CA1090650A - Concentrating aqueous solutions - Google Patents
Concentrating aqueous solutionsInfo
- Publication number
- CA1090650A CA1090650A CA260,220A CA260220A CA1090650A CA 1090650 A CA1090650 A CA 1090650A CA 260220 A CA260220 A CA 260220A CA 1090650 A CA1090650 A CA 1090650A
- Authority
- CA
- Canada
- Prior art keywords
- hydrate
- solute
- solid
- ice
- former
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12J—VINEGAR; PREPARATION OR PURIFICATION THEREOF
- C12J1/00—Vinegar; Preparation or purification thereof
- C12J1/04—Vinegar; Preparation or purification thereof from alcohol
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D7/00—Sublimation
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/42—Separation; Purification; Stabilisation; Use of additives
- C07C51/48—Separation; Purification; Stabilisation; Use of additives by liquid-liquid treatment
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Bioinformatics & Cheminformatics (AREA)
- General Health & Medical Sciences (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Biochemistry (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- General Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Genetics & Genomics (AREA)
- Wood Science & Technology (AREA)
- Zoology (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Extraction Or Liquid Replacement (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process for removing water from an aqueous solution. A
hydrate forming fluid is contacted with an aqueous solution at a temperature below the maximum temperature at which said hydrate forming fluid forms a solid hydrate in the presence of said solution and at a temperature at which the amount of solute present in the aqueous solution originally, exceeds its solubility in any solution remaining after hydrate formation so as to form a magma comprising solid hydrate, any unreacted hydrate forming fluid and any unreacted aqueous solution. The hydrate forming fluid and at least part of the water constituent of the solid hydrate are separated from the solute by fractional sublimation and/or elution to produce a substantially hydrate forming fluid-free product comprising said solute and any remaining water.
A process for removing water from an aqueous solution. A
hydrate forming fluid is contacted with an aqueous solution at a temperature below the maximum temperature at which said hydrate forming fluid forms a solid hydrate in the presence of said solution and at a temperature at which the amount of solute present in the aqueous solution originally, exceeds its solubility in any solution remaining after hydrate formation so as to form a magma comprising solid hydrate, any unreacted hydrate forming fluid and any unreacted aqueous solution. The hydrate forming fluid and at least part of the water constituent of the solid hydrate are separated from the solute by fractional sublimation and/or elution to produce a substantially hydrate forming fluid-free product comprising said solute and any remaining water.
Description
lU90~;50 ~his invention relates to the removal of water from aqueous solutions. ;
It previously has been known that solid hydrates may be formed between certain hydrate-forming fluids, referred to here-inafter as hydrate formers, and water from aqueous solutions such as sea water and that after separation of the solid hydrate by filtration or similar mechanical handling processes, pure water may be obtained from the separated hydrate by decomposition thereof. However, in the case of solutions wherein the solute solidifies at the temperatures used to form the solid hydrate, techniques such as filtration cannot be used to separate the solid hydrate from the remainder of the mixture. ~
Accordingly, it is an object of the present invention -~ -to provide, for the removal of water from aqueous solutions, a process of the type in which a solid hydrate is formed wherein the solid hydrate and at least part of the solid phase containing ,, solid solute are separated from each other, preferably by non-mechanical means. -. ~ . . .
The present invention provides a process for removing - ~ : - . . .
~20 water from an aqeuous solution which comprises:
(a) contacting an aqueous solution with a hydrate former at a temperature below the maximum temperature at which said hydrate former forms a solid~hydrate in the presence of the solution, and at a temperature at which there is precipitation of solid solute so as to form a magma comprising solid hydrate, solid solute, any unreacted hydrate former and any unreacted aqueous solution; and (b) separating (i) the hydrate former and at least part of the aqueous constituents of the solid hydrate, and (il) at least part 30 of the solute, from each other, by fractional sublimation, eva- -~' ~
B
.
~osvtjso poration and/or elution, so as to produce a substantially hydrate former-free product comprising the solute and any re-maining water.
In a preferred separation process, the solid mixture -~
resulting from the treatment of the aqueous solution with hydrate former is subjected to temperature and pressure condi-tions that result in the decomposition of the solid hydrate in which the hydrate breaks down into ice and hydrate former, the ~ -hydrate former is removed by vacuum evaporation, and the mix-ture of ice and solid solute is preferably separated by dif- ~-ferential or fractional sublimation. In the case where the `
solute is acetic acid and the hydrate forming fluid is trichlo- ~-rofluoromethane (also known under the Trade Mark Freon II but hereinafter referred to as ~.C.F.M.), decomposition of the hydrate formed usually is effected at about 0C or below and at a pressure of about 750mm of mercury or lower at 0C or a cor-respondingly lower pressure at lower temperatures. Fractional ~
sublimation removing the ice then may be carried out at about ~-0C and 4.5mm of mercury or lower, for example at 0.0075C and 4.5mm of mercury, though other suitable combinations readiiy may be determined by trial and error and/or by the use of vapour pressure data at various temperatures to select conditions ~.~
under which at the chosen temperature the vapour pressure of the ice exceeds that of the chosen pressure whilst the vapour pressure of the solute is less than the chosen pressure and vice versa. If difficulty is experienced in selecting suitable conditions, for example, when the solute has a similar triple point to water, high yields can be obtained by passing the combined solute and water vapours through a column of water vapour absorbing material such as silica gel or anhydrous copper 1090~i5U
sulphate (which can be regenerated), the non aqueous vapour being collected.
In a further aspect the present invention provides a process for removing water from an aqueous solution which comprises:
(a) contacting an aqueous solution with a hydrate former at a temperature below the maximum temperature at which said hydrate former forms a solid hydrate in the presence of the solution and above the maximum temperature at which ice forms in the aqueous solution so that the hydrate former forms a solid hydrate with water from the aqueous solution; and (b) decomposing the solid hydrate so as to produce hydrate former and ice, removing the hydrate former, and separating at least part of the ice and at least part of the solute, from each other, by fractional sublimation of the mixture, so as to produce a substantially hydrate former-free product comprising the solute and any remaining water.
; As used herein the term "sublimation" is a process wherein a solid is converted directly into a vapour and includes such processes wherein the solid hydrate is decomposed without passing through a liquid phase into hydrate former gas and water vapour or ice.
Another separation process is differential elution using a solvent or solvents in which the solute is soluble but in which the solid hydrate of the hydrate fluid used is substan-tially insoluble at the temperatures at which the hydrate is formed and is stable. In the case where the solute is acetic acid suitable elution solvents for the solute include, ethanol, formaldehyde and butanol, as well as trichlorofluoromethane and dichloromethane.
'-'B~ ' 1090~;50 A preferred method of differential elution is when the magma of solid hydrate and solid solute i5 separated from the liquid component which may contain one or more of unreacted hydrate former, unreacted a~ueous solution, and unreacted minor constituents that may be present in the solution being concen-trated. The latter fraction may be distilled to recover any such minor constituents that may be present, as for example, in the case of vinegar, and any dissolved solute.
Although the minor constituents also comprise solutes of the aqueous solution from which water is being removed they will be referred to herein as the minor constituents whilst the --major constituent(s), will be referred to herein as the ~- solute, for convenience. - -~
Conveniently, the solid phase then is rapidly dried by evaporation of the unseparated unreacted former and then by increasing the vacuum (i.e. decreasing pressure) so that the solid hydrate becomes unstable and is broken down to ice and hydrate former. The hydrate former is at once evaporated and may be collected for recycling. This leaves a mixture of ice and solid solute (e.g. acetic acid). The ice will start to melt at below 0C due to the depression of the freezing point by the solute solution. However if the solute is highly soluble in water at this temperature it is possible to obtain a signifi-cant degree of concentration if the solute is dissolved and the solution removed prior to the ice all melting, the solute in this , ,~
case being effectively preferentially eluted in water as an elu-tion solvent. The unmelted ice recovered then represents the amount of water extracted from the original solution. An al-- ternative method is to treat the ice/solid solute mixture be-fore much melting occurs with another solvent which gives rapid .
~B 4 ,rJ''' -10S'~;50 solution of the solute but little effect on the ice (examples are T.C.F.M. or Methylene dichloride when the solute is acetic acid). It will be noted that in the case of concentration of aqueous acetic acid, T.C.F.M. can be used as both hydrate form-er and subsequently as an elution solvent. The solution is then separated from the ice by filtration and the solute recovered by evaporation.
Although T.C.F.M. is a particularly valuable hydrate former, especially for use with aqueous acetic acid solutions, on account of its non-toxicity, commercial availability, low cost and ease of handling due to the fact that it is a liquid at ambient temperatures and pressures hence avoiding the need ;
for costly pressurised storage and reaction vessels, and due to the fact that it can form a solid hydrate (also sometimes re-ferred to in the art as clathrates) at ambient pressures when the temperature is sufficiently reduced, other hydrate formers may also be used. Known hydrate formers together with their hydrate formulae are shown in Table 1 wherein M represents any of the individual hydrate forming molecules in the given section.
Table 1 ~
Hydrate Formula Hydrate Former, M -M.5.75 H2O A'Kr'N2'2H2S'H2Se'C2 2o~pH3~AsH3~cH3F~cH3cl~cH4 M.5.75 H2O or M.7.66 H2O SO2,CH2F2~C2H2'c2 4 M.7.66 H2O Xe,Br2,NF2,CHF3,CF4,CH3Br C2H3F~ CH3CHF2' C2H6 M.17 H2O CH2C12,CHC13,CC14,CH3I,C2H5C1 CH3cF3~c~3cHcl2~cHBrF2~cclF3 CC12F2 ' CBr2F2 ~ CBrClF2 3 ,C3H6,C3H8~ cyclo C5H10 B 5 _ The selection of operating conditions for formulation of tlle solid hydrate are well known and understood in the art.
Briefly the actual operating conditions for a given system are based on the press~re-temperature equilibrium line data for a given hydrate former as pre-determined and calculated for a desired solution concentration, operating temperature and -pressure limit utilising the formula:
Plto = (PO/xn-)to where: -t = preselected temperature of operation for forma-tion of the solid hydrate and the concentrated aqueous solution. ~-P = minimum absolute pressure of the hydrate former - to be exerted at temperature t to achieve the desired final concentration of the aqueous solu-tion through solid hydrate formation.
PO = absolute pressure of the hydrate former to be -exerted at temperature t to achieve formation of solid hydrate with pure water.
(Assumes water is saturated with hydrate former, but contains substantially no other solute).
; x = mole fraction of water at desired final concen-tration of the concentrated aqueous solution.
n = num~er of water molecules associated with one ; molecule of hydrate former in the solid gas ~ hydrate.
; The values of PO at a preselected t can be obtained from experimental and published data.
Although ordinarily the formula will be utilized to determine the operating pressure (Pl) for a preselected ~B
~ ` 1090650 temperature (t), known pressure (PO) of formation of solid hydrate with pure water and for a desired final solution con-centration as represented by a residual mole fraction of water (x) in the solution, generally it is to be understood that if any two of the operating variables, i.e. Pl,Pt, and x at a preselected t are known, the third can be found by calculation using the above formula.
In the case where T.C.F.M. is used to remove water from acetic acid solutions it has been found that substantially complete reaction of the available water to form solid hydrate can be obtained in the presence an excess of T.C.F.M. over the stoichiometrically required amount, at atmospheric pressure provided a sufficiently low temperature, preferably below 5C, is used.
The selection of the hydrate former will depend on various factors such as safety, cost and availability but is primarily determined by the particular solute which it is --~
desired to concentrate and its properties as well as on the process selected for the separation of the solute concentrate from the hydrate or vice versa. Thus in general the hydrate former is chosen for maximising ease of the separation process, subject to the other abovementioned criteria, for example -where differential sublimation is employed the hydrate former is chosen to provide a solid hydrate which may be readily ~;
sublimed pre~erentially to the solute. On the other hand, where the solid hydrate is first decomposed and the released hydrate former then separated off by differential evaporation, leaving the solute behind, then the hydrate former selection will take into account the need for the hydrate former to be ~-evaporated preferentially to the solute. In the case of aqueous ~B
.. . .
- 10~
acetic solutions where the separation process used is differen- -tial sublimation, especially suitable hydrate former other than T.C.F.M. include dichloromethane, trichloromethane and dichloro-fluoromethane.
The amount of hydrate former used in the initial solid hydrate formation stage of the process of the invention may be varied within broad limits. Desirably though the amount used will be at least an amount that is sufficient to react with all the water present in the solution to be concentrated and advan-tageously an excess of the hydrate former is used especiallywhen vinegar is to be concentrated since in that case the minor constituents of the vinegar (which contribute to its flavour and character) may be conveniently recovered in the excess unreact-ed hydrate former.
In practice the reaction of hydrate formers, such as T.C.F.M. with water to form solid hydrates, is substantially ~-stoichiometric so that the required amount of hydrate former usually may be readily calculated though it will be appreciated that if ~ome of the water solidifies before reaction with the ~0 hydrate former, it no longer will be available to react with the latter.
; Thus, in the case where the hydrate former is T.C.F.M., the amount of T.C.F.M. theoretically required to react with all the water initially present is at least 1 molecule of T.C.F.M.
for every 17 molecules of water (i.e. at least about 1 part of T.C.F.M. to 2 parts of vinegar by weight). Conveniently, approximately equal parts of vinegar and T.C.F.M., by volume, are used.
The above processes of the present invcntion have been found to be especially valuable for the concentration of vinegar.
10~)~' jO
Vinegar is essentially an aqueous acetic acid solution with an acetic acid content of the order of 5 to 10% w/v depending on its source and method of manufacture which solution contains small amounts of various other natural products constituents which contribute to the flavour of the particular vinegar.
Particular vinegars that may be mentioned include distilled malt vinegar, alcohol (spirit) vinegar, grain vinegar, wine vinegar, cider vinegar and flavoured vinegars. Malt vinegar in England usually contains at least 4~ w/v acetic acid and wine vinegar in France and Italy is required to contain at least 6 and at le~ast 7% w/v acetic acid, respectively.
From the above it will be apparent that in general vinegars comprise some 90 - 95% w/v of water. It is therefore clearly desirable that if vinegar transporation costs are to be significantly reduced, the vinegar should be substantially con-centrated. On the other hand it must be borne in mind that many of the minor natural products constituents of vinegar which are essential to the flavour of the vinegar are suscept-ible to denaturation at elevated temperatures and under other --~
severe conditions.
It is, therefore, another object of the present inven-tion to provide a process for the concentration of vinegar which process does not substantially denature the vinegar con-stituents or result in any substantial loss of the vinegar constituen~s - other than the water.
Accordingly, a further aspect of the present inven-tion provides a process for producing a vinegar concentrate by removing water from vinegar comprising:
(a) contacting the vinegar with a hydrate-forming fluid at a temperature below the maximum temperature at which said hydrate B~
lO9V~iSO
former forms a solid hydrate in the presence of the vinegar and at a temperature at which there is precipitation of solid acetic acid, so as to form a magma comprising solid hydrate, solid acetic acid, any unreated hydrate former, any unreacted aqueous vinegar solution, and minor vinegar constituents; and (b) separating (i) the hydrate former and at least part of the agueous, constituents of the- solid hydrate an~ any unreacted ~ -hydrate former, and (ii) at least part of the acetic acid, from each other, so as to produce a substantially hydrate former-free acetic acid concentrate, and, where the minor vinegar consti-tuents are not separated with the acetic acid concentrate; re-covering the minor vinegar constituents and recombining them with the acetic acid concentrate, so as to produce a vinegar concentrate.
A particularly preferred hydrate former for use in -;
this process is trichlorofluoromethane.
Preferably the solid hydrate is separated from the concentrated vinegar and any solid acetic acid that has pre-cipitated out of the vinegar solution, by sublimation or solution of solid hydrate, optionally with decomposition of the latter, under temperature and pressure conditions at which any solid acetic acid is substantially not vapourised or dissolved and substantially not denatured. In another preferred process though, where the solute is separated from the solid hydrate by elution of the solvent, separation conveniently may be carried out under ambient temperature and pressure.
On the other hand in some cases the minor constituents of the vinegar are conveniently separated off from the solute, for example, in solution in any excess hydrate former present, and after recovery may ~e recombined with the solute concentrate !B' lOS~V~ O
1, ¦ obtained after completion of the concentration process (pro-viding the required final concentration).
j It will of course be appreciated that where the highest degrees of concentration are required it may be neces-sary or more convenient to carry out the concentration in more j than one step, i.e. by repeating the concentration process one or more times. In this case where any minor constituents have been separated from the solute (e.g. in solution in excess hydrate former), they need not be recombined with the concen- -~
trated aqueous solution of the solute until the final concentra-tion cycle has been completed.
The degree of concentration obtainable by the process of the present invention will depend on various factors such as the nature of the solute and of the hydrate former used, the ~-particular separation process used and the number of concentra-tion cycles carried out. Nevertheless concentrations of at least 40%, 60% or even 80~ w/v acetic acid may be achieved by the selection of suitable conditions in the case of vinegar concentration by a process of the present invention, the con-centrated vinegar being, after reconstitution with water, sub-stantially indistinguishable, for practical purposes, from un-treated vinegar.
Example 1. Concentration of aqueous acetic acid.
A Solid hydrate formation.
To aqueous acetic acid solution (1 litre of 10% w/v) was added liquid trichlorofluoromethane (TCFM, 1 litre) and the mixture cooled to 3C. Vigorous agitation together with external cool-ing and internal cooling, by the addition of solid carbon dioxide, was then carried out so as to ensure that the tempera-ture of the mixture remained below 5C throughout the hydra-109{~0 ., , tion formation step. After a few minutes a magma comprising unreacted TCFM, solid acetic acid, residual aqueous acetic acid ~i.e. liquid or solid acetic acid solution in unreacted water) and solid hydrate, was obtained.
B. SeParation of Hydrate The magma was subjected to vacuum evaporation (3 mm Hg at 0C) for 60 minutes until no more hydrate sublimed. The unused TCFM
' was first removed by this step and was subsequently recovered together with the TCFM trapped in the hydrate. The removal of the TCFM and later removal of the hydrate reduces the tempera-ture to 0C and this temperature is maintained thereafter by ~f` suitable heat application for rapid TCFM removal. This process yielded a mixture of solid glacial acetic acid and residual aqueous acetic acid which at ambient temperatures gave 82% w/v ~ aqueous acetic acid solution.
i, Example 2. Concentration of malt vinegar. 1 A ~olid Hydrate Formation.
Liquid trichlorofluoromethane (TCFM, 500 ml) was added to malt vinegar (500 ml. j and the mixture stirred vigorously for 3 minutes at 3C. Excess TCFM and other liquids were then drained off from the solid hydrate and acetic acid which were then divided into two equal parts.
B Separation of Hydrate , ~ (1) One part of the solids was subjected to vacuum evaporation ~! (3.4 mm Hg at - 0.5C) until no more TCFM or water was removed.
¦~ ~ This step yielded aqueous acetic acid solution containing 69%
w/v acetic acid.
~ (2) The other part of the solids was homogenised with a little ,' ice cold water for 10 minutes in a cold room at -4C. The ~0 liquid phase was then filtered off under vacuum. The liquid :
~9.
.~.,,~ . ~ `
'~
phase yielded under ambient conditions an aqueous solution con-taining 42.5% w/v acetic acid.
The liquids from the first stage were then added, after removal of the TCFM from them by evaporation, to the acetic acid solutions obtained after the separation of the hy-drate to finally yield concentrated malt vinegar.
Example 3. Concentration of Spirit Vinegar.
.
A Solid Hydrate Formation ..
Liquid trichlorofluoromethane(TCFM, 250 ml) was added to spirit vinegar (250 ml.) and the mixture stirred vigorously for 3 minutes at 3C. Excess TCFM and other liquids were then strained off from the solid hydrate and acetic acid.
~ B. Separation of Hydrate s The solids resulting from the first stage were subjected to vacuum evaporation (10 mm Hg at -5C) until no more TCFM came ' off. The pressure was then reduced to 3 mm Hg and the tempera-ture increased to -1C. Initially ethanol and acetaldehyde were removed and collected. Evaporation was then continued until no more water could be removed. This process yielded a residue which at ambient temperatures gave an aqueous solution contain-~` ing 68% w/v acetic acid.
To the aqueous acetic acid solution were then added the recovered ethanol and acetaldehyde and the liquids from the first stage after the TCFM has been evaporated from them, finally yielding concentrated spirit vinegar.
Example 4. Concentration of Spirit Vinegar.
Solid Hydrate Formation i' ~a) 50 ml. of Spirit Vinegar was added to 50 ml. of T.C.F.M.
and the mixture attempered at 0C. and agitated with an air bleed until most or all the aqueous phase had reacted. The ~_ D
^, . ~ ~ . . . .. ..
~,:., - - - ` . `
lO~t)~'jO
exce$s T.C.F.M. was then drained off and stored for recovery of -~
solutes. The solid magma was similarly stored at 0C. until ,f required for evaporation and sublimation.
(b) A second method of solid hydrate formation was used: to , 100 ml. of spirit vinegar at 0C., 75 ml. of T.C.F.M. was added dropwise over a period of 6 hours. The temperature was main-tained at 0C. and agitation was achieved by an air bleed.
After 6 hours the excess T.C.F.M. and dissolved constituents were filtered off from the solid magma constituents and stored until required for recovery of solutes. The solid magma was stored at 0C. until required for evaporation and sublimation.
Separation of Hydrate .' f The solid magmas from hydrate formations (a) and ~b) were placed in a freeze dryer and a vacuum applied. The excess 5. T.C.F.M. was initially removed and the vacuum was then increased until the solid hydrate decomposed and the T.C.F.M. was released.
The temperature was maintained just below 0C. by infra red 1, j radiation. As the hydrate decomposes, ice and gaseous T.C.F.M.
are formed. The T.C.F.M. was condensed for later re-use. After a substantial part of the T.C.F.M. was removed the thin layer of magma consisted of ice crystals and solid acetic acid. The pressure was now reduced so as to sublime the ice (3 mm. Hg at 0C.), leaving a substantial portion of the acetic acid which was allowed to regain room temperature at normal atmospheric pressure.
The excess T.C.F.M. from the solid hydrate formation i stages was carefully distilled at 20C. until all traces of ¦ T.C.F.M. were removed as shown by gas liquid chromatography (G.L.C.) examination of the product. Hydrate formation method (b) gave higher yields of dissolved acetic acid than method (B
1~901i50 L~
~, (a): after combining the distillates and the sublimed samples the former method yielded a concentrate with 84% w/v acetic acid and the latter gave a concentration of 89%.
Example 5 A 100 ml. aliquot of Malt Vinegar was reacted with 100 mls. T.C.F.M. as in Example 4. The excess T.C.F.M. contain-ing the minor constituents of the malt vinegar was drained from the solid magma and the dissolved acetic acid and minor con-stituents were recovered by distillation at 20C. until no T.C.F.M. was detected by G.L.C. analysis of the residue.
The solid magma was then subjected to vacuum evapora-tion under mild conditions until the excess unreacted T.C.F.M.
was removed. The vacuum was then increased until the hydrate decomposed leaving solid acetic acid and ice. Some melting ice was observed at -1C. and in addition to this 1 ml. of ice cold water was added. T~e slurry was agitated briefly and the liquid drained off by vacuum filtration. This liquid was con-centrated acetic acid and when recombined with the solutes from ~;
the excess T.C.F.M., concentrated vinegar was obtained, the level of concentration of the acetic acid in the aqueous solu-tion being governed by the amount of ice that had melted into the liquid eventually drained off from the slurry. After the -addition of the T.C.F.M. dissolved acetic acid and minor con-stituents the acetic acid content of the samples was 54% w/v.
Example 6 i Hydrate formation was carried out as in Example 4a).
The solid magma was then subjected to an initially low vacuum to remove excess T.C.F.M. and then the hydrate was rapidly broken down to give ice and solid acetic acid. To the mixture of ice and acetic acid, at a recorded temperature of -4C, an equal S~' ~0!~0~;50 volume of T.C.F.M., at 1C, was added and the mixture agitated.
The T.C.F.M. was then removed by filtration from the ice and liquid was evaporated at 20C. until no more T.C.F.M. was de-tected. This method yielded after recombination with the minor constituents recovered from the distilled T.C.F.M. an acetic acid content of 89% w/v.
Analysis of reconstituted concentrated vinegars by Gas liquid chromatography (G.L.C.) showed that the concentrated product resembled the original vinegar very closely. The com-pounds acetaldehyde and ethanol found in vinegar were determinedindividually and the remainder of the volatile constituents were groups together. The determinations of quantity were based on the G.L.C. peak areas.
The following table gives the acetic acid content (% w/v) of and the percentages (by Weight) of the minor con-stituents recovered in, five vinegar concentrates obtained by the method of Example 6 but carried out on a small scale using 10 ml. vinegar samples. The error in the minor constituent $ determinations is of the order of i 7 to 8%.
Proportions of minor constituents retained in vinegar concentrates % % Other Vinegar Type Acetic Acet-aldehyde Ethanol Volatiles Acid Conc.
% w/v*
Spirit 67 94 89 93 ~i Wine 71 64 76 77 I Wine (White) 61 81 73 82 Malt 82 92 98 102 Cider 58 84 86 91 * The acetic acid concentrations given were determined by acid-base titration and include any minor acidic constituents re-covered that may be present in the vinegar being concentrated.
i~l .. .. .
It previously has been known that solid hydrates may be formed between certain hydrate-forming fluids, referred to here-inafter as hydrate formers, and water from aqueous solutions such as sea water and that after separation of the solid hydrate by filtration or similar mechanical handling processes, pure water may be obtained from the separated hydrate by decomposition thereof. However, in the case of solutions wherein the solute solidifies at the temperatures used to form the solid hydrate, techniques such as filtration cannot be used to separate the solid hydrate from the remainder of the mixture. ~
Accordingly, it is an object of the present invention -~ -to provide, for the removal of water from aqueous solutions, a process of the type in which a solid hydrate is formed wherein the solid hydrate and at least part of the solid phase containing ,, solid solute are separated from each other, preferably by non-mechanical means. -. ~ . . .
The present invention provides a process for removing - ~ : - . . .
~20 water from an aqeuous solution which comprises:
(a) contacting an aqueous solution with a hydrate former at a temperature below the maximum temperature at which said hydrate former forms a solid~hydrate in the presence of the solution, and at a temperature at which there is precipitation of solid solute so as to form a magma comprising solid hydrate, solid solute, any unreacted hydrate former and any unreacted aqueous solution; and (b) separating (i) the hydrate former and at least part of the aqueous constituents of the solid hydrate, and (il) at least part 30 of the solute, from each other, by fractional sublimation, eva- -~' ~
B
.
~osvtjso poration and/or elution, so as to produce a substantially hydrate former-free product comprising the solute and any re-maining water.
In a preferred separation process, the solid mixture -~
resulting from the treatment of the aqueous solution with hydrate former is subjected to temperature and pressure condi-tions that result in the decomposition of the solid hydrate in which the hydrate breaks down into ice and hydrate former, the ~ -hydrate former is removed by vacuum evaporation, and the mix-ture of ice and solid solute is preferably separated by dif- ~-ferential or fractional sublimation. In the case where the `
solute is acetic acid and the hydrate forming fluid is trichlo- ~-rofluoromethane (also known under the Trade Mark Freon II but hereinafter referred to as ~.C.F.M.), decomposition of the hydrate formed usually is effected at about 0C or below and at a pressure of about 750mm of mercury or lower at 0C or a cor-respondingly lower pressure at lower temperatures. Fractional ~
sublimation removing the ice then may be carried out at about ~-0C and 4.5mm of mercury or lower, for example at 0.0075C and 4.5mm of mercury, though other suitable combinations readiiy may be determined by trial and error and/or by the use of vapour pressure data at various temperatures to select conditions ~.~
under which at the chosen temperature the vapour pressure of the ice exceeds that of the chosen pressure whilst the vapour pressure of the solute is less than the chosen pressure and vice versa. If difficulty is experienced in selecting suitable conditions, for example, when the solute has a similar triple point to water, high yields can be obtained by passing the combined solute and water vapours through a column of water vapour absorbing material such as silica gel or anhydrous copper 1090~i5U
sulphate (which can be regenerated), the non aqueous vapour being collected.
In a further aspect the present invention provides a process for removing water from an aqueous solution which comprises:
(a) contacting an aqueous solution with a hydrate former at a temperature below the maximum temperature at which said hydrate former forms a solid hydrate in the presence of the solution and above the maximum temperature at which ice forms in the aqueous solution so that the hydrate former forms a solid hydrate with water from the aqueous solution; and (b) decomposing the solid hydrate so as to produce hydrate former and ice, removing the hydrate former, and separating at least part of the ice and at least part of the solute, from each other, by fractional sublimation of the mixture, so as to produce a substantially hydrate former-free product comprising the solute and any remaining water.
; As used herein the term "sublimation" is a process wherein a solid is converted directly into a vapour and includes such processes wherein the solid hydrate is decomposed without passing through a liquid phase into hydrate former gas and water vapour or ice.
Another separation process is differential elution using a solvent or solvents in which the solute is soluble but in which the solid hydrate of the hydrate fluid used is substan-tially insoluble at the temperatures at which the hydrate is formed and is stable. In the case where the solute is acetic acid suitable elution solvents for the solute include, ethanol, formaldehyde and butanol, as well as trichlorofluoromethane and dichloromethane.
'-'B~ ' 1090~;50 A preferred method of differential elution is when the magma of solid hydrate and solid solute i5 separated from the liquid component which may contain one or more of unreacted hydrate former, unreacted a~ueous solution, and unreacted minor constituents that may be present in the solution being concen-trated. The latter fraction may be distilled to recover any such minor constituents that may be present, as for example, in the case of vinegar, and any dissolved solute.
Although the minor constituents also comprise solutes of the aqueous solution from which water is being removed they will be referred to herein as the minor constituents whilst the --major constituent(s), will be referred to herein as the ~- solute, for convenience. - -~
Conveniently, the solid phase then is rapidly dried by evaporation of the unseparated unreacted former and then by increasing the vacuum (i.e. decreasing pressure) so that the solid hydrate becomes unstable and is broken down to ice and hydrate former. The hydrate former is at once evaporated and may be collected for recycling. This leaves a mixture of ice and solid solute (e.g. acetic acid). The ice will start to melt at below 0C due to the depression of the freezing point by the solute solution. However if the solute is highly soluble in water at this temperature it is possible to obtain a signifi-cant degree of concentration if the solute is dissolved and the solution removed prior to the ice all melting, the solute in this , ,~
case being effectively preferentially eluted in water as an elu-tion solvent. The unmelted ice recovered then represents the amount of water extracted from the original solution. An al-- ternative method is to treat the ice/solid solute mixture be-fore much melting occurs with another solvent which gives rapid .
~B 4 ,rJ''' -10S'~;50 solution of the solute but little effect on the ice (examples are T.C.F.M. or Methylene dichloride when the solute is acetic acid). It will be noted that in the case of concentration of aqueous acetic acid, T.C.F.M. can be used as both hydrate form-er and subsequently as an elution solvent. The solution is then separated from the ice by filtration and the solute recovered by evaporation.
Although T.C.F.M. is a particularly valuable hydrate former, especially for use with aqueous acetic acid solutions, on account of its non-toxicity, commercial availability, low cost and ease of handling due to the fact that it is a liquid at ambient temperatures and pressures hence avoiding the need ;
for costly pressurised storage and reaction vessels, and due to the fact that it can form a solid hydrate (also sometimes re-ferred to in the art as clathrates) at ambient pressures when the temperature is sufficiently reduced, other hydrate formers may also be used. Known hydrate formers together with their hydrate formulae are shown in Table 1 wherein M represents any of the individual hydrate forming molecules in the given section.
Table 1 ~
Hydrate Formula Hydrate Former, M -M.5.75 H2O A'Kr'N2'2H2S'H2Se'C2 2o~pH3~AsH3~cH3F~cH3cl~cH4 M.5.75 H2O or M.7.66 H2O SO2,CH2F2~C2H2'c2 4 M.7.66 H2O Xe,Br2,NF2,CHF3,CF4,CH3Br C2H3F~ CH3CHF2' C2H6 M.17 H2O CH2C12,CHC13,CC14,CH3I,C2H5C1 CH3cF3~c~3cHcl2~cHBrF2~cclF3 CC12F2 ' CBr2F2 ~ CBrClF2 3 ,C3H6,C3H8~ cyclo C5H10 B 5 _ The selection of operating conditions for formulation of tlle solid hydrate are well known and understood in the art.
Briefly the actual operating conditions for a given system are based on the press~re-temperature equilibrium line data for a given hydrate former as pre-determined and calculated for a desired solution concentration, operating temperature and -pressure limit utilising the formula:
Plto = (PO/xn-)to where: -t = preselected temperature of operation for forma-tion of the solid hydrate and the concentrated aqueous solution. ~-P = minimum absolute pressure of the hydrate former - to be exerted at temperature t to achieve the desired final concentration of the aqueous solu-tion through solid hydrate formation.
PO = absolute pressure of the hydrate former to be -exerted at temperature t to achieve formation of solid hydrate with pure water.
(Assumes water is saturated with hydrate former, but contains substantially no other solute).
; x = mole fraction of water at desired final concen-tration of the concentrated aqueous solution.
n = num~er of water molecules associated with one ; molecule of hydrate former in the solid gas ~ hydrate.
; The values of PO at a preselected t can be obtained from experimental and published data.
Although ordinarily the formula will be utilized to determine the operating pressure (Pl) for a preselected ~B
~ ` 1090650 temperature (t), known pressure (PO) of formation of solid hydrate with pure water and for a desired final solution con-centration as represented by a residual mole fraction of water (x) in the solution, generally it is to be understood that if any two of the operating variables, i.e. Pl,Pt, and x at a preselected t are known, the third can be found by calculation using the above formula.
In the case where T.C.F.M. is used to remove water from acetic acid solutions it has been found that substantially complete reaction of the available water to form solid hydrate can be obtained in the presence an excess of T.C.F.M. over the stoichiometrically required amount, at atmospheric pressure provided a sufficiently low temperature, preferably below 5C, is used.
The selection of the hydrate former will depend on various factors such as safety, cost and availability but is primarily determined by the particular solute which it is --~
desired to concentrate and its properties as well as on the process selected for the separation of the solute concentrate from the hydrate or vice versa. Thus in general the hydrate former is chosen for maximising ease of the separation process, subject to the other abovementioned criteria, for example -where differential sublimation is employed the hydrate former is chosen to provide a solid hydrate which may be readily ~;
sublimed pre~erentially to the solute. On the other hand, where the solid hydrate is first decomposed and the released hydrate former then separated off by differential evaporation, leaving the solute behind, then the hydrate former selection will take into account the need for the hydrate former to be ~-evaporated preferentially to the solute. In the case of aqueous ~B
.. . .
- 10~
acetic solutions where the separation process used is differen- -tial sublimation, especially suitable hydrate former other than T.C.F.M. include dichloromethane, trichloromethane and dichloro-fluoromethane.
The amount of hydrate former used in the initial solid hydrate formation stage of the process of the invention may be varied within broad limits. Desirably though the amount used will be at least an amount that is sufficient to react with all the water present in the solution to be concentrated and advan-tageously an excess of the hydrate former is used especiallywhen vinegar is to be concentrated since in that case the minor constituents of the vinegar (which contribute to its flavour and character) may be conveniently recovered in the excess unreact-ed hydrate former.
In practice the reaction of hydrate formers, such as T.C.F.M. with water to form solid hydrates, is substantially ~-stoichiometric so that the required amount of hydrate former usually may be readily calculated though it will be appreciated that if ~ome of the water solidifies before reaction with the ~0 hydrate former, it no longer will be available to react with the latter.
; Thus, in the case where the hydrate former is T.C.F.M., the amount of T.C.F.M. theoretically required to react with all the water initially present is at least 1 molecule of T.C.F.M.
for every 17 molecules of water (i.e. at least about 1 part of T.C.F.M. to 2 parts of vinegar by weight). Conveniently, approximately equal parts of vinegar and T.C.F.M., by volume, are used.
The above processes of the present invcntion have been found to be especially valuable for the concentration of vinegar.
10~)~' jO
Vinegar is essentially an aqueous acetic acid solution with an acetic acid content of the order of 5 to 10% w/v depending on its source and method of manufacture which solution contains small amounts of various other natural products constituents which contribute to the flavour of the particular vinegar.
Particular vinegars that may be mentioned include distilled malt vinegar, alcohol (spirit) vinegar, grain vinegar, wine vinegar, cider vinegar and flavoured vinegars. Malt vinegar in England usually contains at least 4~ w/v acetic acid and wine vinegar in France and Italy is required to contain at least 6 and at le~ast 7% w/v acetic acid, respectively.
From the above it will be apparent that in general vinegars comprise some 90 - 95% w/v of water. It is therefore clearly desirable that if vinegar transporation costs are to be significantly reduced, the vinegar should be substantially con-centrated. On the other hand it must be borne in mind that many of the minor natural products constituents of vinegar which are essential to the flavour of the vinegar are suscept-ible to denaturation at elevated temperatures and under other --~
severe conditions.
It is, therefore, another object of the present inven-tion to provide a process for the concentration of vinegar which process does not substantially denature the vinegar con-stituents or result in any substantial loss of the vinegar constituen~s - other than the water.
Accordingly, a further aspect of the present inven-tion provides a process for producing a vinegar concentrate by removing water from vinegar comprising:
(a) contacting the vinegar with a hydrate-forming fluid at a temperature below the maximum temperature at which said hydrate B~
lO9V~iSO
former forms a solid hydrate in the presence of the vinegar and at a temperature at which there is precipitation of solid acetic acid, so as to form a magma comprising solid hydrate, solid acetic acid, any unreated hydrate former, any unreacted aqueous vinegar solution, and minor vinegar constituents; and (b) separating (i) the hydrate former and at least part of the agueous, constituents of the- solid hydrate an~ any unreacted ~ -hydrate former, and (ii) at least part of the acetic acid, from each other, so as to produce a substantially hydrate former-free acetic acid concentrate, and, where the minor vinegar consti-tuents are not separated with the acetic acid concentrate; re-covering the minor vinegar constituents and recombining them with the acetic acid concentrate, so as to produce a vinegar concentrate.
A particularly preferred hydrate former for use in -;
this process is trichlorofluoromethane.
Preferably the solid hydrate is separated from the concentrated vinegar and any solid acetic acid that has pre-cipitated out of the vinegar solution, by sublimation or solution of solid hydrate, optionally with decomposition of the latter, under temperature and pressure conditions at which any solid acetic acid is substantially not vapourised or dissolved and substantially not denatured. In another preferred process though, where the solute is separated from the solid hydrate by elution of the solvent, separation conveniently may be carried out under ambient temperature and pressure.
On the other hand in some cases the minor constituents of the vinegar are conveniently separated off from the solute, for example, in solution in any excess hydrate former present, and after recovery may ~e recombined with the solute concentrate !B' lOS~V~ O
1, ¦ obtained after completion of the concentration process (pro-viding the required final concentration).
j It will of course be appreciated that where the highest degrees of concentration are required it may be neces-sary or more convenient to carry out the concentration in more j than one step, i.e. by repeating the concentration process one or more times. In this case where any minor constituents have been separated from the solute (e.g. in solution in excess hydrate former), they need not be recombined with the concen- -~
trated aqueous solution of the solute until the final concentra-tion cycle has been completed.
The degree of concentration obtainable by the process of the present invention will depend on various factors such as the nature of the solute and of the hydrate former used, the ~-particular separation process used and the number of concentra-tion cycles carried out. Nevertheless concentrations of at least 40%, 60% or even 80~ w/v acetic acid may be achieved by the selection of suitable conditions in the case of vinegar concentration by a process of the present invention, the con-centrated vinegar being, after reconstitution with water, sub-stantially indistinguishable, for practical purposes, from un-treated vinegar.
Example 1. Concentration of aqueous acetic acid.
A Solid hydrate formation.
To aqueous acetic acid solution (1 litre of 10% w/v) was added liquid trichlorofluoromethane (TCFM, 1 litre) and the mixture cooled to 3C. Vigorous agitation together with external cool-ing and internal cooling, by the addition of solid carbon dioxide, was then carried out so as to ensure that the tempera-ture of the mixture remained below 5C throughout the hydra-109{~0 ., , tion formation step. After a few minutes a magma comprising unreacted TCFM, solid acetic acid, residual aqueous acetic acid ~i.e. liquid or solid acetic acid solution in unreacted water) and solid hydrate, was obtained.
B. SeParation of Hydrate The magma was subjected to vacuum evaporation (3 mm Hg at 0C) for 60 minutes until no more hydrate sublimed. The unused TCFM
' was first removed by this step and was subsequently recovered together with the TCFM trapped in the hydrate. The removal of the TCFM and later removal of the hydrate reduces the tempera-ture to 0C and this temperature is maintained thereafter by ~f` suitable heat application for rapid TCFM removal. This process yielded a mixture of solid glacial acetic acid and residual aqueous acetic acid which at ambient temperatures gave 82% w/v ~ aqueous acetic acid solution.
i, Example 2. Concentration of malt vinegar. 1 A ~olid Hydrate Formation.
Liquid trichlorofluoromethane (TCFM, 500 ml) was added to malt vinegar (500 ml. j and the mixture stirred vigorously for 3 minutes at 3C. Excess TCFM and other liquids were then drained off from the solid hydrate and acetic acid which were then divided into two equal parts.
B Separation of Hydrate , ~ (1) One part of the solids was subjected to vacuum evaporation ~! (3.4 mm Hg at - 0.5C) until no more TCFM or water was removed.
¦~ ~ This step yielded aqueous acetic acid solution containing 69%
w/v acetic acid.
~ (2) The other part of the solids was homogenised with a little ,' ice cold water for 10 minutes in a cold room at -4C. The ~0 liquid phase was then filtered off under vacuum. The liquid :
~9.
.~.,,~ . ~ `
'~
phase yielded under ambient conditions an aqueous solution con-taining 42.5% w/v acetic acid.
The liquids from the first stage were then added, after removal of the TCFM from them by evaporation, to the acetic acid solutions obtained after the separation of the hy-drate to finally yield concentrated malt vinegar.
Example 3. Concentration of Spirit Vinegar.
.
A Solid Hydrate Formation ..
Liquid trichlorofluoromethane(TCFM, 250 ml) was added to spirit vinegar (250 ml.) and the mixture stirred vigorously for 3 minutes at 3C. Excess TCFM and other liquids were then strained off from the solid hydrate and acetic acid.
~ B. Separation of Hydrate s The solids resulting from the first stage were subjected to vacuum evaporation (10 mm Hg at -5C) until no more TCFM came ' off. The pressure was then reduced to 3 mm Hg and the tempera-ture increased to -1C. Initially ethanol and acetaldehyde were removed and collected. Evaporation was then continued until no more water could be removed. This process yielded a residue which at ambient temperatures gave an aqueous solution contain-~` ing 68% w/v acetic acid.
To the aqueous acetic acid solution were then added the recovered ethanol and acetaldehyde and the liquids from the first stage after the TCFM has been evaporated from them, finally yielding concentrated spirit vinegar.
Example 4. Concentration of Spirit Vinegar.
Solid Hydrate Formation i' ~a) 50 ml. of Spirit Vinegar was added to 50 ml. of T.C.F.M.
and the mixture attempered at 0C. and agitated with an air bleed until most or all the aqueous phase had reacted. The ~_ D
^, . ~ ~ . . . .. ..
~,:., - - - ` . `
lO~t)~'jO
exce$s T.C.F.M. was then drained off and stored for recovery of -~
solutes. The solid magma was similarly stored at 0C. until ,f required for evaporation and sublimation.
(b) A second method of solid hydrate formation was used: to , 100 ml. of spirit vinegar at 0C., 75 ml. of T.C.F.M. was added dropwise over a period of 6 hours. The temperature was main-tained at 0C. and agitation was achieved by an air bleed.
After 6 hours the excess T.C.F.M. and dissolved constituents were filtered off from the solid magma constituents and stored until required for recovery of solutes. The solid magma was stored at 0C. until required for evaporation and sublimation.
Separation of Hydrate .' f The solid magmas from hydrate formations (a) and ~b) were placed in a freeze dryer and a vacuum applied. The excess 5. T.C.F.M. was initially removed and the vacuum was then increased until the solid hydrate decomposed and the T.C.F.M. was released.
The temperature was maintained just below 0C. by infra red 1, j radiation. As the hydrate decomposes, ice and gaseous T.C.F.M.
are formed. The T.C.F.M. was condensed for later re-use. After a substantial part of the T.C.F.M. was removed the thin layer of magma consisted of ice crystals and solid acetic acid. The pressure was now reduced so as to sublime the ice (3 mm. Hg at 0C.), leaving a substantial portion of the acetic acid which was allowed to regain room temperature at normal atmospheric pressure.
The excess T.C.F.M. from the solid hydrate formation i stages was carefully distilled at 20C. until all traces of ¦ T.C.F.M. were removed as shown by gas liquid chromatography (G.L.C.) examination of the product. Hydrate formation method (b) gave higher yields of dissolved acetic acid than method (B
1~901i50 L~
~, (a): after combining the distillates and the sublimed samples the former method yielded a concentrate with 84% w/v acetic acid and the latter gave a concentration of 89%.
Example 5 A 100 ml. aliquot of Malt Vinegar was reacted with 100 mls. T.C.F.M. as in Example 4. The excess T.C.F.M. contain-ing the minor constituents of the malt vinegar was drained from the solid magma and the dissolved acetic acid and minor con-stituents were recovered by distillation at 20C. until no T.C.F.M. was detected by G.L.C. analysis of the residue.
The solid magma was then subjected to vacuum evapora-tion under mild conditions until the excess unreacted T.C.F.M.
was removed. The vacuum was then increased until the hydrate decomposed leaving solid acetic acid and ice. Some melting ice was observed at -1C. and in addition to this 1 ml. of ice cold water was added. T~e slurry was agitated briefly and the liquid drained off by vacuum filtration. This liquid was con-centrated acetic acid and when recombined with the solutes from ~;
the excess T.C.F.M., concentrated vinegar was obtained, the level of concentration of the acetic acid in the aqueous solu-tion being governed by the amount of ice that had melted into the liquid eventually drained off from the slurry. After the -addition of the T.C.F.M. dissolved acetic acid and minor con-stituents the acetic acid content of the samples was 54% w/v.
Example 6 i Hydrate formation was carried out as in Example 4a).
The solid magma was then subjected to an initially low vacuum to remove excess T.C.F.M. and then the hydrate was rapidly broken down to give ice and solid acetic acid. To the mixture of ice and acetic acid, at a recorded temperature of -4C, an equal S~' ~0!~0~;50 volume of T.C.F.M., at 1C, was added and the mixture agitated.
The T.C.F.M. was then removed by filtration from the ice and liquid was evaporated at 20C. until no more T.C.F.M. was de-tected. This method yielded after recombination with the minor constituents recovered from the distilled T.C.F.M. an acetic acid content of 89% w/v.
Analysis of reconstituted concentrated vinegars by Gas liquid chromatography (G.L.C.) showed that the concentrated product resembled the original vinegar very closely. The com-pounds acetaldehyde and ethanol found in vinegar were determinedindividually and the remainder of the volatile constituents were groups together. The determinations of quantity were based on the G.L.C. peak areas.
The following table gives the acetic acid content (% w/v) of and the percentages (by Weight) of the minor con-stituents recovered in, five vinegar concentrates obtained by the method of Example 6 but carried out on a small scale using 10 ml. vinegar samples. The error in the minor constituent $ determinations is of the order of i 7 to 8%.
Proportions of minor constituents retained in vinegar concentrates % % Other Vinegar Type Acetic Acet-aldehyde Ethanol Volatiles Acid Conc.
% w/v*
Spirit 67 94 89 93 ~i Wine 71 64 76 77 I Wine (White) 61 81 73 82 Malt 82 92 98 102 Cider 58 84 86 91 * The acetic acid concentrations given were determined by acid-base titration and include any minor acidic constituents re-covered that may be present in the vinegar being concentrated.
i~l .. .. .
Claims (52)
1. A process for removing water from an aqueous solution, which process includes the steps of: (a) contacting an aqueous solution with a hydrate former at a temperature below the maximum temperature at which said hydrate former forms a solid hydrate in the presence of the solution, and at a temperature at which there is precipitation of solid solute so as to form a magma comprising solid hydrate, solid solute, any unreacted hydrate former and any unreacted aqueous solution;
and (b) separating (i) the hydrate former and at least part of the aqueous constituents of the solid hydrate and (ii) at least part of the solute, from each other, by fractional subli-mation, evaporation and/or elution, so as to produce a substan-tially hydrate former-free product comprising the solute and any remaining water.
and (b) separating (i) the hydrate former and at least part of the aqueous constituents of the solid hydrate and (ii) at least part of the solute, from each other, by fractional subli-mation, evaporation and/or elution, so as to produce a substan-tially hydrate former-free product comprising the solute and any remaining water.
2. A process for removing water from an aqueous solu-tion, which process includes the steps of: (a) contacting an aqueous solution with a hydrate former at a temperature below the maximum temperature at which said hydrate former forms a solid hydrate in the presence of the solution and above the maximum temperature at which ice forms in the aqueous solution so that said hydrate former forms a solid hydrate with water from the aqueous solution; and decomposing the solid hydrate so as to produce hydrate former and ice; (b) removing the hydrate former, and separating at least part of the ice and at least part of the solute from each other so as to produce a substan-tially hydrate former-free product comprising the solute and any remaining water.
3. A process as defined in claim 1, wherein the solid hydrate is decomposed into ice and hydrate former by in-creasing temperature and/or reducing pressure to provide tem-perature and pressure conditions at which said solid hydrate decomposes and at which the solute is substantially unaffected.
4. A process as defined in claim 2, wherein the solid hydrate is decomposed into ice and hydrate former by increasing temperature and/or reducing pressure to provide temperature and pressure conditions at which said solid hydrate decomposes and at which the solute is substantially unaffected.
5. A process as defined in claim 3, wherein decom-position is effected at temperature and pressure conditions at which the solute remains substantially in the solid phase.
6. A process as defined in claim 2, 3 or 5 wherein the solute and at least part of the ice are separated from each other by fractional sublimation at temperature and pressure conditions such that one of the ice and the solute is volatilised whilst the other of said ice and the solute remains substantially in the liquid and/or solid phase.
7. A process as defined in claim 2, 3 or 5, wherein the solute and at least part of the ice are separated from each other by sublimation at temperature and pressure conditions such that both the ice and solute are volatilised and the resulting vapour contacted with a water vapour-absorbing material to absorb the water vapour entrained with the solute vapour.
8. A process as defined in claim 2, 3, or 5, where-ing the solute and at least part of the ice are separated from each other by sublimation at temperature and pressure condi-tions such that both the ice and solute are volatilised and the resulting vapour contacted with a water vapour-absorbing material selected from silica gel and anhydrous copper sul-phate to absorb the water vapour entrained with the solute vapour.
9. A process as defined in claim 1, wherein the solute is separated from the solid hydrate by differential elution using a solvent in which the solute is substantially more soluble than is the solid hydrate.
10. A process as defined in claim 9, wherein when the solute is acetic acid, the elution solvent is selected from ethanol, formaldehyde and butanol.
11. A process as defined in claim 9, wherein when the solute is acetic acid, the elution solvent is dichloro-methane.
12. A process as defined in claim 9, wherein when the solute is acetic acid, the elution solvent is trichloro-fluoromethane.
13. A process as defined in claim 12, wherein the trichlorofluoromethane elution solvent containing dissolved acetic acid is separated off by filtration.
14. A process as defined in claim 12 or 13, where-in the trichlorofluoromethane is removed from the solution of acetic acid in trichlorofluoromethane by fractional evapora-tion.
15. A process as defined in claim 3, wherein at least part of the ice is maintained in the solid state and the solute is mechanically separated from said ice in the solid state, in the form of a concentrated aqueous solution.
16. A process as defined in claim 5, wherein at least part of the ice is maintained in the solid state and the solute is mechanically separated from said ice in the solid state, in the form of a concentrated aqueous solution.
17. A process as defined in claim 15, or 16, wherein part of the ice is allowed to melt into liquid water in which solute dissolves to form a concentrated aqueous solution of the solute.
18. A process as defined in claim 15, or 16, where-in liquid water is added and solute allowed to dissolve in said added liquid water to form a concentrated aqueous solu-tion of the solute.
19. A process as defined in claim 15 or 16, where-in the concentrated aqueous solution is separated from the solid ice by filtration.
20. A process as defined in claim 3, wherein at least part of the ice is maintained in the solid state and a non-aqueous solvent, in which ice is substantially less sol-uble than is the solute, is added to form a solution of the solute, which solution is then mechanically separated from the solid ice, and the solute is then recovered from said solution by separation from said elution solvent.
21. A process as defined in claim 5, wherein at least part of the ice is maintained in the solid state and a non-aqueous solvent, in which ice is substantially less sol-uble than is the solute, is added to form a solution of the solute, which solution is then mechanically separated from the solid ice, and the solute is then recovered from said solution by separation from said elution solvent.
22. A process as defined in claim 20, or 21, wherein the solute is acetic acid and the non-aqueous solvent is trichlorofluoromethane and said acetic acid is recovered by evaporation of said non-aqueous solvent.
23. A process as defined in claim 20 or 21, wherein the solute is acetic acid and the non-aqueous solvent is dichloromethane and said acetic acid is recovered by evapora-tion of said non-aqueous solvent.
24. A process as defined in claim 1, 2, or 3, wherein at least the stoichiometric amount of hydrate former required to react with all the water in the aqueous solution, is used.
25. A process as defined in claim 9, 12 or 13, where-in at least the stoichiometric amount of hydrate former required to react with all the water in the aqueous solution, is used.
26. A process as defined in claim 15 or 20, wherein at least the stoichiometric amount of hydrate former required to react with all the water in the aqueous solution, is used.
27. A process as defined in claim 1, 2, or 3, wherein the hydrate former is dichloromethane, trichloromethane or dichlorofluoromethane.
28. A process as defined in claim 9, 15 or 20, where-in the hydrate former is dichloromethane, trichloromethane or dichlorofluoromethane.
29. A process as defined in claim 1, 2, or 3, wherein the hydrate former is trichlorofluoromethane.
30. A process as defined in claim 9, 15 or 20, where-in the hydrate former is trichlorofluoromethane.
31. A process as defined in claim 1, 2, or 3, wherein, as the hydrate former, at least 1 mole of trichlorofluoromethane is used for every 17 moles of water in the aqueous solution from which the water is being removed.
32. A process as defined in claim 9, 15 or 20, where-in, as the hydrate former, at least 1 mole of trichlorofluoro-methane is used for every 17 moles of water in the aqueous solu-tion from which the water is being removed.
33. A process as defined in claim 1, 2, or 3, where-in the hydrate former is trichlorofluoromethane and the hydrate formation is carried out at atmospheric pressure and at a temperature below 5°C.
34. A process as defined in claim 9, 15, or 20, where-in the hydrate former is trichlorofluoromethane and the hydrate formation is carried out at atmospheric pressure and at a temperature below 5°C.
35. A process as defined in claim 1, 2, or 3, where-in an excess of hydrate former over the amount required to react with all the water in the aqueous solution is used and wherein the liquid phase remaining after solid hydrate formation and containing the excess unreacted hydrate former is filtered off from the solid phase and then evaporated to recover any minor constituents of the solution being concentrated which remain in the liquid phase during the solid hydrate formation, said minor constituents being recombined with the concentrated aqueous solu-tion of the solute.
36. A process as defined in claim 9, 12 or 13, where-in an excess of hydrate former over the amount required to react with all the water in the aqueous solution is used and wherein the liquid phase remaining after solid hydrate formation and containing the excess unreacted hydrate former is filtered off from the solid phase and then evaporated to recover any minor constituents of the solution being concentrated which remain in the liquid phase during the solid hydrate formation, said minor constituents being recombined with the concentrated aqueous solution of the solute.
37. A process as defined in claim 15 or 20, wherein an excess of hydrate former over the amount required to react with all the water in the aqueous solution is used and wherein the liquid phase remaining after solid hydrate formation and containing the excess unreacted hydrate former is filtered off from the solid phase and then evaporated to recover any minor constituents of the solution being concentrated which remain in the liquid phase during the solid hydrate formation, said minor constituents being recombined with the concentrated aqueous solution of the solute.
38. A process as defined in claim 1, 2, or 3, wherein the hydrate former is dichloromethane, trichloromethane or dichlorofluoromethane and the aqueous solution from which water is to be removed is aqueous acetic acid.
39. A process as defined in claim 9, 15, or 20, where-in the hydrate former is dichloromethane, trichloromethane or dichlorofluoromethane and the aqueous solution from which water is to be removed is aqueous acetic acid.
40. A process as defined in claim 1, 2, or 3, where-in the aqueous solution from which water is to be removed is aqueous acetic acid, the hydrate former is trichlorofluoromethane and the hydrate formation is carried out at atmospheric pressure and at a temperature below 5°C, hydrate decomposition is carried out at a temperature not higher than 0°C. and a pressure not higher than 750 mm of mercury so that said hydrate is decomposed and the trichlorofluoromethane volatilised whilst the solid acetic acid is maintained in substantially solid form.
41. A process as defined in claim 9, wherein the aqueous solution from which water is to be removed is aqueous acetic acid, the hydrate former is trichlorofluoromethane and the hydrate formation is carried out at atmospheric pressure and at a temperature below 5°C., hydrate decomposition is carried out at a temperature not higher than 0°C. and a pressure not higher than 750 mm of mercury so that said hydrate is decomposed and the trichlorofluoromethane volatilised whilst the solid acetic acid is maintained in substantially solid form.
42. A process as defined in claim 41, wherein the hydrate decomposition is carried out at a temperature and pres-sure such that the hydrate is decomposed into ice and hydrate former and that the ice is then fractionally sublimed off by reducing the pressure to a value not greater than 4.5 mm of mercury when a temperature of about 0°C is used.
43. A process as defined in claim 42, wherein ice sublimation is carried out at about 3 mm of mercury and about 0°C.
44. A process as defined in claim 41, 42 or 43, where-in the aqueous acetic acid solution is vinegar.
45. A process for producing a vinegar concentrate by removing water from vinegar, which process includes the steps of: (a) contacting the vinegar with a hydrate former at a temperature below the maximum temperature at which said hydrate former forms a solid hydrate in the presence of the vinegar and at a temperature at which there is precipitation of solid acetic acid, so as to form a magma comprising solid hydrate, solid acetic acid, any unreacted hydrate former, any unreacted aqueous vinegar solution, and minor vinegar constituents; and (b) separating (i) the hydrate former and at least part of the aqueous constituents of the solid hydrate and any unreacted hydrate former, and (ii) at least part of the acetic acid, from each other and, where minor vinegar constituents are not separat-ed with the acetic acid concentrate, recovering at least part of the minor vinegar constituents; and recombining them with the acetic acid concentrate so as to produce a vinegar concen-trate.
46. A process as defined in claim 45 wherein the hydrate former is trichlorofluoromethane.
47. A process as defined in claim 45, or 46, wherein the vinegar is selected from spirit vinegar, grain vinegar, wine vinegar, cider vinegar and a flavoured vinegar.
48. A process as defined in claim 45 or 46, wherein the vinegar is malt vinegar.
49. A process as defined in claim 45 or 46, wherein the vinegar is concentrated to provide a final concentration of acetic acid of at least 40% w/v.
50. A process as defined in claim 45 or 46, wherein the final concentration is at least 60% w/v.
51. A process as defined in claim 45 or 46, wherein the final concentration is at least 80% w/v.
52. A process as defined in claim 1, 2, or 3, wherein the water removal process is carried out at least twice on the aqueous solution from which water is to be removed.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB36629/75A GB1535336A (en) | 1975-09-05 | 1975-09-05 | Concentrating aqueous solutions |
| GB36629/75 | 1975-09-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1090650A true CA1090650A (en) | 1980-12-02 |
Family
ID=10389845
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA260,220A Expired CA1090650A (en) | 1975-09-05 | 1976-08-31 | Concentrating aqueous solutions |
Country Status (16)
| Country | Link |
|---|---|
| JP (1) | JPS5232882A (en) |
| AT (1) | AT363052B (en) |
| BE (1) | BE845866A (en) |
| CA (1) | CA1090650A (en) |
| CH (1) | CH624854A5 (en) |
| DE (1) | DE2639594A1 (en) |
| DK (1) | DK381876A (en) |
| ES (1) | ES451228A1 (en) |
| FR (1) | FR2322636A1 (en) |
| GB (1) | GB1535336A (en) |
| IE (1) | IE43317B1 (en) |
| LU (1) | LU75715A1 (en) |
| NL (1) | NL7609825A (en) |
| NO (1) | NO762921L (en) |
| SE (1) | SE7609535L (en) |
| ZA (1) | ZA765105B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3122865B1 (en) | 2014-03-24 | 2019-12-11 | Purac Biochem B.V. | Neutralized vinegar concentrates and liquid food grade blends containing said neutralized vinegar concentrates |
| DK3660138T3 (en) | 2014-03-24 | 2023-06-06 | Purac Biochem Bv | Neutralized vinegar concentrates and food grade liquid mixtures with the neutralized vinegar concentrates |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1492717A (en) * | 1922-08-11 | 1924-05-06 | Frank E Lichtenthaeler | Method of concentrating aqueous solutions of volatile substances |
| US1492718A (en) * | 1923-11-24 | 1924-05-06 | Frank E Lichtenthaeler | Method of concentrating aqueous solutions of volatile substances |
| US1817993A (en) * | 1925-05-19 | 1931-08-11 | Frank E Lichtenthaeler | Method of concentrating aqueous solutions of volatile substances |
| US1912585A (en) * | 1930-09-17 | 1933-06-06 | Frank E Lichtenthaeler | Method of concentrating dilute aqueous solutions |
| DE668812C (en) * | 1936-07-28 | 1938-12-10 | Linde Eismasch Ag | Process for the elimination of water from aqueous solutions and mixtures |
| US3058832A (en) * | 1960-09-12 | 1962-10-16 | Dow Chemical Co | Solution treatment |
| FR1330681A (en) * | 1961-08-11 | 1963-06-21 | Lummus Co | Process for the formation and separation of ice crystals from an aqueous solution |
| US3415747A (en) * | 1965-03-08 | 1968-12-10 | Dow Chemical Co | Solution treatment |
-
1975
- 1975-09-05 GB GB36629/75A patent/GB1535336A/en not_active Expired
-
1976
- 1976-08-23 IE IE1874/76A patent/IE43317B1/en unknown
- 1976-08-24 DK DK381876A patent/DK381876A/en unknown
- 1976-08-25 NO NO762921A patent/NO762921L/no unknown
- 1976-08-25 ZA ZA00765105A patent/ZA765105B/en unknown
- 1976-08-27 SE SE7609535A patent/SE7609535L/en unknown
- 1976-08-30 AT AT0642476A patent/AT363052B/en not_active IP Right Cessation
- 1976-08-31 CA CA260,220A patent/CA1090650A/en not_active Expired
- 1976-09-02 DE DE19762639594 patent/DE2639594A1/en not_active Withdrawn
- 1976-09-02 FR FR7626537A patent/FR2322636A1/en not_active Withdrawn
- 1976-09-03 BE BE170367A patent/BE845866A/en unknown
- 1976-09-03 CH CH1125176A patent/CH624854A5/en not_active IP Right Cessation
- 1976-09-03 JP JP51105103A patent/JPS5232882A/en active Pending
- 1976-09-03 NL NL7609825A patent/NL7609825A/en not_active Application Discontinuation
- 1976-09-03 LU LU75715A patent/LU75715A1/xx unknown
- 1976-09-03 ES ES451228A patent/ES451228A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1535336A (en) | 1978-12-13 |
| CH624854A5 (en) | 1981-08-31 |
| ES451228A1 (en) | 1977-12-01 |
| NL7609825A (en) | 1977-03-08 |
| ZA765105B (en) | 1978-04-26 |
| IE43317B1 (en) | 1981-01-28 |
| BE845866A (en) | 1977-03-03 |
| NO762921L (en) | 1977-03-08 |
| LU75715A1 (en) | 1977-04-27 |
| AT363052B (en) | 1981-07-10 |
| SE7609535L (en) | 1977-03-06 |
| DK381876A (en) | 1977-03-06 |
| JPS5232882A (en) | 1977-03-12 |
| ATA642476A (en) | 1980-12-15 |
| IE43317L (en) | 1977-03-05 |
| DE2639594A1 (en) | 1977-03-17 |
| FR2322636A1 (en) | 1977-04-01 |
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| MKEX | Expiry |