34%）at 750℃and the catalyst/raw material ratio is 1:1.From the composition of liquid fuel,the main components of liquid fuel obtained at without catalyst are long-chain olefins,alkanes and oxy-alkanes derivatives,no aromatic hydrocarbons.With the increase of temperature and catalyst ratio,more unsaturated olefins,short chain,medium and long chain alkanes were generated.The main pyrolysis products were alkanes at the optimal catalytic temperature,with the content of 59.27%.This is because the catalytic effect of NCBC is promoted at higher temperature.At higher temperature,NCBC was more powerful for the reorganization and decomposition of pyro-gas.NCBC can not only reduce tar production,but also remove oxygen from pyrolysis gas.According to the changes of liquid fuel composition,it can be seen that the amount of oxy-hydrocarbon derivatives was obviously decreased.It could be inferred that the long-chain hydrocarbon derivatives in pyrolysis gas were broken into short-chain hydrocarbon derivatives by the acidic sites of NCBC.Combined with the change of olefin content and the increase of hydrogen content in gas composition,it can be inferred that NCBC has high reducibility.4.Research on reducing coking phenomenon and improving bio-oil composition in the process of HZSM-5 catalytic conversion of polyolefin waste plasticsUnlike the molecular sieve catalysts which have been widely used in pyrolysis,the catalytic mechanisms of the nanocarbon-based catalysts have not been extensively studied or understood.In this chapter,we studied the external catalytic conversion of food packaging plastics（PP）and bamboo scraps with HZSM-5 as catalyst from the perspective of co-pyrolysis.Compared to the use of bamboo biomass alone,PP contains high hydrogen and low oxygen content and has a high effective hydrogen to carbon ratio(H/C_eff.).As a result,by adding PP,the pyrolysis gas generated during the pyrolysis of bamboo biomass can be converted into aromatic hydrocarbons to obtain higher quality of liquid fuel.At the same time,the hydrogen radicals generated during the pyrolysis of PP can be used to reduce the polymerization reaction that occurs on the surface of HZSM-5,thereby reducing the production of biocoke.In this chapter,we studied the effects of ratios of raw material/catalyst and bamboo scrap/plastic on the yield of co-pyrolysis products and the chemical composition of bio-oil.With the increase of catalytic temperature and catalyst ratio,the yield of bio-oil and the yield of carbon deposition decreased.When the raw material/catalyst ratio and the bamboo shavings/PP ratio are 1:2 and 2:1,respectively,the yield of biocoke is the lowest 3.03wt.%,and the yield of bio-oil in the pyrolysis product reaches the maximum of 61.62wt.%,The content of aromatic hydrocarbons in bio-oil components is 29.29%.The proportion of oxygen-containing compounds decreased with the increase of catalyst content.The addition of PP increases the H/Ceff.It not only reduces the yield of biocoke,but also improves the ratio of aromatic compounds and cycloalkanes.From the perspective of liquid fuels,the quality of bio-oil has been greatly improved.5.Preparation of high aromatic fuel oil from food packaging plastics by pyrolysis of nanocellulose-based carbon composite catalystThe advantages and disadvantages of the nanocellulose carbon-based catalysts and HZSM-5 can be identified by comparing their structures and pyrolysis characteristics.In this work,we introduced HZSM-5 into the preparation process of nanocellulose carbon-based catalyst to synthesize a new catalyst with the advantages of both nanocellulose carbon-based catalyst and HZSM-5.Different types of composite catalysts were synthesized by adjusting the ratio of nanocellulose and HZSM-5 and characterized by TEM,SEM,FT-IR,NH₃-TPD,and BET.The characterization results exhibited that HZSM-5 was sintered together with the nanocellulose carbon-based composite catalyst and the composite catalyst had all the characteristics of the two catalysts.By analyzing the pyrolysis LDPE of nanocellulose carbon-based composite catalyst,we found that with the increase of HZSM-5 content in the composite catalyst and the increase of pyrolysis temperature,the aromatic hydrocarbon content demonstrated a trend of increasing first and then decreasing.The increase of HZSM-5content in the composite catalyst significantly increases the selectivity of aromatic hydrocarbons and decreases the selectivity of long-chain alkanes.The increase of the pyrolysis temperature will reduce the biocoke produced during the pyrolysis process by3.6%.The increase of nano-cellulose carbon in the composite catalyst will significantly reduce the yield of biocoke.The minimum yield of biocoke is 3.4%,which is a decrease of 7.85%compared to 11.25%when HZSM-5 is used alone.The aromatization ability of HZSM-5 is 30%higher than the theoretical value under the promotion of NC,indicating that there is a synergistic relationship between the two,which can promote the conversion of chain hydrocarbon and unsaturated hydrocarbon to aromatic hydrocarbon.The best effect of catalytic pyrolysis of LDPE can be achieved with the ratio of nanocellulose to HZSM-5 at 1:1.The catalytic transformation mechanism of nano-cellulose carbon based composite catalyst can be inferred by analyzing the change of liquid product component content and gas component content.First,LDPE is decomposed into alkanes and olefins at high temperature and the pyrolysis gas is driven by carrier gas into the nanocellulose carbon based composite catalyst.The nanocellulose carbon-based catalyst is highly absorbent and will capture the pyrolysis gas into the catalyst.The captured pyrolysis gas will be subsequently decomposed into alkanes and olefins with small molecular weight due to the reductivity and acidity of the nanocellulose carbon-based catalyst.Since the HZSM-5 is closely combined with nanocellulose carbon-based catalyst,the small-molecular weight alkanes and olefins decomposed by nanocellulose carbon-based catalyst are captured for secondary catalytic reforming during the catalytic reforming of pyrolysis gas by nanocellulose carbon-based catalyst,resulting in a large number of aromatic hydrocarbon compounds.