Vinyl acetate purification

Vinyl Acetate Purification with Aqueous Alkali Extraction. 210... 

Vinyl Acetate Purification with Aldehyde Reagents. 211... 

Schemem 4.29 Lipase-catalyzed purification by removal of undesired stereoisomers from the product. Chirazyme L2 (CALB), vinyl acetate, n-heptane, mol. sieves , 25°C.

Commercial vinyl acetate (Aldrich Chemical Company, Inc.) was used directly without purification. The checkers observed that distilled vinyl acetate afforded slightly higher yields and improved product purity (Note 7). 

The hexane-soluble impurity is believed to originate in the vinyl acetate. This purification may not be necessary in all cases. 

Initial Batch Reactor Studies. An agitated 2000 ml thick-walled glass reactor was blanketed with nitrogen and operated at 50°C. Vinyl acetate containing about 15 ppm hydroquinone was used without purification. The ionic emulsifier was Sipex EST-30, advertised as a sodium tridecyl ether sulfate, and the nonionic surfactant was Siponic L-25, a lauryl alcohol ethoxy-late. Table I shows the recipes and properties of the three seed latexes produced in the batch reactor. Essentially complete conversions were obtained in 30 to 45 minutes, but with a temperature rise of almost 50°C. 

The condensates are, purified by distillation in a sequence of columns. The light components are first separated ( 35 trays) including gaseous acetylene, which is recycled, and acetaldehyde, acetone, propionaldehyde, acrolein, etc. in the liquid state. An additional column may be used to purify the acetaldehyde contained in this mixture and to return the stripped vinyl acetate and acetic acid to the previous distillation stage. The sequence of operations includes the recovery of pure vjnyl acetate ( 50 to 60 trays), the separation of divinylacetylene and crotonaddehyde (packed column), and the purification of unconverted acetic add by heavy ends separation of the heavier components ( 30 trays). 

In fact, one important parameter is the water content of the medium, which causes the undesirable production of acetaldehyde by its reaction with ethylene in the presence of palladium chloride, or by the hydrolysis of the vinyl acetate formed. This operating variable can be adjusted to make the acetate production plant self-sufficient in terms of acetic acid. In this case, die acetaldehyde co-produced is oxidized to the arid in a separate section. It is the water content of the acetic arid employed, controlled by the degree of purification of the by-product arid which is recycled, which ultimately serves to determine the vinyl acetate to acetaldehyde ratio. Longer reridence time in the reactor or higher temperature also favors the formation of acetaldehyde. 

Vinyl acetate recovery and purification require operation in the presence of an inhibitor, which may be gaseous (such as a mixture of 02 and C02). The various units must be built of high-alloy steels (Cr-Ni 18/8). 

Materials. VEC was prepared by the catalyzed addition of CO2 to 3,4-epoxy-l-butene using conditions typical of that used industrially [77], then purified by vacuum distillation. Other raw materials were used as received without any additional purification. Mixed xylenes, vinyl acetate (VA), butyl acrylate (BA), butyl methacrylate (BMA), methyl methacrylate (MMA), styrene (St), and t-butyl hydroperoxide were obtained from Aldrich Chemical Company. Lupersol 575 (t-amyl peroxy (2-ethylhexanoate)) was supplied by Elf Atochem. Vazo 67 (2,2 -azobis(2-methylbutyronitrile)) was obtained from DuPont Chemical Company. Vinyl pivalate (NE05), vinyl 2-ethylhexanoate (V2EH), Tergitol NP-40 (non-ionic surfactant) and QP-300 (hydroxy ethyl cellulose) were obtained from Union Carbide Coq)oration. Aerosol OT-75 (surfactant) was obtained from Cytec. Sodium formaldehyde sulfoxylate was obtained from Henkel Corporation. Ethyl 3-ethoxy propionate (EEP), propylene glycol monomethyl ether (PM) and PM acetate (PM Ac) are Eastman Chemical Company products. 

The purification procedures of vinyl acetate for precise kinetic studies are not entirely satisfactory. Many of the impurities mentioned in Table II, for example, may form azeotropic compositions with the monomer. Dissolved oxygen seems... 

TABLE III Effect of Purification Procedure on Conversion of Vinyl Acetate [22]°... 

The process, first disclosed in 1968, was commercialized in 1973. Yields in this process were very high (99%) and ease of operation was excellent. The major difficulty encountered was with catalyst precipitation during product removal. To minimize the problematic catalyst precipitation and to stabilize the catalyst, 10-15% water was included in the reaction mixture and the catalyst -product separation was conducted as an adiabatic flash. The inclusion of large amounts of water and the restriction to an adiabatic flash meant that the conversion was limited by product removal, not the reaction rate, and that there were large recycle streams of acetic acid and water. Additional minor difficulties were the cogeneration of traces of acetaldehyde which ultimately lead to propionic acid and iodine containing impurities. While the propionic acid was removable by distillation (with a dedicated unit of operation), the iodine has proven more problematic. It was important to remove essentially all the iodine (to < 40 ppb) during purification since iodine is a poison for the Pd/Au catalyst used in vinyl acetate production. 

Practical considerations have thus far precluded commercial manufacture of vinyl acetal polymers from higher molecular weight aldehydes or from mixed aldehydes. At an aldehyde chain length of more than four carbon atoms, the aldehyde becomes insoluble in water, with the result that washing and purification of the resin are extremely difficult. Tg drops with increasing aldehyde chain length and... 

Maleic copolymers with methyl vinyl ether, N-vinyl-pyrrolidone, styrene, vinyl acetate, divinyl ether, were proved to be biocompatible [6-11], but the impurities (solvent traces, unreacted monomers, oligomers) need to be removed by advanced purification [12], Molar mass also influences the toxidty polymers with relatively high molar mass cannot be eliminated renally and accumulate in the body, inducing toxic reactions [6,13]. On the other hand, high molar mass is required for the biological activity of the polymer, which is why a proper choice of molar mass and a narrow distribution are needed in order to provide reduced toxicity together with efficiency [6,14]. 

Roberts et al. [46] have enzymatically resolved bicyclic lactone 128 using Pseudomonasfluorescens lipase and vinyl acetate. The enantio-pure ester, (-)-151 (>95% ee), obtained by this process is converted in three steps into diol 153 via triol 152 in 50% overall yield without purification of the intermediates... 

The nanoparticles consist of pyrogenic colloidal SiOj (Aerosol 1380, Degussa Co., Germany) with an average particle size of 7 nm. Styrene, acrylamide, methyl methacrylate, butyl acrylate, ethyl acrylate, methyl acrylic acid, and vinyl acetate, were used as grafting monomers without further purification. 

The subsequent treatment of this mixture with Amano PS lipase and vinyl acetate for 14 days leads exclusively to the acetyl derivative 68, which derives from the acetylation of 66. After high-performance liquid chromatography (HPLC) purification, the isolated yield for 68 was 46%, although a higher yield (60%) was calculated taking the recovered starting material into account. In addition, the same diastereomeric acetate 68 was obtained when the enzymatic reaction was repeated starting from the pure... 

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