Base Stocks processing steps

Chemical manufacturing companies produce materials based on chemical reactions between selected feed stocks. In many cases the completion of the chemical reactions is limited by the equilibrium between feed and product. The process must then include the separation of this equilibrium mixture and recycling of the reactants. The fundamental process steps of bringing material together, causing them to react, and then separating products from reactants are common to many processes. 

Miller[72] has described a process for the production of hydrocarbons in the lube base stock range. The process involves the use of a Ni-ZSM5 zeolite as catalyst for dimerization of C5-C11 olefins into a first product containing C10-C22 olefins. This first product is subjected to an additional dimerization step, using the same or similar catalyst giving a second product that includes hydrocarbons in the lube base stock range. 

The waxy distillates and DAO require three further processing steps to obtain acceptable base stock ... 

Processing steps which act by chemical separation The undesirable chemical compounds (e.g., polyaromatics) are removed using solvent-based separation methods (solvent refining). The by-products (extracts) represent a yield loss in producing the base stock. The base stock properties are determined by molecules originally in the crude, since molecules in the final base stock are unchanged from those in the feed or... 

To dewax via the toluene-MEK process, the waxy feed/toluene mixture is initially heated above the cloud point to remove any microcrystals, then it is cooled in a heat exchanger with water and subsequently using scraped surface pipe chillers to about 10°F to 20°F below the target pour point (Figure 6.5). Filtration normally employs rotary filters using specially manufactured filter cloths. The wax produced usually contains 5% to 20% oil, depending on the feed, and can be deoiled in a subsequent step to produce hard wax and a by-product soft wax stream called foots oil, which is largely isoparaffins. The solvent is stripped from the oil and recycled. This process is applicable both to solvent refined and hydrocracked waxy base stocks. 

One of Sun s objectives for the new plant was that the base stocks be at least of the same quality as those from solvent refining, therefore this hurdle had to be overcome. Their solution was to give the total dewaxed hydrocrackate product a light furfural extraction (about 97% raffinate) to remove the tri+ aromatics which appeared to be at the root of the problem.1516 Thus their process involved two solvent extraction steps, one before the hydrocracker and one afterwards. This route gave stable base stocks, but with some residual color. An example of the improvement obtained can be seen in Table 7.10, where 100, 200, and 500 SUS base stocks ( 1, 2, and 3 in Table 7.10) of approximately 110 VI from hydrocracking a distillate/DAO blend were tested for stability before and after furfural extraction. The results show that the extraction improves color relative to unextracted samples for the immediate hydrocracker products and that their performance in the stability test was improved as well by extraction. 

Shell has produced group HI base stocks with Vis greater than 145 at their Petit Couronne, France, refinery since the 1970s. The feed used was slack wax which was catalytically isomerized and then dewaxed, and presumably finished if that last step was part of the process—no details appear to have been published. 

Aromatic levels in lubricant feedstocks and base stocks are obvious parameters of interest to both the processor and the user. Table 8.1 shows how the compositions of fractions can vary depending on their distillation positions in a crude oil, in this case heavy crude.1 The analysis here should not be taken as representative of any crude used for lubes, but the general trends are typical for most crudes, that is, what are usually labeled as the impurities —nitrogen, sulfur, aromatics, and polars—all increase as boiling point increases. These components are essentially those which must be reduced in whatever lubes manufacturing process is employed. In hydroprocessing, these steps all consume hydrogen. 

As we have seen, reduction of aromatics levels in lubricating oil base stocks relative to the feed has always been a significant part of their overall processing. The extraction step in the traditional solvent refining technology removes some aromatics, particularly the low VI polycyclic aromatics that contribute to oxidation instability and deposit formation. Hydrofinishing further reduces the levels of polynuclear aromatics, since conditions are generally too mild to reduce mono and... 

Solvent dewaxing removes wax (normal paraffins) from deasphalted lube base stocks. The main process steps include mixing the feedstock with the solvent, chilling the mixture to crystallize wax, and recovering the solvent. Commonly used solvents include toluene and methyl ethyl ketone (MEK). Methyl isobutyl ketone (MIBK) is used in a wax deoiling process to prepare food-grade wax. 

AAB sols were prepared by a three-step process involving acid-catalyzed hydrolysis of aged stock solution (r = 2.5) followed by a base-catdyzed hydrolysis step (r s= 3.7). The final hydrolysis ratio, pH, and silicon concentration were identical to those of B2 sols. Comparing the NMR spectra of the stock solution and the AAB sol, we observed that the effect of the second (acid-catalyzed) hydrolysis step was to promote extensive hydrolysis and condensation. Monomer and species are consumed to produce primarily a variety of and species. Various cyclic tetramers are prominent sol species after the second hyckolysis step as was evident from a strong q2 resonance observed near -95 ppm. 

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