Recovery of sodium sulfate

Naphthalenol. 2-Naphthol or p-naphthol or 2-hydroxynaphthalene/7i3 -/5 -i7 melts at 122°C and boils at 295°C, and forms colorless crystals of characteristic, phenoHc odor which darken on exposure to air or light. 2-Naphthol [135-19-3] is manufactured by fusion of sodium 2-naphthalenesulfonate with sodium hydroxide at ca 325°C, acidification of the drowned fusion mass which is quenched ia water, isolation and water-washing of the 2-naphthalenol, and vacuum distillation and flaking of the product. A continuous process of this type has been patented (69). The high sulfate content ia the primary effluent from 2-naphthol production is greatiy reduced ia modem production plants by the recovery of sodium sulfate. 

Recovery of sodium sulfate from waste is an important waste control strategy within synthetic organic pharmaceutical plants. A sodium sulfate waste recovery system was employed... 

Jung J. and Sun G. (2001) Recovery of sodium sulfate from farm drainage salt for use in reactive dyeing of cotton. Enviroru Sci. Technol. 35, 3391—3395. 

In the same process during the up-stream conversion of say, p-cresol to PCME during etherification process, sodium sulfate is invariably produced as a liquid by-product and that needs careful processing of liquid PCME and separation of the inorganic layer from the organic mass. A proper system for recovery of sodium sulfate from the mass is no doubt one of the preconditions for a GMP and production of p-anisic aldehyde with a proper eco-system. 

Purification of the crude 2-naphthol is carried out by vacuum distillation. The high sulfate content in the primary effluent from 2-naphthol production is greatly reduced in modem production plants by the recovery of sodium sulfate. 

Figure 9.14 is a waste water application of FC-types for the recovery of Sodium sulfate in South Africa, and Figure 9.15 shows the conversion crystallisation of... 

Of the various byproduct utilization options, the most attractive is the separation and recovery of sodium sulfate for sale or reuse (Bennett and Nastri, 1990). Reuse options include recovery and use of sodium compounds in mineral filler, grout, and bricks (Eklund and Golden, 1990). Producing high purity Na2S04 for sale by dissolving the byproduct and... 

The aqueous sodium naphthenate phase is decanted from the hydrocarbon phase and treated with acid to regenerate the cmde naphthenic acids. Sulfuric acid is used almost exclusively, for economic reasons. The wet cmde naphthenic acid phase separates and is decanted from the sodium sulfate brine. The volume of sodium sulfate brine produced from dilute sodium naphthenate solutions is significant, on the order of 10 L per L of cmde naphthenic acid. The brine contains some phenolic compounds and must be treated or disposed of in an environmentally sound manner. Sodium phenolates can be selectively neutralized using carbon dioxide and recovered before the sodium naphthenate is finally acidified with mineral acid (29). Recovery of naphthenic acid from aqueous sodium naphthenate solutions using ion-exchange resins has also been reported (30). 

Manufacture. The oldest method for producing Na2S is by the reduction of sodium sulfate with carbon in a refractory oven at 900—1000°C. Whereas this method is no longer used commercially in the United States, a variation is used to produce sodium sulfide captively during kraft pulp processing to replace lost sodium and sulfur values that were initiated into the system by merchant-suppHed sodium sulfide. In this method, sodium sulfate is added to the system in the recovery furnace, where it is reduced by carbon from the wood pulp to produce sodium sulfide. 

Obana et alP reported a modified ethyl acetate extraction which used a super absorbent polymer instead of sodium sulfate to absorb water. Eollowing cleanup by carbon-based SPE and/or gel permeation chromatography (GPC), recoveries in excess of 70% were achieved for the majority of the 107 pesticides of interest in asparagus, orange, potato and strawberry. The super absorbent polymers are now being incorporated into ASE procedures. 

Alba et al. used ethyl acetate to extract imidacloprid residues from fruits and vegetables. A 15-g sample of vegetable or fruit is weighed into a blender tube and 60 mL of ethyl acetate and 15g of sodium sulfate are added. The mixture is homogenized for 30 s, using a Polytron, and filtered. The filtrate is evaporated and the residue obtained is dissolved in acetonitrile-water (1 1, v/v). Alba etal. considered the low recoveries of these polar pesticides as the major disadvantage of the acetone extraction method. In their previous work they evaluated the efficacy of ethyl acetate for the extraction of pesticide residues. 

Alkaline delignification in the form of the Kraft or Sulfate process is now the most widely used method of lignin removal. It uses a mixture of sodium hydroxide and sodium sulfide—the latter being produced in the recovery process by the reduction of sodium sulfate... 

Special recovery and subsequent sale of sodium sulfate. 

Liquors from Neutral Semichemical Pulping and from Kraft Pulping. In making neutral sulfite semichemical pulp, the black liquors may have about 10 parts of water to 1 part of total solids, of which about one-third is sodium acetate and sodium formate. After evaporation to about 1 part solids to 1 part water, sulfuric acid is added to the concentrate to free the acetic and formic acids. When the concentrate is extracted with acetone, the mixed acids are obtained, the acetone is separated for recycle, and the acids are concentrated and refined. The raffinate is stripped and is passed to the usual furnace to be burned for recovery of the inorganic salt values. This process gives a smelt of sodium sulfate, which may be used in the kraft process as chemical makeup. The loss of the fuel value of the acetic and formic acids is practically negligible. 

Hence, a part of the black liquors (10-50%) of a kraft plant may be processed to free, and subsequently to recover, the acetic acid as described by the addition of sulfuric acid and the formation of sodium sulfate. This new sodium sulfate from the sulfuric acid is present in the raffinate from the extractor it is thus the makeup for the balance of the liquors (50-90% ) that can be processed conventionally without recovery of the acetic and formic acids. The liquors from the raffinate are added to the other liquors before they go to the drier and the furnace. This part of the liquors (10-50%) recovers that much of the volatile acids that would otherwise be lost in the burner as salts. 

Raisglid and co-workers (1993) found that methylene chloride did not give the best absolute recovery for the 46 compounds (63%), but a mixture of acetone/ethyl acetate (75 25) gave recoveries of 84%. These recoveries were based on a 1-L sample and 500 mg of C-18 sorbent. The ability of the acetone to solvate and remove water from the bonded silica columns (C-8 and C-18) improved the recoveries. Drying times were reduced from 10 min with methylene chloride to 1 min with the acetone/ethyl acetate. Furthermore, the removal of sodium sulfate from the drying of methylene chloride further increased the recoveries of the analytes. 

However, disposal will become increasingly difficult, if not impossible, in the near future due to tighter environmental regulations. In any case, it will certainly become increasingly expensive and for this reason, at least, the recovery by electrolysis of sodium sulfate—and in general of other neutral salts, such as sodium nitrate and sodium chloride, which are also generated in some chemical processes—is expected to have a bright future. 

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