Preparation Of Synthetic Lubricating Base Oil By Oligomerization Of Fischer-tropsch Wax Cracking Mixed α-Olefins

Due to the obvious shortage ofα-olefin preparation and poly-α-olefin（PAO）synthetic lubricating base oil production technology in China,the technology ofα-olefin preparation has been monopolized by western developed countries,and high-quality PAO has long relied on imports.Therefore,the development of economically viableα-olefin preparation and polymerization technology is very necessary for the development of China’s PAO base oil,in order to promote the development of China’s base oil and shorten the gap with foreign countries.With the increasingly tense oil resources,the development of the Fischer-Tropsch wax cracking mixedα-olefin synthetic lubricating oil base oil technology.It not only increases the added value of Fischer-Tropsch products and increases the source ofα-olefin raw materials.In this paper,high temperature gas chromatography,infrared spectroscopy and simultaneous thermal analysis-mass spectrometry were used to analyze the carbon number distribution,molecular structure and thermal cracking characteristics of Fischer-Tropsch wax.The results show that the carbon number distribution of Fischer-Tropsch wax is between C₁₉ and C₁₂₀;Infrared spectroscopy analysis shows that the Fischer-Tropsch wax has a simple structure and is mainly composed of long-chain and saturated aliphatic hydrocarbons.The results of simultaneous thermal analysis-mass spectrometry showed that the weight loss stage of Fischer-Tropsch wax was 166-502°C,the weight loss rate was the highest at 458°C,the cracking was the most severe,and the total weight loss rate was 98.62%（w）.The cracking property index was2.76×10^-6.The pyrolysis kinetic parameters of Fischer-Tropsch wax were calculated by Coats-Redfern integration method.The apparent activation energy and frequency factor were 62.16 kJ/mol and 7.07×10³/min.Then,according to the pyrolysis analysis results of Fischer-Tropsch wax,the pyrolysis test of Fischer-Tropsch wax in high pressure reactor was designed,and the cracking products were divided into pyrolysis gas,lysate and xenon wax.The effects of single variable factors such as thermal cracking temperature and residence time on product distribution and yield were investigated,and the optimal cracking conditions were obtained.Under the experimental conditions of reaction temperature 460°C and residence time 4 h,the Fischer-Tropsch wax conversion rate was 75.60%（w）,the lysate yield was66.33%（w）,and theα-olefin yield and selectivity were 42.90%（w）and 56.75%,The volatile gases produced are mainly propylene,butene and butane.Subsequently,theα-olefins in the Fischer-Tropsch wax lysate were separated and purified by complex extraction method,and the effects of different extraction systems on the separation ofα-olefins were investigated.The experimental results show that the separation ofα-olefins is better with silver nitrate as the complexing agent and N-methylpyrrolidone solvent with3mol/L absorption liquid.The complex ratio ofα-olefin to Ag⁺in the complex formed was 1:1.The purity of theα-olefin obtained after decomplexation is increased from 64.68%（w）to 94.98%（w）.The results of GC-MS analysis showed that the carbon number distribution ofα-olefins after purification by complex extraction was between C₅ and C₁₅.The content of C₈^C₁₀α-olefin is37.78%（w）,which is a high-quality raw material for preparing high-grade synthetic lubricating base oil.Finally,after the complex extraction,theα-olefin is cleaved and separated into 120¹70°C fractions,which is used as a polymerization raw material to prepare PAO by catalytic polymerization under BF₃ catalysis.The effects of initiator type,reaction pressure,reaction temperature,polymerization time and amount of initiator added on the properties and yield of the polymerization product were investigated.The results showed that under the experimental conditions of reaction pressure 0.4 MPa,reaction temperature 25°C,reaction time 3h,and n-butanol mass fraction 0.1%（w）,the yield of PAO was97.16%（w）.The synthetic viscosities of synthetic PAO at 40°C and 100°C were 31.01 mm ²/s and 6.05 mm ²/s respectively,the viscosity index was 146,the pour point was-62°C,and the product performance reached the PAO-6quality standard.The results of synthetic PAO characterization showed that the PAO polymerization degree of Fischer-Tropsch wax cracking mixedα-olefins was concentrated,and the content of trimer and tetramer was 70.45%（w）,and its main component was long-chain saturated alkanes.