Fractionation, cost efficiency

The fourth desorbent characteristic is that the desorbent material should be readily available (at a sustainable cost). It is important that the desorbent be readily available and not cost-prohibitive because desorbent is gradually lost during operations. Since the desorbent is separated from both the extract and raffinate components by fractionation, trace quantities (parts per million) of desorbent are present in the respective product streams due to fractionation tray efficiencies and fractionation control optimization of reflux to feed ratio. Ultimately, each n-paraffn separation facility must balance the operating expenses (utilities consumed during fractionation) to minimize desorbent loss against the replacement value of desorbent to maintain inventory. 

These separators are characterized by a fairly low separation efficiency for particle sizes below 5 pm. The separation limit, defined by a size of particles o , for which the fractional separation efficiency S( = 0.5, ranges between 3 and 30 pm. Such devices are characterized by simple design, operation and maintenance, and by low initial and operating costs, low pressure losses and energy consumption. 

Blanket energy multiplication Direct conversion efficiency Thermal conversion efficiency Gross electric power Injection system efficiency Power recirculated to injectors Power recirculated to copper coils Net electric power Recirculated power fraction System efficiency Direct capital cost... 

Reductive alkylations and aminations requite pressure-rated reaction vessels and hiUy contained and blanketed support equipment. Nitrile hydrogenations are similar in thein requirements. Arylamine hydrogenations have historically required very high pressure vessel materials of constmction. A nominal breakpoint of 8 MPa (- 1200 psi) requites yet heavier wall constmction and correspondingly more expensive hydrogen pressurization. Heat transfer must be adequate, for the heat of reaction in arylamine ring reduction is - 50 kJ/mol (12 kcal/mol) (59). Solvents employed to maintain catalyst activity and improve heat-transfer efficiency reduce effective hydrogen partial pressures and requite fractionation from product and recycle to prove cost-effective. 

Cost. The catalytically active component(s) in many supported catalysts are expensive metals. By using a catalyst in which the active component is but a very small fraction of the weight of the total catalyst, lower costs can be achieved. As an example, hydrogenation of an aromatic nucleus requires the use of rhenium, rhodium, or mthenium. This can be accomplished with as fittie as 0.5 wt % of the metal finely dispersed on alumina or activated carbon. Furthermore, it is almost always easier to recover the metal from a spent supported catalyst bed than to attempt to separate a finely divided metal from a liquid product stream. If recovery is efficient, the actual cost of the catalyst is the time value of the cost of the metal less processing expenses, assuming a nondeclining market value for the metal. Precious metals used in catalytic processes are often leased. 

One of the most important operations in a refinery is the initial distillation of the crude oil into its various boiling point fractions. Distillation involves the heating, vaporization, fractionation, condensation, and cooling of feedstocks. This subsection discusses the atmospheric and vacuum distillation processes which when used in sequence result in lower costs and higher efficiencies. This subsection also discusses the important first step of desalting the crude oil prior to distillation. 

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