Lube dewaxing processes

MLDW [Mobil lube dewaxing] A catalytic process for removing waxes (long-chain linear aliphatic hydrocarbons and alkyl aromatic hydrocarbons) from lubricating oil. Developed by Mobil Research Development Corporation and operated at Mobil Oil refineries since 1981. Eight units were operating in 1991. 

Chevron s wax isomerization process uses Pt-SAPO-11 [46,47], Wax isomerization is far superior than previous catalytic dewaxing processes because it reduces the pour point of lubes and fuels with minimum hydrocracking, and because it makes very high VI products Multiple branching, which decreases the viscosity index, is limited. Low selectivity for cyclic coke precursors makes long catalyst life possible. 

Smith, K.W, Starr, W.C. and Chen, N.Y. (1980) A new process for dewaxing lube base stocks Mobil lube dewaxing. API 45 Midyear refining meeting. May 1980. 

Catalytic dewaxing can also be used to produce high viscosity index (VI) lube oils, as in the Mobil s Lube Dewaxing (MLDW) process. This process uses a two-reactor system, where a ZSM-5 based catalyst is placed in the first reactor, and the product stream is then sent without intermediate separation to the second reactor containing a hydrofinishing catalyst to meet the desired final product specifications [167]. 

Source K. W. Smith, W. C. Starr, and N. Y. Chen, A New Process for Dewaxing Lube Basestocks Mobil Lube Dewaxing, Proceedings of the American Petroleum Institute Meeting, Refining Department 59 151 (1980). With permission. 

Source S. J. Miller, New Molecular Sieve Process for Lube Dewaxing by Wax Isomerization, Paper presented at the Symposium on New Catalytic Chemistry Utilizing Molecular Sieves, 206th National Meeting of the American Chemical Society, Aug 23-27, 1993. Table copyrighted by the Chevron Corporation and used with permission. 

Source S. J. Miller, New Molecular Sieve Process for Lube Dewaxing by Wax Isomerization, Microporous Materials 2 439—149 (1994). With permission. 

The solvent dewaxing process involves addition of solvent during the chilling of the waxy feed. The chilling process induces crystallization of the wax and the solvent is added to maintain the fluidity. The wax crystals are filtered by rotating drum filters, resulting in a lube oil filtrate and a slack wax with entrained solvent and oil. In both fractions, the solvent is recovered by successive vaporization and distillation. 

Molecular structure affects Lube quality. Solvent extraction and dewaxing processes preferentially separate the molecules as shown in Figure 10. Extraction separates -paraffins, /-paraffins, naphthenes and some aromatics fi om the distillate into the raffinate phase. Dewaxing rejects the n-paraffins and some /-paraffins from the raffinate to produce a dewaxed oil or base stock. The dewaxed oil will contain the slice of molecular types as shown in Figure 10. 

Lubricants. Petroleum lubricants continue to be the mainstay for automotive, industrial, and process lubricants. Synthetic oils are used extensively in industry and for jet engines they, of course, are made from hydrocarbons. Since the viscosity index (a measure of the viscosity behavior of a lubricant with change in temperature) of lube oil fractions from different cmdes may vary from +140 to as low as —300, additional refining steps are needed. To improve the viscosity index (VI), lube oil fractions are subjected to solvent extraction, solvent dewaxing, solvent deasphalting, and hydrogenation. Furthermore, automotive lube oils typically contain about 12—14% additives. These additives maybe oxidation inhibitors to prevent formation of gum and varnish, corrosion inhibitors, or detergent dispersants, and viscosity index improvers. The United States consumption of lubricants is shown in Table 7. 

Catalysis. As of mid-1995, zeoHte-based catalysts are employed in catalytic cracking, hydrocracking, isomerization of paraffins and substituted aromatics, disproportionation and alkylation of aromatics, dewaxing of distillate fuels and lube basestocks, and in a process for converting methanol to hydrocarbons (54). 

Consider the oil-recycling plant shown in Fig. 3.16. In this plant, two types of waste oil are handled gas oil and lube oil. The two streams are first deashed and demetallized. Next, atmospheric distillation is used to obtain light gases, gas oil, and a heavy product. The heavy product is distilled under vacuum to yield lube oil. Both the gas oil and the lube oil should be further processed to attain desired properties. The gas oil is steam stripped to remove light and sulfur impurities, then hydrotreated. The lube oil is dewaxed/deasphalted using solvent extraction followed by steam stripping. 

The major solvent refining processes include solvent deasphalting, solvent dewaxing, lube oil solvent refining, aromatic extraction, and butadiene extraction. These processes are briefly described below. 

The state of the art, today, is based on an all catalytic lube plant, which does not rely on solvent processing. An example of such a plant is Mobil s Jurong plant located in Singapore (11). The configuration of the plant relies on the use of a lube hydrocracker, coupled with a selective catalytic dewaxing unit (Fig. 8.2). 

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