Finishing Process

A number of processes exist which can be utilized to improve the quality of refined and blended fuels. These processes are often an essential part of ensuring that finished fuels are free of contamination and meet required specifications. Some of the common fuel constituents which can cause fuel storage, handling, and performance problems are outlined in TABLE 2-6. 

Processes such as caustic washing, sweetening, hydrodesulfurization, and water removal are common examples of processes used to improve the quality of finished fuels. These processes are described in the remaining portion of this chapter. 

Aqueous solutions of NaOH or KOH are very effective at removing a variety of compounds from fuel. Components removed by extracting or washing the fuel with either of these caustic solutions include mercaptans, phenols, hydrogen sulfide, and naphthenic acids. Removal of these compounds can improve the color, odor, 

TABLE 2-6. Common Fuel Contaminants Resulting from Refining Processes 

Ammonia Results from catalytic cracking and hydrotreating of nitrogen-containing compounds, typically heterocyclic compounds 

Hydrotreating processes are applied to finished products to improve their characteristics sulfur content, cetane number, smoke point and the aromatics and olefins contents. 

The feedstocks in question are primary distillation streams and some conversion products from catalytic cracking, coking, visbreaking, and residue conversion units. 

In regard to kerosene, the hydrotreating processes are used to reduce aromatics in order to improve the smoke point. 

For gas oil sulfur and aromatics reduction serves to increase the cetane number and to improve color and thermal stability. 

By-products of these processes of hydrotreating are gases, H2S, and some naphtha. The hydrogen consumption is relatively high as a function of the required performance. 

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Finishing Processes that eliminate (most often by hydrogenation) undesirabie compounds. 

Tail gas containing traces of SO2, H2S, COS and CS2 are usually sent to a finishing processing before being incinerated. 

The overall yield of the operation is 99.5 to 99.8 wt % depending on the type of finishing process employed. 

Deterioration. The causes of degradation phenomena in textiles (155—158, 164) are many and include pollution, bleaches, acids, alkaUes, and, of course, wear. The single most important effect, however, is that of photodegradation. Both ceUulosic and proteinaceous fibers are highly photosensitive. The natural sensitivity of the fibers are enhanced by impurities, remainders of finishing processes, and mordants for dyes. Depolymerization and oxidation lead to decreased fiber strength and to embrittlement. 

These are water-soluble crystalline compounds sold as concentrated aqueous solutions. The methylol groups are highly reactive (118—122) and capable of being cured on the fabric by reaction with ammonia or amino compounds to form durable cross-linked finishes, probably having phosphine oxide stmctures after post-oxidizing. This finishing process, as developed by Albright Wilson, is known as the Proban process. 

Whitening in combination with the finishing process is used primarily for woven fabrics of ceUulosic fibers and their blends with synthetic fibers. 

Part of the continuously recirculated solution is bled off and sent to the iodine finishing process. Iodine finishing consists of contacting this bleed of concentrated acidic iodide solution with gaseous chlorine, through which iodine is formed by oxidation and precipitated. After iodine precipitation, the resulting acidic mother Hquor, saturated with free iodine, is pumped back to acidify the clarified brine and to recover the remaining iodine. 

D. Murphy and G. Tupper, Users Guide to Powder Coating Association for Finishing Processes of the Society of Manufacturing Engineers, Dearborn, Mich., 1985, pp. 33-58. 

Finishing may also be viewed as another means for providing nonwovens with additional appHcation-dependent chemical and/or physical properties. Finishing processes bring about value-added fabrics with technically sophisticated properties for specific end use appHcations. 

Like methylolureas, cycHc ureas are based on reactions between urea and formaldehyde however, the amino resin is cycHc rather than linear. Many cychc urea resins have been used in textile-finishing processes, particularly to achieve wrinkle resistance and shrinkage control, but the ones described below are the most commercially important. They ate all in use today to greater or lesser extents, depending on specific end requirements (see also Textiles, finishing). 

R. W. Pmy, A New Took at Infrared, SME Pubfleation FC78-543, Association for Finishing Processes of SME, Dearborn, Mich., 1978. 

Shade Stains. These stains are usually applied after the sealer or first topcoat and are typically sprayed on specific areas to compensate for uneven color distribution during the initial finishing process. For instance, perhaps the gla2e was wiped too clean on an edge. Rather than going back to restain or gla2e that small area, the finisher can spray a small amount of this shade stain on the desired area and achieve the same result in a fraction of the time. 

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization iavolves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular ia cross-section and smoother ia surface appearance, which iacreases their luster. At the molecular level, mercerization causes a decrease ia the degree of crystallinity and a transformation of the cellulose crystal form. These fine stmctural changes iacrease the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving ceUulase enzymes, to produce special surface effects (15). 

The standard conventional finishing process has been modified to suit the purposes for different fabrics and garments. Eor example, tubular knits are frequently handled using specialized equipment to control tension and to get adequate padding. Some tubular knits are subjected to wet-on-wet padding, dried and cured in large dmm dryers, and steam-treated to achieve a relaxed and nondistorted knit. 

J. M. Lipscomb, Suface Coating 83 Chemical Coaters Association, Finishing 83 Conference Proceedings Association for Finishing Processes of SME, pp. 10—1, 10-10. 

Chemical modification of the cotton fiber must be achieved within the physical framework of this rather compHcated architecture. Uniformity of reaction and distribution of reaction products are iaevitably iafiuenced by rates of diffusion, swelling and shrinking of the whole fiber, and by distension or contraction of the fiber s iadividual stmctural elements duting finishing processes. 

The choice of coagulant for breaking of the emulsion at the start of the finishing process is dependent on many factors. Salts such as calcium chloride, aluminum sulfate, and sodium chloride are often used. Frequentiy, pH and temperature must be controlled to ensure efficient coagulation. The objectives are to leave no uncoagulated latex, to produce a cmmb that can easily be dewatered, to avoid fines that could be lost, and to control the residual materials left in the product so that damage to properties is kept at a minimum. For example, if a significant amount of a hydrophilic emulsifier residue is left in the polymer, water resistance of final product suffers, and if the residue left is acidic in nature, it usually contributes to slow cure rate. 

Die pressing allows such precision that no subsequent finishing processes are necessary but the dies, and thus the process, are expensive. 

Solvent Action. Materials that tend to respond well to extraction by pressing will be more effective in solids removal when solvents are used. The complication is that it becomes necessary to separate not only the solids and the containing liquid from the finished process, but the solvent as well. 

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