Catalytic Conversion Of ?-Pinene To Prepare Biomass High Energy Density Fuels

In view of the exhaustibility of fossil resources,the growing greenhouse effect issue and the higher and higher requirements of modern aircrafts for fuels performance,the use of biomass resources for the preparation of high-performance high energy density fuels?HEDF?has important scientific significance.As one of the most abundant natural renewable resources,turpentine has rigid polycyclic structures in its components and can provide C10^C15 frameworks,making it an ideal raw material for the preparation of biomass HEDF.At present,the preparation of HEDF using turpentine usually require multiple steps,ie.dipolymerization,purification,hydrogenation,and formulation,which possesses several problems such as high energy consumption,uneven acid sites distribution and poor reproducibility of the catalysts.In this paper,two types of DES catalysts were designed,prepared and used to catalyze the dimerization of?-pinene,the main component of turpentine.A series of HEDFs with different composition distributions were prepared by changing the amount of catalyst.Three catalytic reaction systems were established:?1?dipolymerzition of?-pinene catalyzed by Lewis acid DES?2?dipolymerzition of?-pinene catalyzed by Br???nsted acid DES?3?one-pot preparation of HEDF from?-pinene catalyzed by difunctional composite catalyst.Among a series of Lewis acid DES with acetamide,tetrabutylammonium chloride,FeCl₃,AlCl₃,SnCl₄ as raw materials,ACA/1.4AlCl₃ was found the best catalyst in the dimerization of?-pinene.A 99.69%conversion of?-pinene and a 77.89%dimerization selectivity were achieved under the optimal reaction conditions:14 wt%ACA/1.4AlCl₃,10 mL?-pinene,10 mL solvent toluene,100°C,and 2 h.After reaction,the catalyst could be separated from product automatically.However,after recycling of three times,the catalytic conversion and selectivity decreased to 27.50%and 47.61%separately due to the easy hydrolysis of AlCl₃ in the air.Under the above optimized conditions,a series of biomass blended fuels with different product distributions catalyzed by ACA/1.4AlCl₃ were prepared by changing the amount of catalyst.Their fuel properties were determined after hydrogenation process.It was found that the hydrogenated product catalyzed by 10 wt%catalyst had excellent fuel performance:60.72 mm²/s low temperature viscosity?-10°C?,0.9162 g/cm³ density,40.40 MJ/L heat of combustion,-91°C freezing point,and 36.4°C flash point.Among a series of water-tolerant Br???nsted acidic DESs with ChCl,TBAC,CF₃SO₃H,and CF₃COOH as raw materials,ChCl/2.4CF₃SO₃H was found the best catalyst in the dimerization of?-pinene.A 99.96%conversion of?-pinene and a 83.49%dimerization selectivity were achieved under the optimal reaction conditions:8 wt%ChCl/2.4CF₃SO₃H,10 m L?-pinene,10 mL solvent toluene,80°C and 5 h,After reaction,the catalyst could be separated from product automatically and kept a dimerization selectivity more than 70%after recycling of five times.Under the above optimized conditions,a series of biomass blended fuels with different product distributions catalyzed by ChCl/2.4CF₃SO₃H were prepared by changing the amount of catalyst.Their fuel properties were determined after hydrogenation process.It was found that the hydrogenated product catalyzed by 4 wt%catalyst had excellent fuel performance:1166.00 mm²/s low temperature viscosity?-10°C?,0.9298 g/cm³density,41.20 MJ/L heat of combustion,-51°C freezing point,and 60.4°C flash point.With the simple combination of ChCl/2.4CF₃SO₃H and Pd/C,the feasibility of one-step one-pot dimerization-hydrogenation process of?-pinene in an autoclave was investigated.It was found that in the presence of both Pd/C and H₂,most of the monomers had undergone hydrogenation before dimerization.As a result,only a small amount of dimer was formed.However,over the above difunctional composite catalyst,a“two-step one-pot”process with 8 wt%ChCl/2.4CF₃SO₃H,0.025 wt%Pd/C.2.5 mL?-pinene,2.5 mL solvent toluene,80°C,and 4 h,could achieve a 53.52%dimer selectivity.It was found that the dehydrogenation/hydrogenation reaction of isomers was more favorable in the presence of Pd/C.The possible reaction mechanism was proposed.In this paper,two types of acidic DES catalysts have been successfully prepared and used in the dimerization reaction of?-pinene.Good catalytic performances have been achieved and biomass HEDF products have been obtained based on the above process,which provides an efficient and green method for the preparation of HEDF through?-pinene dimerization.