Isomerization of paraffin wax

In a number of hydro-isomerization experiments paraffin wax (average molecular weight 375) was vaporized with hydrogen and treated with different catalysts (W.H.-S.V. 0.89-1.04, temperature 4io-450°C, hydrogen pressure 32-102 atm., molar ratio hydrogen wax=61 183). The reaction products were distilled at atmospheric pressure... 

ExxonMobil developed two hydroprocessing technologies for isomerization of slack waxes and similar very high wax streams to highly paraffinic 140+ VI base stocks. These were used at their Fawley, England, refinery and illustrate aspects of the development of catalyst technology. 

Hydroisomerization is the catalytic process for dewaxing waxy lubes and conversion of waxes to high VI base stocks by isomerization of n-paraffin structures to isoparaffins with one or more branches. These branches are usually methyl branches. We have already seen in Chapters 2 and 3 that iso-paraffins have lower pour points than n-paraffins and can have quite high Vis if the branches are close to the chain ends. Hydroisomerization is distinguished from catalytic dewaxing via ZSM-5-type catalysts in that the latter cracks n-paraffin structures to C3 to C8 molecules (Figure 10.18), whereas the former causes isomerization and has... 

Due to the high concentration of linear n-paraffin hydrocarbons in fnel derived from PE, it is desirable to isomerize them in order to lower the cloud point and the freezing point of the fuel. The branched isomers do not exhibit the same tendency to crystallize as linear paraffins, so that wax crystals do not form nntil lower temperatures are reached. 

It is evident that the above approach was followed to arrive at a high selectivity towards middle distillates, the prerequisite being a second stage which can convert the heavy wax fraction in the HPS effluent very selectively into middle distillates, the Heavy Paraffin Conversion (HPC) stage (see Fig. 2). In the HPC the waxy product of the HPS is hydro-isomerized and hydrocracked to give the maximum yield of middle distillates. 

Commercial dIamyl ether consists principally of di-n-amyl ether and di-isMmyl ether, with mall percentages of Isomeric amyl ethers and diamylene. It is a colorless to light yellow liquid which is quite stable. It is insoluble in water but soluble in methanol, ethyl ether, ethyl acetate, ocetone, aliphatic and aramatic hydrocarbons, fixed ails, oleic and hot stearic acids, hat paraffin and carnauba waxes, the latter twa solidifying when coaled. Unlike the lower aliphotic ethers, it will not dissolve nitrocellulose when admixed with ethanol. However, a mixture af diamyl ether and 20% ethanol will dissolve ethylcellulose. 

With this level of hydrodewaxing capability, some refiners have moved to all catalytic processes with a ring conversion hydroprocessing step complemented by a single step paraffin conversion process that achieves the desired low temperature specifications by completely converting residual wax components, primarily into lube range isomerate. (See further discussion under Process Combinations , below.)... 

The Isodewaxing Process, commercialized in 1993 by ChevronTexaco, catalytically isomerizes n-paraffms into iso-paraffins. This decreases the wax content and increases the concentration low-viscosity hydrocarbons, both of which are desirable. Isodewaxing also removes sulfur and nitrogen, and it saturates aromatics. Products have a high viscosity index (VI), low pour point, and excellent response to additives. 

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