Vapor stripping

Aniline Oxidation. Even though this is quite an old process, it still has limited use to produce hydroquinone on a commercial scale. In the first step, aniline is oxidized by manganese dioxide in aqueous sulfuric acid. The resulting benzoquinone, isolated by vapor stripping, is reduced in a second step by either an aqueous acidic suspension of iron metal or by catalytic hydrogenation. 

At 220°C a water-paraffin mixture is distilled off in a circulating evaporator (8). The product mixture passes to a second circulating evaporator (9) where the paraffin is stripped at 270°C with overheated water vapor, and finally the paraffin content in the resulting alkanesulfonate melt is further reduced by vapor stripping in a packed column (10). A heat transfer oil dissipates excess heat. 

Siegrist RL, OR West, MI Morris, DA Pickering, DW Greene, CA Muhr, DD Davenport, JS Gierke (1995) In situ mixed region vapor stripping in low-permeability media. 2. Pull-scale field experiments. Environ Sci Technol 29 2198-2207. 

Goltz MN, RK gandhi, SM Gorelick, GD Hopkins, LH Smith, BH Timmins, PL McCarthy (2005) Field evaluation of in situ source reduction of trichloroethylene in groundwater using bioenhanced in-situ vapor stripping. Environ Sci Technol 39 8963-8970. 

Figure 37.1. Continuous Vapor Stripped Process for the Rh Catalyzed Carbonylation of MeOH in the absence of Mel.

Given the absenee (or near absenee) of Mel in these reaetions, we sought to demonstrate the proeess on a eontinuous proeess. We purposely ehose to employ the same vapor take-off (vapor stripped) reaetor we used in om earher studies of the Rh/Mel co-catalyzed carbonylation of methanol (3) since the vapor stripping procedure used in the process would force any Mel formed in situ overhead where we could detect it in the effluent. This would represent the most rigorous test of the new non-Mel process we could contrive. 

Figure 7. Simultaneously monitoring vapor signatures of 1000 sensors for 2,4-DNT, 1,3-DNB, and TNT vapor strips at 8% saturated vapor levels. The (noisy) responses for 250 individual sensors are compared to the averaged response profile for 1000 individual sensors. Reprinted with permission from ref. 12a. Copyright 2000 American Chemical Society.

Concentration Methods. The GCMS analysis of an environmental sample starts with the isolation of the organic compounds from the matrix (air, water, food, etc.) into a form suitable for introduction into the GCMS instrument, typically a solution in a volatile solvent. This concentration step includes essentially three major methods vapor stripping, solvent extraction, and lipophilic adsorption. We have recently reviewed the detailed operation of these methods (Ij, (See also Bellar, Budde and Eichel-berger, this volume) but their general features will be outlined here. 

An application of in-well vapor stripping (NoVOCs) for remediation of TCE in groundwater was conducted at Edwards Air Force Base in California between 1995 and 1996. Total expenditures for installation of the weUs, assembly of the equipment, and operations and maintenance were approximately 600,000. An additional 217,000 was allocated for personnel, equipment, a trailer, and software (D188709, p. 4). 

Phosphate-induced metals stabilization can be used for the remediation of metals in mixed waste streams concurrently with other remediation technologies such as vapor stripping or bioremediation of organics. Using apatite to treat soils contaminated with lead, cadmium, and/or zinc can significantly reduce the amount of metals leached from the soil. The amount of apatite needed for treatment is less than 1% by weight. The reaction between metals and apatite is immediate, and the apatite can be heavily loaded with metals. 

Despite our personal skepticism, a sample of / was obtained (8) and tested in a bench test unit that simulates continuous vapor stripped reactor operation (9). The... 

Vane, L.M. and Alvarez, F.R. (2008) Membrane-assisted vapor stripping energy-efficient hybrid distillation vapor permeation processes for alcohol-water separation. Journal of Chemical Technology and Biotechnology, 83(9), 1275-1287. 

Hybrid systems, where gaseous decomposition occurs before reaching boiling, but the rate of reaction is tempered by vapor stripping. The pressure developed in the system is due to the vapor pressure of the volatile components and to the partial pressure of noncondensible gases. 

Organic solvents, residual monomer and dimers (Sect. 2.2.5) are usually removed by vapor stripping during which an aqueous slurry of Nd-BR is obtained. BR is isolated from the slurry by appropriate dewatering screws prior to drying by hot air [82]. The final process steps of Nd-BR-solutions are not unique to Nd-BR. Therefore, these aspects are not addressed in this review. 

Stripping stages (Fig. 2.3a) concentrate the lees-volatile components in a liquid stream. A vapor recycle vaporizes ("strips ) the more-volatile components from the liquid. To generate the vapor recycle, heat is supplied to vaporize a portion of the bottom-stage liquid. This vapor recycle is termed boUup. 

The chemical properties of the contaminants have to be considered when selecting separation techniques. Some of the liquids are absolutely immiscible in water, and if the process stream involves water and the contamination is liquid/liquid, then the separation technique can greatly reduce the volume of contaminated water. For example, if acetone is the contaminant of concern, a simple vapor stripping technique can be effective in making a separation. In the case of refined oil, which has a solubility limit of approximately 50 ppm, one of the oil/water separation techniques could be effective. Some general guidelines to consider are ... 

A large part of the vapors stripped by the residual air is cooled and condensed. Traces of toluene remaining in the incondensables are retained on activated charcoal, while part of the remaining vent gases may be recycled, after recompression, to increase the content of inerts in the gas holdup present in the reactors and thus reduce the explosion hazard. 

The incoming beer feed, if well-filtered, may be used as part of the cooling fluid in the condenser. This will bring about condensation of the reflux and finished product, while at the same time preheating the beer feed just before it enters the stripper section. Thus, a minimum of added heat is needed to bring about the initial alcohol vaporization (stripping) operation. 

When the reflux liquid reaches the bottom of the rectifier, it enters the feed input level and joins the feed, which is preheated beer. The mixture enriches the alcohol content of the hot beer and facilitates the vaporizing (stripping) process as the liquids flow down against the upward flow of steam and alcohol vapor. As the steam moves upward, it causes the alcohol to vaporize from the liquid as some of the water vapor condenses. 

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