Solvent dewaxing compared to Catalytic dewaxing, Russell Hedrick

There are currently two types of dewaxing that are being used commercially. The first dewaxing process is called solvent dewaxing. Solvent dewaxing is a physical process that separates the wax by freezing or solvent transport. The other type of dewaxing, Catalytic dewaxing, is a chemical process, which is unlike the physical process used for solvent dewaxing. Catalytic dewaxing uses a chemical process to remove the wax through a reaction of long chain n-alkenes. First the solvent dewaxing process will be discussed. The solvent is cooled until the wax compound freeze to form crystals. The solvent with the frozen wax crystals is carried into a rotary filter where the wax crystals get caught in a filter cloth. The layer of wax on this cloth is then scrapped by a blade and carried away in a solvent stream. The solution then goes through a steam stripping process to recover the solvent. The chemical process of catalytic dewaxing is much different then the process of solvent dewaxing. This process uses a selective cracking processe to “crack” n-alkanes. This cracking process takes place in pores of a catalyst that has openings about 0.6nm in diameter. This keeps out the i-paraffins because of their larger size. Hydrogen is also introduced into this process to prevent coking on the catalyst. Hydrogen prevents disproportionation which in turn prevents coking. This process has a much higher yield then the solvent dewaxing as well as producing a lube base stock with a much lower pour point. The catalytic dewaxing has many advantages over the solvent dewaxing. The chemical process of catalytic dewaxing has a much lower capital investment then that of the physical process of solvent dewaxing. The cracking of n-paraffins that takes place in catalytic dewaxing produces a by product of distillate fuels such as gasoline. Overall catalytic dewaxing is a more advantageous process then solvent dewaxing.

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