US 4,303,478 AGranted

Process for distillatively separating liquid mixtures

AssigneeArthur D. Little, Inc.

InventorEdwin L. Field

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Abstract

Process for distillatively separating a liquid mixture containing at least two miscible volatile components having different boiling points using low-grade heat and, if necessary, low-grade cooling. Distillation is carried out at a pressure sufficiently low to cause the mixture at the bottom of the distillation column to boil below the temperature of the low-grade heat supplied and condensation of at least a portion of the vapor fraction is carried out at a pressure which permits using available cooling liquid. Condensed liquid is returned as reflux to the distillation column at a temperature and pressure essentially equal to the temperature and pressure prevailing near the top of the column. The progressive increase of vapor recompression in the system makes it possible to provide an increasing proportion of the energy to the system in the form of electrical energy, up to the total energy requirement. The process and apparatus of this invention are particularly suited to separating ethyl alcohol from dilute aqueous mixtures, where the formation of the ethyl alcohol azeotrope can be reduced or eliminated.

Claims18

Dependent claims

A process for distillatively separating liquid mixtures containing at least two miscible volatile components having different boiling points, comprising the steps of

(a) supplying to a distillation column a source of low-grade heat between about 30.degree. C. and about 80.degree. C.;
(b) supplying a cooling liquid having a temperature up to about 75.degree. C.;
(c) distilling a liquid mixture of at least two miscible volatile components of different boiling points in said distillation column, to form a lower-boiling fraction and a higher-boiling fraction, under a pressure sufficiently below atmospheric to cause said higher-boiling fraction of said liquid mixture to boil below the temperature of said low-grade heat supplied to said distillation column;
(d) discharging said higher-boiling fraction from the bottom of said distillation column;
(e) withdrawing from said distillation column said lower-boiling fraction at a pressure essentially equivalent to that prevailing near the top of said distillation column;
(f) elevating the pressure of said lower-boiling fraction to a level which is no greater than that which effects the condensing of at least a portion of said lower-boiling fraction above the temperature of said cooling liquid supplied, to form lower-boiling liquid product;
(g) condensing a portion of said lower-boiling fraction to provide said lower-boiling fraction at a low temperature and at a pressure essentially equal to that prevailing near the top of said distillation column;
and
(h) returning at least a portion of said low-temperature lower-boiling fraction from step (g) to the top of said distillation column as reflux liquid.

6 more elements

A process for recovering ethyl alcohol from a dilute aqueous mixture containing noncondensable components, comprising the steps of

(a) supplying to a distillation column a source of low-grade heat between about 30.degree. C. and about 80.degree. C.;
(b) supplying a cooling liquid having a temperature up to about 75.degree. C.;
(c) distilling a dilute aqueous mixture of ethyl alcohol and noncondensables in said distillation column, to form an ethyl alcohol product mixture and an aqueous waste mixture, under a pressure sufficiently below atmospheric to cause said aqueous waste mixture to boil below the temperature of said low-grade heat supplied to said distillation column;
(d) discharging said aqueous waste mixture from the bottom of said distillation column;
(e) withdrawing from said distillation column said ethyl alcohol product mixture containing said noncondensables at a pressure essentially equivalent to that prevailing near the top of said distillation column;
(f) elevating the pressure of said withdrawn ethyl alcohol product mixture to a level which is no greater than that which effects the condensing of said ethyl alcohol above the temperature of said cooling liquid supplied, to form ethyl alcohol product and gaseous noncondensables;
(g) separating said liquid ethyl alcohol product and said noncondensables;
(h) throttling a portion of said ethyl alcohol product mixture to provide a low-temperature liquid ethyl alcohol at a pressure essentially equal to that prevailing near the top of said distillation column;
and
(i) returning at least a portion of said low-temperature liquid ethyl alcohol from step (h) to the top of said distillation column as reflux liquid.

7 more elements

Dependencies are inferred from the claim text.