High-boiling fractions of crude from Tengiz field as raw material for lube oil production

Abstract

Tengiz crude, as has been shown by classification studies [1, 2], is light, medium-sulfur, low-resin, and medium-wax. Its content of light fractions distilling below 350~ is 75-78% by weight, which is 1.5 times the content in the major West Siberian crudes. Therefore, it has been recommended that the Tengiz should be processed in the "fuel variant," i.e., primarily to obtain fuels. In order to evaluate the high-boiling fractions of Tengiz crude as a raw material for lube oil production, its atmospheric resid was subjected to vacuum distillation, taking 300-400, 400-450, and 450-500~ distillate cuts. The residue above 500~ (vacuum resid) was propane-deasphalted. Such distillates and deasphalted oil are commonly used as raw materials for the production of lube oil components. Judging from the data of Table 1, the Tengiz atmospheric resid has greater amounts of lube distillates but a considerably smaller amount of deasphalted resid in comparison with the atmospheric resids from largevolume West Siberian crudes [3]. Another distinctive feature of the Tengiz atmospheric resid is the gradual decrease of the lube distillate content with increasing boiling point. As a result, the content of low-viscosity distillate is more than twice that of viscous distillate or deasphalted oil. The comparatively low dewaxing yields from the distillates and deasphalted oil are evidence of higher wax contents in the original distillates and deasphalted oil in comparison with the analogous products from major medium-sulfur medium-wax crudes. The high density, refractive index, and specific dispersion that are observed for the dewaxed distillates and deasphalted oil can be attributed to specific features of their hydrocarbon composition (Tables 2 and 3): high contents of saturated hydrocarbons (47-54% by weight) and comparatively low contents of aromatic hydrocarbons with specific dispersion in the 125-160 interval. Because of the high content of isoparaffins (Table 4), we observe high viscosity indexes (120-140) for the saturated part, which is the main part of the oils. The saturated and aromatic hydrocarbons of the deasphalted oil from the Tengiz crude differ from the corresponding groups of hydrocarbons in the deasphalted oils from large-volume crudes that are used in lube oil production; also, the hydrocarbons from the Tengiz crude have lower viscosities. The heavy polycyclic hydrocarbons with specific dispersion above 160 have high densities and refractive indexes and very low viscosity indexes -a considerable difference from the properties of the corresponding hydrocarbons in major medium-sulfur medium-wax crudes. On the whole, the aromatic part of the Tengiz hydrocarbons includes considerable quantities of naphthenoaromatic hydrocarbons (10-11% by weight), aromatic hydrocarbons (15-16%), and sulfur-containing compounds (12-15 %). The sulfur is present mainly in the form of thiophene derivatives, along with thiocyclanes and sulfides.* The distillates and residue from vacuum distillation of the atmospheric resid of Tengiz crude are also characterized by high contents of resinous compounds, 7-11%, in comparison with the 4-5 % in the analogous products from vacuum distillation of atmospheric resids of other crudes that are used in lube oil production. The hydrocarbon groups that were segregated in these studies were blended to obtain samples characterizing the potential content of oils in both the distillate and residual stocks, with different levels of viscosity. The quality indexes of these products are listed in Table 5.