Stripped solvents

The component C in the separated extract from the stage contact shown in Eigure 1 may be separated from the solvent B by distillation (qv), evaporation (qv), or other means, allowing solvent B to be reused for further extraction. Alternatively, the extract can be subjected to back-extraction (stripping) with solvent A under different conditions, eg, a different temperature again, the stripped solvent B can be reused for further extraction. Solvent recovery (qv) is an important factor in the economics of industrial extraction processes. 

Raffinate acid from the first cycle, containing approximately 7 to 14 g/L U Og is then reoxidized and re-extracted in the second, purification cycle using a solvent containing 0.3 Af D2EHPA and 0.075 AfTOPO. The loaded solvent is washed with iron-free acid to remove iron and then with water to remove extracted and entrained acid. The solvent is stripped with ammonium carbonate [506-87-6] to yield ammonium uranyl tricarbonate [18077-77-5] which is subsequendy calcined to U Og (yellow cake). The stripped solvent is regenerated with mineral acid before recycling (39). 

Choice of Solvent. As indicated by Averell and Norris (1), and independently confirmed by the authors, technical benzene is a superior stripping solvent for parathion residues. It is almost completely miscible with technical grade parathion at room temperatures, it is universally available and low in cost, it is readily volatile, it fails to contribute to storage decomposition (6), it is a good solvent for plant oils and waxes, and it is immiscible with water. On the other hand, benzene is highly flammable and its vapors are very toxic to human beings, especially as a chronic toxicant even in small doses. 

Purification processes are used to remove impurities such as sulfiirs, mercury, gums and waxes. The processes include absorption and stripping, solvent extraction and thermal diffusion... 

Stripping the uranium from the solvent can be accomplished by using either acid or alkaline solutions. If an alkali carbonate solution is used, the stripped solvent then requires equilibrating with sulfuric acid before recycling to the extraction stage. Sulfuric acid stripping obviates the need for such equilibration. 

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. 

Recently investigated methods of treating waste waters contaminated with 1,3-DNB or 1,3,5-TNB and related products include biological treatment, stripping, solvent extraction, and activated carbon adsorption (HSDB 1994). 

The extract is pumped from the bottom of D-l to a stripper D-2 with 35 trays. The stripped solvent is cooled with water and returned to D-l. An isoprene-acetonitrile azeotrope goes overhead, condenses, and is partly returned as top tray reflux. The net overhead proceeds to an extract wash column D-3 with 20 trays where the solvent is recovered by countercurrent washing with water. The overhead from D-3 is the finished product isoprene. The bottoms is combined with the bottoms from the raffinate wash column D-4 (20 trays) and sent to the solvent recovery column D-5 with 15 trays. 

Nevertheless, the radiolytic (and hydrolytic) stability of an extractant must be considered not only from the quantitative, but also from the qualitative aspect. The objective is not perfect resistance to the aggressive medium, but sufficient for an industrial implementation of the process. The nature of the stable compounds, their distribution in the process steps, and their impact are also important when proposing an efficient solvent cleanup. For such studies, dedicated representative loops in which the main treatments, extraction-irradiation-stripping-solvent treatment, could be run on the solvent are of key importance. 

Yang, L., Man, M.Q., Taljebini, M., Elias, P.M., and Feingold, K.R. (1995) Topical stratum corneum lipids accelerate barrier repair tape stripping, solvent treatment and some but not all types of detergent treatment. Br. J. Dermatol. 133 679-685. 

The hot-stripped solvent from the bottom of the degasser passes through the heat economizers (a train of heat exchangers) and is fed to the extractive distillation columns. 

The stripped solvent is practically free from water. The water undergoes overhead azeotropic distillation and is produced as separate subphase in the reflux drum. This water is then fed to the solvent recovery stage of the extraction process. 

The berkelium (IV) extraction coefficients have been determined by stripping solvents previously loaded with tetravalent cerium and berkelium in the presence of sodium bismuthate. Sodium bismuthate has been found to be an efficient oxidizing agent for trivalent cerium. Because of its small solubility it does not affect the distribution coefficients of tetravalent cerium. These two properties have been demonstrated by comparing the distribution coefficients of cerium (IV) measured by spectrophotometry with those of cerium oxidized by sodium bismuthate and measured by beta counting of the cerium isotope tracer. The data are summarized in Table I and indicate no real difference in the distribution coefficients of cerium obtained by these two methods when using trilaurylmethylammonium salts-carbon tetrachloride as solvent. 

Modem solvent extraction plants recover over 99.9% of the solvent pumped to the extractor. The solvent recovery system includes solvent and water vapor condensation, solvent-water separation, stripping solvent from water and air effluent streams, as well as heating the solvent prior to reuse in the extractor. 

Our column runs showed (as predicted by the batch studies) that benzene is the most efEcient stripping solvent. o-Xylene was quite slow to desorb 2,7-DMN and was dropped from consideration in any cyclic process. 

With heated gas, it is possible to break the upper surface of the moisture film, aiding in dewatering, or to dry or strip solvents. Steam washing can reduce wash quantities required. 

A typical carbon dioxide removal system consists of an absorber where the feed gas is introduced at the bottom and the lean propylene carbonate solution is contacted with the rising gas in a countercurrent manner. The carbon dioxide content of the treated gas depends upon the initial content of C02 in the lean gas. The rich gas (containing the removed C02 and other compounds) is passed through an intermediate flash tank from where some of the low molecular hydrocarbons are recycled to the absorber. The stripped solvent is then passed through a low pressure flash tank where the carbon dioxide is flashed to the atmosphere and the lean gas is pumped back to the absorber. This process can be modified further to achieve lower C02 exit concentrations in the treated natural gas by adding strippers operating at atmospheric pressure followed by vacuum strippers. Power requirements for any of these units are very low, thus keeping the process very efficient and economical. 

Equation (13.14) is linear in a plot of Y vs. X. The slope is L/G, and the intercept is Fj -L xyY +i and for the often-encountered case of no solute in the entering solvent (once-through solvent or fully stripped solvent in a recirculating system), the intercept is simply Fj. In Equations... 

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