Treating processes sweetening

Bender process a chemical treating process using lead sulfide catalyst for sweetening light distillates by which mercaptans are converted to disulfides by... 

Inhibitor sweetening a treating process to sweeten gasoline of low mercaptan content, using a phenylenediamine type of inhibitor, air, and caustic. 

If the natural gas stream contains unacceptable quantities of hydrogen sulfide and/or carbon dioxide, they must be removed in order to make the gas suitable for transmission and sale. The details of removal of H2S and C02 from natural gas streams are beyond the scope of this chapter, but excellent discussions are available.10,12 There are many different processes available, depending upon the contaminants to be removed and their concentration in both the sour gas available and the sweetened gas to be produced. The dominant treating process is still the use of an alka-nolamine. A typical flow diagram for an amine sweetening installation for removal of hydrogen sulfide and carbon dioxide from a natural gas stream is shown in Fig. 20.10.12... 

When the sulfur content of the crude oil is low (usually less than one percent by weight), the crude oil is known as a sweet crude, while crude oil with higher concentrations of sulfur is called sour crude. Removal of sulfur and other impurities form part of the treating processes and sulfur itself can form a valuable by-product in a refinery as an input into the chemical industry. Other impurities include nitrogen, oxygen, and salt, as well as small quantities of metals such as vanadium and nickel that are common in certain of the heavier crude oils. As well as extraction processes to purify oil and its products of impurities, specific additives are also used to react with corrosive or odiferous constituents to produce harmless and odorless substances. Such processes are generally termed sweetening processes. 

There are three major ways of attaining sweetening (1) processes that oxidize mercaptans to disulfides, (2) processes that remove the mercaptans, and (3) processes that destroy and remove other sulfur compounds along with mercaptans, hydrogen sulfide, and sulfur. The last of these methods is usually considered as a desulfurization process. Walker and Kenney present a comprehensive discussion of the various treating processes. ... 

Two undesirable aspects of FCC naphtha quaUty are that it may contain unacceptably high amounts of foul smelling mercaptans, and that its thermal stabiUty may be too low. Mercaptans are usually found in the light FCC naphtha and may be removed or converted to sulfides and disulfides by a sweetening process such as Merox, developed by UOP. Thermal stabiUty is improved in sweetening processes through removal of cresyUc and naphthenic acids. It may be further improved by clay treating and by addition of oxidation inhibitors such as phenylene diamine. 

A large use of molecular sieves ia the natural gas industry is LPG sweetening, in which H2S and other sulfur compounds are removed. Sweetening and dehydration are combined in one unit and the problem associated with the disposal of caustic wastes from Hquid treating systems is eliminated. The regeneration medium is typically natural gas. Commercial plants are processing from as Htde as ca 30 m /d (200 bbl/d) to over 8000 m /d (50,000 bbl/d). 

Conversion Processes. Most of the adsorption and absorption processes remove hydrogen sulfide from sour gas streams thus producing both a sweetened product stream and an enriched hydrogen sulfide stream. In addition to the hydrogen sulfide, this latter stream can contain other co-absorbed species, potentially including carbon dioxide, hydrocarbons, and other sulfur compounds. Conversion processes treat the hydrogen sulfide stream to recover the sulfur as a salable product. 

This process uses propylene carbonate as a physical solvent to remove CO2 and H2S. Propylene carbonate also removes C2+ hydrocarbons, COS, SO2, CS2, and H2O from the natural gas stream. Thus, in one step the natural gas can be sweetened and dehydrated to pipeline quality. In general, this process is used for bulk removal of CO2 and is not used to treat to less than 3% CO2, as may be required for pipeline quality gas. The system requires special design features, larger absorbers, and higher circulation rates to obtain pipeline quality and usually is not economically applicable for these outlet requirements. 

Other waste streams from the process result from water washing of the treated product and regeneration of the treating solution such as sodium plumbite (Na2Pb02) in doctor sweetening. These waste streams contain small amounts of oil and the treating material, such as sodium plumbite (or copper from copper chloride sweetening). 

Removal of the objectionable odors due to the presence of H2S and mercaptans is the objective of the fuel sweetening process. Several methods can be utilized to remove these undesirable compounds including caustic washing, copper chloride sweetening, sulfuric acid treating, Merox processing, and hydrotreating. These methods will be discussed below. 

Sulfur removal, as practiced in various refineries, can take several forms for instance, concentration in refinery products such as coke (Table 7-1), hydrode-sulfurization, or chemical removal (acid treating and caustic treating, i.e., sweetening or finishing processes). Nevertheless, the desulfurization of petroleum is almost universally accomplished by the catalytic reaction of hydrogen with the sulfur-containing constituents of petroleum to produce hydrogen sulfide that can be readily separated from the liquid products (Chapter 9). 

Linde copper sweetening a process for treating gasoline and distillates with a slurry of clay and cupric chloride. 

In Japan, the term additive means anything added to, mixed with, permeating, etc., food in the process of manufacturing, processing, or preserving it [8], In Japanese food law, synthetic and naturally occurring additives are treated differently. The latter, especially naturally occurring flavors and vitamins, do not require any special permission for use. This explains, for example, why sweeteners isolated from plants must be specifically permitted as additives everywhere else in the world, while they can be used freely in Japan. 

SulfaTreat A process for removing hydrogen sulfide and mercaptans from natural gas or carbon dioxide streams, using a proprietary solid absorbent, which is subsequently dumped. First developed by Gas Sweetener Associates, now licensed by Sulfa Treat, a business unit of MI-SWACO, MO. More than 1,000 plants were operating in 2000. 

At termination of the loading cycle under fixed bed operation the column remains flooded with partially treated feed. In processes where the feed liquor commands a high monetary value with respect to its constituents, as in for example, such processes as carbohydrate refining, metal recovery, and pharmaceutical production it is common practice to sweeten off the column by displacing up to about one bed volume of column residual which is saved for reprocessing. 

Sulfur compounds such as alkyl and aryl thiols are treated with concentrated alkaline solutions in a process known as sweetening and cresols and xylenols are recovered from spent caustic washes, producing sodium cresolates/ xylenolates. 

The treated gas had to meet typical pipeline gas specifications, that is, less than 4 ppm vol. H2S and less than 2.0 vol.% CO2. The add gas liberated is sent to conventional two-stage Claus units followed by a Sulfreen tail gas treating unit. Figure 10.4 illustrates the original amine sweetening units process flow-scheme. There are two identical trains, each equipped with two high-pressure absorbers and two regenerators. 

Liquid water and sometimes water vapor are removed from natural gas to prevent corrosion and formation of hydrates in transmission lines and to attain a water dew point requirement of the sales of gas. Many sweetening agents employ an aqueous solution for treating the gas. Therefore dehydrating the natural gas that normally follows the sweetening process involves ... 

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