| abstract |
The present invention relates to a process for the preparation of pure fumaric acid from by-products of the preparation of maleic anhydride from benzene and of the preparation of phthalic anhydride from naphthalene or orthoxylene. This process is characterized in that one uses solutions with a maleic acid content of 14 to 40%, preferably 20 to 30% and these solutions are isomerized in the presence of activated carbon, and also of thiourea. , hydrochloric acid and NaHSO3 or Na2 SO3, at a temperature of 40 to 90 degree (s) C. |