Aspi K. Kolah

Extractive reactions with cationic exchange resins as catalysts (acetalization of aldehydes with alcohols)

Abstract The acid catalysed acetalization of aldehydes such as formaldehyde, acetaldehyde, glyoxal and glyoxylic acid, with alcohols are reversible reactions. In order to enhance the conversion of aldehydes, extractive reactions were carried out with the alcohols (e.g. 2-ethyl hexanol and n -butanol) having very low to low solubility in water. In such cases alcohols, in addition to being reactants act as extractive solvents for the acetals formed in the reaction. An experimental investigation was carried out using cation-exchange resins (Indion-130, Amberlist-15 and Amberlite IR-120) as catalysts and significant conversion levels were realised for the reactions of formaldehyde and acetaldehyde; results were not encouraging for the extractive reactions of glyoxal and glyoxylic acid. The effect of different parameters, such as catalyst loading, temperature, mole ratio and aqueous phase concentration of aldehyde on the rate of reaction was studied.

Inorganic supported polymeric catalysts

Acidic polystyrene based resins are not very suitable for use in reactive distillation column as well as for temperatures greater than 393 K. To overcome these problems porous silica has been coated with divinylbenzene (DVB) or styrene-DVB and polymerized using azoisobutyronitrile as initiator. Sulfonation of the polymer was carried out by using chlorosulfonic acid. Thus acidic polymeric material of exchange capacity of up to 0.41 meq/g has been obtained, in convenient size of 2-5 mm which can be directly used in reactive distillation column as demonstrated for methylal preparation in this paper and which is also suitable for use up to 433 K, verified by successfully carrying out reaction of phthalic anhydride with 2-ethyl-hexanol. Reusability of this catalyst was also tested by performing the reaction of iso-propyl alcohol with acetic acid.

Removal of formaldehyde from aqueous solutions

The removal of formaldehyde from aqueous solutions of 2-butyne-1,4-diol (BD), which are prepared from ethynylation of acetylene with aqueous formaldehyde, was successfully accomplished by a number of approaches: reaction with sodium bisulfite and removal of the resultant ionic product with an anion exchange resin in a fixed bed system or using an anion exchange resin bed in bisulfite form; reactive distillation with methanol and ethylene glycol in the presence of cation exchange resin as catalyst to give the corresponding acetals; internal acetalization with BD in the presence of cation exchange resin as catalyst; Cannizzaros reaction with sodium hydroxide; and aldol type condensation in the presence of sodium hydroxide. Residual concentrations of formaldehyde as low as 20 ppm could be achieved through more than one of the methods mentioned above.