Process for making a lube base stock from a lower molecular weight feedstock using at least two oligomerization zones

#The present invention relates to a process for making a lube base stock from olefin-containing feedstocks having lower molecular weights than the lube base stock, using more than one oligomerization zone. Included in this invention is a process for making predominately bright stock lube base stock.

#Lubricant oils of high viscosity and high oxidation stability are desirable. Such materials can be prepared by hydrocracking, hydroisomerizing and otherwise hydroprocessing various wax fractions and by polymerizing normal alpha olefins such as 1-decene. The former route has the advantage of moderate costs, but the oxidation stability is not exceptional. As attempts are made to improve the oxidation stability by increasing the severity of the hydroprocessing steps, the yield of lube declines, as does its viscosity. The latter route gives an exceptionally stable product, but suffers the disadvantage of high cost. It would be desirable to provide new processes for generating high viscosity and highly stable products. The present invention provides such a process.

#U.S. Pat. No. 6,025,533 to Vora et al. (“Oligomer Production with Catalytic Distillation”) teaches production of heavy oligomers (C7+ oligomers) from C4 paraffins and olefins by a combination of dehydrogenation and oligomerization. The process has at least one catalyst bed in the top of a distillation column for separating the oligomerization effluent of the dehydrogenation and oligomerization combination.

#In order to assist the understanding of this invention, reference will now be made to the appended drawings. The drawings are exemplary only, and should not be construed as limiting the invention.

#FIG. 1 shows a block diagram of a specific embodiment of a process for making a lube base stock from a lower molecular weight feedstock, wherein the production of bright stock is maximized.

#In its broadest aspect, the present invention involves a process for making a lube base stock from a lower molecular weight olefinic feedstock. That process has at least four steps. A light olefin fraction and a medium olefin fraction are obtained, in one embodiment by separation of an olefinic feedstock. The light olefin fraction is contacted with a first oligomerization catalyst in a first oligomerization zone to produce a first product having an increased molecular weight relative to the light olefin fraction. The medium olefin fraction and the product from the first oligomerization zone are contacted with a second oligomerization catalyst in a second oligomerization zone to produce a second product having an increased molecular weight relative to the medium olefin fraction. (The first oligomerization catalyst can be the same as the second oligomerization catalyst, or it can be different.) That second product is separated into a light byproduct fraction and a heavy product fraction, wherein the heavy product fraction comprises a lube base stock.

#As used herein the following terms have the following meanings unless expressly stated to the contrary:

#The term “catalytic distillation unit” refers to a distillation unit having, within it, at least one bed of catalyst.