CA1195258A - Vapor phase adsorption process for concentration of ethanol from dilute aqueous mixtures thereof - Google Patents
Vapor phase adsorption process for concentration of ethanol from dilute aqueous mixtures thereofInfo
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- CA1195258A CA1195258A CA000420436A CA420436A CA1195258A CA 1195258 A CA1195258 A CA 1195258A CA 000420436 A CA000420436 A CA 000420436A CA 420436 A CA420436 A CA 420436A CA 1195258 A CA1195258 A CA 1195258A
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Abstract
Abstract Described herein is a vapor phase adsorption separation process for removing and concentrating at least one organic molecular species such as ethanol present in a minor amount from a dilute aqueous mixture such as fermentation beer.
Ethanol in the vapor phase is selectively adsorbed into a hydrophobic adsorbent mass consisting of a molecular sieve material such as silica-bonded F-silicalite which has a greater selectivity for ethanol than for water. The vapor phase adsorption separation process is especially useful in providing concentrated ethanol from fermentation beer to supplement the world energy and chemical needs.
Ethanol in the vapor phase is selectively adsorbed into a hydrophobic adsorbent mass consisting of a molecular sieve material such as silica-bonded F-silicalite which has a greater selectivity for ethanol than for water. The vapor phase adsorption separation process is especially useful in providing concentrated ethanol from fermentation beer to supplement the world energy and chemical needs.
Description
~L9S2S~3 VAPOR PHASE ADSORPTION PRCCESS FOR
CONCENTRATION OF ETHANOL FROM DILUTE
AQUEOUS MIXTURES THEREOF
Brief Summary of the Invention Technical Field _ This invention i5 directed in general to a vapor phase adsorption process for selectively adsorbing at least one organic molecular species present in a minor amount from a dilute aqueous mixturs using a hydrophobic adsorbent mass. ~he hydrophobic adsorbent mass consists of a molecular sieve material having greater selectivity for at least one organic molecular species than for water.
More particularly, this invention is directed to a vapor phase adsorption process or removing and concentrating ethanol from water-ethanol mixtures such as fermentation beer which contains typically from about 8 to about 12 percent by weight ethanol utilizing a molecular sieve material adsorbent such as silica bonded F-silicalite or alumina-bonded silicalite. As a viable alternative to the preparation of ethanol from petroleum-bas~d ethylene, the preparation o~ concentra~ed ethanol from fermentation beer by the vapor phase adsorption separation process oE the present invention is especially important or supplementing world energy and chemical needs.
Background Art ~thanol in dilute aqueous mixtures can be pro~uced by fermentation processes utilizing a ~s~s~
variety of agricultural and biomass raw materials ~uch as grains, molasses, sugar cane juice, miscellaneous fruits, wood and the like. However, the large propoxtion of industrial ethanol produced in the world is made from petroleum-based ethylene.
In view of the limited petroleum resources available, the production of ethanol from renewable raw material resources by fermentation processes to supplement the world energy and chemical needs is understandably of major importance. It is anticipated that in the near future a significant amount of ethanol for fuel and chemicals will be derived from fermentation processes.
In a conventional fermentation process, yeast and other microorganisms convert sugars to alcohol and carbon dioxide. Since sugar concentrations in excess of about 16 weight percent typic~lly inhibit the growth of yeast cells in the initial stages of fermentation, dilution of the s~arting sugar concentration with water is necessary to properly control the sugar concentration and permit the normal growth of yeast cells. The diluted sugar concentrations result in lower ethanol concentrations and hence high energy requirements for distillation and purification of ethanol. It has also been demonstrated that ethalnol concentrations greater than about 10 weight percen~
in fermentation beer result in a phenomenon known as "feedback inhibition" which inhibits further ethanol production. The maximum ethanol concentration which is typically attainable after about 36 hours of conventional fermentation is usually about 8 to 12 weight percent. The major byproducts of the --fermentation process in addition to carbon dioxide .
s~
are dissolved and undissolved (distiller's dry grain) solids, aldehydes, ketones and fusel oils.
The presence of ethanol in a minor amount in dilute aqueous mixtures such as fermentation beer obtained from the fermentation process requires large amounts of heat energy to distill and purify the ethanol therefrom.
Ethanol is conventionally recovered from dilute aqueous mixtures such as fermentation beer by traditional distillation processes. The fermentation beer containing from about 8 to about 12 weight percent ethanol and byproducts is fed into a still where ethanol is removed as overhead in a concentration ranging from about 100- to about l90-proof. The bo~toms from the still contain dissolved and undissolved solids and the byproducts are usually taken off as side draws. The concentrated ethanol, nominally l90-proof, can be further upgraded to nearly anhydrous l99-proof ethanol needed for gasohol by azeotropic distillation. However, as previously mentioned, the conventional distillation process for recovering and concentrating ethanol from dilute aqueous mixtures such as fermentation beer is very energy intensive.
Large amounts of heat energy are required because the major component of fermentation beer, i.e., water, is being heated to recover a minor component of fermentation beer, i.e., ethanol. Also, azeotropic distillation is an energy-intensive operation. Energy consumptions from about 30,000 to about 40,000 BTU per gallon of anhydrous ethanol are not uncommon for typical distillation processes.
Since the cost of producing ethanol frcm agricultural and biomass raw materials depends not ~, ;2S~
only on the fermentation of the raw materials but also on the recovery and purification of ethanol produced by the fermentation process, higher energy consumptions during distillation and purification result in higher ethanol-per-gallon cost and can also contribute towards offsetting the energy balance of ethanol production by fermentation processes for fuel and chemical needs.
There have been various attempts to develop lower cost processes for recovering and concentrating ethanol from fermentation beer. It has been previously found that ethanol can be recovered from dilute fermentation beers by a liquid phase adsorption process utilizing certain adsorbent materials such as activated carbons, ion exchange resins and molecular sieves. TheSe adsorbent materials can selectively adsorb either water from aqueous ethanol or ethanol from dilute aqueous solutions. In carrying out the liquid phase adsorption processes, a fermentation beer is usually pumped through a packed adsorbent bed wherein either the liquid ethanol or water is adsorbed on the adsorbent material. If ethanol is adsorbed on the adsorbent material, ~he adsorbent material is typically regenerated with a purge gas in which concentrated ethanol is recovered therefrom. If water is adsorbed on the adsorbent material, ethanol is recoversd in the effluent from the adsorbent material. However, such liquid phase adsorption processes are usually not very efficient. The main drawbacks of liquid phase adsorption processes are poox ethanol recovery due to entrapment of part of the dilute aqueous mixture, i.e., fermentation beer, between and within particles of the adsorbent 52S~3 material and lower ethanol product purity due to residual water being retained in the ethanol product. Another major and perhaps more critical drawback is the distinct possibility that the solids contained in the`liquid fermentation beer can plug up voids in the packed adsorbent bed and cause substantial mechanical problems~
The present invention consisting of a vapor phase adsorption separation process provides a practical and efficient low energy process for recovering and concentrating at least one organic molecular species such as ethanol from a dilute aqueous mixture such as fermentation beer without encountering any of the drawbacks associated with liquid phase adsorption processes. According to the present invention, a stripping gas enriched with ethanol vapor and water vapor is passed through an adsorbent material such as silicalite described in U.S. Patent 4,0blj~24 or F-silicalite described in ~ U.S. Patent 4,073,865, both assigned to Union Carbide Corporation. Ethanol in the vapor phase is selectively adsorbed by the adsorbent material which has a greater selectivity for ethanol than for water. The adsorption of ethanol vapor is conducted at a temperature and pressure which prevents the capillary condensation of water in the adsorbent material. The adsorbed ethanol is removed from the adsorbent material by a non-sorbable heated purge ~as which is subsequently cooled to condense ethanol. Essentially no liquid phase is present in the ethanol adsorption step of the highly desirable adsorption separation process of this invention.
Various liquid phase adsorption processes and the drawbacks inheEent therewith are less desirable for concentrating ethanol from dilute aqueous mixtures such as fermentation beer.
U.S. Patent 4,277,635 disclose~ a process for concentrating ethanol from aqueous solutions thereof, such as fermentation beer containing from 6 to 13~ by weight ethanol. The ethanol is remoYed from the fermentation beer by liquid adsorption on a molecular sieve material such as silicalite. The patent states that residual fermentation beer remaining in the adsorption column can be removed by passing highly concentrated ethanol through the adsorption column.
U.SO Patent 4,061,724 and U.S n Patent 4,073,865, both assigned to Vnion Carbide Corporation, describe crystalline silica compositions designated herein as silicalite and F-silicalite respectively, which can ~e used as the adsorbent mass in the pre~ent invention. These patents describe the hydrophobic/organophilic character of both silicalite and F-silicalite which permits their use in selectively adsorbing organic materials from water either in the liquid or vapor phase.
U.SO Patent 3,732,326 relates to a method of selectively sorbing a compound of generally low polarity such as various hydrocarbons in admixture with a compound of the same or greater polarity such as water by passing the mixture over a crystalline aluminosilicate having a silica/alumina mole ratio of at least 35 such as mernbers of the amily of ZSM-5 zeolites.
However, none of these references discloses or suggests the vapor phase adsorption separation process as claimed in the instant invention or ~5~5~
removing and concentrating at least one organic molecular species such as ethanol present in a minor amount from a dilute aqueous mixture such as fermentation beer utilizing a molecular sieve material adsorbent.
Disclosure of Invention The present invention is directed to an adsorption separation process which comprises:
(a) vaporizing water and at least one organic molecular species contained in a dilute aqueous mixture by contacting the dilute aqueous mixture with an essentially non-sorbable stripping gas (b) passing the stripping gas enriched with water and at least one organic molecular species into a fixed adsorption zone containing a hydrophobic adsorbent mass consisting essentially of a molecular sieve material having selectivity for at least one organic molecular species (c) adsorbing at least one organic molecular species into the adsorbent mass at a temperature and pressure which prevents capillary condensation of the water (d) terminating the flow of stripping gas enriched with water and at least one organic molecular species into the adsorp~ion bed prior to breakthrough of at least one organic molecular species from the effluent end of said adsorption bed;
(e) removing at least one adsorbed organic molecular species by heating the adsorbent mass by passing an essentially non-sorbable hea~ed purge gas through the adsorbent mass countercurrent to such enriched strippin~ gas, which purge gas can be the same gas used for stripping the dilute aqueous mixture in step (a);
If) condensing at least one organic molecular species by cooling the purge gas enriched with at leas~ one organic molecular species; and (g) recovering at least one organic molecular species in a concentrated form.
The present invention is also directed to an adsorption separation process as described in steps (a~ through (g~ above further comprising cooling the adsorbent mass until the ~empera~ure is essentially the same as at the beginning of step (b) and repeating steps (a) through (g) until a predetermined amount of at least one organic molecular species is recovered in a concentrated form from the dilute aqueous mixture.
More particularly, the present invention is directed to an adsorption separation process which comprises:
(a) vaporizing water and ethanol contained in a fermentation beer by contacting the fermentation beer with an essentially non-sorbable stripping gas such as nitrogen, carbon dioxide helium or argon;
(b) passing the stripping gas enriched with water and ethanol into a fixed adsorption zone containing a hydrophobic adsorbent mass con~isting essentially of a silica-bonded F-silicalite adsorbent or an alumina-bonded silicalite adsorbent;
(c) adsorbing ethanol into the adsorbent mass at a temperature and pressure which prevents capillary condensation of the water7 ~d) terminating the flow of stripping gas enriched with water and ethanol into the adsorption bed prior to breakthrough of ethanol from - the effluent end of the adsorption bed;
(e) removing ethanol by heating the adsorbent mass by passing an essentially non-sorbable heated purge gas such as nitrogen, carbon dioxide, helium or argon ~hrough the adsorbent mass countercurrent to such enriched stripping gas (f) condensing ethanol by cooling the purge gas enriched with ethanol;
~g) recovering ethanol in a co~centrated form;
(h) cooling the adsorbent mass until the temperature is essentially the same as at the beginning of step (b); and ~i) repeating steps (a) through ~h) until a predetermined amount of ethanol is recovered from the fermentation beer.
Brief Description of Drawings The present invention is further described with reference to the accompanying drawings in which:
Fig. 1 is a schematic flowsheet of an illustrative embodiment for carrying out the process of this invention.
Fig. 2 illustrates an adsorption step breakthrough profile of ethanol and water concentrations in the effluent from the adsorption column a~ 125F using alumina-bonded silicalite adsoebent as determined by gas chromatographic analysis.
Fig, 3 illustra~es a regeneration step profile of ethanol and water concentrations in the ~ ~3258 1~
nitrogen gas regeneration effluent at 200~ ~s determined by gas chromatographic analysis.
Fig. 4 illustrates a profile of the dependency of water and ethanol adsorption loadings on their relative stauration (p/po) values at adsorption temperatures ranging from about 75F to about 150F and using alumina-bonded silicalite adsorbent.
Fig. 5 illustrates an adsorption step breakthrough profile of ethanol and water concentrations in the effluent from the adsorption column at 75F using silica-bonded F-silicalite adsorbent as determined by gas chromatographic analysis.
Detailed_Description A dilute aqueous mixture such as fermentation beer containing from about 8 to about 12 percent by weight ethanol can be stripped of ethanol by any suitable stripping procedure. For example, with reference to Fig. 1, a stripping gas can be charged into the bottom of an external packed-bed stripping column wherein fermentation beer is flowing downward to give a stripping gas enriched with ethanol vapor and some water vapor.
After ethanol and some water are stripped from the fermentation beer, the enriched stripping gas is removed f~om the top of the stripping column and essentially ethanol-free fermentation beer is removed from the bottom of the column. The stripping column temperature and pressure are not narrowly critical and can vary over a wide range.
The temperature in the stripping column can range from about ambient to about 200F and the pressure ~s~
in the stripping column can range from abut 15 psig to about 200 psig. The flow of stripping gas is dependent on the stripping col~mn temperature and pressure and the liquid, i.e., fermentation beer, feed rate. Alternatively, in the absence of an external packed bed stripping column, a stripping gas may be bubbled through the fermentation tanks or holding tank ~o strip ethanol from the fermentation beer.
The stripping gas used in the vaporizing step (a) of this adsorption separation process can be any vapor phase compound which does not appreciably react with the dilute aqueous mixture, e.g., fermented beer, constituents under the imposed conditions~ Also, the stripping gas should not be harmful to the adsorbent mass and should not be appreciably adsorbed by the adsorbent mass. The non-adsorbability of the stripping gas can be due either to molecular size exclusion or to a weak adsorptive attraction between it and the adsorbent massO The preferred strippiny gas for use in the adsorption ~eparation process of this invention is selected from the group consisting of nitrogen, carbon dioxide, helium and argon. The stripping gas can also be the off-gases generated by the fermentation process which can consist of essentially carbon dioxide enriched with some ethanol. For example, with reference to Fig. 1, the off-gases from the battery of fermentation tanks may be used as the stripping gas in the process of this invention~ The stripping gas can be recycled for further stripping in vaporizing step (a) described above after passing through the adsorption bed during adsorbing step ~c) also described above.
~S~5~
The dilute aqueous mixture feedstock can be any mixture of water and one or more organic molecular species. Preferred feedstocks are those obtained by ermentation processes, i.e., fermentation beers, utilizing a variety of agricultural and biomass raw materials such as grains, molasses, sugar cane juice, miscellaneous fruits, wood and the like. P~rticularly preferred dilute aqueous mixture feedstocks are mixtures of water and one or more organic molecular species containing from 2 to about 6 carbon atoms inclusive. ~n especially preferred dilute aqueous mixture feedstock is one in which the organic molecular species is a primary alcohol containing from 2 to about S carbon atoms inclusive, most pre~erably ethanol and/or isopropanol. A
fermentation beer containing from about 8 to about 12 percent by weight ethanol is the most preferred dilute aqueous mixture or use in the proc~ss of this invention.
The stripping gas enriched with at least one organic molecular species vapor, e~g., ethanol vapor, and water vapor is passed into any suitable fixed adsorption zone containing a hydrophobic adsorbent mass consisting essentially of a molecular sieve material. The particular species of molecular sieve material employed in the present invention is not a narrowly critical factor. In all event, however, it should be capable of adsorbing from 5 to i 30 50 times more organic molecular species, e.g., ethanol, than water under the process conditions of temperature and pressure, and ~o subs~antially exclude from adsorption essentially all of the other constituents of the dilu~e aqueous mixture feedstock , ;2S~ ~
1~
under those conditions. The preferred adsorbent mass for use in the process of this invention includes substantially hydrophobic molecular sieve materials such as silica-bonded F-silicalite described in U.S. Patent 4,073,865, alumina-bonded silicalite described in U.S. Patent 4,061,724 and Ultrahydrophobic Zeolite Y (U~P-Y) described in copending Canadian Patent No. 1,131,195, September 7, 1982. Other suitable memb~rs of the high silica adsorbent group may also be used in the process of this invention. With reference to ~ig. l, the stripping gas enriched with ethanol vapor and water vapor is passed through ~he adsorbent mass con~ained in the adsorption column, ethanol is adsorbed by the adsorbent mass and the stripping gas depleted of ethanol is removed from the adsorption column. Certain organic byproducts ~uch as aldehydes and fusel oils may also be adsorbed ln minor amounts into the adsorbent mass.
If the stripping gas is the o~f-gases generated by the fermentation process which can consist of ~ essentially carbon dioxide enriched with ~ome - ethanol as describea above, the adsorbent ma-~s can further adsorb ethanol vapor which would be naturally lost and vented as a byproduct ~rom ~he fermentation process, and thereby improve the overall e~ficiency o ethanol recovery from the fermentation process.
The temperature and press;ure conditions for the adsorption step must be ~elected to maintain the ~tripping gas enriched wlth at least one organic 201ecular specie~ vapor, e.g., ethanol vapor, and water vapor in the vapor phase ~nd prevent capillary condensation o~ the organic constituent, e.g., .` ~ ' ' ' , i ,, _ , . . .
~52~
1~
ethanol, and water in the adsorption bedu Capillary condensation contributes to poor ethanol recovery due to entrapment of liquid water and ethanol preventing further adsorption of ethanol vapor and also lower ethanol product purity due to residual water being retained in the adsorbent mass and hence the regenerated ethanol product. It is preferred that the stripping gas enriched with at least one organic molecular species, e.g., ethanol, and water passing into the adsorption bed and the adsorption bed itself be at a temperature within the range of from about ambient to abou 200F and at an appropriate corresponding pressu~e within the range of from about 1 atmosphere (absolute) up to about lS 100 psia. It is preferred that steps (b) and (c) of the adsorption separation process described above be conducted at a tempera~ure of from about 25F to about 50F higher than the temperature of vaporizing step (a~ also described above in order to decrease the relative saturation (p/po) of water in the enriched stripping gas passing into and adsorbing into, in part, the fixed adsorption bed containing alumina-bonded silicalite adsorbent described in U.S. Patent 4,061,724. Heating the enriched stripping gas adjusts the relative saturation (p/po) of ethanol and water 50 as to minimize the coadsorption of water on the ethanol selective adsorbent mass. This is more fully illustrated in working Example 1 hereinbelow. The relative saturation values (p/po) of water and ethanol and the extent or amount of water and ethanol loadings onto the adsorbent mass are different for various adsorbent materials. For example, as illustrated in working ~amp~e 2 hereinbelow, when using silica-bonded F-silcalite described in U.S. Patent 4,073,865 as the adsorbent mass, it is not necessary to heat the enriched stripping gas to adjust the relative saturation (p/po) of ethanol and water because essentially no coadsorption of water occurs on the silica-bonded F-silicalite adsorbent.
Accordingly, the stripping gas enriched with ethanol and water may optionally be heated to adjust the relative saturation (p/po) of water and ethanol depending on the particular adsorbent mass utilized in the process of this invention.
Immediately prior to or after the initial breakthrough of the organic molecular species, e.g., ethanol, from the adsorption bed, regeneration of the adsorbent mass with a heated non-sorbable purge gas in commenced in a countercurrent direction with respect to the directional flow of the enriched stripping gas through the adsorption bed. Ethanol is removed or desorbed from the adsorbent mass by the heated non-sorbable purge gas. During the countercurrent purge-desorption step, the temperature of the non-sorbaable heated purge gas entering the adsorption bed can range from about 100°F to about 700°F, and is preferably from about 100°F ti abiyt 300°F higher than the temperature of the enriched stripping gas stream during the adsorption step. The countercurrent purge-desorption step can be carried out in any suitable manner, for example, either in a conventional open-purge or closed loop manner.
Regeneration of the adsorption bed can be accomplished by using either conventional thermal-swing or pressure-swing desorption. After desorption of the organic molecular species, e.g., S2~
ethanol, from the adsorbent mass, the purge gas enriched with ethanol is removed and the adsorbent mass is cooled until the temperature is essentially the same as at the beginning of the vaporizing step (a) described aboveO The adsorbent mass can again be used to adsorb an organic molecular species, e.g., ethanol, in concentrated form from the dilute aqueous mixture.
The purge gas utilized in the countercurrent purge-desorption step is preferably the same gas used for stripping the dilute agueous mixture in vaporizing step (a) described above. The purge gas can be any vapor phase compound which is not harmful to the adsorbent mass and does not appreciably react with any of the enriched stripping gas constituents under the imposed conditions. The purge gas is also essentially non-sorbable in the adsorbent mass. The non adsorbability of the purge gas can be due either to molecular size exclusion or to weak adsorptive attraction between it and the adsorption mass. The preferred purge gas for use in the adsorption separation process of this invention is selected from the group consisting of nitrogen, carbon dioxide, helium and argon. The purge gas can also be the off-gases generated by the fermentation process which can consist of essentially carbon dioxide enriched with some ethanol. For example, with reference to Fig. 1, the off-gases from the battery of fermentation tanks may be used as the purge gas in the process of this invention. The purge gas can be recycled for further desorption after the organic molecular species and minor amounts of water are condensed therefrom.
The purge gas enriched with ethanol and some water can be dried by any suitable procedure \ ~9s~s~
such as by passing the gas through a dehydration ~olumn containing a bed of desiccant material such as Type 3A zeoli~e to remove e~sentially all of the : remaining water coadsorbed in the previous step.
~ha purge gas enriched wi~h ethanol is then cooled, for example in a condenser/k~ock-out arangement, to condense at least one organic molecular species, e.g., ethanol, which is recovered in a concentrated form. If the purge gas is the off-gases generated by the fermentation process which can consist of essentially c~rbon dioxide enriched with some ethanol as desc~ibed above, additional ethanol vapor can further be recovered in a concentrated form which would be naturally lost and vented as a byproduct from thefermentation p~ocess, and thereby improve the overall efficiency of ethanol recovery from the fermentation process. The concentration of ethanol recovered from the process of this invention is dependent on several factor~, prin~ipal amon~
which is the relative selectivity of the adsorbent mass for ethanol. Ethanol is recovered from the process of this invention in a concentraPed form, for example, from about 180- to about 195-proo~. If the purge gas enriched wi~h ethanol and some water i~ dried before condensing, essentially 200-proof ethanol product can be obtained. The 180- to 195-proof ethanol product ~an be further dehydrated by azeotropic distillation or by t:he adsorptive heat rise process described in Canadian Serial No.
401843.5, filed April 28, 1982 to obtain essentiallY
200-proof ethanol.
The proce~s o~ this invention is illustrated by the following speciic embodiment described wlth reference to Fig~ 1 of the drawings.
~ith reference to the adsorption system shown in Fig. 1, a fermentation beer containing about 11 percent ethanol by volume is transferred periodically from fermentation tanks 10 and 12 to holding tank 14 though lines 16 and 18 respectively. The transfer of fermentation beer is controlled by valves 20 and 22. The fermentation beer is fed into the system at a rate of 5400 gallons per hour through line 24 and pump 26 and thereafter through line 28 and heater 30 where the temperature is raised to about 35 to 65C. The fermentation beer enters the top of stripping column 34 from line 32. The strippiny column 34 is heated to a temperature of 35C to 65C to enhance ethanol stripping. Nitrogen, the stripping gas that will be used in stripping ethanol from the fermentation beer, enters the bottom side of stripping column 34 through line 36 essentially ethanol-free and at a temperature to maintain the desired column conditions. The nitrogen stripping gas is introduced into the system through line 38. Line 38 also serves as the means to introduce make-up nitrogen stripping gas into the operating system as required~ The flow of stripping gas is dependent on the column temperature and pressure and ranges from 100 to 1200 standard cubic feet per hour. An optimization between compression and thermal energy determines the exact column conditions. As the fermentation beer flows downward in stripping column 34, the ethanol is stripped by the nitrogen and the essentially ethanol-free fermentation beer is removed from the bottom of stripping column 34 through line 40 and can be sent for recovery of dissolved solids.
$~5~i8 The nitrogen stripping gas enriched with ethanol is removed from the top of stripping column 34 through line 42 and heater 44 and thereafter through line 46 into the top of adsorption column 48. The nitrogen stripping gas enriched with ethanol can be heated by heater 44 to adjust tbe relative satura~ion ~p/po) thereof so as to minimize the coadsorption of water on the ethanol selective adsorbent mass~ The adsorption column 48 contains an adsorbent mass of 1~8 inch diameter extrudates of silica-bonded F-silicalite adsorbent within the scope of U.S. Patent 4,073,865 which, under the process conditions utilized herein, is capable of adsorbing ethanol from the ethanol enriched nitrogen stripping gas. As the nitrogen stripping gas enriched with ethanol passes downward through the adsorption mass contained in adsorption column 48, the ethanol is adsorbed by the silica-bonded F-silicalite adsorbent and the nitrogen stripping gas depleted of ethanol is removed from adsorption column 48 through line 50 and recycled back to the stripping column 34 through blower 52 and line 36.
The nitrogen stripping gas depleted of ethanol is recirculated to stripping column 34 utilizing a compressor to make up the pressure drop through the nitrogen stripping gas loop. When the adsorbent mass is saturated with ethanol and ethanol begins to break through into the effluent through line 50, the adsorption column 48 is temporarily removed from service and regenerated. A freshly regenerated adsorption column replaces the ethanol satura~ed adsorption column to continue the adsorption of ~ ethanol from the nitrogen s~ripping ga~ enriched with ethanol.
~s~s~
Regeneration of the ethanol saturated adsorption column can be accomplished by a thermal-swing m~thod. The selection of a particular regeneration method depends on the relative energy S efficiency of each method and the selectivity and capacity of the adsorbent mass for ethanol. The thermal-swing regeneration method is accomplished using nitrogen as a purge gas which is introduced into the system through line 54. Line 54 also serves as the means to introduce make-up purge gas into the operating system as required. The purge gas is preferably the same as the stripping gas.
The nitrogen purge gas is forced at a pressure of 40 psia by blower 56 through valve 58 and heater 62 where its temperature is raised to 175C. The nitrogen purge gas is forced through valve 58 when valve 60 is closed and through valve 60 when valve 58 is closed. Valves 58 and 60 control the flow of nitrogen purqe gas to heater 62 and thereby control the sequence of heating or cooling adsorption column 48. The heated nitrogen purge gas passes through line 64 into the bottom of adsorption column 48 in a flow direction countercurrent to the direction of flow of the stripping gas enriched with ethanol thereinto. The action of the nitrogen purge gas stream is to ~lush the void space between the adsorbent pellets and to desorb the ethanol from the adsorbent mass. The adsorbent mass is heated to a temperature of 50C to 150C above the adsorption temperature by means oE the heated nitrogen purge gas during regeneration of adsorption column 48.
When essentially all of the ethanol is desorbed, the adsorbent mass in adsorption column 48 is cooled back to the adsorption conditions previously D 1325a ) s~
establishedO The nitrogen purge gas enriched wi~h e~hanol is removed from adsorption column 48 through line 66 and is passed through cooler 68 where the temperature is lowered to 5C and ethanol is condensed and collected in knock-out ~0 at 180~ to 195-proof. The 180- to 195-proof ethanol is removed ~rom the system through line 72 and the nitrogen purge ~as depleted with ethanol is passed from knock-out 70 through line 74 and recycled back to blower 5~ where the essentially ethanol-free nitrogen purge gas can be ei~her heated or unheated before entering adsorption column 4A by controlling valves 58 and 60 as described previously. The 180-to 195-proof ethanol product can be dehydrated with azeotropic distillation or by the adsorptive heat rise process described in Canadian Serial No.
40184~.5, file~ Anril 2~, 1982 to -obt~in essentiallv 200-proof ethanol.
Alternatively, the nitrogen purge gas enriched with ethanol is removed from adsorption column 48 through line 66 and is partially cooled in cooler 76 before passing directly into the top of dehydration column 78 containing a bed of desiccant material consisting of Type 3A zeolite to remove essentially all o~ the remaining water which was coadsorbed in the previou~ step. The dry nitrogen purge gas enriched with ethanol is removed from dehydration column 78 through line 80 and is passed through cooler 82 wherein the temperature is lowered to 0C and ethanol is condensed andl collected in knock~out B4 to recover essen~ially 200-proo~
ethanol plus other volatile organics such as aldehydes and fusel oils which were also ~tripped from the fermentation beer and coadsorbed by the ~2 adsorbent mass. The essentially 200-proof ethanol is removed from the system through line 86 and the nitrogen purge gas depleted with ethanol is passed from knock-out 84 and recycled back into the operational system as described aboveO
The dehydration column 78 can also be regenerated using the thermal swing method in a manner slmilar to regeneration of adsorption column 48 using nitrogen purge gas. Heated nitrogen purge gas is passed through the desiccant material bed of dehydration column 7~ to desorb water which is removed from the operational system by a condenser and knock-out arrangement described previously in regard to removing ethanol from the systemO When the bed of desic~ant material is saturated with water and water begins to break through into the effluent through line 80, the dehydration column 78 is temporarily removed from service and regenerated. A freshly regenerated dehydration column replaces the water saturated dehydra~ion column to continue the adsorption of water from the nitrogen stripping gas enriched with ethanol.
Although this invention has been described with respect to a number of details, it is not intended that this invention should be limited thereby. The examples which follow are intended solely to illustrate the embodiments of this invention which to date have been determined and are not intended in any way to limit tbe scope of and the intent of this invention.
As used in the examples appearing hereinafter, the following designations, terms and abbreviaions have the indicated meanings:
psig: pounds per s~uare inch gauge.
i !
i8 ~: partial vapor pressure of ethanol or water po vapor pressure of pure ethanol or pure water at a specified temperature.
relative saturation (p/po): refers to the partial vapor pressure of ethanol or water in a ratio relationship with the vapor pressure of pure ethanol or pure water at a specified temperature.
loading~ refers to the amoun~ of ethanol or water adsorbed into a specified amount of adsorbent material and can be expressed by the following formula:
Adsorbent ~oading = Wt- Adsorbate x lO0 ~ Wt%.
- Wt. Adsorbent ~xample 1 Into a laboratory saturator/bubbler device was added a dilute aqueous mixture containing lO
percent by weight ethanol at ambient temperature and 20 psig. The saturator/bubbler device was attached to an adsorption column constructed of l/2-inch Schedule 40 stainless-steel plpe containing 65 grams of alumina-bonded silicalite adsorbent within the scope of U.S. Patent 4,061,724 and having a 16 x 40 mesh particle size. Nitrogen gas was used as the stripping gas to vaporize ethanol from the dilute a~ueous mixture. Nitrogen gas was buhbled into the dilute aqueous mixture contained in the saturator/bubbler device and effluent nitrogen gas from the saturator/bubbler device was saturated with both water and ethanol vapors. Gas chromatographic analysis of this effluent nitrogen gas enriched with water vapor and ethanol vapor showed about 0O6 percent by weight ethanol and about 0.8 percent by weight water. The ef~luent nitrogen gas enriched i;25~il
CONCENTRATION OF ETHANOL FROM DILUTE
AQUEOUS MIXTURES THEREOF
Brief Summary of the Invention Technical Field _ This invention i5 directed in general to a vapor phase adsorption process for selectively adsorbing at least one organic molecular species present in a minor amount from a dilute aqueous mixturs using a hydrophobic adsorbent mass. ~he hydrophobic adsorbent mass consists of a molecular sieve material having greater selectivity for at least one organic molecular species than for water.
More particularly, this invention is directed to a vapor phase adsorption process or removing and concentrating ethanol from water-ethanol mixtures such as fermentation beer which contains typically from about 8 to about 12 percent by weight ethanol utilizing a molecular sieve material adsorbent such as silica bonded F-silicalite or alumina-bonded silicalite. As a viable alternative to the preparation of ethanol from petroleum-bas~d ethylene, the preparation o~ concentra~ed ethanol from fermentation beer by the vapor phase adsorption separation process oE the present invention is especially important or supplementing world energy and chemical needs.
Background Art ~thanol in dilute aqueous mixtures can be pro~uced by fermentation processes utilizing a ~s~s~
variety of agricultural and biomass raw materials ~uch as grains, molasses, sugar cane juice, miscellaneous fruits, wood and the like. However, the large propoxtion of industrial ethanol produced in the world is made from petroleum-based ethylene.
In view of the limited petroleum resources available, the production of ethanol from renewable raw material resources by fermentation processes to supplement the world energy and chemical needs is understandably of major importance. It is anticipated that in the near future a significant amount of ethanol for fuel and chemicals will be derived from fermentation processes.
In a conventional fermentation process, yeast and other microorganisms convert sugars to alcohol and carbon dioxide. Since sugar concentrations in excess of about 16 weight percent typic~lly inhibit the growth of yeast cells in the initial stages of fermentation, dilution of the s~arting sugar concentration with water is necessary to properly control the sugar concentration and permit the normal growth of yeast cells. The diluted sugar concentrations result in lower ethanol concentrations and hence high energy requirements for distillation and purification of ethanol. It has also been demonstrated that ethalnol concentrations greater than about 10 weight percen~
in fermentation beer result in a phenomenon known as "feedback inhibition" which inhibits further ethanol production. The maximum ethanol concentration which is typically attainable after about 36 hours of conventional fermentation is usually about 8 to 12 weight percent. The major byproducts of the --fermentation process in addition to carbon dioxide .
s~
are dissolved and undissolved (distiller's dry grain) solids, aldehydes, ketones and fusel oils.
The presence of ethanol in a minor amount in dilute aqueous mixtures such as fermentation beer obtained from the fermentation process requires large amounts of heat energy to distill and purify the ethanol therefrom.
Ethanol is conventionally recovered from dilute aqueous mixtures such as fermentation beer by traditional distillation processes. The fermentation beer containing from about 8 to about 12 weight percent ethanol and byproducts is fed into a still where ethanol is removed as overhead in a concentration ranging from about 100- to about l90-proof. The bo~toms from the still contain dissolved and undissolved solids and the byproducts are usually taken off as side draws. The concentrated ethanol, nominally l90-proof, can be further upgraded to nearly anhydrous l99-proof ethanol needed for gasohol by azeotropic distillation. However, as previously mentioned, the conventional distillation process for recovering and concentrating ethanol from dilute aqueous mixtures such as fermentation beer is very energy intensive.
Large amounts of heat energy are required because the major component of fermentation beer, i.e., water, is being heated to recover a minor component of fermentation beer, i.e., ethanol. Also, azeotropic distillation is an energy-intensive operation. Energy consumptions from about 30,000 to about 40,000 BTU per gallon of anhydrous ethanol are not uncommon for typical distillation processes.
Since the cost of producing ethanol frcm agricultural and biomass raw materials depends not ~, ;2S~
only on the fermentation of the raw materials but also on the recovery and purification of ethanol produced by the fermentation process, higher energy consumptions during distillation and purification result in higher ethanol-per-gallon cost and can also contribute towards offsetting the energy balance of ethanol production by fermentation processes for fuel and chemical needs.
There have been various attempts to develop lower cost processes for recovering and concentrating ethanol from fermentation beer. It has been previously found that ethanol can be recovered from dilute fermentation beers by a liquid phase adsorption process utilizing certain adsorbent materials such as activated carbons, ion exchange resins and molecular sieves. TheSe adsorbent materials can selectively adsorb either water from aqueous ethanol or ethanol from dilute aqueous solutions. In carrying out the liquid phase adsorption processes, a fermentation beer is usually pumped through a packed adsorbent bed wherein either the liquid ethanol or water is adsorbed on the adsorbent material. If ethanol is adsorbed on the adsorbent material, ~he adsorbent material is typically regenerated with a purge gas in which concentrated ethanol is recovered therefrom. If water is adsorbed on the adsorbent material, ethanol is recoversd in the effluent from the adsorbent material. However, such liquid phase adsorption processes are usually not very efficient. The main drawbacks of liquid phase adsorption processes are poox ethanol recovery due to entrapment of part of the dilute aqueous mixture, i.e., fermentation beer, between and within particles of the adsorbent 52S~3 material and lower ethanol product purity due to residual water being retained in the ethanol product. Another major and perhaps more critical drawback is the distinct possibility that the solids contained in the`liquid fermentation beer can plug up voids in the packed adsorbent bed and cause substantial mechanical problems~
The present invention consisting of a vapor phase adsorption separation process provides a practical and efficient low energy process for recovering and concentrating at least one organic molecular species such as ethanol from a dilute aqueous mixture such as fermentation beer without encountering any of the drawbacks associated with liquid phase adsorption processes. According to the present invention, a stripping gas enriched with ethanol vapor and water vapor is passed through an adsorbent material such as silicalite described in U.S. Patent 4,0blj~24 or F-silicalite described in ~ U.S. Patent 4,073,865, both assigned to Union Carbide Corporation. Ethanol in the vapor phase is selectively adsorbed by the adsorbent material which has a greater selectivity for ethanol than for water. The adsorption of ethanol vapor is conducted at a temperature and pressure which prevents the capillary condensation of water in the adsorbent material. The adsorbed ethanol is removed from the adsorbent material by a non-sorbable heated purge ~as which is subsequently cooled to condense ethanol. Essentially no liquid phase is present in the ethanol adsorption step of the highly desirable adsorption separation process of this invention.
Various liquid phase adsorption processes and the drawbacks inheEent therewith are less desirable for concentrating ethanol from dilute aqueous mixtures such as fermentation beer.
U.S. Patent 4,277,635 disclose~ a process for concentrating ethanol from aqueous solutions thereof, such as fermentation beer containing from 6 to 13~ by weight ethanol. The ethanol is remoYed from the fermentation beer by liquid adsorption on a molecular sieve material such as silicalite. The patent states that residual fermentation beer remaining in the adsorption column can be removed by passing highly concentrated ethanol through the adsorption column.
U.SO Patent 4,061,724 and U.S n Patent 4,073,865, both assigned to Vnion Carbide Corporation, describe crystalline silica compositions designated herein as silicalite and F-silicalite respectively, which can ~e used as the adsorbent mass in the pre~ent invention. These patents describe the hydrophobic/organophilic character of both silicalite and F-silicalite which permits their use in selectively adsorbing organic materials from water either in the liquid or vapor phase.
U.SO Patent 3,732,326 relates to a method of selectively sorbing a compound of generally low polarity such as various hydrocarbons in admixture with a compound of the same or greater polarity such as water by passing the mixture over a crystalline aluminosilicate having a silica/alumina mole ratio of at least 35 such as mernbers of the amily of ZSM-5 zeolites.
However, none of these references discloses or suggests the vapor phase adsorption separation process as claimed in the instant invention or ~5~5~
removing and concentrating at least one organic molecular species such as ethanol present in a minor amount from a dilute aqueous mixture such as fermentation beer utilizing a molecular sieve material adsorbent.
Disclosure of Invention The present invention is directed to an adsorption separation process which comprises:
(a) vaporizing water and at least one organic molecular species contained in a dilute aqueous mixture by contacting the dilute aqueous mixture with an essentially non-sorbable stripping gas (b) passing the stripping gas enriched with water and at least one organic molecular species into a fixed adsorption zone containing a hydrophobic adsorbent mass consisting essentially of a molecular sieve material having selectivity for at least one organic molecular species (c) adsorbing at least one organic molecular species into the adsorbent mass at a temperature and pressure which prevents capillary condensation of the water (d) terminating the flow of stripping gas enriched with water and at least one organic molecular species into the adsorp~ion bed prior to breakthrough of at least one organic molecular species from the effluent end of said adsorption bed;
(e) removing at least one adsorbed organic molecular species by heating the adsorbent mass by passing an essentially non-sorbable hea~ed purge gas through the adsorbent mass countercurrent to such enriched strippin~ gas, which purge gas can be the same gas used for stripping the dilute aqueous mixture in step (a);
If) condensing at least one organic molecular species by cooling the purge gas enriched with at leas~ one organic molecular species; and (g) recovering at least one organic molecular species in a concentrated form.
The present invention is also directed to an adsorption separation process as described in steps (a~ through (g~ above further comprising cooling the adsorbent mass until the ~empera~ure is essentially the same as at the beginning of step (b) and repeating steps (a) through (g) until a predetermined amount of at least one organic molecular species is recovered in a concentrated form from the dilute aqueous mixture.
More particularly, the present invention is directed to an adsorption separation process which comprises:
(a) vaporizing water and ethanol contained in a fermentation beer by contacting the fermentation beer with an essentially non-sorbable stripping gas such as nitrogen, carbon dioxide helium or argon;
(b) passing the stripping gas enriched with water and ethanol into a fixed adsorption zone containing a hydrophobic adsorbent mass con~isting essentially of a silica-bonded F-silicalite adsorbent or an alumina-bonded silicalite adsorbent;
(c) adsorbing ethanol into the adsorbent mass at a temperature and pressure which prevents capillary condensation of the water7 ~d) terminating the flow of stripping gas enriched with water and ethanol into the adsorption bed prior to breakthrough of ethanol from - the effluent end of the adsorption bed;
(e) removing ethanol by heating the adsorbent mass by passing an essentially non-sorbable heated purge gas such as nitrogen, carbon dioxide, helium or argon ~hrough the adsorbent mass countercurrent to such enriched stripping gas (f) condensing ethanol by cooling the purge gas enriched with ethanol;
~g) recovering ethanol in a co~centrated form;
(h) cooling the adsorbent mass until the temperature is essentially the same as at the beginning of step (b); and ~i) repeating steps (a) through ~h) until a predetermined amount of ethanol is recovered from the fermentation beer.
Brief Description of Drawings The present invention is further described with reference to the accompanying drawings in which:
Fig. 1 is a schematic flowsheet of an illustrative embodiment for carrying out the process of this invention.
Fig. 2 illustrates an adsorption step breakthrough profile of ethanol and water concentrations in the effluent from the adsorption column a~ 125F using alumina-bonded silicalite adsoebent as determined by gas chromatographic analysis.
Fig, 3 illustra~es a regeneration step profile of ethanol and water concentrations in the ~ ~3258 1~
nitrogen gas regeneration effluent at 200~ ~s determined by gas chromatographic analysis.
Fig. 4 illustrates a profile of the dependency of water and ethanol adsorption loadings on their relative stauration (p/po) values at adsorption temperatures ranging from about 75F to about 150F and using alumina-bonded silicalite adsorbent.
Fig. 5 illustrates an adsorption step breakthrough profile of ethanol and water concentrations in the effluent from the adsorption column at 75F using silica-bonded F-silicalite adsorbent as determined by gas chromatographic analysis.
Detailed_Description A dilute aqueous mixture such as fermentation beer containing from about 8 to about 12 percent by weight ethanol can be stripped of ethanol by any suitable stripping procedure. For example, with reference to Fig. 1, a stripping gas can be charged into the bottom of an external packed-bed stripping column wherein fermentation beer is flowing downward to give a stripping gas enriched with ethanol vapor and some water vapor.
After ethanol and some water are stripped from the fermentation beer, the enriched stripping gas is removed f~om the top of the stripping column and essentially ethanol-free fermentation beer is removed from the bottom of the column. The stripping column temperature and pressure are not narrowly critical and can vary over a wide range.
The temperature in the stripping column can range from about ambient to about 200F and the pressure ~s~
in the stripping column can range from abut 15 psig to about 200 psig. The flow of stripping gas is dependent on the stripping col~mn temperature and pressure and the liquid, i.e., fermentation beer, feed rate. Alternatively, in the absence of an external packed bed stripping column, a stripping gas may be bubbled through the fermentation tanks or holding tank ~o strip ethanol from the fermentation beer.
The stripping gas used in the vaporizing step (a) of this adsorption separation process can be any vapor phase compound which does not appreciably react with the dilute aqueous mixture, e.g., fermented beer, constituents under the imposed conditions~ Also, the stripping gas should not be harmful to the adsorbent mass and should not be appreciably adsorbed by the adsorbent mass. The non-adsorbability of the stripping gas can be due either to molecular size exclusion or to a weak adsorptive attraction between it and the adsorbent massO The preferred strippiny gas for use in the adsorption ~eparation process of this invention is selected from the group consisting of nitrogen, carbon dioxide, helium and argon. The stripping gas can also be the off-gases generated by the fermentation process which can consist of essentially carbon dioxide enriched with some ethanol. For example, with reference to Fig. 1, the off-gases from the battery of fermentation tanks may be used as the stripping gas in the process of this invention~ The stripping gas can be recycled for further stripping in vaporizing step (a) described above after passing through the adsorption bed during adsorbing step ~c) also described above.
~S~5~
The dilute aqueous mixture feedstock can be any mixture of water and one or more organic molecular species. Preferred feedstocks are those obtained by ermentation processes, i.e., fermentation beers, utilizing a variety of agricultural and biomass raw materials such as grains, molasses, sugar cane juice, miscellaneous fruits, wood and the like. P~rticularly preferred dilute aqueous mixture feedstocks are mixtures of water and one or more organic molecular species containing from 2 to about 6 carbon atoms inclusive. ~n especially preferred dilute aqueous mixture feedstock is one in which the organic molecular species is a primary alcohol containing from 2 to about S carbon atoms inclusive, most pre~erably ethanol and/or isopropanol. A
fermentation beer containing from about 8 to about 12 percent by weight ethanol is the most preferred dilute aqueous mixture or use in the proc~ss of this invention.
The stripping gas enriched with at least one organic molecular species vapor, e~g., ethanol vapor, and water vapor is passed into any suitable fixed adsorption zone containing a hydrophobic adsorbent mass consisting essentially of a molecular sieve material. The particular species of molecular sieve material employed in the present invention is not a narrowly critical factor. In all event, however, it should be capable of adsorbing from 5 to i 30 50 times more organic molecular species, e.g., ethanol, than water under the process conditions of temperature and pressure, and ~o subs~antially exclude from adsorption essentially all of the other constituents of the dilu~e aqueous mixture feedstock , ;2S~ ~
1~
under those conditions. The preferred adsorbent mass for use in the process of this invention includes substantially hydrophobic molecular sieve materials such as silica-bonded F-silicalite described in U.S. Patent 4,073,865, alumina-bonded silicalite described in U.S. Patent 4,061,724 and Ultrahydrophobic Zeolite Y (U~P-Y) described in copending Canadian Patent No. 1,131,195, September 7, 1982. Other suitable memb~rs of the high silica adsorbent group may also be used in the process of this invention. With reference to ~ig. l, the stripping gas enriched with ethanol vapor and water vapor is passed through ~he adsorbent mass con~ained in the adsorption column, ethanol is adsorbed by the adsorbent mass and the stripping gas depleted of ethanol is removed from the adsorption column. Certain organic byproducts ~uch as aldehydes and fusel oils may also be adsorbed ln minor amounts into the adsorbent mass.
If the stripping gas is the o~f-gases generated by the fermentation process which can consist of ~ essentially carbon dioxide enriched with ~ome - ethanol as describea above, the adsorbent ma-~s can further adsorb ethanol vapor which would be naturally lost and vented as a byproduct ~rom ~he fermentation process, and thereby improve the overall e~ficiency o ethanol recovery from the fermentation process.
The temperature and press;ure conditions for the adsorption step must be ~elected to maintain the ~tripping gas enriched wlth at least one organic 201ecular specie~ vapor, e.g., ethanol vapor, and water vapor in the vapor phase ~nd prevent capillary condensation o~ the organic constituent, e.g., .` ~ ' ' ' , i ,, _ , . . .
~52~
1~
ethanol, and water in the adsorption bedu Capillary condensation contributes to poor ethanol recovery due to entrapment of liquid water and ethanol preventing further adsorption of ethanol vapor and also lower ethanol product purity due to residual water being retained in the adsorbent mass and hence the regenerated ethanol product. It is preferred that the stripping gas enriched with at least one organic molecular species, e.g., ethanol, and water passing into the adsorption bed and the adsorption bed itself be at a temperature within the range of from about ambient to abou 200F and at an appropriate corresponding pressu~e within the range of from about 1 atmosphere (absolute) up to about lS 100 psia. It is preferred that steps (b) and (c) of the adsorption separation process described above be conducted at a tempera~ure of from about 25F to about 50F higher than the temperature of vaporizing step (a~ also described above in order to decrease the relative saturation (p/po) of water in the enriched stripping gas passing into and adsorbing into, in part, the fixed adsorption bed containing alumina-bonded silicalite adsorbent described in U.S. Patent 4,061,724. Heating the enriched stripping gas adjusts the relative saturation (p/po) of ethanol and water 50 as to minimize the coadsorption of water on the ethanol selective adsorbent mass. This is more fully illustrated in working Example 1 hereinbelow. The relative saturation values (p/po) of water and ethanol and the extent or amount of water and ethanol loadings onto the adsorbent mass are different for various adsorbent materials. For example, as illustrated in working ~amp~e 2 hereinbelow, when using silica-bonded F-silcalite described in U.S. Patent 4,073,865 as the adsorbent mass, it is not necessary to heat the enriched stripping gas to adjust the relative saturation (p/po) of ethanol and water because essentially no coadsorption of water occurs on the silica-bonded F-silicalite adsorbent.
Accordingly, the stripping gas enriched with ethanol and water may optionally be heated to adjust the relative saturation (p/po) of water and ethanol depending on the particular adsorbent mass utilized in the process of this invention.
Immediately prior to or after the initial breakthrough of the organic molecular species, e.g., ethanol, from the adsorption bed, regeneration of the adsorbent mass with a heated non-sorbable purge gas in commenced in a countercurrent direction with respect to the directional flow of the enriched stripping gas through the adsorption bed. Ethanol is removed or desorbed from the adsorbent mass by the heated non-sorbable purge gas. During the countercurrent purge-desorption step, the temperature of the non-sorbaable heated purge gas entering the adsorption bed can range from about 100°F to about 700°F, and is preferably from about 100°F ti abiyt 300°F higher than the temperature of the enriched stripping gas stream during the adsorption step. The countercurrent purge-desorption step can be carried out in any suitable manner, for example, either in a conventional open-purge or closed loop manner.
Regeneration of the adsorption bed can be accomplished by using either conventional thermal-swing or pressure-swing desorption. After desorption of the organic molecular species, e.g., S2~
ethanol, from the adsorbent mass, the purge gas enriched with ethanol is removed and the adsorbent mass is cooled until the temperature is essentially the same as at the beginning of the vaporizing step (a) described aboveO The adsorbent mass can again be used to adsorb an organic molecular species, e.g., ethanol, in concentrated form from the dilute aqueous mixture.
The purge gas utilized in the countercurrent purge-desorption step is preferably the same gas used for stripping the dilute agueous mixture in vaporizing step (a) described above. The purge gas can be any vapor phase compound which is not harmful to the adsorbent mass and does not appreciably react with any of the enriched stripping gas constituents under the imposed conditions. The purge gas is also essentially non-sorbable in the adsorbent mass. The non adsorbability of the purge gas can be due either to molecular size exclusion or to weak adsorptive attraction between it and the adsorption mass. The preferred purge gas for use in the adsorption separation process of this invention is selected from the group consisting of nitrogen, carbon dioxide, helium and argon. The purge gas can also be the off-gases generated by the fermentation process which can consist of essentially carbon dioxide enriched with some ethanol. For example, with reference to Fig. 1, the off-gases from the battery of fermentation tanks may be used as the purge gas in the process of this invention. The purge gas can be recycled for further desorption after the organic molecular species and minor amounts of water are condensed therefrom.
The purge gas enriched with ethanol and some water can be dried by any suitable procedure \ ~9s~s~
such as by passing the gas through a dehydration ~olumn containing a bed of desiccant material such as Type 3A zeoli~e to remove e~sentially all of the : remaining water coadsorbed in the previous step.
~ha purge gas enriched wi~h ethanol is then cooled, for example in a condenser/k~ock-out arangement, to condense at least one organic molecular species, e.g., ethanol, which is recovered in a concentrated form. If the purge gas is the off-gases generated by the fermentation process which can consist of essentially c~rbon dioxide enriched with some ethanol as desc~ibed above, additional ethanol vapor can further be recovered in a concentrated form which would be naturally lost and vented as a byproduct from thefermentation p~ocess, and thereby improve the overall efficiency of ethanol recovery from the fermentation process. The concentration of ethanol recovered from the process of this invention is dependent on several factor~, prin~ipal amon~
which is the relative selectivity of the adsorbent mass for ethanol. Ethanol is recovered from the process of this invention in a concentraPed form, for example, from about 180- to about 195-proo~. If the purge gas enriched wi~h ethanol and some water i~ dried before condensing, essentially 200-proof ethanol product can be obtained. The 180- to 195-proof ethanol product ~an be further dehydrated by azeotropic distillation or by t:he adsorptive heat rise process described in Canadian Serial No.
401843.5, filed April 28, 1982 to obtain essentiallY
200-proof ethanol.
The proce~s o~ this invention is illustrated by the following speciic embodiment described wlth reference to Fig~ 1 of the drawings.
~ith reference to the adsorption system shown in Fig. 1, a fermentation beer containing about 11 percent ethanol by volume is transferred periodically from fermentation tanks 10 and 12 to holding tank 14 though lines 16 and 18 respectively. The transfer of fermentation beer is controlled by valves 20 and 22. The fermentation beer is fed into the system at a rate of 5400 gallons per hour through line 24 and pump 26 and thereafter through line 28 and heater 30 where the temperature is raised to about 35 to 65C. The fermentation beer enters the top of stripping column 34 from line 32. The strippiny column 34 is heated to a temperature of 35C to 65C to enhance ethanol stripping. Nitrogen, the stripping gas that will be used in stripping ethanol from the fermentation beer, enters the bottom side of stripping column 34 through line 36 essentially ethanol-free and at a temperature to maintain the desired column conditions. The nitrogen stripping gas is introduced into the system through line 38. Line 38 also serves as the means to introduce make-up nitrogen stripping gas into the operating system as required~ The flow of stripping gas is dependent on the column temperature and pressure and ranges from 100 to 1200 standard cubic feet per hour. An optimization between compression and thermal energy determines the exact column conditions. As the fermentation beer flows downward in stripping column 34, the ethanol is stripped by the nitrogen and the essentially ethanol-free fermentation beer is removed from the bottom of stripping column 34 through line 40 and can be sent for recovery of dissolved solids.
$~5~i8 The nitrogen stripping gas enriched with ethanol is removed from the top of stripping column 34 through line 42 and heater 44 and thereafter through line 46 into the top of adsorption column 48. The nitrogen stripping gas enriched with ethanol can be heated by heater 44 to adjust tbe relative satura~ion ~p/po) thereof so as to minimize the coadsorption of water on the ethanol selective adsorbent mass~ The adsorption column 48 contains an adsorbent mass of 1~8 inch diameter extrudates of silica-bonded F-silicalite adsorbent within the scope of U.S. Patent 4,073,865 which, under the process conditions utilized herein, is capable of adsorbing ethanol from the ethanol enriched nitrogen stripping gas. As the nitrogen stripping gas enriched with ethanol passes downward through the adsorption mass contained in adsorption column 48, the ethanol is adsorbed by the silica-bonded F-silicalite adsorbent and the nitrogen stripping gas depleted of ethanol is removed from adsorption column 48 through line 50 and recycled back to the stripping column 34 through blower 52 and line 36.
The nitrogen stripping gas depleted of ethanol is recirculated to stripping column 34 utilizing a compressor to make up the pressure drop through the nitrogen stripping gas loop. When the adsorbent mass is saturated with ethanol and ethanol begins to break through into the effluent through line 50, the adsorption column 48 is temporarily removed from service and regenerated. A freshly regenerated adsorption column replaces the ethanol satura~ed adsorption column to continue the adsorption of ~ ethanol from the nitrogen s~ripping ga~ enriched with ethanol.
~s~s~
Regeneration of the ethanol saturated adsorption column can be accomplished by a thermal-swing m~thod. The selection of a particular regeneration method depends on the relative energy S efficiency of each method and the selectivity and capacity of the adsorbent mass for ethanol. The thermal-swing regeneration method is accomplished using nitrogen as a purge gas which is introduced into the system through line 54. Line 54 also serves as the means to introduce make-up purge gas into the operating system as required. The purge gas is preferably the same as the stripping gas.
The nitrogen purge gas is forced at a pressure of 40 psia by blower 56 through valve 58 and heater 62 where its temperature is raised to 175C. The nitrogen purge gas is forced through valve 58 when valve 60 is closed and through valve 60 when valve 58 is closed. Valves 58 and 60 control the flow of nitrogen purqe gas to heater 62 and thereby control the sequence of heating or cooling adsorption column 48. The heated nitrogen purge gas passes through line 64 into the bottom of adsorption column 48 in a flow direction countercurrent to the direction of flow of the stripping gas enriched with ethanol thereinto. The action of the nitrogen purge gas stream is to ~lush the void space between the adsorbent pellets and to desorb the ethanol from the adsorbent mass. The adsorbent mass is heated to a temperature of 50C to 150C above the adsorption temperature by means oE the heated nitrogen purge gas during regeneration of adsorption column 48.
When essentially all of the ethanol is desorbed, the adsorbent mass in adsorption column 48 is cooled back to the adsorption conditions previously D 1325a ) s~
establishedO The nitrogen purge gas enriched wi~h e~hanol is removed from adsorption column 48 through line 66 and is passed through cooler 68 where the temperature is lowered to 5C and ethanol is condensed and collected in knock-out ~0 at 180~ to 195-proof. The 180- to 195-proof ethanol is removed ~rom the system through line 72 and the nitrogen purge ~as depleted with ethanol is passed from knock-out 70 through line 74 and recycled back to blower 5~ where the essentially ethanol-free nitrogen purge gas can be ei~her heated or unheated before entering adsorption column 4A by controlling valves 58 and 60 as described previously. The 180-to 195-proof ethanol product can be dehydrated with azeotropic distillation or by the adsorptive heat rise process described in Canadian Serial No.
40184~.5, file~ Anril 2~, 1982 to -obt~in essentiallv 200-proof ethanol.
Alternatively, the nitrogen purge gas enriched with ethanol is removed from adsorption column 48 through line 66 and is partially cooled in cooler 76 before passing directly into the top of dehydration column 78 containing a bed of desiccant material consisting of Type 3A zeolite to remove essentially all o~ the remaining water which was coadsorbed in the previou~ step. The dry nitrogen purge gas enriched with ethanol is removed from dehydration column 78 through line 80 and is passed through cooler 82 wherein the temperature is lowered to 0C and ethanol is condensed andl collected in knock~out B4 to recover essen~ially 200-proo~
ethanol plus other volatile organics such as aldehydes and fusel oils which were also ~tripped from the fermentation beer and coadsorbed by the ~2 adsorbent mass. The essentially 200-proof ethanol is removed from the system through line 86 and the nitrogen purge gas depleted with ethanol is passed from knock-out 84 and recycled back into the operational system as described aboveO
The dehydration column 78 can also be regenerated using the thermal swing method in a manner slmilar to regeneration of adsorption column 48 using nitrogen purge gas. Heated nitrogen purge gas is passed through the desiccant material bed of dehydration column 7~ to desorb water which is removed from the operational system by a condenser and knock-out arrangement described previously in regard to removing ethanol from the systemO When the bed of desic~ant material is saturated with water and water begins to break through into the effluent through line 80, the dehydration column 78 is temporarily removed from service and regenerated. A freshly regenerated dehydration column replaces the water saturated dehydra~ion column to continue the adsorption of water from the nitrogen stripping gas enriched with ethanol.
Although this invention has been described with respect to a number of details, it is not intended that this invention should be limited thereby. The examples which follow are intended solely to illustrate the embodiments of this invention which to date have been determined and are not intended in any way to limit tbe scope of and the intent of this invention.
As used in the examples appearing hereinafter, the following designations, terms and abbreviaions have the indicated meanings:
psig: pounds per s~uare inch gauge.
i !
i8 ~: partial vapor pressure of ethanol or water po vapor pressure of pure ethanol or pure water at a specified temperature.
relative saturation (p/po): refers to the partial vapor pressure of ethanol or water in a ratio relationship with the vapor pressure of pure ethanol or pure water at a specified temperature.
loading~ refers to the amoun~ of ethanol or water adsorbed into a specified amount of adsorbent material and can be expressed by the following formula:
Adsorbent ~oading = Wt- Adsorbate x lO0 ~ Wt%.
- Wt. Adsorbent ~xample 1 Into a laboratory saturator/bubbler device was added a dilute aqueous mixture containing lO
percent by weight ethanol at ambient temperature and 20 psig. The saturator/bubbler device was attached to an adsorption column constructed of l/2-inch Schedule 40 stainless-steel plpe containing 65 grams of alumina-bonded silicalite adsorbent within the scope of U.S. Patent 4,061,724 and having a 16 x 40 mesh particle size. Nitrogen gas was used as the stripping gas to vaporize ethanol from the dilute a~ueous mixture. Nitrogen gas was buhbled into the dilute aqueous mixture contained in the saturator/bubbler device and effluent nitrogen gas from the saturator/bubbler device was saturated with both water and ethanol vapors. Gas chromatographic analysis of this effluent nitrogen gas enriched with water vapor and ethanol vapor showed about 0O6 percent by weight ethanol and about 0.8 percent by weight water. The ef~luent nitrogen gas enriched i;25~il
2~
with water vapor and ethanol vapor was passed into the adsorption column having a temperature of 125F
and at a rate of 3.6 standard cubic feet per hour.
The adsorption was allowed to continue until full breakthrough occurred as indicated when the effluent water and ethanol concentrations from the adsorption column became equal to the corresponding concentrations of water and ethanol in the enriched nitrogen gas which entered the adsorption column.
The water and ethanol concentrations in the effluent nitrogen gas from the adsorption column were also determined by gas chromatographic analysis.
Following the adsorption step, the alumina-bonded silicalite adsorbent contained in the adsorption column was regenerated by the thermal swing method at 200F using nitrogen gas which was passed through the adsorption column at a rate of 3.7 standard cubic feet per hour. The water and ethanol concentrations in the nitrogen gas regeneration effluent were determined by gas chromatographic analysis.
Fig. 2 illustrates an adsorption step breakthrough profile of ethanol and water Goncentrations in the effluent from the adsorption column at 125F as determined by gas chromatographic analysis. As can be seen from Fig. 2, water i5 the first component to break through into the adsorption column effluent after about 1 hour o operation followed by the more strongly adsorbed ethanol after about 3 1/2 hours o operation. Essentially only nitrogen gas is present in the adsorption column effluent during the first hour of opera~ion.
Although the alumina-bonded silicalite adsorbent has a higher capacity for ethanol, there is some water , ~5;~
.
adsorption capacity also. A small or nil water adsorption capacity is desired to obtain higher ethanol purity in the regeneration ~tep.
Fig. 3 illustrates a regeneration step S profile of ethanol and water concentrations in the nitrogen gas regeneration effluen~ as determined by gas chromatographic analysis. As is readily apparent from ~his profile, siqnificant ethanol enrichment is obtained using nitrogen gas to purge the adsorbed ethanol and some water from the alumina-bonded silicalite adsorbent at a temperature of 200F.
The temperature of the adsorption step was varied and found to be an important process parameSer due to the effect of temperature on the relative saturation (p/ps) values of both water and ethanol for the alumina-honded silicalite adsorbent. As illustrated in Table A below, the loading selectivity for ethanol increases with increasing adsorption temperatures when utilizing ~he alumina-bonded silicalite adsorbent within the scope of the U.S. Patent 4,061,724.
TABLE A
Ethanol/ Weight Adsorption Water Percent Temperature Ethanol Water Loading of Ethanol (F~ Loading* Loading* Ratio ~Condensate) , 75 7.05 ~.4~ l.g~ 61~2 lO0 6.19 3.3~ 1.88 65.3 125 5.35 2.13 2.51 71.5 150 4.7g 1.44 3.29 76.7 *The ethanol and water loading val~es are given in grams per lO0 grams of adsorbent mass.
, D-13~58 .
,~ .
Table A illustrates that although ethanol and water loading decrease at elevated temperatures, the rate of decrease of ethanol loading is not as great as the rate of decrease of water loading and thus the loading selectivity for ethanol increases with increasing adsorption temperatures when utilizing the alumina-bonded silicalite adsorbent. The ethanol concentration in the alumina-bonded silicalite adsorbent is dependent on adsorption temperature and was found to increase from 61.2 to 76.7 weight percent for the increasing temperature range from 75F to 150F re~pectively~ This variation in ethanol product purity i5 due to the dependence of both water and ethanol adsorption loadings on the relative saturation (p/po) value of water and ethanol at the adsorption temperature.
Increasing the adsorption temperature increases the vapor pressure (po) of liquid ethanol or liquid water and thus decreases the relative saturation (p/po) value of ethanol or water, thereby increasing the loading selectivity of ethanol for the alumina-bonded silicalite adsorbent. This is illustrated in Fig. 4.
Fig. 4 illustrates a profile of the dependency of water and ethanol adsorption loadings on their relative saturation (p/po) values at adsorption temperatures ranging from about 75F to about 150F and using alumina-bonded silicalite adsorbent. It is noted that the water loading show~
a critical ~knee" at a relative saturation (p/po) value of about 0.95. When using alumina-bonded silicalite adsorbent in the process of this invention, it is important to stay to the left of this ~knee" or obtaining high ethanol concentration product... For example, before passing nitrogen stripping gas enriched with ethanol and water into the adsorption columnt the enriched stripping gas can be heated to adjust the relative saturation (p/po) of ethanol and water so as to minimize the coadsorption of water on the ethanol selective adsorbent mass. The relative saturation (p/po~
values of water and ethanol and the extent or amount of water and ethanol loadings are different for various adsorbent materials. It is therefose necessary to optimize the trade-off be~ween ethanol selectivity and ethanol loading.
Example 2 Into a laboratory saturator/bubbler device was added a dilute aqueous mixture containing lO
percent by weight ethanol at ambient temperature and 20 psig. The saturator/bubbler device was at~ached to an adsorption column ~onstructed of l/2-inch Schedule 40 stainless-steel pipe containing 57 grams of silica-bonded F-silicalite adsorbent within the scope of U.S. Patent 4/073~865. The silica-bonded F-silicalite adsorbent was in the form of l/B-inch diameter extrudates. Helium gas was used as the stripping gas to vaporize ethanol from the dilute aqueous mixture. Helium gas was bubbled into the dilute aqueous mixture contained in the saturator/bubbler device and effluent helium gas from the saturator/bubbler device was saturated with both water and ethanol vapors. Gas chromatographic
with water vapor and ethanol vapor was passed into the adsorption column having a temperature of 125F
and at a rate of 3.6 standard cubic feet per hour.
The adsorption was allowed to continue until full breakthrough occurred as indicated when the effluent water and ethanol concentrations from the adsorption column became equal to the corresponding concentrations of water and ethanol in the enriched nitrogen gas which entered the adsorption column.
The water and ethanol concentrations in the effluent nitrogen gas from the adsorption column were also determined by gas chromatographic analysis.
Following the adsorption step, the alumina-bonded silicalite adsorbent contained in the adsorption column was regenerated by the thermal swing method at 200F using nitrogen gas which was passed through the adsorption column at a rate of 3.7 standard cubic feet per hour. The water and ethanol concentrations in the nitrogen gas regeneration effluent were determined by gas chromatographic analysis.
Fig. 2 illustrates an adsorption step breakthrough profile of ethanol and water Goncentrations in the effluent from the adsorption column at 125F as determined by gas chromatographic analysis. As can be seen from Fig. 2, water i5 the first component to break through into the adsorption column effluent after about 1 hour o operation followed by the more strongly adsorbed ethanol after about 3 1/2 hours o operation. Essentially only nitrogen gas is present in the adsorption column effluent during the first hour of opera~ion.
Although the alumina-bonded silicalite adsorbent has a higher capacity for ethanol, there is some water , ~5;~
.
adsorption capacity also. A small or nil water adsorption capacity is desired to obtain higher ethanol purity in the regeneration ~tep.
Fig. 3 illustrates a regeneration step S profile of ethanol and water concentrations in the nitrogen gas regeneration effluen~ as determined by gas chromatographic analysis. As is readily apparent from ~his profile, siqnificant ethanol enrichment is obtained using nitrogen gas to purge the adsorbed ethanol and some water from the alumina-bonded silicalite adsorbent at a temperature of 200F.
The temperature of the adsorption step was varied and found to be an important process parameSer due to the effect of temperature on the relative saturation (p/ps) values of both water and ethanol for the alumina-honded silicalite adsorbent. As illustrated in Table A below, the loading selectivity for ethanol increases with increasing adsorption temperatures when utilizing ~he alumina-bonded silicalite adsorbent within the scope of the U.S. Patent 4,061,724.
TABLE A
Ethanol/ Weight Adsorption Water Percent Temperature Ethanol Water Loading of Ethanol (F~ Loading* Loading* Ratio ~Condensate) , 75 7.05 ~.4~ l.g~ 61~2 lO0 6.19 3.3~ 1.88 65.3 125 5.35 2.13 2.51 71.5 150 4.7g 1.44 3.29 76.7 *The ethanol and water loading val~es are given in grams per lO0 grams of adsorbent mass.
, D-13~58 .
,~ .
Table A illustrates that although ethanol and water loading decrease at elevated temperatures, the rate of decrease of ethanol loading is not as great as the rate of decrease of water loading and thus the loading selectivity for ethanol increases with increasing adsorption temperatures when utilizing the alumina-bonded silicalite adsorbent. The ethanol concentration in the alumina-bonded silicalite adsorbent is dependent on adsorption temperature and was found to increase from 61.2 to 76.7 weight percent for the increasing temperature range from 75F to 150F re~pectively~ This variation in ethanol product purity i5 due to the dependence of both water and ethanol adsorption loadings on the relative saturation (p/po) value of water and ethanol at the adsorption temperature.
Increasing the adsorption temperature increases the vapor pressure (po) of liquid ethanol or liquid water and thus decreases the relative saturation (p/po) value of ethanol or water, thereby increasing the loading selectivity of ethanol for the alumina-bonded silicalite adsorbent. This is illustrated in Fig. 4.
Fig. 4 illustrates a profile of the dependency of water and ethanol adsorption loadings on their relative saturation (p/po) values at adsorption temperatures ranging from about 75F to about 150F and using alumina-bonded silicalite adsorbent. It is noted that the water loading show~
a critical ~knee" at a relative saturation (p/po) value of about 0.95. When using alumina-bonded silicalite adsorbent in the process of this invention, it is important to stay to the left of this ~knee" or obtaining high ethanol concentration product... For example, before passing nitrogen stripping gas enriched with ethanol and water into the adsorption columnt the enriched stripping gas can be heated to adjust the relative saturation (p/po) of ethanol and water so as to minimize the coadsorption of water on the ethanol selective adsorbent mass. The relative saturation (p/po~
values of water and ethanol and the extent or amount of water and ethanol loadings are different for various adsorbent materials. It is therefose necessary to optimize the trade-off be~ween ethanol selectivity and ethanol loading.
Example 2 Into a laboratory saturator/bubbler device was added a dilute aqueous mixture containing lO
percent by weight ethanol at ambient temperature and 20 psig. The saturator/bubbler device was at~ached to an adsorption column ~onstructed of l/2-inch Schedule 40 stainless-steel pipe containing 57 grams of silica-bonded F-silicalite adsorbent within the scope of U.S. Patent 4/073~865. The silica-bonded F-silicalite adsorbent was in the form of l/B-inch diameter extrudates. Helium gas was used as the stripping gas to vaporize ethanol from the dilute aqueous mixture. Helium gas was bubbled into the dilute aqueous mixture contained in the saturator/bubbler device and effluent helium gas from the saturator/bubbler device was saturated with both water and ethanol vapors. Gas chromatographic
3~ analysis of this effluent helium gas enriched with water vapor and ethanol vapor showed about 0.65 mole percent ethanol and about 1.6 mole percent water.
The effluent helium gas enriched with water vapor and ethanol vapor was passed into the adsorption ;
~5~25~3 2~
column at a temperature of 75~F and at a rate of 3.5 standard cubic feet per hour. The adsorption was allowed to continue until full breakthrough occurred as indicated when the effluent water and ethanol concentrations from the adsorption column became equal to the corresponding concentrations of water and ethanol in the enriched helium gas which entered the adsorption column. The water and ethanol concentrations in the effluent helium gas from the adsorption column were also determined by gas chromatographic analysis.
In a manner similar to Example 1, the silica-bonded F-silicalite adsorbent contained in the adsorption column can then be regenerated by the thermal-swing method at 200F using helium gas which is passed through the adsorption column at a rate of about 3.6 standard cubic feet per hour. The water and ethanol concentrations in the helium gas regeneration effluent can be determined by gas chromatographic analysis.
Fig. ~ illustrates an adsorption step breakthrough profile of ethanol and water concentrations in the effluent from the adsorption column at 75F as determined by gas chromatographic analysis. As can be seen from Fig. 5, it is apparent that silica-bonded F-silicalite adsorbent has very little water adsorption capacity as evidenced by~the nearly instantaneous water breakthrough. The relative adsorption capacity of ethanol is much greater using silica-bonded F-silicalite adsorbent rather than alumina-bonded silicalite adsorbent in Example l. It is noted that the relative satura~ion ~p/po) value of water is nearly equal to unity at an adsorption temperature D-13~58 of 75F. However, even at a relative saturation lP/P) value near unity for water, high ethanol concentrations of up to 95 weight percent are attainable using this silica-bonded F-silicalite adsorbent. It is not necessary to heat the helium stripping gas enriched with ethanol and water prior to entering the adsorption column so as to adjust the relative saturation ~p/po) of ethanol and water because essentially no coadsorption of water occurs on the silica-bonded F-silicalite adsorbent.
,
The effluent helium gas enriched with water vapor and ethanol vapor was passed into the adsorption ;
~5~25~3 2~
column at a temperature of 75~F and at a rate of 3.5 standard cubic feet per hour. The adsorption was allowed to continue until full breakthrough occurred as indicated when the effluent water and ethanol concentrations from the adsorption column became equal to the corresponding concentrations of water and ethanol in the enriched helium gas which entered the adsorption column. The water and ethanol concentrations in the effluent helium gas from the adsorption column were also determined by gas chromatographic analysis.
In a manner similar to Example 1, the silica-bonded F-silicalite adsorbent contained in the adsorption column can then be regenerated by the thermal-swing method at 200F using helium gas which is passed through the adsorption column at a rate of about 3.6 standard cubic feet per hour. The water and ethanol concentrations in the helium gas regeneration effluent can be determined by gas chromatographic analysis.
Fig. ~ illustrates an adsorption step breakthrough profile of ethanol and water concentrations in the effluent from the adsorption column at 75F as determined by gas chromatographic analysis. As can be seen from Fig. 5, it is apparent that silica-bonded F-silicalite adsorbent has very little water adsorption capacity as evidenced by~the nearly instantaneous water breakthrough. The relative adsorption capacity of ethanol is much greater using silica-bonded F-silicalite adsorbent rather than alumina-bonded silicalite adsorbent in Example l. It is noted that the relative satura~ion ~p/po) value of water is nearly equal to unity at an adsorption temperature D-13~58 of 75F. However, even at a relative saturation lP/P) value near unity for water, high ethanol concentrations of up to 95 weight percent are attainable using this silica-bonded F-silicalite adsorbent. It is not necessary to heat the helium stripping gas enriched with ethanol and water prior to entering the adsorption column so as to adjust the relative saturation ~p/po) of ethanol and water because essentially no coadsorption of water occurs on the silica-bonded F-silicalite adsorbent.
,
Claims (23)
1. An adsorption separation process which comprises:
(a) vaporizing water and at least one organic molecular species contained in a dilute aqueous mixture by contacting the dilute aqueous mixture with an essentially non-sorbable stripping gas;
(b) passing the stripping gas enriched with water and at least one organic molecular species into a fixed adsorption zone containing a hydrophobic adsorbent mass consisting essentially of a molecular sieve material having selectivity for at least one organic molecular species;
(c) adsorbing at least one organic molecular species into the adsorbent mass at a temperature and pressure which prevents capillary condensation of the water;
(d) terminating the flow of stripping gas enriched with water and at least one organic molecular species into the adsorption bed prior to breakthrough of at least one organic molecular species from the effluent end of said adsorption bed;
(e) removing at least one adsorbed organic molecular species by heating the adsorbent mass by passing an essentially non-sorbable heated purge gas through the adsorbent mass countercurrent to such enriched stripping gas, which purge gas can be the same gas used for stripping the dilute aqueous mixture in step (a);
(f) condensing at least one organic molecular species by cooling the purge gas enriched with at least one organic molecular species; and (g) recovering at least one organic molecular species in a concentrated form.
(a) vaporizing water and at least one organic molecular species contained in a dilute aqueous mixture by contacting the dilute aqueous mixture with an essentially non-sorbable stripping gas;
(b) passing the stripping gas enriched with water and at least one organic molecular species into a fixed adsorption zone containing a hydrophobic adsorbent mass consisting essentially of a molecular sieve material having selectivity for at least one organic molecular species;
(c) adsorbing at least one organic molecular species into the adsorbent mass at a temperature and pressure which prevents capillary condensation of the water;
(d) terminating the flow of stripping gas enriched with water and at least one organic molecular species into the adsorption bed prior to breakthrough of at least one organic molecular species from the effluent end of said adsorption bed;
(e) removing at least one adsorbed organic molecular species by heating the adsorbent mass by passing an essentially non-sorbable heated purge gas through the adsorbent mass countercurrent to such enriched stripping gas, which purge gas can be the same gas used for stripping the dilute aqueous mixture in step (a);
(f) condensing at least one organic molecular species by cooling the purge gas enriched with at least one organic molecular species; and (g) recovering at least one organic molecular species in a concentrated form.
2. A process according to claim 1 further comprising drying the purge gas enriched with at least one organic molecular species before step (f).
3. A process according to claim 2 further comprising cooling the adsorbent mass until the temperature is essentially the same as at the beginning of step (b) and repeating steps (a) through (g) until a predetermined amount of at least one organic molecular species is recovered in a concentrated form from the dilute aqueous mixture.
4. A process according to claim 3 wherein the dilute aqueous mixture consists essentially of water and at least one organic molecular species containing from 2 to about 6 carbon atoms inclusive.
5. A process according to claim 4 wherein at least one organic molecular species is a primary alcohol containing from 2 to about 6 carbon atoms inclusive.
6. A process according to claim 5 wherein the primary alcohol is selected from the group consisting of ethanol and isopropanol.
7. A process according to claim 6 wherein the dilute aqueous mixture is fermentation beer containing from about 8 to about 12 percent by weight ethanol.
8. A process according to claim 7 wherein the stripping gas of step (a) is selected from the group consisting of nitrogen, carbon dioxide, helium and argon.
9. A process according to claim 8 wherein the stripping gas is generated by a fermentation process and consists essentially of carbon dioxide enriched with some ethanol.
10. A process according to claim 8 wherein step (a) is conducted at a temperature of from about ambient to about 200°F and a pressure of from about 15 psig to about 200 psig.
11. A process according to claim 10 wherein the adsorbent mass is a molecular sieve material having from 5 to 50 times more loading capacity for the organic molecular species than for water.
12. A process according to claim 11 wherein the adsorbent mass is selected from the group consisting of silica-bonded F-silicalite, alumina-bonded silicalite and Ultrahydrophobic Zeolite Y (UHP-Y).
13. A process according to claim 12 wherein the adsorbent mass is silica-bonded F-silicalite.
14. A process according to claim 12 wherein the steps (b) and (c) are conducted at a temperature of from about ambient to about 200°F and a corresponding pressure of from about 1 atmosphere (absolute) to about 100 psig.
15. A process according to claim 14 wherein steps (b) and (c) are conducted at a temperature of from about 25°F to about 50°F higher than the temperature of step (a) in order to decrease the relative saturation (p/po) of water in the enriched stripping gas.
16. A process according to claim 14 wherein the purge gas of step (e) is selected from the group consisting of nitrogen, carbon dioxide, helium and argon.
17. A process according to claim 16 wherein the purge gas is generated by a fermentation process and consists essentially of carbon dioxide an some ethanol.
18. A process according to claim 16 wherein the purge gas of step (e) is heated to a temperature of from about 100°F to about 700°F.
19. A process according to claim 18 wherein the purge gas of step (e) is heated to a temperature of from about 100°F to about 300°F
higher than the temperature of steps (b) and (c).
higher than the temperature of steps (b) and (c).
20. A process according to claim 18 in which ethanol is recovered in a concentration of at least 180-proof.
21. A process according to claim 18 in which ethanol is recovered in a concentration of at least 195-proof.
22. A process according to claim 18 in which ethanol is recovered in a concentration of essentially 200-proof.
23. A process according to claim 1 further comprising dehydrating the concentrated product of step (g) by azeotropic distillation or by adsorptive heat rise.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US36204982A | 1982-03-26 | 1982-03-26 | |
| US362,049 | 1982-03-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1195258A true CA1195258A (en) | 1985-10-15 |
Family
ID=23424489
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000420436A Expired CA1195258A (en) | 1982-03-26 | 1983-01-28 | Vapor phase adsorption process for concentration of ethanol from dilute aqueous mixtures thereof |
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| Country | Link |
|---|---|
| CA (1) | CA1195258A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5231980A (en) * | 1987-03-04 | 1993-08-03 | Praxair Canada, Inc. | Process for the recovery of halogenated hydrocarbons in a gas stream |
| EP1808222A1 (en) * | 2004-10-04 | 2007-07-18 | Bussan Nanotech Research Institute Inc. | Method for separation of components and separation unit |
| EP2168656A1 (en) * | 2008-09-30 | 2010-03-31 | Sued-Chemie AG | Recovery and purification process for organic molecules |
| EP2333092A1 (en) | 2009-12-08 | 2011-06-15 | Süd-Chemie AG | Method for the recovery of ethanol during fermentation |
| CN110732155A (en) * | 2019-11-14 | 2020-01-31 | 江苏润普食品科技股份有限公司 | continuous evaporation crystallization process and device for calcium propionate with controllable particle size |
-
1983
- 1983-01-28 CA CA000420436A patent/CA1195258A/en not_active Expired
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5231980A (en) * | 1987-03-04 | 1993-08-03 | Praxair Canada, Inc. | Process for the recovery of halogenated hydrocarbons in a gas stream |
| US5515845A (en) * | 1987-03-04 | 1996-05-14 | Praxair Canada Inc. | Canister for the recovery of halogenated hydrocarbons in a gas stream |
| EP1808222A1 (en) * | 2004-10-04 | 2007-07-18 | Bussan Nanotech Research Institute Inc. | Method for separation of components and separation unit |
| EP1808222A4 (en) * | 2004-10-04 | 2008-09-17 | Bussan Nanotech Res Inst Inc | Method for separation of components and separation unit |
| EP2168656A1 (en) * | 2008-09-30 | 2010-03-31 | Sued-Chemie AG | Recovery and purification process for organic molecules |
| WO2010037635A1 (en) * | 2008-09-30 | 2010-04-08 | Süd-Chemie AG | Recovery and purification process for organic molecules |
| CN102202761A (en) * | 2008-09-30 | 2011-09-28 | 苏德-化学股份公司 | Recovery and purification process for organic molecules |
| EP2333092A1 (en) | 2009-12-08 | 2011-06-15 | Süd-Chemie AG | Method for the recovery of ethanol during fermentation |
| WO2011070061A1 (en) | 2009-12-08 | 2011-06-16 | Süd-Chemie AG | Method for obtaining ethanol during fermentation |
| CN110732155A (en) * | 2019-11-14 | 2020-01-31 | 江苏润普食品科技股份有限公司 | continuous evaporation crystallization process and device for calcium propionate with controllable particle size |
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