Solvent removal and recovery

There are two main techniques for removal of the solvent from the rubber solution  

The criteria used for choosing either a steam stripping technique for solvent removal, or devolatilising extrusion, depends primarily on the properties of the rubber and the customer s process requirements. For example, some end applications require a porous expanded crumb form rubber particle (only produced via steam stripping and mechanical drying), while others request a solid pellet, or a baled product. 

In the first stripper, the solvent amount is reduced from t3qiically 85 - 70 % weight down to 10 % weight. In order to optimise the energy consumption, the temperature in the first stripper is chosen in such a way that the solvent is boiling off with minimal entrainment of water. The steam injected in the first stripper is usually a mix of fi esh steam and steam plus solvent vapours originating from the downstream stripper(s). The solvent evaporation proeess in the first stripper is thermodynamically controlled. 

The vapour mixture of steam and solvent leaving the first stripper is condensed and recovered in decanter vessels, where water and solvent separate. The solvent is recycled into the wet solvent storage tanks for re-use and Ihe water phase is recycled into the strippers. Decantation is controlled by an interface detector system based on the density difference between the water and the solvent. 

In the second stripper, fresh steam is injected, thereby reducing the solvent content of the rubber crumbs further down to typically 0.3 - 0.5 % by weight. Solvent removal is diffusion controlled. The temperature in the second stripper is usually 20 °C higher than in the first stripper, for speeding up the diffusion process. 

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Suspension Polymerisation This method is extensively used for polymerising styrene. This method is very simple and unlike the solution methods, does not involve solvent removal and recovery. 

Solvent removal and recovery is more efficient, that is, a pressure reduction has the ability to precipitate the extract almost completely. 

This contribution deals with adsorptive solvent removal and recovery and some other hybrid processes using activated carbon in combination with other purification steps. 

This technique involves adding a small amount of catalyst or initiator and heating to a temperature where the initiator becomes active. In principle, it is the simplest and cheapest process and should give the purest product with no expense of solvent removal and recovery. However, the main problem is removal of heat from polymerization which for an average polymer is 500 kWh tonne" of polymer. Hence, runaways are always a danger. Broad MWD often occurs. This can be somewhat overcome by using reactors with high... 

Suspension processes are very widely used for the polymerization of styrene. These processes simplify the heat transfer problems associated with bulk methods and, unlike solution methods, they do not involve solvent removal and recovery. The disadvantages of the suspension technique are that it requires the added step of drying and it does not readily lend itself to continuous operation. Typically, polymerization is carried out batch-wise in a stirred reactor, jacketed... 

Hood system for organic solvent removal and recovery... 

Sample recovery tubes are available commercially for the removal and recovery of adsorbent from a preparative layer. An example is shown in Figure 8.2. A similar sample recovery tube is available from Bodman (Aston, PA Catalog No. GSRT-2). With these tubes, the scrapings are direcdy recovered from the plate using suction, and elution is accomphshed with an appropriate solvent under vacuum while the adsorbent is retained on the disc. 

Onium salts, crown ethers, alkali metal salts or similar chelated salts, quaternary ammonium and phosphonium are some of the salts which have been widely used as phase transfer catalysts (PTC). The choice of phase transfer catalysts depends on a number of process factors, such as reaction system, solvent, temperature, removal and recovery of catalyst, base strength etc. 

Method 413.1 wastewater are completely or partially lost in the solvent removal operation. Recoveries of some crude oils and heavy fuel oils will be low. 

One other method of recovering mercury from the vapor phase is to extract mercury using a suitable solvent (e.g. toluene or chloroform) in a scrubber, e.g. a packed tower. The mercury in the solvent can be reprocessed commercially. But, the poor solubility of mercury in such solvents warrants consumption of huge quantities of solvent thus limiting the use of a packed tower process for mercury recovery. It is therefore apparent that a preconcentration step must be used to facilitate the removal and recovery of mercury from the air phase. 

Kim, B.M. (1984) Membrane-based solvent extraction for selective removal and recovery of metals. Journal of Membrane Science, 21, 5. 

BPA is separated from byproducts in a proprietary solvent crystallization and recovery system (5) to produce the adduct of p,p BPA and phenol. Mother liquor from the purification system is distilled in the solvent recovery column (6) to recover dissolved solvent. The solvent-free mother liquor stream is recycled to the reaction system. A purge from the mother liquor is sent to the purge recovery system (7) along with the recovered process water to recover phenol. The recovered purified adduct is processed in a BPA finishing system (8) to remove phenol from product, and the resulting molten BPA is solidified in the prill tower (9) to produce product prills suitable for the merchant BPA market. 

For liquid-liquid extraction, water is usually the polar solvent. Since most extractions involve getting the required compound into the organic solvent (or removing unwanted ionic chemicals from it), it should have good solvent power for the desired compound and a low boiling point for ease of removal and recovery of the compound. The common organic solvents used in liquid-liquid extraction are diethyl ether (ethoxyethane) b.pt. 34 °C, dichloromethane (DCM) b.pt. 41 °C and ethyl acetate (ethyl ethanoate) b.pt. 77 °C. Dichloromethane is denser than water and forms the lower layer, whereas diethyl ether and ethyl acetate float on water and are the upper layer. 

As Fig. 1 indicates, reuse of the solvent (following solute removal) and recovery of the solvent dissolved in the raffinate phase are usually necessary aspects of the overall... 

Use stationary phases whose retention and selectivity can be adjusted by simple solvents. Solvent removal and solvent recovery can become an expensive step. 

The application of solvent extraction to removal and recovery of templates or SDAs from zeolite channels was initiated by Whitehurst[7] in the 1990s for the extraction of surfactant from mesoporous M41S materials. This method or its improved analogs have become one of the most important techniques to recover surfactants from mesoporous molecular sieves. However, it is still difficult to use this technique to remove and to recover the SDAs from microporous molecular sieves because, first, the size of SDA molecules is similar to that of the channel openings and the molecules are not able to diffuse out from the channels, and, secondly, there are usually strong interactions between the microporous frameworks and the SDA molecules that prevent the SDA molecules from being extracted solely by solvents. Modification of the conventional solvent-extraction technique, such as addition of chemical agents which can adjust the... 

Activated carbon columns are frequently used to remove trace or dilute organic impurities from an inert nonadsorbing gas. These impurities may consist of toxic compounds, odor-forming compounds, solvent vapors, volatile organic compounds, etc. A TSA process is generally used for these applications. However, both TSA and PSA processes are used for the particular application of solvent vapor removal and recovery which are described in Section 22.4.1.1... 

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