Because of environmental concerns, automobile manufacturers and government regulators have introduced new, more stringent performance requirements for lubricants. As a result, the specifications for finished lubricants are requiring products having excellent low temperature properties, high oxidation stability, and low volatility. Currently, only a small fraction of the base oils manufactured today are able to meet these demanding specifications.
Group II+ base oil, though not an official American Petroleum Institute (API) designation, is a term used to describe API Group II stocks of higher viscosity index (110-119) and lower volatility than comparable Group II stocks.
Due to their low viscosity and low volatility, API Group III base oils have become the base stocks of choice for the next generation of lubricant compositions. This in turn has lead to a greater demand for Group III base oils. However, producing Group III base oils can be difficult requiring the use of special high viscosity index gas oils which can be higher in cost than gas oils used to make Group II base oils. In addition, the production of Group III base oils can also involve hydrocracking gas oils at higher severity in order to get the viscosity index to at least 120 which can result in lower yield, downgrading potential base oil to lower valued diesel and other light products, and shortening the hydrocracker catalyst life.
It would be advantageous if a refiner could simply switch from Group II base oil production to Group II+ or Group III base oil production by adding a minor amount of a different second feed to a lube oil feedstock ahead of a hydrocracking unit in order to boost the viscosity index for as long as the Group II+ or Group III base oil production was required. It would also be advantageous if the second feed were low in cost and had additional benefits, such as reduction of environmental waste.
One potential low cost feed is waste plastics. Transforming waste plastic material and particularly polyethylene into useful products presents a unique opportunity to address a growing environmental problem.
Various processes for converting waste plastic into lubricating base oils have been developed. For example, U.S. Pat. No. 6,150,577 discloses a process wherein waste plastic is fed to a pyrolysis reactor. The pyrolysis effluent is separated into at least a heavy fraction which is hydrotreated and hydroisomerization dewaxed to form a high viscosity index (VI) lubricating base oil. In U.S. Pat. No. 6,288,296, waste plastic is fed to a pyrolysis reactor. The middle fraction from the pyrolysis effluent is dimerized and subsequently fed to an isomerization dewaxing zone to produce a high VI lubricating base oil. In U.S. Pat. No. 6,774,272 a blend of waste plastic and a Fischer-Tropsch waxy fraction is fed to a pyrolysis reactor. The heavy fraction from the pyrolysis effluent is hydrotreated and hydroisomerization dewaxed to produce a high VI lubricating base oil. U.S. Pat. No. 6,822,126 discloses a process wherein a waste plastic feed is continuously passed to a pyrolysis reactor. The reactor effluent is then fed to a hydroisomerization dewaxing unit and fractionated to recover lube oil stocks. U.S. patent application Ser. No. 13/008,153 discloses a process wherein wax derived from a pyrolysis of a plastic feed is added to a base oil stream going to a hydroisomerization unit to increase the VI of the base oil, raising it to a higher value product. Because of the sensitivity of the hydroisomerization dewaxing catalyst to poisoning by sulfur and nitrogen impurities, the waxy feed from the pyrolyzer either has to be very low in sulfur and nitrogen to start or the waxy feed has to be hydrotreated prior to hydroisomerization dewaxing in order to reduce sulfur and nitrogen to very low levels.
Accordingly, it would be desirable to have a process for producing high VI lube oils whereby the waxy product from a pyrolyzer would not have to be hydrotreated in a separate step and the plastic feed would not have to be segregated to keep sulfur and nitrogen impurities low.