Sweetening process, selective

Selective Absorption in the Sweetening Process. In recent years removal of the acid gas (H2S, CO2) components from a gas stream has increasingly been by absorption in a solvent system containing amines. While non-reactive solvent sweetening processes are in use, the ability of the basic amine to react chemically with the acid gas to yield water soluble salts has favored the chemical sweetening system. Thus... 

The selected catalyst, DSg, was tested over a long period (17 days) with a pilot modeling the fixed-bed sweetening process. Knowing that the actual norm of mercaptan amount in carbureactor product is about 15 ppm maximum, we observed after one day, a residual mercaptan of about 0.8 ppm corresponding to 99.4 % removal (Fig. 6). 

The Stretford Process sweetens and also produces sulfur. It is good for low feed gas concentrations of H2S. Economically, the Stretford Process is comparable to an amine plant plus a Claus sulfur recovery plant. Usually, the amine/Claus combination is favored over Stretford for large plants. Stretford can selectively remove H2S in the presence of high CO2 concentrations. This is the process used in the coal gasification example in the Introduction. 

The R D activities of GRI led to a group of two patents, for gas sweetening (and also useful for flue gas treatment), based on biocatalytic processes for the selective removal of sulfur compounds in the presence of other reactive gases. 

Apart from liquid phase adsorption on a solid adsorbent such as bauxite, the early processes for sweetening and desulfurization were of a chemical nature. Some are in operation today in substantially their original forms, some have been greatly improved, and new processes performing similar functions have been developed. It is beyond the scope of this paper to cover them all, even in outline, therefore a comparative selection has been made to illustrate the advances achieved. The division, which is on a rather arbitrary basis, is given in Table V. 

Enzymes are characterized by unusual specific activities and remarkably high selectivities. They are effective catalysts at relatively low temperatures and ambient pressure. The primary driving force for efforts to develop immobilized forms of these biocatalysts is cost, especially when one is comparing process alternatives involving either conventional inorganic catalysts or soluble enzymes. Immobilization can permit conversion of labile enzymes into forms appropriate for use as catalysts in industrial processes—production of sweeteners, pharmaceutical intermediates, and fine chemicals—or as biosensors in analytical applications. Because of their high specificities, immobilized versions of enzymes are potentially useful in situations where it is necessary to obtain high yields of the desired product... 

When the MDEA process was developed in the mid-1970s it was principally destined for the sweetening of gases that did not require complete CO2 removal [ 1 ], or required the removal of only a controlled part of the CO2. Typical applications of the selective MDEA process are ... 

In brief statement, the distillation process consists in macerating the selected aromatic flavoring substances in alcohol for a fixed period. The liquid is then distilled and the aroma and flavor of the herbs, seeds, fruits, etc., will be found in the distillate. This is then sweetened and colored and may also be diluted and blended with alcohol and water, and other materials as required. 

It appears evident that where quality is a paramount consideration selection of sweeteners and processing techniques should be governed by careful testing and controlled experiments. 

Production of the artificial low-calorie sweetener aspartame from Z-L-aspartate and D/L-phenylalanine methylester by peptide bond formation with immobilized thermolysin from Bacillus thermoproteolyticus (Tosoh Corp., Ajinomoto, Toyo-Soda, DSM, annual world production approx. 10000 tons). Aspartame is about 200 times as sweet as sucrose, and is used in drinks such as Coca Cola and Pepsi Cola Light. In contrast to the older chemical process, the enzymatic process can - due to the L-selectivity of the enzyme - use the cheaper D/L-phenylalanine methylester instead of the pure L-form. The enzymatic process (Fig. 15) yields a-aspartame exclusively, whereas the chemical route yields a mixture of a-aspartame and bitter-tasting (5-aspartame, thus requiring an additional separation step. 

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