Branching Structure of Diesel and Lubricant Base Oils Prepared by Isomerization/Hydrocracking of Fischer−Tropsch Waxes and α-Olefins

Abstract

Lubricant base oils were prepared from two Fischer-Tropsch (FT) waxes and two R-olefins with different carbon number distributions under several isomerization/hydrocracking conditions. The molecular structures of the resulting oils were investigated using 13 C NMR analysis to determine the location and length of branches. Peak areas assigned to the CH carbons were divided into eight groups and correlated with the progress of the isomerization reaction. Each group showed good correlation with the density of branching, which was expressed as the ratio of the average branching number (ABN) to the average carbon number (ACN). This trend was independent of the feedstock used and the reaction conditions. The probability of methyl branching at a carbon atom depended on its location from the terminal carbon; that is, in order of decreasing probability, the carbon location is second > third > fourth, and so forth, and the probability of the seventh and eighth or inner carbon atoms was almost equal. A trend of increasing proportion of branches located at the second carbon was observed. Diesel oils were also obtained by isomerization/hydrocracking of FT waxes, and the most likely position of methyl branching was the second carbon from the terminal carbon. Branching at the second carbon showed a decreasing trend with increasing density of branching in diesel oil, whereas that in lubricant base oil showed an increasing trend. The present work demonstrated that the position and length of the branches in lubricant base oils, and diesel oils prepared by isomerization/hydrocracking of FT waxes and R-olefins, are determined by the density of branching, thus supporting previous findings that viscosity properties of lubricant oils, such as the kinematic viscosity and viscosity index, can be expressed using only the ACN and ABN.

Refining Technology Selection

“…4) Lubricating base oils can be prepared from Fischer-Tropsch waxes by hydroisomerization to improve the cold-flow properties of the otherwise solid material [105,106]. With longer chain feed materials, there is always the risk of cracking, which is why mildly acidic catalysts perform so much better for the hydroisomerization of heavier n-alkane feed materials than their more acidic counterparts.…”

“…Lubricant base oils can be produced from LTFT syncrude [105,106], as well as from HTFT syncrude [114]. 2) Production of distillate from C 23 and heavier material.…”

Catalysis in the Upgrading of Fischer–Tropsch Syncrude

“…Nevertheless, a number of investigations have been reported that studied LTFT wax HCR over the metal-promoted zeolites USY, Beta and mordenite. 429,463,464 There is also the possibility that in the future zeolite catalysts may be developed to exploit the 'window effect' for hydrocracking of Fischer-Tropsch waxes. 465 The 'window effect' was reported for HCR over ERI zeolite catalysts, which yielded a bimodal product distribution with maxima at C 3 -C 4 and C 10 -C 12 , but few products in the C 5 -C 8 range.…”

Upgrading of Fischer–Tropsch Waxes

“…Kobayashi and co-workers used a 13 C NMR method to investigate the molecular structures of the lube base oil and diesel fuel that can be prepared from Fischer-Tropsch waxes by HIS/HCR. [45][46][47] The aim was to determine the location and length of the branches. It was observed that the probability of methyl branching on the main carbon chain decreased in the order 2nd43rd44th and so on; the probability of methyl branching on the seventh, eighth and inner carbon atoms was almost equal.…”