US 8,172,987 B2 · Low-energy extractive distillation process for dehydration of aqueous ethanol

Abstract

An energy-efficient extractive distillation process for producing anhydrous ethanol from aqueous/ethanol feeds containing any range of ethanol employs an extractive distillation column (EDC) that operates under no or greatly reduced liquid reflux conditions. The EDC can be incorporated into an integrated process for producing anhydrous ethanol used for gasoline blending from fermentation broth. By using a high-boiling extractive distillation solvent, no solvent, is entrained by the vapor phase to the EDC overhead stream, even under no liquid reflux conditions. The energy requirement and severity of the EDC can be further improved by limiting ethanol recovery in the EDC. In this partial ethanol recovery design, ethanol which remains in the aqueous stream from the EDC is recovered in a post-distillation column or the aqueous stream is recycled to a front-end pre-distillation column where the ethanol is readily recovered since the VLE curve for ethanol/water is extremely favorable for distillation.

Claims24

Dependent claims

An improved extractive distillation (ED) process for dehydrating an aqueous feedstock containing ethanol and water that comprises the steps of:

(a) introducing an aqueous feedstock comprising ethanol and water into a middle portion of an extractive distillation column (EDC);
(b) introducing a high-boiling water selective, salt-free solvent into an upper portion of the EDC to contact the aqueous feedstock under extractive distillation conditions to produce a liquid bottoms stream that comprises water and high-boiling water selective solvent and to produce a vaporous overhead stream that comprises greater than 99.5 weight percent ethanol, wherein the EDC is operated with no liquid reflux at the top of the EDC;
(c) withdrawing at least a portion of the vaporous overhead from the EDC as a purified ethanol product;
(d) feeding at least a portion of the liquid bottoms stream of the EDC into a solvent recovery column (SRC) to remove water therefrom and to yield a lean high-boiling water selective solvent stream;
and
(e) recycling at least a portion of the lean high-boiling water selective solvent stream into the upper portion of the EDC wherein step (a) comprises forming a liquid bottoms stream comprising water, ethanol, and high-boiling water selective solvent and in step (d) the SRC produces an overhead stream comprising water and ethanol that is condensed to form a condensate that is fed into a distillation column to yield a liquid bottoms stream consisting essentially of water and an overhead stream comprising ethanol and water which is recycled to the EDC.

3 more elements

An improved extractive distillation (ED) process for dehydrating an aqueous feedstock containing ethanol and water that comprises the steps of:

(a) introducing an aqueous feedstock comprising ethanol and water into a middle portion of an extractive distillation column (EDC);
(b) introducing a high-boiling ethanol selective, salt-free solvent into an upper portion of the EDC to contact the aqueous feedstock under extractive distillation conditions to produce a liquid bottoms stream consisting essentially of ethanol and high-boiling ethanol selective solvent and a vaporous overhead stream consisting essentially of water, Wherein the EDC is operated with no liquid reflux at the top of the column;
(c) feeding at least a portion of the liquid bottoms stream of the EDC into a solvent recovery column (SRC) to remove ethanol therefrom and to yield a bottoms stream that comprises lean high-boiling ethanol selective solvent and an overhead stream whereby at least a portion of the overhead is withdrawn as a purified ethanol product with higher than 99.5 wt % purity;
and
(d) recycling at least a portion of the lean high-boiling ethanol selective solvent from the bottoms stream of the SRC into the upper portion of the EDC wherein step (b) comprises introducing a high-boiling ethanol selective, salt-free solvent through an entry point at the upper portion of the EDC wherein the temperature of the high-boiling ethanol selective solvent is about 10° C. to 20° C. lower than that of the EDC at the entry point in order to generate internal reflux.

2 more elements

Dependencies are inferred from the claim text.

Low-energy extractive distillation process for dehydration of aqueous ethanol

Life of this patent

Low-energy extractive distillation process for dehydration of aqueous ethanol

Life of this patent

Abstract

Claims24