Acrylic acid dehydration

It is interesting to reconsider the case of a poly(acrylic acid) dehydration reaction where two different steps can be distinguished for the atactic polymer the first step is five to six times faster than the second one and obviously corresponds to dehydration of meso dyads (isotactic sequences). Hydrolysis of syndiotactic... 

One example will show the manifold types of reactions studied by Mok et al. (1989). Lactic acid decomposes in supercritical water to give acetaldehyde, which then reacts further it can also undergo dehydration to give acrylic acid, which is either hydrogenated to give propionic acid or decarboxylated to give ethene (Fig. 7.4). 

Methyl acrylate is also produced by the carboxylation of acetylene in aqueous methanol, by the dehydration of methyl lactate and by the methanolysis of p-propiolactone or acrylic acid. 

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). 

PVA dense membranes treated by acrylic acid (Acr.Ac) plasma were obtained by A. Essamri et al. [38], These membranes were used for dehydration of the EtOH-H20 mixtures by pervaporation. The behaviour of these films on ethanol-water pervaporation has increased performances after plasma treatment. 

Alternatively, acrylic acid can be obtained in a two-step reactor in which glycerol is catalytically dehydrated with an acid catalyst like H3PO4 on a-alumina [67]. The obtained acrolein is then oxidized with a commercially available oxidation catalyst, viz. Mo/V/W/Cu-oxide on a-alumina, yielding up 55% polymerization grade acrylic acid (Scheme 11.8) [68]. 

The fundamental property at work is the interaction of water and polymer, hi the Kuhn experiments, the acrylic acid functioned as the contractile unit. A change in pH or ionic strength will either hydrate or dehydrate a gel. This affects the size of the molecule, which in turn causes the molecule to contract or expand. This phenomenon is most pronounced in ionic polymers. 

Acrylic acid - [ACRYLIC ACID AND DERIVATIVES] (Vol 1) - [ACRYLIC ACID ANDDERIVATTVES] (Vol 1) - [FEEDSTOCKS - COALCHEMICALS] (Vol 10) - [COATINGS] (Vol 6) - [PLANT SAFETY] (Vol 19) - [ACRYLONITRILE POLYMERS - SURVEY AND SAN (STYRENE-ACRYLONITRILECO-POLYMERS)] (Vol 1) -from acetic acid [ACETIC ACID AND DERIVATIVES - ACETIC ACID] (Vol 1) -acrylic ester comonomer [ACRYLIC ESTER POLYMERS - SURVEY] (Vol 1) -m acrylonitrile copolymers [ACRYLONITRILE POLYMERS - SURVEY AND SAN (STYRENE-ACRYLONITRILECO-POLYMERS)] (Vol 1) -cesium in prdn of [CESIUM AND CESIUM COMPOUNDS] (Vol 5) -dehydration of piSTILLATTON, AZEOTROPIC AND EXTRACTIVE] (Vol 8) -polymerization in SCFs [SUPERCRITICAL FLUIDS] (Vol 23) -from propylene [PROPYLENE] (Vol 20) -VP copolymerization [VINYL POLYMERS - N-VINYLAMIDEPOLYMERS] (Vol24)... 

Gas-phase oxidation of glycerol has been less investigated than liquid-phase oxidation it occurs via a two-step catalyzed reaction involving first the dehydration of glycerol into acrolein, catalyzed by an acid, and then its oxidation. The same reactions can be conducted in two distinct reactors, in which the first step can be carried out with an acid catalyst such as phosphoric acid over alumina [107]. Then acrolein is oxidized to acrylic acid with a conventional alumina-supported Mo/V/Cu/O catalyst. 

Arkema has recently issued patents on the gas-phase dehydration of glycerol to acrolein and on the oxidation of glycerol to acrylic acid [ 107]. The dehydration can be carried out at 300 ° C, with a Zr02/W03 catalyst the conversion of glycerol is total, and the yield to acrolein is 72%, when a feed made of an aqueous solution of glycerol (20%) is used. The addition of 02 in the feed stream has the effect of yielding also the formation of acrylic acid (4.5%), and of lowering the yield to acrolein. 

Acrylonitrile based membranes were also used in acetic acid-water separation. Lee and Oh [11] copolymerized 4-vinylpyridine with acrylonitrile in order to prepare a membrane for the dehydration of water-acetic acid mixture by pervaporation. Yoshikava et al. [25] reported that membranes prepared from poly (acrylic acid-co-acrylonitrile)... 

Another important bulk chemical that could be derived from glycerol is acrylic acid (Craciun et al., 2005 Shima and Takahashi, 2006 Dubois et al., 2006). Shima and Takahashi (2006) reported a complete process for acrylic acid production involving the steps of glycerol dehydration in a gas phase followed by the application of a gas phase oxidation reaction to a gaseous reaction product formed by the dehydration reaction. Dehydration of glycerol could lead to commercially viable production of acrolein, which is an important and versatile intermediate for the production of acrylic acid esters, superabsorber polymers or detergents (Ott et al., 2006). Sub- and supercritical water have been applied by Ott et al. (2006) as the reaction media for glycerol dehydration, but the conversion and acrolein selectivities that have been achieved so far are not satisfactory for an economical process. 

Vinylselenophene was obtained from selenophene-2-aldehyde in three ways decarboxylation of /3-(selenien-2-yl)acrylic acid,111 the Wittig reaction,112 and dehydration of l-(selenien-2-yl)ethanol.ni The most convenient method is the last, conducted in the vapor phase. 2-Vinylselenophene is brominated112 and formylated in the side chain,111 and it reacts with diazomethane and p-nitrophenyl-diazonium chloride.112 2-Cyclopropylselenophene (12, R = H) was... 

It is possible to dispense with the extraction step if the oxidation section is operated at high propylene concentrations and low steam levels to give a concentrated absorber effluent. In dais case, the solvent recovery column operates at total organic reflux to effect azeotropic dehydration of the concentrated aqueous acrylic acid. Tliis results in a reduction of aqueous waste at the cost of somewhat higher eneigy usage. 

The bottoms from the solvent recovery (or azeotropic dehydration column) are fed to the foreruns column where acetic acid, some acrylic acid, and final traces of water are removed overhead The overhead mixture is sent to an acetic acid purification column where a technical grade of acetic acid suitable for ester manufacture is recovered as a by-product. The bottoms from the acetic acid recovery column are recycled to the reflux to the foreruns column. 

The bottoms from the foreruns column are fed to the product column where the glacial acrylic acid of commerce is taken overhead Bottoms from the product column are stripped to recover acrylic acid values and the high boilers are burned The principal losses of acrylic acid in this process are to the aqueous raf finate and to the aqueous layer from the dehydration column and to dimerization of acrylic acid to 3-acryloxypropionic acid If necessary, the product column bottoms stripper may include provision for a short-contact-time cracker to crack tliis dimer back to acrylic acid (60). 

Losses by polymer formation kept the yield of acrylic acid to 60—70%. Preferably, esters were prepared directly by a simultaneous dehydration—esterification process. 

Other Syntheses. Acrylic acid and other unsaturated compounds can also be made by a number of classical elimination reactions. Acrylates have been obtained from the thermal dehydration of hydracrylic acid (3-hydroxypropanoic acid [503-66-2]) (84), from the dehydrohalogenation of 3-halopropionic acid derivatives (85), and from the reduction of dilaalopropionates (2). These studies, together with the related characterization and chemical investigations, contributed significantly to the development of commercial orgaioic chemistry. 

Esters of acrylic acid are made by pyrolytic decomposition of a-acetoxypropionates. Direct dehydration of the a-hydroxy esters fails. 

In many cases the organic to be dehydrated (e.g., acetic acid) attacks the ether linkage in the PVA membrane. Indeed, the PVA membrane has very limited fife in the presence of most acids. Ray et al. [14] used the concept of copolymer membranes to dehydrate acetic acid over the entire range of concentration from 0% to 100%. These investigators prepared copolymers of acrylonitrile (AN) with different hydrophUic monomers like hydroxy ethyl methacrylate, acrylic acid, methacrylic acid, and itaconic acid. These copolymers have carbon-carbon bonds, which unlike the ether linkage in the cross-hnked PVA membrane are stable to the attack by carboxyhc acids. The acrylonitrile part is not sufficiently hydrophihc but imparts mechanical strength while the other monomers improve the hydrophilicity. The overall result is an efficient yet stable membrane. Variation of the ratio of AN to (the other) monomer allows freedom of adjusting the hydrophUicity of the membrane to achieve certain... 

Problem 27.5 Acrolein, CH2 CHCHO, is prepared by heating glycerol with sodium hydrogen sulfate, NaHS04. (a) Outline the likely steps in this synthesis, which involves acid-catalyzed dehydration and keto-enol tautomerization. (Hinf Which OH is easier to eliminate, a primary or a secondary ) (b) How could acrolein be converted into acrylic acid ... 

Reduction of the pyruvic acid would give the lactic acid (214, 502), and dehydration of this would give the acrylic acid (p-coumaric acid from tyrosine (e.g., 391) and cinnamic acid from phenylalanine). However, the acrylic acid derivative might be formed directly from the amino acid (c/. the direct conversion of histidine to urocanic acid). Reduction of the acrylic acids might be the origin of the propionic acid derivatives sometimes encountered (e.g., 100). 

This anhydride may be suitable for some of the uses of maleic anhydride in the preparation of polymers. Dehydration of lactic acid to the important monomer, acrylic acid, gave only a 17% yield.32 Pyrolysis of the acetate of methyl lactate gave methyl acrylate in 90% yield, but was reported to be too expensive to use commercially. Oligomers of lactic acid can be prepared by simple heating.33 It may be possible to pyrolyze them to acrylic acid in high yields. 

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