The first issue is the reason that the 90% v/v stream “cannot be used in a process.” Is it solely due to ethanol concentration or is it due to impurities or other component? If it cannot be used in a process due solely to ethanol concentration at 90%, and 95% concentration is acceptable for reuse into the process, the most direct recovery method would azeotropic distillation.

If it cannot be used in a process due solely to ethanol concentration at 90%, and >99% is required for reuse into the process, dehydration can be obtained via distillation with cyclohexane or benzene, or via absorption with molecular sieve absorption.

If a distillation processing system is already in place, the economics at 10,000 lpd may favor concentrating to 95% via distillation and then followed by either approach to 99% ethanol.