Acid plants

A continuous bleed is taken from the reactor to remove high boilers. Values contained in this bleed are recovered in the bleed stripper and the distillate from this operation is recycled to the esterification reactor. The bleed stripper residue is a mixture of high boiling organic material and sulfuric acid, which is recovered for recycle in a waste sulfuric acid plant. 

Because of the highly corrosive nature of the nitric acid streams, adipic acid plants are constmcted of stainless steel, or titanium in the more corrosive areas, and thus have high investment costs. 

Because of projected nylon-6,6 growth of 4—10% (167) per year in the Far East, several companies have announced plans for that area. A Rhc ne-Poulenc/Oriental Chemical Industry joint venture (Kofran) announced a 1991 startup for a 50,000-t/yr plant in Onsan, South Korea (168,169). Asahi announced plans for a 15,000-t/yr expansion of adipic acid capacity at their Nobeoka complex in late 1989, accompanied by a 60,000-t/yr cyclohexanol plant at Mizushima based on their new cyclohexene hydration technology (170). In early 1990 the Du Pont Company announced plans for a major nylon-6,6 complex for Singapore, including a 90,000-t/yr adipic acid plant due to start up in 1993 (167). Plans or negotiations for other adipic acid capacity in the area include Formosa Plastics (Taiwan) (171) and BASF-Hyundai Petrochemical (South Korea) (167). Adipic acid is a truly worldwide... 

Precipitators are currently used for high collection efficiency on fine particles. The use of electric discharge to suppress smoke was suggested in 1828. The principle was rediscovered in 1850, and independently in 1886 and attempts were made to apply it commercially at the Dee Bank Lead Works in Great Britain. The installation was not considered a success, probably because of the cmde electrostatic generators of the day. No further developments occurred until 1906 when Frederick Gardiner Cottrell at the University of California revived interest (U.S. Pat. 895,729) in 1908. The first practical demonstration of a Cottrell precipitator occurred in a contact sulfuric acid plant at the Du Pont Hercules Works, Pinole, California, about 1907. A second installation was made at Vallejo Junction, California, for the Selby Smelting and Lead Company. 

A widely used type of pump—mixer—settler, developed by IsraeH Mining Industries (IMI) (115), is shown in Figure 13a. A unit having capacity 8.3 m /min (2000 gal /min) has been used in phosphoric acid plants (116). The unique feature of this design is that the pumping device is not required to act as the mixer, and the two phases are dispersed by a separate impeller mounted on a shaft miming coaxially with the drive to the pump. 

The selection of a process can be complex, requiring carehil evaluation of the many variables for each appHcation. The hemihydrate process is energy efficient, but this may not be an overriding consideration when energy is readily available from an on-site sulfuric acid plant. The energy balance in the total on-site complex may be the determining factor. 

The abatement of fluorine emissions and disposal of by-product calcium sulfate from phosphoric acid plants are environmental concerns. 

Alternative Processes. Because of the large quantity of phosphate rock reserves available worldwide, recovery of the fluoride values from this raw material source has frequently been studied. Strategies involve recovering the fluoride from wet-process phosphoric acid plants as fluosiUcic acid [16961-83-4] H2SiFg, and then processing this acid to form hydrogen fluoride. 

Owing to the cycHc nature of the TBRC operation, waste heat recovery from the off-gases is not practical and the SO2 content of the gas varies with the converter cycle. In order to supply a relatively uniform flow and strength SO2 gas to a sulfuric acid plant, a system has been installed at RonnskAr whereby the SO2 from fluctuating smelter gases is partially absorbed in water. During smelter gas intermption, SO2 is stripped with air and the concentrated gas deflvered to the acid plant. 

Other developing or potential appHcations for lime are neutralization of tail gas from sulfuric acid plants, neutralization of waste hydrochloric and hydrofluoric acids and of nitrogen oxide (NO ) gases, scmbbing of stack gases from incinerators (qv), and of course, from small industrial coal-fired boilers. 

Data for the production and sales of maleic anhydride and fumaric acid ia the United States between 1979 and 1992 are shown ia Table 5. Production of maleic anhydride during this time grew - 2% on average per year. Production of fumaric acid has declined during the same period as customers have switched to the less cosdy maleic anhydride when possible. All production of maleic anhydride in the United States in 1992 was from butane-based plants which used fixed-bed reactor technology as shown in Table 6. The number of fumaric acid producers has been reduced considerably since the early 1980s with only two producers left in the United States in 1992 as shown in Table 6. Pfizer shut down its fumaric acid plant at the end of 1993. However, Bartek of Canada will start up an expanded fumaric acid faciUty to supply the North American market for both their own and Huntsman s requirements. 

The sulfur dioxide produced by the process is usually converted to sulfuric acid, or sometimes Hquified, and the design of modem roasting faciUties takes into account the need for an efficient and environmentally clean operation of the acid plant (see SuLFURiC ACID AND SULFURTRIOXIDe). 

NO Abatement. Source performance standards for nitric acid plants in the United States were introduced by the U.S. EPA in 1971 (55). These imposed a discharge limit of 1.5 kg of NO as equivalent nitrogen dioxide per 1000 kg of contained nitric acid, which corresponds to about 200—230... 

Process Licensors. Some of the well-known nitric acid technology licensors are fisted in Table 3. Espindesa, Grande Paroisse, Humphreys and Glasgow, Rhfyne Poulenc, Uhde, and Weatherly are all reported to be licensors of weak acid technology. Most weak acid plant licensors offer extended absorption for NO abatement. Espindesa, Rhfyne Poulenc, Weatherly, and Uhde are also reported (53,57) to offer selective catalytic reduction (SCR) technology. 

It is generally unacceptable to emit sulfur dioxide, thus the scmbber effluent must be treated for sulfur dioxide removal. If the plant aheady possesses faciUties for the production of sulfuric acid, this rather concentrated sulfur dioxide stream can be easily fed into the wet gas cleaning circuit and disposed of in the sulfuric acid plant. The quantity is so small that it does not put any additional burden on the sulfuric acid plant. Because no tellurium is carried over with the selenium dioxide during roasting, it is possible to produce a selenium product which can be purified to commercial grade (99.5-99.7%). 

The resulting nitrous oxide can be recirculated to the nitric acid plant or be used for other purposes. Free acid remaining in the impregnation water of sodium nitrate crystals is neutralized by adding some NaOH to the washing water. Whereas several nitric acid plants utilize absorption of nitrous gases to treat tail gases, almost all of these plants produce small volumes of sodium nitrate. 

Industrial production of sodium nitrite is by absorption of nitrogen oxides (NO ) into aqueous sodium carbonate or sodium hydroxide. NO gases originate from catalytic air oxidation of anhydrous ammonia, a practice common to nitric acid plants ... 

Certain of the above reactions are of practical importance. The oxidation of hydrogen sulfide in a flame is one means for producing the sulfur dioxide required for a sulfuric acid plant. Oxidation of hydrogen sulfide by sulfur dioxide is the basis of the Claus process for sulfur recovery. The Claus reaction can also take place under mil der conditions in the presence of water, which catalyzes the reaction. However, the oxidation of hydrogen sulfide by sulfur dioxide in water is a complex process leading to the formation of sulfur and polythionic acids, the mixture known as Wackenroeder s Hquid (105). 

Large sulfuric acid plants are based on spray burners, where the sulfur is pumped at 1030—1240 kPa (150—180 psig) through several nossles iato a refractory-lined combustion chamber. An improved nossle, resistant to plugging or fouling, has been iatroduced (256). The combustion chambers are typically horizontal baffle-fitted refractory-lined vessels. The largest plants ia fertiliser complexes bum up to 50 t/h of sulfur. 

---