Treating processes caustic wash

Several processes use the principle of an alkali (caustic) wash, which is a process in which distillate is treated with sodium hydroxide to remove acidic contaminants... 

Isomerization processes produce sour water and caustic wastewater. The ether manufacturing process utilizes a water wash to extract methanol or ethanol from the reactor effluent stream. After the alcohol is separated, this water is recycled back to the system and is not released. In those cases where chloride catalyst activation agents are added, a caustic wash is used to neutralize any entrained hydrogen chloride. This process generates a caustic wash water that must be treated before being released. This process also produces a calcium chloride neutralization sludge that must be disposed of off-site. 

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. 

Caustic wash the process of treating a product with a solution of caustic soda to remove minor impurities often used in reference to the solution itself. 

Reduced wastewater. The EDC product needs no washing, thus, lowering wastewater volume to be post treated. Also, caustic soda consumption is very low for the HTC process. 

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 traditional method of manufacturing is by a separation method (like most traditional methods) with a solvent extracted and dewaxed base oil as the usual feedstock. By reaction of either a paraffinic or a naphthenic base oil with oleum, aromatics are converted to the corresponding sulfonic acids and separate out. This may require several mixing steps to complete reaction of all the aromatics. Paraffins and naphthenes are essentially unaffected by the acid treatment.7 After separation of the sulfonic acids, the remaining oil, now free of aromatics, is neutralized with caustic, washed with alcohol, and finally treated with bauxite or clay. Figure 11.1 provides a schematic for this type of process. 

This decision was made to treat each phase separately. The sludge would be jetted from the bottom of the tank, treated with caustic to remove the A1 solids, washed with inhibited alkaline water and the remaining sludge transferred directly to the DWPF. The wash water would be processed at the low level waste Saltstone facility. 

Pardun (1979) has described two methods for the continuous refining of soybean oil using ammonia. The first treats water-degummed oil with aqueous ammonia followed by weak (0.5 m) caustic soda, and in the second, crude undegummed oil is treated with citric or formic acid solution followed, without gum separation, by neutralization with ammonia. The soapstock is separated and the ammonia boiled off, leaving, in the second case, a by-product of lecithin enriched with fatty acids. These processes avoid the environmental hazards of the splitting of soapstock with mineral acids. The oil from both processes is washed, dried, bleached and deodorized according to normal practice. 

More recendy, the molten caustic leaching (MCL) process developed by TRW, Inc. has received attention (28,31,32). This process is illustrated in Eigure 6. A coal is fed to a rotary kiln to convert both the mineral matter and the sulfur into water- or acid-soluble compounds. The coal cake discharged from the kiln is washed first with water and then with dilute sulfuric acid solution countercurrendy. The efduent is treated with lime to precipitate out calcium sulfate, iron hydroxide, and sodium—iron hydroxy sulfate. The MCL process can typically produce ultraclean coal having 0.4 to 0.7% sulfur, 0.1 to 0.65% ash, and 25.5 to 14.8 MJ/kg (6100—3500 kcal/kg) from a high sulfur, ie, 4 wt % sulfur and ca 11 wt % ash, coal. The moisture content of the product coal varies from 10 to 50%. 

The first step of the process is performed in a separate, dedicated building. The drums of arsenic trioxide are opened in an air-evacuated chamber and automatically dumped into 50% caustic soda. A dust collection system is used. The drums are carefully washed with water, the washwater is added to the reaction mixture, and the dmms are crushed and sold as scrap metal. The intermediate sodium arsenite is obtained as a 25% solution and is stored in large tanks prior to further reaction. In the next step, the 25% sodium arsenite is treated with methyl chloride to produce the disodium salt DSMA (disodium methanearsenate, hexahydrate). This DSMA can be sold as a herbicide however, it is more generally converted to MSMA, which has more favorable application properties [8]. 

Several bituninous coals have been treated with molten mixtures of NaOH plus KOH at 350-370 C in a 1 10 coal-to-caustic ratio for 1 hour and then washed with water, dilute acid, and finally with water again. By this procedure, which is similar to that of the TRW Gravi-melt Process, 80-90% of the ash and 70-80% of the total sulfur have been removed with a recovery of 80-90% of the coal on a moisture- and ash-free basis. The desulfurization could be improved by using a finer grind of coal, better washing procedures, or a recleaning step. 

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