| Due to the lack of advanced technology on a-olefins production and polyalphaolefins (PAO) synthesis, the imported PAO is still the main resource of the high-performance synthetic lubricant. The increasing scarcity status of petroleum resource is pushing us to widen the raw materials for wax cracking plants and develop the proper technology for producing high-performance PAO using a-olefins cracked from coal liquefaction wax in order to meet the national conditions of being rich in coal but lack of petroleum resource and change the situation of import dependency of PAO products. This kind of work, thus, is of great importance not only for improving the value of coal wax but also for coping with the urgent problem of lacking of petroleum resource and producing excellent synthetic lubricant base oil.The synthesis process of PAO base oil using a-olefins cracked from coal liquefaction wax with high melting point was achieved. The mixed a-olefins were produced by cracking coal liquefaction wax and the high-performance PAOs were synthesized using improved catalyst. The properties of synthetic PAO can meet the performance requirement of superior commercial PAO-8products. Meanwhile, the synthetic PAO could be blended with mineral base oil in order to upgrade the viscosity index of the base oil.Firstly, the cracking performances of three kinds of coal liquefaction wax were studied and discussed on a steam cracking experimental equipment based on the reliability testing of this equipment. Under the optimal conditions of preheating temperature of540℃, cracking temperature of670℃, the residence time of2.5s, and the steam ratio of16%, the results indicate that the single pass conversions of waxl#is62.6%, the single pass yield and selectivity of the liquid product are43.1%and68.9%, and the single pass yield and selectivity of a-olefins are28.4%and45.4%. In addition, the contents of a-olefins, diolefins, and alkanes in cracked liquid product are65.9%,9.7%, and18.3%respectively. Compared with54# petroleum wax, the coal liquefaction waxes show around30percentage higher single pass conversion and10percentage higher single pass yield of a-olefins, therefore, will make the cracking plant have lower recycling amount, lower energy consumption, and better economy.Then the oligomerization performance of mixed a-olefins produced from coal liquefaction waxes was investigated while the optimal catalyst system and reaction conditions of decene-1oligomerization were found. The results show that AlCl3/TiCl4catalyst exhibits high catalytic activity under low temperature. Under the oligomerization conditions of catalyst of AICl3/TiCl4, temperature of80℃, time of3h, n(Al)/n(Ti) of5, and catalyst dosage of3%,1#coal wax, which has a normal a-olefins content of65.25%, shows a yield of73.27%,v40of54.75mm2/s, v100of8.77mm2/s, VI of138, and FP of-51℃. As for2#coal wax with a normal a-olefins content of64.06%, the yield, v40, v100, VI, and FP are76.21%,54.19mm2/s,8.68mm2/s,137, and-52℃, respectively. PAO products synthesized from cracked a-olefins is mainly consisted of oligomers with the degree of oligomerization of3-5. Moreover, the fraction with distillation range of280～350℃has the highest content in PAO products. Besides, the pseudo slurry bed oligomerization process was investigated and the synthesis of PAO can be performed continuously for more than150h at the present pseudo slurry bed reactor.The analysis results of cracking mechanism indicate that the main cracking reactions are the chain scission reactions and dehydrogenation reactions of alkane molecules. A high temperature, low partial pressure of alkane, and short retention time are beneficial to the selectivity of a-olefins. The calculation results based on quantum mechanical method show that olefins can crack into diolefins more easily at higher temperature. The mechanism of a-olefins oligomerization is also discussed and the results indicate that the oligomerization reactions occur along with isomerization, hydrogen transfer, and cracking reactions. Furthermore, the oligomers, which have one linear main chain and proper branches, are the excellent components of high performance PAO.In addition, the kinetics of the coal wax cracking and oligomerization of a-olefins were studied. A lumping kinetic model of coal wax cracking was developed based on the assumption of first order consecutive reaction. The kinetic model exhibits high accuracy for predicting the conversion of coal wax and the yields of liquid and gas products. The rate constants of decence-1oligomerization at the temperature from343K to373K with AlCl3/TiCl4catalyst are found in the range of0.165min-1and0.300min-1. The kinetic model can be expressed as:Xm/(1-Xm)=294.71×exp(-21383.61/(RT))t. AlCl3/TiCl4catalyst gives higher catalytic reaction rate constants and3.14kJ/mol lower activation energy as compared to AlCl3catalyst, suggesting higher catalytic activity than AlCl3catalyst.In the end, the application performance of synthesized PAO was researched and discussed. It is found that the refined PAO product exhibits the similar properties to the commercial PAO-8product. Meanwhile, the synthesized PAO can be blended into petroleum base oil to upgrade the viscosity index of the base oil. The viscosity index of petroleum base oil can be improved from60to above95by blending30%mass fraction of synthesized PAO. As a result, the blended petroleum base oil was upgraded from LVI to HVI. As compared to the petroleum base oil, the blended base oil shows a lower freezing point and similar flash point. |
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