Acrylic acid process control

This process yields satisfactory monomer, either as crystals or in solution, but it also produces unwanted sulfates and waste streams. The reaction was usually mn in glass-lined equipment at 90—100°C with a residence time of 1 h. Long residence time and high reaction temperatures increase the selectivity to impurities, especially polymers and acrylic acid, which controls the properties of subsequent polymer products. 

These enable temperature control with built-in exchangers between the beds or with pumparound exchangers. Converters for ammonia, 80.3, cumene, and other processes may employ as many as five or six beds in series. The Sohio process for vapor-phase oxidation of propylene to acrylic acid uses hvo beds of bismuth molybdate at 20 to 30 atm (294 to 441 psi) and 290 to 400°C (554 to 752°F). Oxidation of ethylene to ethylene oxide also is done in two stages with supported... 

Degenerate Explosion it was a free radical autocatalytic process and control was difficult, but manageable. The main disadvantage was that it produced as much or more acrolein as propylene oxide. Because no market existed for acrolein at that time, the project was abandoned. Within two years, the acrylic market developed and a new project was initiated to make acrolein and acrylic acid by vapor-phase catalytic oxidation of propylene. 

Because the polymer degrades before melting, polyacrylonitrile is commonly formed into fibers via a wet spinning process. The precursor is actually a copolymer of acrylonitrile and other monomer(s) which are added to control the oxidation rate and lower the glass transition temperature of the material. Common copolymers include vinyl acetate, methyl acrylate, methyl methacrylate, acrylic acid, itaconic acid, and methacrylic acid [1,2]. 

Abstract. Auto-accelerated polymerization is known to occur in viscous reaction media ("gel-effect") and also when the polymer precipitates as it forms. It is generally assumed that the cause of auto-acceleration is the arising of non-steady-state kinetics created by a diffusion controlled termination step. Recent work has shown that the polymerization of acrylic acid in bulk and in solution proceeds under steady or auto-accelered conditions irrespective of the precipitation of the polymer. On the other hand, a close correlation is established between auto-acceleration and the type of H-bonded molecular association involving acrylic acid in the system. On the basis of numerous data it is concluded that auto-acceleration is determined by the formation of an oriented monomer-polymer association complex which favors an ultra-fast propagation process. Similar conclusions are derived for the polymerization of methacrylic acid and acrylonitrile based on studies of polymerization kinetics in bulk and in solution and on evidence of molecular associations. In the case of acrylonitrile a dipole-dipole complex involving the nitrile groups is assumed to be responsible for the observed auto-acceleration. 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

Control of fiber friction is essential to the processing of fibers, and it is sometimes desirable to modify fiber surfaces for particular end-uses. Most fiber friction modifications are accomplished by coating the fibers with lubricants or finishes. In most cases, these are temporary treatments that are removed in final processing steps before sale of the finished good. In some cases, a more permanent treatment is desired, and chemical reactions are performed to attach different species to the fiber surface, e.g. siliconized slick finishes or rubber adhesion promoters. Polyester s lack of chemical bonding sites can be modified by surface treatments that generate free radicals, such as with corrosive chemicals (e.g. acrylic acid) or by ionic bombardment with plasma treatments. The broken molecular bonds produce more polar sites, thus providing increased surface wettability and reactivity. 

Polymerization of a monomer in a solvent overcomes many of the disadvantages of the bulk process. The solvent acts as diluent and aids in the transfer of the heat of polymerization. The solvent also allows easier stirring, since the viscosity of the reaction mixture is decreased. Thermal control is much easier in solution polymerization compared to bulk polymerization. On the other hand, the presence of solvent may present new difficulties. Unless the solvent is chosen with appropriate consideration, chain transfer to solvent can become a problem. Further, the purity of the polymer may be affected if there are difficulties in removal of the solvent. Vinyl acetate, acrylonitrile, and esters of acrylic acid are polymerized in solution. 

The industrial catalytic Reppe process is usually applied in the production of acrylic acid. The catalyst is NiBr2 promoted by copper halides used under forcing conditions. The BASF process, for example, is operated at 225°C and 100 atm in tetrahydrofuran solvent.188 Careful control of reaction conditions is required to avoid the formation of propionic acid, the main byproduct, which is difficult to separate. Small amounts of acetaldehyde are also formed. Acrylates can be produced by the stoichiometric process [Eq. (7.20)], which is run under milder conditions (30-50°C, 1-7 atm). The byproduct NiCl2 is recycled ... 

The yield of acrylonitrile based on propylene is generally lower than the yield of acrylic acid based on the direct oxidation of propylene. Hence, for the large volume manufacture of acrylates, the acryloioitrile route is not attractive since additional processing steps are involved and the ultimate yield of acrylate based on propylene is much lower. Hydrolysis of acryloioitrile can be controlled to provide acrylamide rather than acrylic acid, but acrylic acid is a by-product in such a process (80). 

---