Synthesis Of Platinum Nanoparticles Modified With Hyperbranched Polyethyleneimine And Application In Hydrocarbon Fuels

Because of important applications in the field of national defense and aerospace,hypersonic vehicles attract a lot of attention in the world.Hypersonic vehicles undergo strong friction against the air during flight,generating a large amount of thermal energy and causing significant temperature rise of the aircraft,which leads to a huge challenge to the high temperature performance of material.An endothermic hydrocarbon fuel with both abilities of energy supply and active cooling was then introduced,and it is hoped that the aircraft temperature can be reduced while achieving energy supply.The enhancement of the cooling capacity of a hydrocarbon fuel mainly depends on its chemical heat sink,which is usually achieved by its catalytic cracking with high conversion and high selectivity.To design a new kind of lipophilic metal nanoparticles for hydrocarbon fuels to be stable nanofluids is a new approach of producing hypersonic vehicle propellant,which can improve selectivity and conversion of catalytic cracking.However,metal nanoparticles dispersed in hydrocarbon fuels are prone to coagulation.Therefore,how to form stable and well-distributed metal nanoparticles for a long-term storage in hydrocarbon fuels is a practical problem that needs to be solved.In this thesis,several kinds of surface-modified platinum nanoparticles were prepared with hyperbranched polyethyleneimine(HPEI)as the stabilizer.The dispersion stability of platinum nanoparticles and their catalytic effects on the cracking of hydrocarbon fuels were investigated.The results are provided for new application of nanofluidic fuels.The main contents of this work are summarized in the following parts.The hyperbranched polyethyleneimine(HPEI)was modified to lipophilic HPEI-Cn(HPEI-C120.73?HPEI-C160.73?HPEI-C200.73?HPEI-C220.73 and HPEI-C1630)by amidation reaction with different carbon chain length of fatty acids(CnH2nO2,n=12,16,20,22).The products of HPEI-Cn have good solubility in hydrocarbon fuels.Then,the lipophilic platinum nanoparticles Pt@HPEI-Cn were synthesized with HPEI-Cn as stabilizer,H2PtCl6·6H2O as the precursor and NaBH4 as the reducing agent.The structural propertiesof the synthesized products were characterized by NMR,FTIR,UV-Vis,TGA and TEM.The effects of reaction temperature,Pt/HPEI-Cn ratio,carbon chain length and degree of substitution of stabilizer molecules on the properties of platinum nanoparticles were discussed.The experimental results show that the modification of metal platinum with HPEI as the stabilizer precursor,the platinum nanoparticles are uniformly dispersed and have particle size of 2 nm.The dispersion stability of various platinum nanoparticles,Pt@HPEI-C120.73,Pt@HPEI-C160.73,Pt@HPEI-C200.73,Pt@HPEI-C220.73 and Pt@HPEI-C160.30,in MCH(platinum content is 25 ppm)was investigated by UV-vis.The time-dependent results of UV-Vis scanning show that the five types of platinum nanoparticles with the characteristic absorption peak at 210 nm can be well-dispersed in MCH.Pt@HPEI-C160.73 has the highest stability and the sedimentation ratio was less than 14%after 1512 h.The platinum nanoparticles,Pt@HPEI-C120,73,Pt@HPEI-C160.73,Pt@HPEI-C200.73,Pt@HPEI-C220.73 and Pt@HPEI-C160.30 were then investigated for the catalytic cracking of MCH.It was found that,with adding platinum nanoparticles(platinum content is 500 ppm),the conversion ratio,gas yield and hydrogen content of MCH cracking were significantly improved at different reaction temperatures(380?410?).At 410?,the cracking conversion ratio of MCH+Pt@HPEI-C160.73 was increased from 3.14 wt%to 23.99 wt%compared with that of MCH.There were no significant differences in the catalytic promotion of MCH cracking by the five kinds of nanoparticles,indicating that the carbon chain length and the degree of substitution of stabilizer molecules had little effects on the catalytic cracking.The catalytic promotion of Pt@HPEI-C160.73 on cracking of the high density hydrocarbon fuel JP-10 was further investigated.It was found that after adding platinum nanoparticles(platinum content is 500 ppm),the conversion rate and hydrogen content of JP-10 cracking were also improved under different reaction temperatures(380?410?).At 410?,the cracking conversion ratio of JP-10+Pt@HPEI-C160.73 was increased from 3.29 wt%to 6.02 wt%compared with that of JP-10,the absolute increase of which was 2.73 wt%,and the relative increase of which was 83.01%.In summary,with HPEI-Cn as a stabilizer,lipophilic platinum nanoparticles with a particle size of 2 run can be successfully prepared and these surface-modified platinum nanoparticles are suitable for the preparation of hydrocarbon fuel nanofluids.The platinum nanoparticles can promote the cracking of hydrocarbon fuels.