Ethanol silicone rubber

The y-radiation-induced grafting of diethylene glycol dimethacrylate and its mixture with (3-hydroxy ethyl methacrylate in ethanol-water systems onto silicone rubber has been reported [ 164]. The grafting yield increases as the radiation dose, concentration of monomer and concentration of transfer agent increase. At the same radiation dose, the degree of grafting decreases, as the dose level increases. However, at the same dose rate, the grafhng level increases with radiation dose. 

An oven-dried 300-ml flask, equipped with a side-arm fitted with a silicone rubber septum, a magnetic stirrer bar, and a reflux condenser connected to a mercury bubbler, is cooled to room temperature under a stream of dry nitrogen. Tetrahydrofuran (20 ml) is introduced, followed by 7.1 g (25 mmol) of cyclooctyl tosylate (1). The mixture is cooled to 0 °C (ice bath). To this stirred solution, lithium triethylborohydride (Section 4.2.49, p. 448) [33.3 ml (50 mmol) of a 1.5 m solution in tetrahydrofuran] is added, and the ice bath removed. The mixture is stirred for 2 hours (c. 25 °C). Excess hydride is decomposed with water. The organoborane is oxidised with 20 ml of 3 m sodium hydroxide solution and 20 ml of 30 per cent hydrogen peroxide [(2) and (3)]. Then the tetrahydrofuran layer is separated. The aqueous layer is extracted with 2 x 20 ml portions of pentane. The combined organic extracts are washed with 4 x 15 ml portions of water to remove ethanol produced in the oxidation. The organic extract is dried (MgS04) and volatile solvents removed by distillation (2). Distillation of the residue yields 2.27 g (81%) of cyclooctane as a colourless liquid, b.p. 142-146 °C, Wq0 1.4630. 

Membranes with improved separation factors would be useful for hydrophilic VOCs such as ethanol, methanol and phenol, for which the separation factor of silicone rubber is in the range 5-10. As yet, no good replacement for silicone rubber has been developed. The most promising results to date have... 

It has been involved in many industrial explosions. Explodes on contact with aluminum + barium nitrate + potassium nitrate + water. Forms explosive mixtures with aluminum powder + titanium dioxide, ethylene glycol (240°C), cotton lint (245°C), furfural (270°C), lactose, metal powders (e.g., aluminum, iron, magnesium, molybdenum, nickel, tantalum, titanium), sulfur, titanium hydride. Reaction with ethanol + heat forms the explosive ethyl perchlorate. Violent reaction or ignition under the proper conditions with aluminum + aluminum fluoride, barium chromate + mngsten or titanium, boron + magnesium + silicone rubber, ferrocenium diammine-tetrakis(thiocyanato-N) chromate(l —), potassium hexacyanocobaltate(3—), A1 +... 

Silicone rubber methanol > ethanol> aldehydes> ketones water paraffins > olehns. 

In one of the early studies Cho and Hwang [3.54] studied the integration of continuous fermentation and membrane separation using ethanol selective silicone rubber hollow-fiber membranes. Relative to conventional continuous fermentation, the performance of PVMBR resulted in high yeast cell densities, reduction of ethanol inhibition, longer substrate residence time of, more glucose consumption, and recovery of clean and concentrated ethanol. A 10-20 % increase in ethanol productivity was achieved. Kaseno et al. 

Test polymers for visualization studies were polyurethane (Pellethane, 2363-80A, Upjohn), filler-free polydimethylsiloxane (Sil-Med Corporation), two forms of Teflon, sintered (TFE, DuPont) and Fluorofilm (Dilectrix Corporation), and polyurethane-silicone rubber copolymer (AVCOthane 51, AVCO). Samples of 1 cm2 or, for shear studies, 5 X 20 X 0.5-cm sheets, were washed in ionic detergent solution (Alconox) at 60°C for 1 h, rinsed in deionized water, and refluxed in absolute ethanol for 1 h. Materials were dried and stored in a desiccator until use. 

Ethanol permselective membrane system has been used for the extraction of ethanol from fermentation broth. However, both membrane distillation and polymeric silicon rubber membranes showed low separation factors of ethanol and were invalid in this case. M. Nomura et al. [26] investigated the continuous extraction of ethanol from ethanol fermentation broth through a silicalite-1 membrane. From 4.73wt.% ethanol concentration of broth, the permeate ethanol concentration was 81.0wt.%. In our group, we have also investigated the potentiality of silicalite-1 membrane for alcohol extraction from aqueous solution [27]. 

The commercial success of pervaporation has been a disappointment to many process developers. Current pervaporation sales worldwide are probably less than US 10 million almost all are for dehydration of ethanol or isopropanol solutions using water-permeable poly (vinyl alcohol) or equivalent membranes. A smaller market also exists for the separation of volatile organics from water using silicone-rubber membranes. 

Figure 6.31 shows some experimental data for the pervaporation of water/ethanol mixtures by a silicone rubber membrane preferentially permeable to ethanol. The experiment was conducted at 23 C for downstream pressures of 667, 1200, and 2100 Pa (5,9, and 16 mmHg). As reported by Hoover and Hwang [250] and Tanigaki et al. [245], the silicone membrane showed preferential permeation to ethanol. Evidently, the downstream pressure has little effect on both permeate composition and permeation rate, supporting the calculated results shown in Figure 6.30. When the experimental data arc closely examined, however, the relative permeation rate decreases slightly with an increase in the downstream pressure. The calculated values in Figure 6.30 show exactly the same tendency, justifying the transport model on which the calculation is based. It has to be noted, however, that the saturation vapor pressure of water and ethanol at 60 C are 1.99 x l(f and 4.69 x lO Pa (149.4 and 351.9 mmHg), respectively. When the downstream pressure approaches the saturation vapor pressure, the assumption on which the theoretical calculation is based (i.e., (he vapor permeation prevails across the membrane cross-.section) becomes invalid, since liquid penetrates more deeply into the pore.

In liquid mixtures of type (2), the solutions of primary interest are azeotropic and other mixtures containing variable amounts of water in organics dehydration of organic solvents containing very small amounts of water. Removal of water from azeotropic mixtures of ethanol-water, isopropanol-water, etc., is extensively practiced using polymeric membranes (of crosslinked polyvinyl alcohol) that are highly polar and selective for water. On the other hand, the membranes that are used to remove VOCs selectively from aqueous solutions are usually highly nonpolar rubbery polymeric membranes, e.g. dimethyl siloxane (silicone rubber). 

Differences in results can occur between tests in a liquid and a gaseous medium. This is often because different times are required to reach equilibrium temperature, and if crystallisation is occurring, for example, the stiffness will be dependent on time of conditioning. It is also essential that if a liquid medium is used the liquid does not affect the rubber by swelling it or removing extractables, as either process can have a considerable effect on low temperature behaviour. Ethanol is most widely used but acetone, methanol, butanol, silicone fluid and n-hexane are all suggested in ISO 2921. Not all of these will be suitable for all rubbers and the suitability of any proposed liquid must be checked by preliminary swelling tests. 

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