Process flowsheet developed for 3 Ton per day of salicylaldehyde manufacturing using phenol and chloroform in the presence of an alkali like sodium hydroxide.
Brief description of salicylaldehyde manufacturing process flowsheet:
A batch reactor operates at temperatures between 50-60oC, aromatic aldehydes are produced widely by Reimer-Tiemann reaction and this reaction occurs in the reactor. In this process, use of alkaline medium produces a mixture of isomers. Thus when phenol is reacted with chloroform in the presence of an alkali at a temperature of about 50-60 oC, both salicylaldehyde and para-hydroxybenzaldehyde are obtained along with resins. The ratio of ortho isomer (Salicylaldehyde) to the para-hydroxybenzaldehyde appears to depend upon the alkali concentration, the nature of the alkali, the chloroform, the solvent and the method employed to separate the isomers.
In the Reimer-Tiemann reaction, although the conversion of phenol to the aldehydes has been low then also the unconverted phenol can be recovered and recycled. The reactor is operated for batch period of 90 min. The effluent is passed to the gravity separator to separate the aqueous mixture. From the bottom of the gravity separator water, sodium phenoxide and sodium chloride are separated and sent to reaction vessel to treat with HCl to recover phenol. The upper portion is sent to Nutsch filter to separate the resins.
Two-batch distillation columns are used to separate the unreacted chloroform and produce pure salicylaldehyde. First column is operated at 61-65 oC and 1 atm and the second column is operated at 127oC temperature and 100mm Hg pressure. The bottom stream of second distillation column is sent to crystallizer to recover the salicylaldehyde by crystallizing the para-hydroxybenzaldehyde.
Para-hydroxybenzaldehyde, produced along with salicylaldehyde in this reaction finds ready uses in the perfume industry and can be methylated to give salicylaldehyde. It also finds application in the pharmaceutical industry.