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US 5,124,004 AGranted
Distillation process for ethanol
AssigneeTrustees of Dartmouth College
InventorsHans E. Grethlein, Lee R. Lynd
Life of this patent
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AssigneeTrustees of Dartmouth College
InventorsHans E. Grethlein, Lee R. Lynd
Estimating the term…
A method of distillation employing a heat pump (which may be driven by a compressor) using a vapor stream from within the distillation system as a heat source and a liquid stream from within the distillation system as a heat sink. The selection of heat-source vapors and heat-sink liquid is such that at least one is withdrawn from the phase-contracting region of the distillation system. The return of streams withdrawn from the phase-contacting region of the distillation system to the distillation system is such that at least one of the streams is returned at a temperature different from that of the point from which it was withdrawn, and all withdrawn streams are returned in manner such that a stream removed as vapor is returned at a point with a temperature at most that at the point it was withdrawn, and a stream removed as liquid is returned at a point with a temperature at least that at which it was withdrawn. Embodiments of the basic method where vapor only, liquid only, or both liquid and vapor are withdrawn from and returned to the phase-contacting region of the distillation system are considered. The impact of the invention is to reduce the heat requirement of distillation in exchange for an amount of work which is usually small because the temperature difference between heat sources and sinks is minimized. Combination of the basic distillation method with multi-effect distillation, convention overhead-to-reboiler heat pumped distillation, azeotropic and extractive distillation, and fermentative production of volatile compounds is described. A system specifically designed for the separation of ethanol-water mixtures which utilizes the present invention and extractive distillation in a system with extensive heat integration is presented.
A method for concentrating an aqueous ethanol solution, comprising, initially partially concentrating said aqueous ethanol solution in a heat-pumped distillation apparatus comprising one or more distillation columns in which a vapor stream is withdrawn from a point in said distillation apparatus having a temperature at the system pressure intermediate between the highest and lowest temperatures in said distillation apparatus for use as a heat source for transferring heat to a heat-sink liquid having a temperature at the system pressure higher than the temperature of said withdrawn vapor stream at the system pressure, the flow of the withdrawn vapor stream having an upper limit which causes the distillation apparatus to be pinched at a return point and a lower limit which provides significant changes in the internal reflux ratio at the point of return for the withdrawn vapor stream and thereafter performing work on vapor resulting from said withdrawn vapor stream to raise the condensation temperature of said vapor above the evaporation temperature of said heat-sink liquid and condensing at least a portion of said vapor resulting from the withdrawn vapor stream and returning the condensed liquid stream to the distillation apparatus at a point having a lower temperature than the temperature at its point of withdrawal and further concentrating the partially concentrated ethanol stream resulting from said initial concentration in an extractive distillation column in which a suitable salt is added to the extractive distillation column to eliminate an azeotrope between water and ethanol thereby increasing the relative volatility of ethanol and thereafter concentrating a salt-containing stream exiting from the extractive distillation column in an evaporator.
A method for separating an aqueous ethanol mixture to produce higher purity ethanol in a system including an extractive distillation column, an evaporator and a heat-pumped distillative apparatus comprising one or more distillation columns and wherein a suitable salt is added to the extractive distillation column to eliminate an azeotrope between water and ethanol thereby increasing the relative volatility of ethanol and wherein salt is thereafter concentrated by evaporation in the evaporator, a vapor stream being withdrawn from a point in said heat-pumped distillative apparatus having a temperature intermediate between the highest and lowest temperatures in said distillative apparatus for use as a heat source for transferring heat to a heat-sink liquid having a temperature at the heat-pumped distillative apparatus system pressure higher than the temperature of said withdrawn vapor stream at the system pressure, the flow rate of the withdrawn vapor stream having an upper limit which causes the heat-pumped distillative apparatus to be pinched at a return point and a lower limit which provides significant changes in the internal reflux ratio at the point of return of the withdrawn vapor stream and performing work on the withdrawn vapor to raise the condensation temperature of said vapor above the evaporation temperature of said heat-sink liquid and thereafter condensing at least a portion of said vapor and returning the resulting stream to the heat-pumped distillative apparatus at a point having a lower temperature than the temperature at its point of withdrawal.
A method for performing a distillative concentration of an aqueous ethanol solution in a system including a heat-pumped distillative apparatus, and extractive distillation column and an evaporator, comprising:
Dependencies are inferred from the claim text.