For maleic anhydride feed, hydrogenation of the dimethyl maleate intermediate proceeds rapidly to produce dimethyl succinate (DMS):
The DMS then undergoes hydrogenolysis to form γ-butyrolactone.
If succinic acid is used as the process feed, DMS passes directly from esterification to hydrogenolysis:
Finally, and depending upon the prevailing reaction conditions, a proportion of the BDO dehydrates to form tetrahydrofuran:
Distillation produces high-purity product, while methanol is recovered and recycled to the esterification stage. Any unreacted DMS is recovered and recycled to hydrogenolysis.
If there is no desire to co-produce GBL, this too can be recycled to yield further BDO.
The GBL product can be either recycled or extracted as required. If extracted, the amount produced can be varied by changing operating conditions.
For THF, altering the operating conditions and the reactants’ exposure to the catalyst adjusts the ratio between BDO and the THF co-product.