Wastewater mercaptan

Typical constituents of sour wastewater streams from crude distillation include hydrogen sulfide, ammonia, suspended solids, chlorides, mercaptans, and phenol, characterized by a high pH. Combined flows from atmospheric and vacuum distillation are about 26.0 gallons per barrel of oil, and represent one of the largest sources of wastewater in a refinery. 

Wastewater from crude oil fractionation generally comes from three sources. The first source is the water drawn off from overhead accumulators prior to recirculation or transfer of hydrocarbons to other fractionators. This waste is a major source of sulfides and ammonia, especially when sour crudes are being processed. It also contains significant amounts of oil, chlorides, mercaptans, and phenols. 

Reforming is a relatively clean process. The volume of wastewater flow is small, and none of the wastewater streams has high concentrations of significant pollutants. The wastewater is alkaline, and the major pollutant is sulfide from the overhead accumulator on the stripping tower used to remove light hydrocarbon fractions from the reactor effluent. The overhead accumulator catches any water that may be contained in the hydrocarbon vapors. In addition to sulfides, the wastewater contains small amounts of ammonia, mercaptans, and oil. 

A number of studies have evaluated the toxicity of pulping hquors, in particular the black liquors generated from Kraft mills. Table 8 shows a partial representation of toxicity data compiled by the NCASI (National Council of the Paper Industry for Air and Stream Improvement) and McKee and Wolf for Kraft mill pulping wastewaters [15,16]. The table indicates that hydrogen sulfide, methyl mercaptan, crude sulfate soap, and salts of fatty and resin acids are particularly... 

Biocube (T0039) is a commercially available off-gas treatment system. A Biocnbe was installed at a domestic wastewater pumping facility in June 1995 at a cost of 15,000. The pumping facility treats approximately 200 m of water per day (50,000 gal per day) (D13550C, pp. 1-4). At a silver reclamation facility in Duval County, Florida, a Biocube biofiltration system used to treat vapors containing mercaptans (mainly 4-mercapto-4-methyl-2-pentanone) cost 18,000 (D13551D). 

Chemical oxidizing agents have been used for the control of organic residues in wastewaters and in potable water treatment. Among the organics for which oxidative treatment has been reported are aldehydes, mercaptans, benzidine, and unsaturated acids. For these applications, sodium hypochlorite, calcium hypochlorite, potassium permanganate, and hydrogen peroxide have been reported as effective oxidants. In one application nitrous acid was used. 

Mercaptans are colorless and odorous gases linked to animal facilities, wastewater treatment plants, and paper and pulp manufacturing. It is released from decaying organic matter in marshes and is present in the natural gas of certain regions of the United States, in coal tar, and in some crude oils. If mercaptans are in the air, even at low concentrations, they are very noticeable. 

Mercaptans (R-SH) [35] are weak acids (pKa around 10) and give rise to an equilibrium in aqueous solution. In basic media, bathochromic and hyperchromic shifts are observed in all cases. This effect is particularly marked with thiophenate ion because of a stabilisation of the negative charge with the n electrons of the aromatic ring. By adjusting the pH of sample to 11 after addition of sodium hydroxide solution 2.5 M, the spectra show a well-defined peak of absorbance at 238 nm for the alkylthiols or 263 nm for the thio-phenols. The application of the deconvolution method allows the estimation of the global concentration of mercaptans in wastewater. 

The characteristics of wastewater drawn from storage tanks will depend on the quality of the crude oil stored and may contain dissolved inorganics, oil, and suspended solids. The steam condensate from the overhead accumulator can be characterized as having oil, sulfides, mercaptans, and phenol. If barometric condensers are used in vacuum distillation, the condenser water will have very stable oil in emulsion. However, if the barometric condensers are replaced by surface condensers, the condenser water will be essentially free of oil. 

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