Hydrocarbon in acid gas

Methane is the most common hydrocarbon in acid gas mixtures. Large quantities of other hydrocarbons are probably indicative of problems with the amine plant and should be addressed. For example, foaming will cause carry-over of the hydrocarbons into the stripper. In the regeneration of the amine, the hydrocarbons will end up in the acid gas. 

Due to the presence of hydrocarbons in the gas feed to the burner section, some undesirable reactions occur, such as the formation of carbon disulfide (CS2) and carbonyl sulfide (COS). A good catalyst has a high activity toward H2S conversion to sulfur and a reconversion of COS and CS2 to sulfur and carbon oxides. Mercaptans in the acid gas feed results in an increase in the air demand. For example, approximately 5-13% increase in the air required is anticipated if about 2 mol% mercaptans are present. The increase in the air requirement is essentially a function of the type of mercaptans present. The oxidation of mercaptans could be represented as ... 

Because of its relevance in environmental chemistry the reaction of photochemically excited sulfur dioxide with hydrocarbons in the gas phase has received considerable attention in recent years. In this reaction the principal path for formation of sulfinic acids is believed (Sherwell and Tedder, 1978) to be that shown in Scheme 2. Sherwell and Tedder do not think that abstraction of a hydrogen atom from RH by RS02-, i.e., RS02 + RH - RS02H + R-, occurs to any significant extent in such systems, although a summary of earlier studies of this reaction (Horowitz and Rajbenbach, 1975) shows that such a reaction has been proposed on occasion in the past. 

The ease of oxidation of polycyclic aromatic hydrocarbons in the gas phase481 as well as in solution is well-documented.482 195 In strong acid solutions, monopositive radical ions and/or dipositive ions, also known as oxidation dications, have been reported.271,494,495 Similar species have been observed in anodic oxidations of... 

The water content of acid gases is significantly different from that of sweet gas. Water is significantly more soluble in acid gas than it is in hydrocarbon gas. In addition, as will be demonstrated, the water content of acid gas mixtures exhibit a minimum. 

The typical hydrocarbon impurity in acid gas is methane. Methane is lighter than the acid gas components, and thus the density of an acid gas mixture is reduced by the presence of methane. Even in a liquid mixture, the density is reduced by the presence of methane. 

Figure 3. Plot of acidities of hydrocarbons in the gas phase vs. (CH3)2SO solution phase. (Reproduced with permission from reference 21. Copyright 1986 Weizmann Science Press.)...

Methods of practical interest for the direct nitration of aliphatic hydrocarbons have been developed only during recent decades. Hass worked out a process for mononitration of lower aliphatic hydrocarbons in the gas phase by 70% nitric acid at temperatures above 400° and this has been carried out on an industrial scale.148 It is not really suitable for laboratory use because the nitration is accompanied by fission of carbon-carbon bonds, so that the... 

Fine particulate matter might be transported and release PH3, whereas particulate acidity decreases and thereby explains why PH3 seems to be ubiquitous in air. Moreover, PH2 probably returns to PH3 via H abstraction from hydrocarbons in the gas phase ... 

Earlier studies had indicated aldehyde and ketone formation in the oxidation of ethylene however, later work using mass spectro-graphic analysis and gas chromatography reported no products other than CO2 and water. The coulombic efficiency determinations for the anodic oxidation of other unsaturated hydrocarbons in acid solution indicate that CO2 is the main reaction product (cf. Table 17). For lower olefins, i.e., C2H4 and oxidation is complete. For larger compounds, other products are formed however, the primary product is CO2. A general equation for hydrocarbon electro-oxidation can thus be written as... 

Carbon dioxide (CO2) is a very common contaminant in hydrocarbon fluids, especially in gases and gas condensate, and is a source of corrosion problems. CO2 in the gas phase dissolves in any water present to form carbonic acid (H2CO3) which is highly corrosive. Its reaction with iron creates iron carbonate (FeCOg) ... 

In 1825 Michael Faraday isolated a new hydrocarbon from illuminating gas which he called bicarburet of hydrogen Nine years later Eilhardt Mitscherlich of the University of Berlin prepared the same substance by heating benzoic acid with lime and found it to be a hydrocarbon having the empirical formula C H ... 

A derivative of the Claus process is the Recycle Selectox process, developed by Parsons and Unocal and Hcensed through UOP. Once-Thm Selectox is suitable for very lean acid gas streams (1—5 mol % hydrogen sulfide), which cannot be effectively processed in a Claus unit. As shown in Figure 9, the process is similar to a standard Claus plant, except that the thermal combustor and waste heat boiler have been replaced with a catalytic reactor. The Selectox catalyst promotes the selective oxidation of hydrogen sulfide to sulfur dioxide, ie, hydrocarbons in the feed are not oxidized. These plants typically employ two Claus catalytic stages downstream of the Selectox reactor, to achieve an overall sulfur recovery of 90—95%. 

Of the four commercial processes for the purification of carbon monoxide two processes are based on the absorption of carbon monoxide by salt solutions, the third uses either low temperature condensation or fractionation, and the fourth method utilizes the adsorption of carbon monoxide on a soHd adsorbent material. AH four processes use similar techniques to remove minor impurities. Particulates are removed in cyclones or by scmbbing. Scmbbing also removes any tars or heavy hydrocarbon fractions. Acid gases are removed by absorption in monoethanolamine, hot potassium carbonate, or by other patented removal processes. The purified gas stream is then sent to a carbon monoxide recovery section for final purification and by-product recovery. 

HYDROCARBONS Organic compounds that contain only hydrogen and carbon. The major sources of hydrocarbons in the atmosphere are vehicle emissions (unburned fuel) and gas leaks. Contributes to acid rain. 

In addition to heavy hydrocarbons and water vapor, natural gas often contains other contaminants that may have to be removed. Carbon dioxide (CO2), hydrogen sulfide (H2S), and other sulfur compounds such as mercaptans are compounds that may require complete or partial removal for acceptance by a gas purchaser. These compounds are known as acid gases. H2S combined with water forms a weak form of sulfuric acid, while CO2 and water forms carbonic acid, thus the term acid gas. ... 

The physical solvent sulfolane provides the system with bulk removal capacity. Sulfolane is an excellent solvent of sulfur compounds such as H2S, COS, and CS2. Aromatic and heavy hydrocarbons and CO2 are soluble in sulfolane to a lesser degree. The relative amounts of DIPA and sulfolane are adjusted for each gas stream to custom fit each application. Sulfinol is usually used for streams with an H2S to CO2 ratio greater than 1 1 or where it is not necessary to remove the CO2 to the same levels as is required for H2S removal. The physical solvent allows much greater solution loadings of acid gas than for pure amine-based systems. Typically, a Sulfinol solution of 40% sulfolane, 40% DIPA and 20% water can remove 1.5 moles of acid gas per mole of Sulfinol solution. 

The non-hydrocarbon constituents in natural gas vary appreciably from one gas field to another. Some of these compounds are weak acids, such as hydrogen sulfide and carbon dioxide. Others are inert, such as nitrogen, helium and argon. Some natural gas reservoirs contain enough helium for commercial production. 

Important processes commercially used are the Selexol, the Sulfinol, and the Rectisol processes. In these processes, no chemical reaction occurs between the acid gas and the solvent. The solvent, or absorbent, is a liquid that selectively absorbs the acid gases and leaves out the hydrocarbons. In the Selexol process for example, the solvent is dimethyl ether of polyethylene glycol. Raw natural gas passes countercurrently to the descending solvent. When the solvent becomes saturated with the acid gases, the pressure is reduced, and hydrogen sulfide and carbon dioxide are desorbed. The solvent is then recycled to the absorption tower. Figure 1-1 shows the Selexol process. ... 

NMe is now commercially available and is prepd by the vapor phase nitration of methane at a ratio of 9 moles of methane to I mole of nitric acid at 475° and a residence time of 0.18sec (Ref 12) or by the similar nitration of aliphatic hydrocarbons (Ref 8). Other prepns are from Me sulfate and Na nitrite (Ref 26) by the oxidn of Me amine with dinitrogen trioxide in the gas phase or in methylene chloride, yield 27%... 

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