US 2009/0014313 A1 · 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.

Claims54

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 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 a liquid reflux-to-distillate ratio of less than about 0.5;
(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 an upper portion of the EDC.

3 more elements

An improved process for dehydrating an aqueous feedstock containing ethanol and water that comprises the steps of:

(a) distilling an aqueous feedstock comprising ethanol and water in a pre-distillation column to produce a first vaporous overhead stream, a vaporous side-cut stream, and a first liquid bottoms stream;
(b) partially condensing the first vaporous overhead stream in a first condenser to yield a condensate phase and a vapor phase;
(c) recycling the condensate phase from the first condenser into the pre-distillation column as reflux;
(d) introducing the vaporous side-cut stream into a middle portion of an extractive distillation column (EDC);
(e) introducing a bottoms stream from a solvent recovery column (SRC) which contains a high-boiling water selective solvent into an upper portion of the EDC to contact the vaporous side-cut stream under extractive distillation conditions to produce a second vaporous overhead stream that comprises greater than 99.5 wt % ethanol and a second liquid bottoms stream comprising water, ethanol and high-boiling water selective solvent wherein the EDC is operated with a liquid reflux-to-distillate (RID) ratio of less than about 0.5;
(f) introducing at least a portion of the second liquid bottoms stream from the EDC that comprises water, ethanol and high-boiling water selective solvent into the SRC to remove water and ethanol from the high-boiling water selective solvent;
(g) recycling at least a portion of a bottoms stream of the SRC that comprises high-boiling water selective solvent into an upper portion of the EDC;
(h) recycling a first portion of an overhead condensate from the SRC as liquid reflux to the SRC and recycling a second portion of the overhead condensate into the pre-distillation column;
and
(i) withdrawing a bottom stream from the pre-distillation column that consists essentially of water.

7 more elements

An improved process for dehydrating an aqueous feedstock containing ethanol and water that comprises the steps of

(a) distilling an aqueous feedstock comprising ethanol and water in a pre-distillation column to produce a first vaporous overhead stream, a vaporous side-cut stream, and a first liquid bottoms stream;
(b) partially condensing the first vaporous overhead stream in a first condenser to yield a condensate phase and a vapor phase;
(c) recycling the condensate phase from the first condenser into the pre-distillation column as reflux;
(d) introducing the vaporous side-cut stream into a middle portion of an extractive distillation column (EDC);
(e) introducing a bottoms stream from a solvent recovery column (SRC) which contains a high-boiling ethanol selective solvent into an upper portion of the EDC to contact the vaporous side-cut stream under extractive distillation conditions to produce a second vaporous overhead stream that comprises water and ethanol and a second liquid bottom streams that comprises ethanol and the high-boiling ethanol selective solvent wherein the EDC is operated with a liquid reflux-to-distillate ratio of less than about 0.5;
(f) recycling at least a portion of the second vaporous overhead stream from the EDC in the form of condensate into the pre-distillation column;
(g) introducing at least a portion of the second liquid bottoms stream from the EDC that comprises ethanol and high-boiling ethanol selective solvent into the SRC to yield an overhead ethanol product that comprises greater than 99.5 weight percent ethanol and a bottoms stream that comprises high-boiling ethanol selective solvent;
(h) recycling at least a portion of the SRC bottoms stream comprising the high-boiling ethanol selective solvent into an upper portion of the EDC;
(i) recycling a portion of the ethanol product in the form of condensate into the SRC as reflux;
and
(j) withdrawing a bottoms stream from the pre-distillation column that consists essentially of water.

8 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

Claims54