Sulfuric acid recovery process

The sulfuric acid recovery process (SARP), developed jointly by Texaco Inc. and Stratford Engineering Corp. to reduce the acid consumption in H2S04 alkylation units, was another contribution to alkylation technology (18). In this process the spent acid from an alkylation... 

Improved product treatment Sulfuric acid recovery process Catalyst promoters... 

A number of different processes involving the absorption of olefin in recycle sulfuric acid alkylation catalyst, extraction of the dialkyl sulfate, treatment of the extract in some manner, and alkylation of the treated dialkyl sulfate have been considered. One such process which has become known in the industry as SARP is the subject of this paper. SARP stands for Sulfuric Acid Recovery Process, which obviously has a rather generic connotation. The process is rather specific. The writer prefers the name originally given to the process, namely, Extractylation. However, SARP has the advantage of being known and is short, so SARP will probably prevail. 

One patented process (40) was introduced in the mid- 60s to reduce the amount of sulfuric acid required by alkylation it was called the Sulfuric Acid Recovery Process (SARP) and was jointly licensed by Texaco Development Corporation and Stratford Engineering Corporation. Chemically, SARP proved all claims made for it. Utilized only with propylene/butylene alkylation the acid requirement was reduced as much as 70% actual acid dilution rates were lower than 0. 2 acid/gallon alkylate. However, the spent acid from SARP was different and could not be regenerated at the same rate as regular spent alkylation acid. This caused the chemical companies to increase the charges for regenerating the SARP spent acid to a point where there was no economic incentive to operate SARP. The two commercial SARP installations are not in use at the present time although new possibilities for SARP have arisen just in the past few months. 

SARP [Sulfuric Acid Recovery Process] A method for recovering sulfuric acid that has been used for alkylation, for reuse. The acid is reacted with propylene, yielding dipropyl sulfate, which is extracted from the acid tar with isobutane. It is not necessary to hydrolyze the sulfate to sulfuric acid because the sulfate itself... 

SAR [Sulfuric Acid Recovery] A process for purifying and concentrating used sulfuric acid for re-use. The acid is heated with oxygen at 1,040°C to convert the acid to sulfur dioxide. This is then oxidized over a vanadium-containing catalyst to sulfur trioxide, which is dissolved in fresh sulfuric acid to give 98 percent acid. Developed by L Air Liquide and ICI. First demonstrated in 1991 at a methyl methacrylate plant in Taiwan. 

Process Alternatives. Sulfur dioxide removal processes can be categorized as throwaway or recovery. Throwaway processes produce a liquid or solid waste that requires disposal. Recovery processes convert the sulfur dioxide to elemental sulfur or sulfuric acid. Throwaway processes have been used in most utility applications, but there could be greater incentives for using the recovery processes in industry. 

In view of the foregoing, it is not surprising that many attempts have been made by many companies almost from the start of alkylation to develop a recovery process unique to the used sulfuric acid alkylation catalyst. Most of the early attempts were not intensive and continuous. Most of the work is unpublished, since it was of a preliminary nature and not very successful. An added incentive was provided for the users and licensors of the Sulfuric Acid Alkylation Process when it was discovered that hydrofluoric acid was also a good alkylation... 

Process used for waste sulfuric acid recovery dependent upon the impurity level ... 

Besides ethanol, large quantities of ethyl ether are produced by the sulfuric acid absorption process from ethylene. In the hydration of ethylene by this method the relative proportions of alcohol and ether obtained are determined by the temperature and concentration of the sulfuric acid solution at the hydration and recovery stage. The more dilute the acid, the higher the proportion of alcohol formed and vice versa. This same process has been applied to the formation of isopropyl ether from propene and this product is now available in tank car lots. 

One subclass of sulfur dioxide recovery processes incorporates a liquid-phase variation of the Claus reaction for regenerating the absorbent and directly producing elemental sulfur. Processes of this type are the Stauffer Aquaclaus process (88), which was developed specifically for Claus plant tail gases, and the Bureau of Mines Citrate process (89). In each, the absorbent is the sodium salt of a stable, nonvolatile weak acid, which forms a basic solution by hydrolysis. The anion of the acid buffers the solution as acid is formed by the absorption of sulfur dioxide. The spent absorbent, which consists of a solution of sodium sulfite and bisulfite and of the weak acid, is contacted directly wtih hydrogen sulfide. The hydrogen sulfide reacts with the sulfite and bisulfite to yield elemental sulfur, and the regenerated basic salt solution is recirculated to the absorption step. 

The manufacture of picrite posed an extremely difficult problem in sulfuric-acid recovery for the substantial amount of spent acid produced contained only about 18% sulfuric acid. Submerged combustion was applied to this duty at ROF Bishopton and while this procedure functioned well as far as actual concentration was concerned, corrosion of the equipment by the nitrate ion present was so severe that the process could only be run intermittently and eventually had to be abandoned leaving the acid to the dealt with by neutralization with limestone followed by prolonged drainage in settling lagoons. 

Most combustion gases that contain sulfiir dioxide also contain a small, but significant amount of sulfur tcioxide (or its reaction product with water, sulfuric acid). This component is of considerable importance because of its highly corrosive nature, its effect on the chemistry of many sulfur dioxide recovery processes, and its suspected critical role in air pollution problems. The amount of sulfur trioxide emitted to the atmosphere is a function of combustion air/fiiel ratio, fuel composition, combustion temperature, time at temperature, the presence or absence of a catalyst, electrostatic precipitator conditioning with ammonia, and the... 

Small amounts of propionitrile and bis(cyanoethyl) ether are formed as by-products. The hydrogen ions are formed from water at the anode and pass to the cathode through a membrane. The catholyte that is continuously recirculated in the cell consists of a mixture of acrylonitrile, water, and a tetraalkylammonium salt the anolyte is recirculated aqueous sulfuric acid. A quantity of catholyte is continuously removed for recovery of adiponitrile and unreacted acrylonitrile the latter is fed back to the catholyte with fresh acrylonitrile. Oxygen that is produced at the anodes is vented and water is added to the circulating anolyte to replace the water that is lost through electrolysis. The operating temperature of the cell is ca 50—60°C. Current densities are 0.25-1.5 A/cm (see Electrochemical processing). 

The ratio of reactants had to be controlled very closely to suppress these impurities. Recovery of the acrylamide product from the acid process was the most expensive and difficult part of the process. Large scale production depended on two different methods. If soHd crystalline monomer was desired, the acrylamide sulfate was neutralized with ammonia to yield ammonium sulfate. The acrylamide crystallized on cooling, leaving ammonium sulfate, which had to be disposed of in some way. The second method of purification involved ion exclusion (68), which utilized a sulfonic acid ion-exchange resin and produced a dilute solution of acrylamide in water. A dilute sulfuric acid waste stream was again produced, and, in either case, the waste stream represented a... 

Essentially all the ammonium sulfate fertilizer used in the United States is by-product material. By-product from the acid scmbbing of coke oven gas is one source. A larger source is as by-product ammonium sulfate solution from the production of caprolactam (qv) and acrylonitrile, (qv) which are synthetic fiber intermediates. A third but lesser source is from the ammoniation of spent sulfuric acid from other processes. In the recovery of by-product crystals from each of these sources, the crystallization usually is carried out in steam-heated sa turator—crystallizers. Characteristically, crystallizer product is of a particle size about 90% finer than 16 mesh (ca 1 mm dia), which is too small for satisfactory dry blending with granular fertilizer materials. Crystals of this size are suitable, however, as a feed material to mixed fertilizer granulation plants, and this is the main fertilizer outlet for by-product ammonium sulfate. 

Production Technology. Processes for extraction of P2O3 from phosphate rock by sulfuric acid vary widely, but all produce a phosphoric acid—calcium sulfate slurry that requires soHds-Hquid separation (usually by filtration (qv)), countercurrent washing of the soHds to improve P2O3 recovery, and concentration of the acid. Volatilized fluorine compounds are scmbbed and calcium sulfate is disposed of in a variety of ways. 

The precipitated cellulose acetate is filtered from the dilute (25—36%) acetic acid. The acetic acid and salts remaining from the sulfuric acid neutrali2ation are removed by washing. The wet polymer is typically dried to a moisture content of 1—5%. The dilute acetic acid obtained from the washing and precipitation steps caimot be used in other stages of the process. Its efficient recovery and recycle are an economic necessity. 

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