Once-through fraction conversion

In the once-through operation low sulfur fuels are produced and the fractionator bottoms are not recycled. In the total conversion mode the fractionator bottoms are recycled to the inlet of the reactor to obtain more middle distillates. 

As shown by Table 22, ethane produces high ethyleoie yields. However, seleodvity decreases as conversion proceeds. In practice, operations are conducted at about 60 per cent once-through conversion, leading to a molar yield of about 80 per cent after recycling of the unconverted fraction. 

Although the transformation of acrylonitrile to acrylamide sulfate is carefully controlled by limiting the water content of the medium and the residence tune (5 to 10 min) in the reactor, a small fraction is hydrolysed to acrylic add. This reaction takes place at atmospheric pressve, between 145 and I55 C, in the presence of 85 per cent weight sulfuric acid solution, in an agitated jacketed reactor, with a once-through conversion of more than 95 to 97 per cent... 

More recently, British Petroleum (BP)37 39 produced two group III stocks, a 4 cSt BP HC-4 and a heavier HC-6 from the fractionator bottoms of their fuels hydrocracker at BP s Lavera, France, refinery. The total bottoms are solvent extracted to stabilize the final products, fractionated, and finally solvent dewaxed. The hydrocracker is operated in a severe mode (relative to lube hydrocracking) at a once-through conversion of 90% (in comparison, lube hydrocrackers may operate at conversions of only about 20%, and perhaps less with a very good quality feed). Like other hydrocracker-sourced group HI products, their compositions are virtually independent of feed source due to the extent of the molecular reorganization that occurs and the molecular structures that are required for those Vis. The properties of the HC-4 are compared in Table 7.26 with those of some competitive group I, II, and IV base stocks. It can be seen that the HC-4 closely resembles the more... 

Waste separation Conversion fraction of CO (once through) 0.4 0 r aci,rr 1... 

The investigation of a single-step pathway usually begins with a crude cell-free extract from a source abundant in the enzyme that catalyzes the conversion. Two of the most popular sources of cells for many biochemical studies are rat liver and E. coli. To investigate a particular reaction, the precursor (substrate) is added to the extract, and the amount of product formed as a function of time is determined. Once an assay for disappearance of precursor and appearance of product has been developed, the crude extract can be processed into fractions that can be tested to see which are active in the conversion. Through further fractionation and assays it should ultimately be possible to purify the enzyme of interest. Some procedures followed in enzyme purification were discussed in chapter 6, and many procedures used to determine the mechanisms of action of the purified enzymes were considered in chapters 8 and 9. 

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