Process for the recovery of low-boiling point components from an ethanol stream
The disclosure provides a process for the production of ethanol and one or more low boiling compound from a fermentable carbon source. The ethanol and the low boiling compound(s) are produced using an ethanol-producing yeast modified to further produce the one or more low boiling point compounds. In one embodiment, the low boiling compound(s) are acetone, 1-propanol, and/or 2-propanol. Additionally, the disclosure provides a process for the isolation ad purification of the one or more low boiling compounds from ethanol.
1 . A process for the isolation of one or more low boiling compounds from a fermentation broth and a fermentation off-gas, the process comprising:
(a) flowing a fermentation off-gas coming from one or more fermenters through a product recovery unit wherein the flow of the off-gas is counter to a solvent flowing through the product recovery unit and obtaining a solvent stream comprising the one or more low boiling compounds and ethanol;
(b) mixing the solvent stream of (a) with the fermentation broth and passing the resulting fermentation mixture through a first separation unit to form a high water content stream comprising about 30-90% w/w water, ethanol, and the one or more low boiling compounds;
(c) passing the high water content stream of (b) through a second separation unit to form an intermediate water content stream comprising water, ethanol, and the one or more low boiling compounds;
(d) passing the intermediate water content stream of (c) through a dewatering unit to form a low water content stream comprising ≤2.5% w/w water; and
(e) passing the low water content stream of (d) through one or more operational units, separating the ethanol and the one or more low boiling compounds;
wherein the process further comprises recycling a gas stream output from at least one of the first separation unit, the second separation unit, or the dewatering unit to the product recovery unit.
2 . The process of claim 1 , wherein the fermentation broth and fermentation off-gas comprise water, the one or more low boiling compounds, ethanol, and one or more contaminants.
3 . The process of claim 1 , wherein the fermentation off-gas of (a) comprises one or more incondensable gases, water, ethanol, and the one or more low boiling compounds.
4 . The process of claim 1 , wherein the process comprises recycling a gas stream output from the first separation unit by passing the gas stream output through steps (a) and (b).
5 . The process of claim 1 , wherein the second separation unit of (c) removes a bottom output stream comprising primarily water and a side output stream comprising fusel oil.
6 . The process of claim 5 , further comprising:
recycling the bottom output stream of (c) to an upstream fermentation process which produces the fermentation broth;
recycling the bottom output stream of (c) by passing the bottom output stream through step (c); or
recycling the bottom output stream of (c) by passing the bottom output stream through steps (b) and (c).
7 . The process of claim 1 , wherein the process comprises removing a top vapor stream from the second separation unit of (c) and recycling the top vapor stream by combining the top vapor stream with the fermentation off-gas and passing the combined stream through steps (a), (b), and (c).
8 . The process of claim 1 , further comprising recycling water removed by the dewatering unit of (d) by passing the removed water through steps (c) and (d).
9 . The process of claim 1 , wherein the process comprises removing a top vapor stream from the dewatering unit of (d) and recycling the top vapor stream by combining the top vapor stream with the fermentation off-gas and passing the combined stream through steps (a), (b), (c), and (d).
10 . The process of claim 1 , wherein the fermentation broth comprises C4 alcohols in an amount of ≤0.5 wt. % relative to ethanol and the one or more low boiling compounds, and the C4 alcohol is 1-butanol, 2-butanol, or a combination thereof.
11 . The process of claim 1 , wherein the low boiling compound is acetone and the one or more operational units of (e) is a pervaporation system, a single distillation column, a sequence of distillation columns, a vacuum column, or a combination thereof, which separates the ethanol from the acetone.
12 . The process of claim 1 , wherein the low boiling compounds are acetone and 1-propanol and the one or more operational units of (e) are:
(i) a first distillation system which separates 1-propanol from a mixture comprising ethanol and acetone,
(ii) a second distillation system which purifies the 1-propanol from (i) to a desired purity, and
(ii) a third distillation system which separates the mixture of (i) into ethanol and acetone to a desired purity.
13 . The process of claim 1 , wherein the low boiling compounds are 1-propanol and 2-propanol and the one or more operational units of (e) are:
(i) one or more distillation columns which separate 1-propanol from a mixture comprising ethanol and 2-propanol,
(ii) an extractive distillation unit which uses a solvent to extract 2-propanol from a vapor phase mixture comprising ethanol and 2-propanol while obtaining a first fraction of ethanol at a desired purity and a second fraction comprising solvent, 2-propanol, and ethanol,
(iii) one or more distillation columns which separate the second fraction of (ii) into solvent and a mixture of ethanol and 2-propanol, and
(iv) one or more distillation columns which separate 2-propanol at a desired purity from the mixture of (iii), leaving a solution of primarily ethanol with 2-propanol,
wherein the operational units (ii) to (iv) can be replaced with a system comprising two distillation columns operating under vacuum conditions.
14 . The process of claim 13 , further comprising recycling the solvent of (iii) for use in the extractive distillation unit of (ii).
15 . The process of claim 13 , further comprising:
recycling the solution of (iv) by heating the solution to form a vapor and passing the vapor through the extractive distillation unit of (ii); or
recycling the solution of (iv) by passing the solution through the extractive distillation unit of (ii).
16 . The process of claim 1 , wherein the low boiling compound is 2-propanol and the one or more operational units of (e) comprise:
(i) an extractive distillation unit which uses a solvent to extract 2-propanol from a vapor phase mixture comprising ethanol and 2-propanol while obtaining a first fraction of ethanol at a desired purity and a second fraction comprising solvent, 2-propanol, and ethanol,
(ii) one or more distillation columns which separate the second fraction of (i) into solvent and a mixture of ethanol and 2-propanol, and
(iii) one or more distillation columns which separate 2-propanol at a desired purity from the mixture of (ii), leaving a solution of primarily ethanol with 2-propanol,
wherein the operational units (i) to (iii) can be replaced with a system comprising two distillation columns operating under vacuum conditions.
17 . The process of claim 16 , further comprising recycling the solvent of (ii) for use in the extractive distillation unit of (i).
18 . The process of claim 16 , further comprising:
recycling the solution of (iii) by heating the solution to form a vapor and passing the vapor through the extractive distillation unit of (i); or
recycling the solution of (iii) by passing the solution through the extractive distillation unit of (i).
19 . The process of claim 1 , wherein the fermentation broth is obtained by a process comprising:
contacting a fermentable carbon source with an ethanol-producing yeast in a fermentation medium; and
fermenting the carbon source by the yeast in the fermentation medium, to produce a fermentation broth and a fermentation off-gas comprising ethanol and the one or more low boiling compounds.
20 . A process for the production and isolation of ethanol and one or more low boiling compounds, the process comprising:
(a) contacting a fermentable carbon source with an ethanol-producing yeast in a fermentation medium;
(b) fermenting the carbon source by the yeast in the fermentation medium of (a) to produce a fermentation broth and a fermentation off-gas comprising ethanol and the one or more low boiling compounds;
(c) flowing the fermentation off-gas coming from one or more fermenters in (b) through a product recovery unit wherein the flow of the off-gas is counter to a solvent flowing through the product recovery unit and obtaining a solvent stream comprising the one or more low boiling compounds and ethanol;
(d) mixing the solvent stream of (c) with the fermentation broth and passing the resulting fermentation mixture through a first separation unit to form a high water content stream comprising about 30-90% w/w water, ethanol, and the one or more low boiling compounds;
(e) passing the high water content stream of (d) through a second separation unit to form an intermediate water content stream comprising water, ethanol, and the one or more low boiling compounds;
(f) passing the intermediate water content stream of (e) through a dewatering unit to form a low water content stream comprising ≤2.5% w/w water; and
(g) passing the low water content stream of (f) through one or more operational units, separating the ethanol and the one or more low boiling compounds;
wherein the process further comprises recycling a gas stream output from at least one of the first separation unit, the second separation unit, or the dewatering unit to the product recovery unit.