CA1311236C - Supercritical separation process for complex organic mixtures - Google Patents

Abstract

ABSTRACT

A process is disclosed for separating low molecular weight components from complex aqueous organic mixtures.
The process includes preparing a separation solution of supercritical carbon dioxide with an effective amount of an entrainer to modify the solvation power of the supercritical carbon dioxide and extract preselected low molecular weight components. The separation solution is maintained at a temperature of at least about 70° C and a pressure of at least about 1,500 psi. The separation solution is then contacted with the organic mixtures while maintaining the temperature and pressure as above until the mixtures and solution reach equilibrium to extract the preselected low molecular weight components from the organic mixtures.
Finally, the entrainer/extracted components portion of the equilibrium mixture is isolated from the separation solution.

Description

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SUPERCRITICAL SEPARATION PROCESS
FOR COMPLEX ORGANIC MIXTURÆS

CB~SX~D 0~ THE n~NTIQN
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1. F~ED OF TEE n~n~TICN

: The present invention relates qenerally to the separation of complex organlc mixtures~into varlous components and, more particularly, to :processes of separating low molecular weight fractions from complex organic : mixtures utilizing supercritical solutions. Specifically, the present m vention~relates~to~the~supercritical separation:of low molecular weight components~rom~compl~ex organlc mixtures utllizing supercriticdl carbon dioxide modified by the presence of an entrainer.

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2. DES~RIPTI~N OF T~ PRI~R A~T

There are a wlde variety of lndustrial biomass processing systems which produce waste ~treams containing substantial portions of useful constituents. Examples of such industxial syste~s include those involved in the manufacturing of pulp and paper such a~ black liquor solutions in kraft p~oeesses, in the production of cheese and whey, and in other biomass process mg ~ystems. The annual vol~me of such ~aste processing streams is very substantial. muS, there have been numerous efforts over ~he years to separate useful components from such waste streams for the purpose of recirculation within the processing system, for the separate sale and/or use of such components, or for environmental purposes to remove environmentally damaging components from the waste streams. Due to the volume involved in such indus~xial systsms, economic factors such as the complexity of the separation process or the energy requirement for such separatlon processes become extremely impor~ant as compared to the ef~icie ~ of the separation proce~s as well as the effectiveness in terms of extraction capability.
For example, the kra~t process of conv~rting w od $nto cellulose pulp includes treating the lignocellulosic material with sodium hydr~xide/sulfide solutions. During this process, lignins are di~solved and hemicelluloses are degrad~d to a complex mixture of orgamc compounds including various carboxylic acids such as sa~charinic acids~ Low molecular weight components such as phenolic compounds derived from lignins are present in streams of the black liquox or in washing operations such as preparation of chem1cally pure cellulose by dissolution o pulp m alkaline solutions.
The separation of large molecular weight components is relatively straightforward and many prior art techniques have been developed to separate such high molecular weight components from the complex orgamc mixtures. Some techniques have also been developed for the separation of the lo~ molecular weight fractions. These prior art techniques contain many stages involving ion exchange, adsorption steps, water evaporation, distillation, and other purification operations. These standard and well known procedures are very complex and expensive to operate. In order to increase the efficiency of separation, use of supercritical fluids to enhance separation has been developed. U.S. Patent No. 3,969,196 is an example wherein a number of organic compounds are separated utilizing a wide variety of supercritical fluids including carbon dioxide. While carbon dioxide is a desirable supercritical fluid due to its relative availability and inexpensiveness, this particular reference was unable to separate the more complex polyhydroxy compounds and other complex phenolic lcw molecular weight compounds utilizing carbon dioxide and, instead, had to utilize different supercritical fluids having differing solvation characteristics. m Pse supercritical fluids are more complex to handle and more expensive than supercritical carbon dioxide.
Other references which disclose the use o~ car~on dioxide in separation - processes include U.S. Patents No. 2,772,965, No. 4,349,415, No. 4,437,939 and No. 4,474j994. None of these references illustra~e the use o~
superoritical carbon dioxide to extract the more co~plex phenolic low - ,A.

molecular weight constituents from complex organic mixtures, nor do they illustrate the mcdi~ication of the carbon dioxide solvating power by the addition of entrainers. Thus, these known processes do not address the effective separation of simple and complex low molecular weight cons~ituents of complex organic mixtures (phenolic, complex hydroxyacids) from biomass processing systems utili~ing inexpensive supercritical fluids.
U.S. Patents No. 2,631,966, No. 2,632,030 and No. 2,698,278 all illustrate the use of li ~id carbon ~ioxide with other co-solvents for separation purposes. However, these patents ~re limited to petroleum refining and do not deal with carbon dioxide at supercri~ical conditions, that is supercritical temperature and pressure conditions. Moreover, the compounds present in oil stocks for petroleum refining have very little in common with separation processes of complex organic mixtures derived from i biomass processing systems as discussed above.
Thus, there remains a need for relatively simple processes of extracting useful low molecular constituents from complex organic mixtures derived from biomass processing stxeams. For such processes to be economically effective, they must preferably utilize mild temperature conditions and intermediate pressure ranges, they must be simple, and they must utilize relatively inexpensive chemical components as well as simplified hardware.

S=XP~Y OF DEE nNVEN~IoN

Accordingly the present invention seeks to provide a ~ -4-.~ .

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simplified and economic process for separating low molecular weight fragments or components from complex organic mixtures.
Further the present invention seeks to provide a process for modifying the solvation characteristics of supercritical carbon dioxide to increase its effectiveness in extract mg low molecular weight components, including complex components, from complex organic mixtures derived from biomass processing systems.
Still further the present invention seeks to provide an economic supercritical extraction process for the separation of low ~olecular weight components from lignin-containing organic mixtures derived from various biomass processing systems such as the kraft wcod pulp process.
Further still the present invention seeks to provide a process for separating complex polyhydroxy compoun~s, co~plex phenols, lcw ~olecular weight lignin-containing compounds and hydroxycarboxylic acids from complex organic mixtures.
Still further the present invention seeks to provide a process-for separating high-value hydroxy acids and co~plex amino acids from solution, useful in food processing and pharmaceutical synthesis.
Additional aspects, advantages and novel features of the present invention shall`be set forth in part in the description that follcws, and in part will become apparent to those skilled in the art upon examination of the foregoing or may be learned by the practice of the invention. The and advantages may be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims.

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To achieve the foregoing and in accordance with the purpose of the present mvention, as embodied and broadly described herein, a process is disclosed for separating low molecular weight compcnents from complexaqueous organic mixtures. The process includes preparing a separation solution of supercritical carbon dioxide with an effective amount of an entralner to modify the sulvation power of the supercritical carbon dioxide and extract preselected low ~olecular weight ComPOnentS.
This separation solution is m2mtained at a temperature of at least about 70 C and at a pressure of at least about 1,500 psi. The separation solution is contacted with the complex organic mixtures while maintaining the aforementioned temperature and pressure un~il the mixtures and the separation solution reach equilibrium to extract the preselected low molecular weight components from the organic mixtures. Finally, the entrainer/extracted components portion is isolated from the separation solution ~RIEF DE~UETICN OF T9E DRAWI~GS

;~ ~ The accompanying drawing which is mcoxporated in and fo~ns a part of the specification illustrates preferred e~bodiments of the present invention, and together with the description, serves to explain the 20 ~ principles of the invention. In the drawing:
g. 1 is a graphical illustration showing mvlecular weight fragments extracted from a black liquor solution utilizing the process of the present invention.

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The present invention involves a p~ocess for the extraction and separation of classes of co~ponents from.complex aqueous mixtures of organic compounds such as those present in liquors fro~ alkaline wccd 5 pulping such as the kra~t process, pulp washing ~n.th alkal~ne solutions for the manufacture of chemically pure cellulose, cheese manufacturing waste st~eans and the l~ke. qhe proces utilizes superc~itical car~on dio~de ~n the presenc~ of entrainers. It was found that supercritical carkon dioxide in and of itself was i~sufficient to extract the desired low molecular weight fragments from such complex aqueous organic mixtures, and in particulax the polyhy~roxy compoun~s and other complex organic material~.
It was found, however, that when effective amounts of entrainers were incorporated with the supercritical carbon dioxide, such entrainers modified the solvation power of the supercritical car~on dioxide and ~ tted th~ desired extraction of preselected fragments~
`~ The supercritical solution of ~he invention is maintained at a temperature of at least 70 C and an operating~condition of at least about 1,500 psi. The pxeferred ranges, as discussed in more detail below, include a temperatuxe range of 70 - lS0 C and operating pressure~ m the : ~o range of 1,S00 ~ 4,000 psig.
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The suFercritical fluid extraction solution is then contacted with the aqueous solution of the complex mixture of organic compounds until equllibrium is reached. A counter-current mode is preferably utilized to achieve this, although any desired p~ocess system may be utili2ed. After ' -7-:, ,, '" ." ~ ~ ' ' ' :

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equilibrium is established between the mixtures, the supercritical solventcontains one or m~re lcw molecular weight components o the complex organic mixture depending on the nature and the concentration of the entrainar present in the supercritical solution. It should be noted here, and is discussed in greater below, that it is possibLe to successiYely extract different classes of compounds by varying the concentration and~or the nature of the entrainer present in the supercritical carbon dioxide. In this manner, the process may be tuned to achieve the desired extraction.
The solution of entrainer/ex~racted components i5 then isolated by reducing the system pressure, by lowering the temperature, or by a combination of both. In a preferred embodiment, the pressure is lowered to about 800 psi or higher. Alternatively, the system's temFerature may be low~red in the amount of 30 - 50 C from its operational temperature. The entrainer/extracted material suspen~ion resultin~ fxom this procedure can then be filtered with the entrainer being recovered a~d recycled.
me broadest application o~ the present invention includes a process for generally se ~ ating low m~l ~ lar weiqht fra~mentc or components from soluble complex organic mdxtures. In particular, the separation of certain components from complex organic mlxtures is of concern wherein the organic mixtures include substitutecl phenols, hydroxycarboxylic acicls, complex carbohydrates, amino aclds and the like. Of par~icular concern are biomass processing streams as previously described and in particular the kraft process for converting wovd into cellulose pulp. This process system treats the lignwellulosic material wlth sodium hyc~oxide~sulfide solutions to c~ssolve lignins and degrade hemicelluloses to a complex mixture of :' ~ -B-; ' ~ ~ ,.... . .

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cax~oxylic acids mcluding saccharinic acids. The black liquox solution produced in such process mg syskems is of particular importance because of the amoun~ of chemicals it contains. Thus, a particularly impor~ant application of the present invention is the separation and extraction of low molecular weight compounds, such as s~bstituted phenols and other phenolic compounds derived from lignins from hydroxycarboxylic acids and other polyhydro~y compounds. Su~h components are present in streams of the black liquor or in washing operations relating to the overall kraft process.
More particularly, black liquor from pulp and paper industry processes is generally concentrated to about 30 - S0~ volume, and carbon dioxide (80 psi, 80 C) is then typically utiliz~d to precipitate a~out 70 - 80% of the lignins present in the liquor, primarily the higher molecular weight lignin components. The residual solu~ion, which is o concern with the present invention, contains salts, low molecular weight lignins, and polyh~droxy compounds such as hydroxycarboxylic acids including sacch~rinic acids as sodium salts. After separation o the solids by filtration or centrifugation, the resultin~ liquor is then treated ~ith -the supercriti~al carbon dioxide separatio~ process of the presen~ inv~ntion to selectively extxact desired components thexeof.
The entrainers useful wlth the present invention ma~ vaxy depending on the mixture being separated and the desixed extraction fragments.
Preferably, the entrainer is a low boiling point organic solvent and is present in approNimately 2 - 30 weight percent of the supercritical carbon dioxide/entrainer solution to be effec~ive. In add1tion; in oxder to _g_ .~

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~xtract polyhydroxy compounds, the entrainer should include active hydroxy groups in the presence of water. ~lis ls particularly true in the black liq~or extraction application of the invention. Suita~le compounds utilized as entrainers include alcohols such as methanol, ethanol and the like, ke~ones such as acetone, methylethylketone and the like, and ethers such as tetrahydrofuran (TE~F) and methyl-t-but~l ether. Such entrainers will extract low molecular weight fragments preferably in the ran~e of 150 - 400 molecular weight.
As previously indicated, the preferxed ef~ective range of entrainer is 2 - 30 weight percent of the separa~ion solution depending on the entrainer utilized and/or the desired extxactant. When alcohol is utilized as the entrainer, the greater the alcohol content, the greater the lignin extracted from lignin-containing complex organic mixtures. More speciically, a low alcohol content of about 2 - 5% will extract low molecular weigh~ phenolics. A medlum alcohol concentration of about 10 - 12% of the supercritical carbon dioxide will extract hydroxy acids such as lactic acid, and a higher alcohol concentration of ahout 20% or more will extract the more complex hydroxy acids such as polyhydroxy carbcxylic acids, and amino acids ~in pharmaceutical processes).
It is also possible to successively extract different classes of compounds or components from the complex organic m1xture by varying not only the concentration but also the nature of the entrainer present. For :
example, in order to extract the polyhydroxy components, the entrainer utilized must have an active hydroxy group. Moreover, by shifting the entrainer type~from alcohol to, ~for example, acetone or I~, extraction of ' -10--, - ~ 3 ~

phenolics is grea~ly enhanced or increased as opposed to extraction of hydroxy acids or amino acids. Thus, by extensively modifying the solvation power of the supercritical carbon dioxide by the addition of various types of entrainers, especially wt.en such entrainers include active hydroxy groups, separation of a vaxiety of complex lcw molecular weight fractions can be performed, particularly polyhydroxy compounds. In addition, by tuning ~he amount of the entrainerf such as alcohol, one can selectively extract desired components such as progresslvely extracting phenolic compounds, then simpler hydroxyacids, and then more complex polyhydroxycarboxylic acids from the black liquor solution. For more particulars, reference should be made to Table III below.
As previously indicated, the preferred temperature range for maintaining the supercritical separation solution is between 70 - 150 C.
At temperatures generally below the preferred minimum of 70 C, very little extraction of low molecular weight fragments is obtained. If the separation solution is operated at temperatures su~stantially greater than the preferred 150 C maxlmum, components of~the separation solution begin to decompose thereby defeatinq ehe effectiveness and capability of the extraction pr~cess. It is also preferred that the supercritical separation solution is operated at a pressure range of about 1,S00 - 4,000 psi. These particular pressure range parameters have been experimentally determined as being the preferred range to operate the separation solution at or above the supercritical range o car~on dioxide, which is 31 C at 1,0~9 psig.
Once ~he supercritical separation solution and the organic mixtures have reached equil~ibrlum, the entrainer/water/extracted fragment :::
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composition i~ then isolated from the separation solution. This is achieved either by reducing the pressure or by reducmg temperature or both. In one preferred orm, the pressure is r~luced to approximately 800 psi, although lower pressures down to 200 psi would wor~ and h~ve been used experimentally. Howevex, 800 psi or higher is preferred in order to maintain the carbon dioxide solution as a liquld. In this instance, suspended particulates are formed, and the suspension is then filtered to recover the entrainer and solidified f~agments. In an alternate em~x~nt, the ~olatile e~tra~ner/water is stripped off the solution after pressure reduction, and the ~ragments are then recGvered. Alternatively, the temperature may ke reduced. me preferred temperature drop is 30 - 50 C although a greater drop may be us~d. However, it should be noted that the smaller the temperature drop, the easier it is to recycle the solution in a continuous process system.

~Xa~eLES I - VIII

A series of ~ ~men~s were performed to determine the parameters and llmitations indicated above. All experiments were carried out in an Autoclave Engineer SCE Screening System. All the experiments with liquid samples were carried out in an extraction vessel which was modified to include an internal tube through which the supercritical fluid was fed and bubbled into the liquid aqueous phase to improve the mixing between the phases. A typical experimental procedure is described to provide a detailed record ~f exFerimRntal sequence of the operations.

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The carbon dioxide/entram er mixture was prepared in a small cylinder having a volu~e of about 2.7 liters. The cylinder was carefully emptied by connecting it to vacuum line and then weighed. The desired amount o~
entrain~r was siphoned into the cyli~der. The cylinder was weighed again and then prescurized wi~h carbon dioxide to the desired weight. It was necessary to ~ressurize slowly to ~ ze the carbon dioxide content.
~cw boiling solvents such as methanol or acetone or tetrahydrofuran tT~) dissolved large amounts o~ carbon dioxide, ~o it was possible to fill the cylinder with about 300 - 350 g of solvent and 1,200 1,400 g of carbon dioxide. Solvents like ethanol or isopropanol and possibly acetonitrile and methylethylk~tone do no~ dissol~e very large a~,ounts of carbon dioxide so ~hat is was better to fill the cylinder with no mvre than 150 - 200 g of such solvents.
The cyl mder was connected to an extrac~ion reaction sys~em, and a cold trap (ice, w~ter and sodium chloride) was prepared to cool the carbon dioxide/entrainRr mi~ture before entering a pump. Usually/ the extraction ~eactor was filled with 10 ml of solution to be ex~racted. It was then connected and slowly a~d carefully pressurized. Once the pressure began to rise, ~he solution was then hea~ed to the desired temper~ture.
In a typical experiment ~3,000 psi, 100 C and 20% o~ entrainer), the pressure in the separating vessel was kept at about 300 psi. Approximately 2.1 cubic foot volume was allowed to pass through th~ reactor before each fraction was collected. Once the final fractlon was recovered from the separa~ing vessel, the system Wa5 completely vented. Heating was turned off when the pressure in the system was at about 1,000 psi during discharge of the system. me liquid sample was recovered from the bottom of the autoclave and weighted. U ually there was a solid at the bsttom and on the walls of the reactor. This solid sample was careully recovered, dried under vacuum and weighed.
A series of samples of black liquor were tested utilizing the carbon dioxide/entrainer process of the presen~ invention wherein the type o~
entrainer utilized was varied~ Samples of the black liquor solution were prepared, for instance, by pulping selected sp~cies such as pine or aspen to obtain the kræt black liquors. Additional s~mples were obtained from the Weyerhaeuser Company. In all these experiments, the volume of black liquor put into the reactor was 10 ml, containing approximately 1 g of lignin. Kraft black liquor solutions were first treated to r~move the higher a~lecular weight lignin components, with the remaining solution treated with ~he extraction proc~ss of the present invention. Table I
belcw provides the results of this series of e~periments which wexe a series of extractions o~ aspen kraft black liquor æter precipitation of high-mol~cular-weigh~ l~gnins wlth carbon dioxide.

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~ar~tity o~
Supercritical Entra~ner ~ ~ ~ ~ Rec~ EXtract, g 1 ~ce~one, 21.1 620 135 0.16 2 Acetone, 2000 625 124 0.14 3 Methanol, 22 . 5 613 153 * 1. 44 4 Methanol, 20.5 830 178 * 1.33 S Ethanol, 19 . 3 460 103 0 . 63 6 Ethanol, 17. 9 5~0 117 0 . 40 7 THF 21.5 51~ 89 0.11 8 ~? 21.5 ~00 119 0.16 * q~he e~tract con~rlsed law molecular weight lignin compounds and hydro~carko~lic adds.
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15As can ba seen from Table I above, both acetone and THF
entrainers with the supercritical carbon dioxide extracted low molecular weight lignins. ~his can also be seen in F$g. 1 wherein the line denoted hy the numeral 10 indicates the molecular weight distribution ~MWP) of the residue from 20the black liquor after having been extracted with supercritical carbon dioxide and acetone, while the line 12 indicates the ~WD of the extracted lignin. As can be seen from Fig. 1, the extracted llgnin ls in a low molecular weight range of approximately ~00, with a small amount of lignin also in the molecular weight :range of approximately 400. Thus, while the acetone and THF e~trac~ed low molecular weight lignins, as illustxated, the alcohols as indicated in Table I extracted hydroxycarboxylic acids in addition to the low molecular weight lignins~ Moreover, methanol can also extract some sodium bicarbonate, which is not extracted with acetone or T~F.

~XAMPLE IX

200 ml o~ crude.black liquor solution was treated by exposing it to carbon dioxide (80 psi at 80 C) for approximately three hours. High molecular weight lignin precipitated out and was separated by centr1fugation. 10 ml : (11 g) of the supernatant fluid were then extracted using the process of the present invention, the supercritical carbon dioxid /methanol entrainer being at 100 C, 3,000 p~ig. With 5~ methanol, 16 mg:of acetovanillone were obtained with about 5 g of methanol. When th~ methanol content was increased to about 17%, ~00 mg of a mixture of lactic and other hydroxy acids were obtained with ahout 50 g : of methanol. The proportions of methanol/carbon dioxide needed for an industrial process would be smaller than those employed in these particular experiments. The operating :
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vessel volume was 75 ml and the flow rate of carbon dioxide/methanol was about 300 - 400 ml/hr. Acetovanillone contents in the liquor were about 1% of lignin, and the expected con~ent of saccharinic acids was about 10 - 20%.
This particular appli~ation of ~he proce~ of the invention would apply to the isolation of acetovanillone and related compounds and the subsequent isolation o saccharinic acids from complex mixtures of industrial interes~.

~YAP9PLE X

An experiment similar to Example IX was carried out using about 17% methanol concentration and the Weyexhaeuser krat lignin sample described above. From about 2.2 g of solid material contained in the liquor, 50% wa~ extracted with 17~ methanol and supercxitical carbon dioxide and 50%
remained in the solid residue. The composition of the extracted phase and of the solid residue, relative to the hydroxycarboxylic actds, is lllustrated in Table II below.

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Table II
Compositit)n of Hydro~carbo~lic Acids in Ext:racted Materials and Residue.
(Hydroxymonocar~oxylic Acids ~n g/100 g of mater.ial *) E;ctract Residue Lactic 3.17 0 23 Glycolic 1. 22 0 32 2-Hydroxy~utanoic 1. 21 0 . 07 2-Hydro~-2~thylbutanoic0 . 04 2-Hydroxypentenoic 0.19 traces 4-Hydro~butanoic 0.14 ~
2-Methylglyceric 0 . 09 0 02 Glyceric 0 . 03 0 02 3-Deox~rtetronic 0 . 20 0 . 05 3, 4-Dide~ypentonic 1. 71 0 . 27 Arhydroisosaccharinic 0.16 0.05 Xyloisosaccharinic 0 . 44 O .17 3-Dideoxypentonic O . 25 0 09 3, 6-Dideoxyhexonic 0 .11 traces 3, 4-Dideoxyhexonic 0 10 0 02 2 o b~lucoisosaccharinic 3 31 1 30 a~lucoisosacchzr~nic 1.27 0.56 * Li~ residues and salt~ were not analyzed.

The data in Table II illustrate the ability of the high methanol concentrations to extract simple and cornplex ~hydroxycarboxylic acids. These conditions al50 extract dicarboxylic acids and glycerol. The ~ are also components - of the black llquor. The analyses above were carried out uclng capil lary gas chromatography of fully sylilated de ~ lvative s ~ :

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EXA}5PLES XI - XXI I

To optimize entrainer concentration and operating conditions, experiments were perormed with a simple simulated black liquor solution containin~ acetovanillone 5 (representative of a low-molecular weight lignin derived compound), lactic acid (a carbohydrate decomposition product), ~nd gluconic acid (a more complex hydroxycarboxylic acid, representative of saccharinic acids) . Table II below summarizes the effects of the 10 various parameters: concentration of ~ntrainer, temperature, pressure and water content. Analyses were performed using high perf ormance liquid chromatography on the column Biora HPX - 8 7H .

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TAB~

~llone ~t P Tenp E~rain~r Gluccnic ~iel~l ~) Ia~ic (Y~eld 9~) (Yiel~ ~) Glua~nic # (E~i) (C) Sol~ (~) Xtd. SR LP~ Xtd S~ L~ xed. 5~ LR 100 5 Variation of methan~l a~t 48 30~ lOQ M~ 20.~ 67.1 2.1 15.2 93.7 0.0 0.0 ga.4 0.0 Q.0 a2.7 S~ 30~0 lOûMeCH 13.427.8 20.6 3.5 ~8.3 0.0 1.8 ~0.3 0.0 0.0 75.9 3000 100ME~ 8.4 2.6 70.7 4.5 ~ 6.1 60.5 ~3.7 4.0 9.0 24.9 . 56 3~0û100 Me~5.7 0.2 3.3 88.4 4.5 2.1 100.1 76.6 1.7 25.1 ~.3 2500 100~aH 20.354.5 35.7 5.6 100.3 0.0 0.9 102.5 0.0 0.0 57.7 61 2000 100~l 20.333.4 51.0 ~.0 1~9.4 0.0 3.4 g~.l 0.0 3.6 ~5.1 Variation of t~rature ar~l al~ol tyEe 48 3000 100 ~ 20.667.1 2.115.2 93.7 0.0 0.0 9~.~ 0.0 0.0 a~.7 53 3000 100E~ 19.3~5.5 51.4 0.5 85.5 0.0 0.6 94.7 0~0 0.0 ~8.1 58 30~70 ~3CH 19.7Sg.6 ~8.7 1.0 10~.9 0.0 0.7 96.1 0.0 0.0 80.3 62 3000 120~H 18.52~.6 25.7 0.5 100.5 0.0 0.5 96.7 0.~ 0.0 73.8 67 3000 100Me~ 20.6 0.0 }~2.7 0.4 0.8 ~0.9 4.4 2~q.7 ~2.1 17.4 -3.1 69 3000 100~# 20.661.1 7.1 17.2 g8.7 0.00.5 97.0 0.0 0.0 75.6 0 3000 100~CE*17.673.2 0.9 10.2 95.3 0.0~.3 g4.8 0.0 0.1 89.0 2 0 * E~ctr~ti~n f~:m solid æ~ a sysl~

X~ cted fractisn 25 g~R hLq~id ~ .
~ratial of glu0nic acid best ~a~ 1~ di~f~ 5R-LR) sir(x upc~ cooling part oP the a~:id E~cipitated frcm the ~th3nolic solut~an .

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From the results of Table III, it is clear that one can extract lignill like compounds at very low entrainer (e.g.
methanoll ethanol) concentration in l:he 2,000 - 4,000 psi range at the inves~iqa~ed ~emperature range. In order to extract the carhoxylic acids, it iS impera~ive to increase the concentration o~ entrainer (me~hanol or ethanol). It should also bQ noted that the entrainer from these particular experlments has to have an active hydroxy group or other polar group to allow extraction of polyhydroxylated 10 carboxylic acids. If the chief interest is in acetovanillone production, methanol, ethanol, acetone, tetrahydrofuxan and the like can be used as entrainers. If the compounds of interest are the acids as well, methanol and ethanol are the preferred entrainers~

~XAMPL~S X~ XXIV

Other examples of ~ubstances that can be extracted with supercritical carbon dioxide with methanol entrainer were also tested. In one example, 0.27 g of Ascorbic acid was disso}ved in 10 ml of water. The Ascorbic acid was 20 completely extracted at 95 C and at 3000 psi carbon dioxide containing 17~ methanol with roughly 30 g of methanol or 0.5 h cQntinuous extrac~ion. Another example utilized the same procedure as just described~ However, L-Alanine (an .:

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amino acid) was su~stituted or the ascorbic acid, and complete extxaction also occurred in this example.
These examples XXIII and XXIV clearly illustrated that the use o methanol and water wi~h supercritical carbon dioxide allows the extraction of polar compounds having active -COOH, -OH and -NH2 groups.
As can be seen from the above, a novel process for extracting or separat~ng low molecular weight components of complex organic mixtures is provided. The process is simple and econo~ic since it is a modification of supercritical carbon dioxide separation, carbon dioxide being a very inexpensive and readily available extractant material. As can be seen, the present invention has particular applicability to selec~i~ely extract reusable components ~ 15 from black liquor waste streams in the kraft pulping process : as well as other biomass processing systems having waste streams. It can also be applicable to the extraction of hlgh value complex compounds from various processin~ ~treams (biological or chemical processes). By merely modifying the type and concentration of entrainer associated with the supercritical carbon dioxide, one can select the material being extracted from the complex organic mixture. Thus, the process is very adaptable to numerous industrial systems, is slmple and economic, and is easLly adapted and modified in accordance with the desired, preseIected low molecular , ~ 3 ^~

weight extracted material.
While the foregoing description and illustration of the present invention has ~een particularly shown in detail with reference to preferred embodiments and modifica~ions thereof, it should be understood by those skilled in the art that the foregoing and other modifications are exemplary only, and that equivalent changes in composition and detail may be employed ~herein withou~ departing from the spirit and scope of the invention as claimed ex~ept as precluded by the prior art.

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Claims (34)

1. A process for separating low molecular weight components having a molecular weight in the range of 150 to 400, from complex aqueous organic mixtures comprising:
preparing a separation solution of supercritical carbon dioxide with an effective amount of a low boiling point entrainer selected from the group consisting of methanol, ethanol, acetone, methylethylketone, tetrahydrofuran and methyl-t-butyl ether to modify the solvation power of said supercritical carbon dioxide and extract preselected low molecular weight components;
maintaining said separation solution at a temperature of at least about 70°C. and a pressure of at least about 1500 psi;
contacting said separation solution with said organic mixtures while maintaining said temperature and pressure until the mixtures and solution reach equilibrium to extract said preselected low molecular weight components from said organic mixtures; and isolating the entrainer/extracted components portion from said separation solution by reducing the pressure, lowering the temperature or a combination of reducing the pressure and lowering the temperature.

2. The process as claimed in claim 1, wherein said temperature ranges from 70° - 150°C. and said pressure ranges from 1,500 - 4,000 psi.

3. The process as claimed in claim 1, wherein said entrainer includes active hydroxy groups in the presence of water to selectively extract polyhydroxy carboxylic acid or amino acids from said complex organic mixtures.

4. The process as claimed in claim 3, wherein said polyhydroxy compounds include polyhydroxycarboxylic acids.

5. The process as claimed in claim 1, wherein said entrainer comprises an effective amount of methanol and water to selectively extract polar compounds having active -COOH, -OH or -NH2 groups.

6. The process as claimed in claim 1, wherein said effective amount of entrainer in said separation solution comprises 2 - 30% by weight.

7. The process as claimed in claim 1, wherein said low molecular weight components which are separated from said complex organic mixture comprises 150 - 400 molecular weight.

8. The process as claimed in claim 1, wherein said complex organic mixtures from which said low molecular weight components are separated are selected from the group consisting of black liquor solutions derived from alkaline wood pulping processes, pulp working solutions from the manufacturing of chemically pure cellulose and cheese manufacturing waste streams.

9. The process as claimed in claim 8, wherein said complex organic mixtures from which said low molecular weight components are separated include phenols, carboxylic acids and complex carbohydrates and wherein said low molecular weight components include hydroxycarboxylic acids and substituted phenols.

10. The process as claimed in claim 1, wherein the entrainer/extracted components portion is isolated by reducing the pressure of the equilibrium solution thereby creating suspended fragments therein.

11. The process as claimed in claim 10, wherein said isolation further includes filtering the suspension and recovering the entrainer.

12. The process as claimed in claim 10, wherein said isolation includes stripping off the volatile entrainer solution to leave the extracted components.

13. The process as claimed in claim 1, wherein said preselected low molecular weight components are progressively separated in accordance with their molecular weight from said complex organic mixtures by progressively changing the entrainer concentration in the supercritical carbon dioxide/entrainer separation solution.

14. The process as claimed in claim 13, wherein low molecular weight lignin compounds are separated from said complex organic mixture by utilizing a low entrainer concentration in said separation solution and wherein the entrainer concentration is increased to shift the extraction and separation to separating carboxylic acids from the lignin-containing complex organic mixtures.

15. The process as claimed in claim 14, wherein said entrainer includes active hydroxy groups to extract polyhydroxylated carboxylic acids.

16. The process as claimed in claim 13, wherein said entrainer comprises an alcohol and wherein said alcohol concentration is selectively varied from 2% to 30% depending on the desired selected low molecular weight extraction component.

17. The process as claimed in claim 16, wherein said alcohol entrainer concentration is in the range of about 2 - 5%
by weight to selectively extract low molecular weight phenolics.

18. The process as claimed in claim 16, wherein said alcohol entrainer concentration is in the range of about 10 - 12 weight percent to selectively extract hydroxy acids.

19. The process as claimed in claim 16, wherein said alcohol entrainer concentration is in the range of about 20 - 30%
by weight to selectively extract complex polyhydroxy acids and amino acids.

20. The process as claimed in claim 1, wherein said preselected low molecular weight components are separated in accordance with their molecularweight from said complex organic mixtures by selectively changing the entrainer composition of the supereritical carbon dioxide/entrainer solution.

21. A process for extracting low molecular weight components having a molecular weight in the range of 150 to 400, from complex polyhydroxycarboxylic acid mixtures derived from biomass processing streams, said process comprising:
admixing a solution of supercritical carbon dioxide and an effective amount of a low boiling point organic entrainer selected from the group consisting of methanol, ethanol, acetone, methylethylketone, tetrahydrofuran and methyl-t-butyl ether to modify the solvation power of said supercritical carbon dioxide and extract preselected low molecular weight components;
maintaining said carbon dioxide solution at a temperature of about 70° - 150°C. and a pressure of 1,500 - 4,000 psi, said carbon dioxide remaining at or about its supercritical level during the extraction phrase;
contacting said carbon dioxide/entrainer solution with said polyhydroxy-carboxylic acid mixtures while maintaining said temperature and pressure until said solution is in equilibrium with said mixtures to extract said preselected low molecular weight components from said mixtures; and isolating the entrainer/extracted components from said solution by reducing the pressure, lowering the temperature or a combination of reducing the pressure and lowering the temperature.

22. The process as claimed in claim 21, wherein said entrainer includes hydroxy groups to extract low molecular weight polyhydroxy carboxylic acid compounds.

23. The process as claimed in claim 21, wherein said effective amount of entrainer in said carbon dioxide/entrainer solution comprises 2 - 30% by weight depending on the preselected component desired to be extracted.

24. The process as claimed in claim 23, wherein the preselected component being extracted may be varied by varying the concentration and/or composition of said entrainer in the supercritical carbon dioxide/entrainer solution.

25. The process as claimed in claim 21, wherein the entrainer/extracted components composition is isolated by reducing the pressure of the equilibrium solution to about 800 psi or above.

26. The process as claimed in claim 21, wherein the entrainer/extracted components composition is isolated by reducing the temperature of the equilibrium solution by 30° -50°C.

27. A process for separating preselected low molecular weight lignin fragments, having a molecular weight in the range of 150 to 400, from soluble lignin-containing mixtures and complex polyhydroxycarboxylic acid comprising:
preparing a solution of supercritical carbon dioxide and an effective amount of a low boiling point organic entrainer selected from the group consisting of methanol, ethanol, acetone, methylethylketone, tetrahydrofuran and methyl-t-butyl ether at a temperature of about 70° - 150°C. and at a pressure of about 1,500 - 4,000 psi to maintain the carbon dioxide solution at or above its supercritical level and selectively extract the desired fragments;
contacting the carbon dioxide/entrainer solution with the lignin-containing mixture until the solution and mixture are in equilibrium to extract the preselected low molecular weight fragments from the mixture; and isolating the entrainer/extracted fragments from the solution by reducing the pressure, lowering the temperature or a combination of reducing the pressure and lowering the temperature.

28. The process as claimed in claim 27, wherein said lignin-containing mixture comprises a black liquor mixture derived from alkaline wood pulping processes.

29. The process as claimed in claim 28, wherein said entrainer includes hydroxy groups in order to extract polyhydroxy carboxylic acid compounds from the black liquor mixtures.

30. The process as claimed in claim 29, wherein said effective amount of entrainer in said supercritical carbon dioxide/entrainer solution comprises approximately 2 - 30% by weight depending on the low molecular weight fragment desired to be extracted.

31. The process as claimed in claim 30, wherein the extracted component varies from low molecular weight lignin compounds to carboxylic acids as said entrainer concentration is increased in the supercritical carbon dioxide/entrainer solution.

32. The process as claimed in claim 27, wherein the entrainer/extracted fragments solution is isolated by reducing the pressure or the temperature of the mixture and solution in equilibrium.

33. The process as claimed in claim 32, wherein the entrainer/extracted fragments solution is isolated by reducing the pressure of the solution/mixture to approximately 800 psi or higher after the solution and mixture have reached equilibrium and the desired preselected fragments have been extracted from the mixture.

34. The process as claimed in claim 32, wherein the entrainer/extracted fragments solution is isolated by reducing the temperature of the solution/mixture by 30° - 50°C after the solution and mixture have reached equilibrium and the desired preselected fragments have been extracted from the mixture.