Cost of fractionation

Other methods for estimating the cost of vessels and fractionators can be used, but weight is usually the best. The cost of fractionators can be correlated as a function of the volume of the vessel times the shell thickness, with an addition for the cost of trays based on their diameter (Reference 13). Fractionator costs can also be correlated based on the volume of the vessel with the operating pressure as a parameter. This requires a great deal of data and does not give as good a correlation as weight. Hall et al. (Reference 14) present curves of column diameter vs. cost. 

Refining Cost. Crude palm oil can be further processed by refining. Presently, most of the palm products obtained in the market are processed using physical or steam refining. Crude or processed palm products may also undergo fractionation where the solid and the liquid portions are separated. The total cost of refining a ton of palm oil is about 25.92 while the cost of fractionation is about 5.55 per ton. 

Low-cost maltodextrins (Mavg = 1200,1800,3600) can be combined with polyethylene glycol (PEG) to form aqueous two-phase systems which are useful for protein separations. The physical characteristics of these maltodextrin/FEG systems are similar in many respects to dextran/FEG systems. Maltodextrins are currently available for a hundredth of the cost of fractionated dextran making the large scale application of polymer-polymer aqueous two-phase extractions more likely. The physical characteristics of the maltodextrin/FEG two-phase systems are described in this paper along with their application towards the purification of yeast alcohol dehydrogenase. 

The main drawback to the widespread use of polymer-polymer aqueous two-phase extraction has been the high cost of fractionated dextran. Crude dextran has been used with some success for the purification of enzymes but is much too viscous for many applications. Conversely, polymer-salt systems have relatively low viscosities, separate rapidly, and are inexpensive. Unfortunately, they lack selectivity and cannot be used for affinity partitioning in most cases since the high salt concentrations interfere with the protein-ligand interaction. The starch derivatives are reasonable alternatives for bottom phase polymers but have been hampered by low solubilities and the tendency for gel formation. Tjemeld has reported that chemically modified starches i.e. hydroxypropyl starch... 

In this chapter the principles of fractionation are discussed and some of the processes that are currently in use are described. In addition, advances in processing, suggested during the last decade of the twentieth century, as well as applications for fractions from selected fats and oils are covered. The costs of fractionation have been extensively reviewed by Kellens [7] and are not discussed here. 

Figure 10.7 shows the basic tradeoff to be considered as additional feed and product materials are recovered from waste streams and recycled. As the fractional recovery increases, the cost of the separation and recycle increases. On the dther hand, the cost of the lost materials decreases. It should be noted that the raw materials cost is a net cost, which means that the cost of lost materials should be adjusted to either... 

The cost of off-sites ranges typically from 20 to 40 percent of the total installed cost of the plant. In general terms, the larger the plant, the larger will be the fraction of the total project cost which goes to off-sites. In other words, a small project will require typically 20 percent of the total installed cost as off-sites. For a large project, the figure will be typically up to 40 percent. 

Any opex estimate should not ignore the cost of overheads which the project attracts, especially for example the cost of support staff and office rental which can form a significant fraction of the total opex, and does not necessarily reduce as production declines. 

If regulations governing specific emission limit VOC concentrations to the low ppm range then, of course, vapor fractions such as those illustrated by the above tabulation will not be acceptable. It may, however, still be justified to consider VOC condensation as a precursor to a final abatement device such as an adsorption bed. Removing most of the solvent from a vent stream by condensation, can drastically reduce the size and cost of a downstream cleanup system. 

Most of the voltage savings in the air cathode electrolyzer results from the change in the cathode reaction and a reduction in the solution ohmic drop as a result of the absence of the hydrogen bubble gas void fraction in the catholyte. The air cathode electrolyzer operates at 2.1 V at 3 kA/m or approximately 1450 d-c kW-h per ton of NaOH. The air cathode technology has been demonstrated in commercial sized equipment at Occidental Chemical s Muscle Shoals, Alabama plant. However, it is not presentiy being practiced because the technology is too expensive to commercialize at power costs of 20 to 30 mils (1 mil = 0.1 /kW). 

When low boiling ingredients such as ethylene glycol are used, a special provision in the form of a partial condenser is needed to return them to the reactor. Otherwise, not only is the balance of the reactants upset and the raw material cost of the resin increased, but also they become part of the pollutant in the waste water and incur additional water treatment costs. Usually, a vertical reflux condenser or a packed column is used as the partial condenser, which is installed between the reactor and the overhead total condenser, as shown in Figure 3. The temperature in the partial condenser is monitored and maintained to effect a fractionation between water, which is to pass through, and the glycol or other materials, which are to be condensed and returned to the reactor. If the fractionation is poor, and water vapor is also condensed and returned, the reaction is retarded and there is a loss of productivity. As the reaction proceeds toward completion, water evolution slows down, and most of the glycol has combined into the resin stmcture. The temperature in the partial condenser may then be raised to faciUtate the removal of water vapor. 

The most volatile product (myristic acid) is a small fraction of the feed, whereas the least volatile product (oleic—stearic acids) is most of the feed, and the palmitic—oleic acid split has a good relative volatility. The palmitic—oleic acid split therefore is selected by heuristic (4) for the third column. This would also be the separation suggested by heuristic (5). After splitting myristic and palmitic acid, the final distillation sequence is pictured in Figure 1. Detailed simulations of the separation flow sheet confirm that the capital cost of this design is about 7% less than the straightforward direct sequence. 

The benzene—toluene fraction is further fractionated in a small column, not shown in Figure 5, to recover benzene for recycle to the alkylation unit and toluene for sale. This toluene can be converted to benzene by hydrodealkylation but the high selectivity catalyst has reduced the formation of toluene in the dehydrogenation reactor to the point where the cost of installing a hydrodealkylation unit is difficult to justify even in a large styrene plant. 

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. 

Continuous processes have lower labor costs but have higher failure risk. Batch processes can be started back up in a shorter period of time than can a complex continuous process. Batch processes are easier to take through the regulatory process than are continuous processes. Thus batch processes are often chosen for mammalian ceU culture systems, even though continuous processes can offer significant cost advantages. CeU culture costs constitute only a smaU (10—30%) fraction of the overaU cost of making a product. 

Many problems need to be solved before chemurgic materials can be economically used as feedstocks. Among these problems are the recovery, purification, and fractionation of the diverse materials. However, none of these problems are insurmountable. Serious concerns are the supply of the raw material, the relative costs of competitive materials, and competition with other uses for the raw materials. Competition is particularly significant because materials, such as wood, could easily be used in many cases for pulping or even higher value products, such as stmctural timber. Municipal soHd waste offers a substitute raw material with few other uses (33). 

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