Research On Concentrated Solar Energy Driven Photothermal Catalytic Pyrolysis Of Waste Plastics For Jet Fuel

With the rapid development of modern society,the increasing demand for plastic products has led to the rapid growth of plastic waste,which not only causes huge environmental pollution,but even threatens the life and health of humans and marine organisms.Therefore,it is urgent to deal with waste plastics.The plastic of simple components（mainly C and H）is an excellent raw material for making jet fuel by pyrolysis.However,pyrolysis progress is accompanied by deficiencies such as rough products,low pyrolysis efficiency and high energy consumption.The catalyst can not only greatly reduce the activation energy of the pyrolysis,but can also directionally control the final product of the pyrolysis.But at the same time,catalytic pyrolysis is also faced with deficiencies of low catalytic efficiency and uneven product quality.Photothermal catalysis is a new method that can integrate the advantages of photocatalysis and thermal catalysis and make up for single thermal catalysis’s defect.Therefore,this article is devoted to exploring the catalyst with photothermal catalysis.And the waste plastics are oriented to prepare jet fuel by the photothermal catalyst.Firstly,the optical photocatalyst is explored and the possible mechanism of photothermal synergistic catalysis is obtained through comparative experiments.Then the pyrolysis temperature（550,600,650,700°C）,photocatalyst loading（10,20,30wt.%）and catalyst:plastic ratio（1,2,3）‘impacts on pyrolysis products are explored.At last,the selectivity of target products is improved by modifying photothermal catalysts.The main work is as follows:Firstly,the product distribution of low-density polyethylene（LDPE）catalystic pyrolysis using four photocatalysts is investigated.The results show that TiO₂ has the best selectivities of H₂and C₈-C₁₆hydrocarbons.On this basis,activated carbon（AC）is selected as the thermal catalyst,and the photothermal catalyst TiO₂-AC is prepared by the sol-gel method.The photothermal catalysis mechanism is explored through further comparative experiments.The study finds that the photothermal catalyst TiO₂-AC has the highest jet fuel selectivity（68.59%）and H₂ selectivity（50.69vol.%）.It exerts a photothermal synergistic catalytic effect.On the one hand,TiO₂ photoactivates the reactant molecules,which improves the probability of thermal catalytic pyrolysis.On the other hand,the AC promotes the separation of TiO₂ photo-generated carriers and enhances the ability to absorb visible light,thus improving the photocatalytic performance.Then,the optimal reaction conditions of LDPE photothermal catalystic pyrolisis by TiO₂-AC are explored.As the pyrolysis temperature increases,more olefins in the oil are converted into aromatics（64.60%）and alkanes（29.20%）.The loading of TiO₂affects the distribution of aromatics in the oil,and excess TiO₂ promotes the formation of monocyclic aromatics below C₈,which in turn leads to a decrease of jet fuel components.As the amount of catalyst increases,the number of catalytic active sites increases,and the catalytic performance becomes better.Therefore,the selectivity of jet fuel in the oil increases,but the oil yield decreases.When the catalyst:raw material is 2:1,the pyrolysis temperature is 650°C,and the TiO₂ loading is 20wt.%,LEPD photothermal catalystic pyrolysis has obtained a high liquid yield（65.09wt.%）and a high jet fuel component（68.59%）.Finally,in order to improve the selectivity of the jet fuel components in the oil.TiO₂-AC was modified by supporting metals and semiconductors.Then,the waste plastics photothermal catalysis pyrolysis is carried out under the optimal reaction conditions.The results show that loading metals or semiconductors does improve the selectivities of jet fuel components and H₂.After the metal is modified,when the interface between the metal and the photocatalyst is irradiated by sunlight,a plasmon effect occurs on the metal surface,which will improve the photocatalytic performance.The formation of heterojunction by supporting semiconductors increases the degree of cracking and isomerization,also shortens the length of the carbon chain,which increases the proportion of the peak area of chain alkanes and monocyclic aromatic hydrocarbons（belonging to jet fuel）.Therefore the photothermal catalytic performance is improved.When the optimal photothermal catalyst Zn O-TiO₂/AC is selected,the peak area ratio of jet fuel components in the oil is 93.97%,which has the increase of 30.39%compared to TiO₂-AC,and the hydrogen content has also increased from 50.60vol.%to 60.67vol.%.