CA1181767A - Fatty acid separation - Google Patents
Fatty acid separationInfo
- Publication number
- CA1181767A CA1181767A CA000413100A CA413100A CA1181767A CA 1181767 A CA1181767 A CA 1181767A CA 000413100 A CA000413100 A CA 000413100A CA 413100 A CA413100 A CA 413100A CA 1181767 A CA1181767 A CA 1181767A
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- acid
- zone
- adsorbent
- desorbent
- fatty acid
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Abstract
ABSTRACT
A process for separating a first fatty acid selected from the group consisting of stearic acid and oleic acid from a mixture of this first fatty acid and a second fatty acid selected from the group consist-ing of palmitic acid and linoleic acid, which process comprises contact-ing the mixture at adsorption conditions with an adsorbent comprising a nonionic hydrophobic insoluble cross-linked polystyrene polymer, thereby selectively adsorbing the first fatty acid, wherein when the first acid is stearic acid then the second acid is palmitic acid and wherein when the first acid is oleic acid then the second acid is linoleic acid.
A process for separating a first fatty acid selected from the group consisting of stearic acid and oleic acid from a mixture of this first fatty acid and a second fatty acid selected from the group consist-ing of palmitic acid and linoleic acid, which process comprises contact-ing the mixture at adsorption conditions with an adsorbent comprising a nonionic hydrophobic insoluble cross-linked polystyrene polymer, thereby selectively adsorbing the first fatty acid, wherein when the first acid is stearic acid then the second acid is palmitic acid and wherein when the first acid is oleic acid then the second acid is linoleic acid.
Description
t76'7 "FATTY ACID SEPARATION"
BACKGROUND OF THE INVENTION
Field of the Invention The field of art to which this invention pertains is the sol;d bed adsorptive separation oF Fatty acids. More specifically, the invention relates to a process for separating fatty acids which process employs an adsorbent comprising particular polymers which selectively adsorb one fatty acid from a feed mixture containing more than one fatty acid.
Descript _n of the Prior Art It is known in the separation art that cer~ain crys~al-line aluminosilicates can be used to separate certa;n esters of fatty acids from mixtures thereof. For example, in U.S. Patent Nos.
4,048,205; 4,049,688 and 4,066,6779 there are claimed processes ~or the separation of esters of fatty acids of various degrees of unsat-urat;on from mixtures of esters of saturated and unsaturated fatty acids. These processes use adsorbents comprising an X or a Y zeolite conta;n;ng a selected cation at the exchangeable cationic sites.
In contrast, this invention relates to the separation o-f certain fatty acids rather than fatty acid esters. We have discovered that adsorbents comprising nonionic hydrophobic insoluble crosslinked polystyrene polymers exhibit adsorptive selectivity for one fatty acid with respect to another fatty acid, thereby making separation of such fatty acids by solid bed selective hdsorption possible.
In one specific embodiment, our process is a process for separating stearic acid from palmitic acid. In another specific embodiment, our process is a process for separating oleic acid from linoleic acid. Substantial uses of fatty acids are in the plasticizer ancl surface active agent fields. uel~v~ s or ral~y a~as ar~ ul Y~IU~ in compounding lubri-cating oil~ as a lubricant ~or the tex~ile and molding trade, in special lacquers, as a water-proofing agent, in the cosmetic and pharmaceutical fields, and in biodegradable detergents.
SUMMARY OF THE INVENTION
-In brief summary, our invention is in one embodiment a process for separating a first fatty acid selected from the group consisting of stearic acid and oleic acid from a mix~ure comprising the first fatty acid and a second fatty acid selected from the group consisting of palmitic acid and linoleic acid, which process comprises contacting at adsorption conditions that mixture with an adsorbent comprising a non-ionic hydrophobic insoluble crosslinked polystyrene polymer having adsorp-tive selectivity for the f;rst fatty acid, thereby selectively adsorbing the first fatty acid, wherein when the first ac;d is stearic acid then the second acid is palmitic acid and wherein when the first acid is oleic acid then the second acid is linoleic actd, In yet another embodlment, our ;nvention is a process for separat-ing a first fatl;y acid selected from the group consisting of stearic acid and oleic acid frûm a mixture comprising the first fatty acid and a second fatty acid selected from the group consistlng of palmitic acid and linoleic acid, wherein, wb~n, the first acid is stearic acid then the second acid is palmitic acid and wherein when the first acid is oleic acid ^then the second acid is linoleic ~cid, which process employs an adsorbent fomprising a non~onic hydrophobic insoluble cross-linked polystryene polymer, which process cbmprises the steps of: (a) main~aining net fluid flow through a column of the adsorbent in a sinyle direction, which column contains at least three zones having separate operat;onal functions occurring therein and being serially interconnected with the terminal zones of said column connected to provide a continuous connection of the zones; (b) maintaining an adsorption zone in the column, the zone defined by the adsorbent located bet~een a feed inputstream at an upstream boundary of the ~one and a raffinate output stream at a downstream boundary of the zone; k) maintaining a purification zone i~nediately upstream from the adsorp-tion zone, the purification zone defined by the adsorbent located between an ex~ract output stream at an upstream boundary of the purification ~one and the feed input stream at a downs~ream boundary of the purification zone; (d) maintaining a desorpt;on zone immedi-ately upstream from the purification zone, the desorption zone defined by the adsorbent located between a desorbent input stream at an upstream boundary of the zone and the extract output stream at a downstream boundary of ~he zone; (e) pass;ng the ~eed mixture into the adsorption zone at adsorption conditions to effect the selective adsorption of the first fatty acid by the adsorbent in the adsorption zone and withdrawing a raffinate output stream com~
prising the second fatty acid from the adsorption zone;
(f) passing a desorbent material into the desorption zone at desorp-: tion conditions to effect the displacement of the first fatty acid from the adsorbent in the desorption zone; (g) withdrawing an extract ou~put stream comprising the first fatty acid and desorbent material from the desorption zone; (h) passing at least a portion of the extract output stream to a separation means and therein separating at separation conditions at least a portion of the desorbent material; and (i) periodically advancing through the column of adsorbent in a downstream direction with respect to fluid flow in the adsorption zone the feed ;nput stream, raffinate output stream, desorbent input stream, and extract output stream to effect the shift-ing of zones through the adsorbent and the production of extract out-put and raffinate output streams.
Other embodiments of our invention encompass details about 7~i7 feed mixtures, adsorbents, desorbents, desorbent materials and operating conditions, all of which are hereinafter disclosed in the following discussion of each of the facets of the prPsent invention.
DESCRIPTION OF THE INVENTION
At the outset the defin;t;ons of various ~er~s used through-out the specification will be useful in making clear the operation, objects and advantages of our process.
A "feed m;xture" is a mixture containing one or more extract components and one or rnore ra~finate components to be separated by our process. The term "feed stream" indicates a stream of a feed mixture which passes to the adsorbent used in the process.
An "extract component" is a compound or type of compound that is more selectively adsorbed by the adsorbent while a "raffinate csmponen'L" is a compound or type of rompound that is less selectively adsorbed. In this process a first fatty acid is an extract com-ponent and a second fatty acid is a raffinate component. The term "desorbent material" shall mean generally a material capable of desorb-~ ~ ~ ...................................... . .
ing an extract component. The term "desorbent stream" or "desorbent input stream" indicates the stream through which desorbent material passes to the adsorbent. The term "raffinate stream" or "raffinate output stream" means a stream ~hrough which a raffinate component is removed from the adsorbent. The composition of the raffinate stream can vary from essentially 100~ desorbent material to essentially 100%
raffinate components. The term "extract stream" or "extract output stream" shall mean a stream through which an extract material which has been desorbed by a desorbent material is removed from the adsor-bent. The composition of the extract stream, likewise, can vary from essentially 100% desorbent material to essentially 100% extract com-ponents. At least a portion of the extract stream and preferably at least a portion of the raffinate stream from the separation process are passed ts separation means, typically fractiona~ors? where at least a portion of desorbent material is separated to produce an ex-tract product and a raffinate product. The terms "extract product"
and "raffinate product" mean products produced by the process contain-;ng, respectively, an extract component and a raffinate component in higher concentrations than those found in the extract stream and the raffinate stream. Although it is possible by the process of this inven-tion to produce a high purity, first fatty acid product or a second fatty acid product (or both) at high recoveries, it will be appreciated that an extract component is never completely adsorbed by the adsorbent, nor is a raffinate component completely non-adsorbed by the adsorbent. Therefore, varying amounts of a raffinate component can appear in the extract stream and, likewise, varying amounts of an extract component can appear in the raffinate stream. The extract and raffinate streams then are further distinguished from each uther and from the feed ~i~17~;~
m;xture by the ratio of the concentrations of an extract component and a raffinate component appeariny in the particular stream. More specifically, the ra~io of the concentration of a first fatty acid to ~hat of a less selectively adsorbed second fatty acid will be lowest in the raffinate stream, next hi~hest in the feed mixture, and the highest in the extract stream. Likewise, the ratio of the concentration of a less selectively adsorbed first fatty acid to that of a more selectively adsorbed second fatty acid will be highest in the raffinate stream, next highest in the feed mixture, and the lowest in the extract stream.
The -term "selective pore volume" of the adsorbent is de-fined as the volume of the adsorbent which select;vely adsorbs an extract component from the feed mixture. The term "non-selective void volume" of ~he adsorbent is the volume of the adsorbent whioh does not selectively retain an extract component from the feed mix-ture. This volume includes the cavities of the adsorbent which con-tain no adsorptive sites and the interstitial void spaces between adsorbent particles. The selective pore volume and the non-selective void volume are generally expressed in volumetric quantities and are of importance in determinin~ the proper flow rates of fluid required to be passed into an operational zone for efficient operations to take place for a given quantity of adsorbent. When adsorbent "passes" into an operational zone (hereinafter defined and described) employed in - one embodiment of this process its non-selective void volume together with its selective pore volume carries fluid into that zone. The non-selective ~oid volume is utilized in determining the amount of fluid which should pass into the same zone in a countercurrent direction to the adsorbent to displa~e the fluid present in the non-selectiYe void ~ !L76~
volume. If the fluid flow rate passing into a zone is smaller than the non-selective void volume rate of adsorbent material passing into that zone, there is a net entrainment of liquid intn the zone by the adsorbent. Since this net entrainmen~ is a fluid present in non-selective void volume of the adsorbent, it in most instances comprises less selectively retained feed components. The selective pore volume of an adsorbent can in certain instances adsorb portions of raffinate material from the fluid surrounding the adsorbent since in certain instances there is competi$ion between extract material and raffinate material for adsorptive sites within the selective pore volume. If a large quantity of raf~inate material with respect to extract material surrounds the adsorbent, raffinate material can be competitive enough to be adsorbed by the adsorbent.
Before considering feed mixtures which can be charged to the process of our invention brief reference is first made to the terminology and to the general production of fatty acids. The fatty acids are a large group of aliphatic monocarboxylic acids, many of which occur as glycerides (esters of glycerol) in natural fats and oils. Although the term "fatty acids" has been restricted by some to the saturated acids of the acetic acid series, both normal and branched chain, it is now generally used, and is so used herein, to include also related unsaturated acids, certain substituted acids, and e~en aliphatic acids containing al;cyclic substituents. The naturally occurring fatty acids with a few exceptions are higher straight chain unsubstituted ~5 acids containing an even number of carbon atoms. The unsaturated fatty acids can be divided, on the basis of the number of double bonds in the hydrocarbon chain, into monoethanoid, diethanoid, triethanoid, etc. (or monoethylenic, etc.) Thus the term "unsaturated fatty acid" is a ~eneric 7~i7 term for a fatty acid having at least one double bond, and the term "polyethanoid fatty acid" means a fatty acid having more than one double bond per molecule. Fatty acids are typically prepared from glyceride fats or oils by one of several "splitting" or hydrolytic processes. In all cases the hydrolysis reaction may be summarized as the reaction of a fat or oil with water to yield fatty acids plus glycerol. In modern fatty acid plants this process is carried out by continuous high pressure, high temperature hydrolysis of the fat.
Starting materials most commonly used for the production of fatty acids include coconut oil, palm oil, inedible animal fats, and the commonly used vegetable oils, soybean oil~ cottonseed oil and corn oil.
The composition of the fatty acids obtained from the "spl;tter" is dependent on the fat or oil from which they were made. As detailed data for ~he fatty acid composition of fats have accumulated over a wide range of rnaterial, it has become more and more apparent that natural fats tend to align themselves, by their component acids, in groups according to their biological origin. Moreover, it has become clear that the fats of the simplest and most primitive organisms are usually made up from a very complex mixture of fatty acids whereas as biological development has proceeded, the chief romponent acids of the fats of the higher organisms have become fewer in number. In the animal kingdom this change in type is remarkably consistent and culmin-ates, in the fats of the higher land animals, in fats in which oleic, palmitic and stearic acids are the only major components. All fats of aquatic origin contain a wide range of combined fatty acids, mainly of the unsaturated series. On passing from fats of aquatic to those of land animals there is also a marked simplification in the composition of the mixed fatty acids, most of the unsaturated acids, except oleic '7~7 acid. disappear. The final result is that in most of the higher land animals the major componen~ acids of the fats are restr;cted to oleic, palmitic and stearic and, morPover, that about 60-65% of the acids belong to the C18 series, saturated or unsaturated. Thus the compo-sition cf the fatty acids obta;ned from the "splitter" can vary widely depending upon the fat or oil charged to the "spl;tter". Rarely will the composition of the fatty acid mixture nbtained from the "splitter"
be ideal or even satisfactory for most uses. Hence fractionation is used almost universally to prepare prsducts more desirable for spec;fic end uses than the mixtures obtained from the "splitter". Fractionation according to molecular weight is usually accomplished in fractional dis-i tillation. ~here is somewhat of a di ff erence in.the volatility of any two fatty acids ofdifferentchainlength~ andin practice,theutility sf fractional distillation is enhaneed by the absence of odd-membered 1~ acids in the natural fats, so that 2 carbon atoms is nearly always the minimum difference in chain ~ength of the fatty acids present in a mixture. Fract'ionating columns in such operation are sometimes ~apable of producing fatty acids of 95% purity or better from the viewpoin~ of chain length depending on the chain length in question. It is not pos-sible~ however, to separate unsaturated fatty acids from each other or . froms~t~r~ted fatty acids or to separate certain saturated fatty ac;ds ; from each other by commercial fractional distillation when all have the same cha~n length or minimum differen~e in chain length.
Our process is directed to separating certain mixtures of these , fatty acids; more specifically, it is directed to separating a f;rst fatty acid from a mixture comprising a first fatty acid and a second fatty acid, wherein when the first fatty acid is stearic acid then the second fatty acid is palmitic acid and where~n when the first fatty acid is oleic acid then the second fatty acid is linoleic acid.
~ . ..... .
An example of a typical feed mixture is known as "tall oil fatty acids"
and comprises abnut 1 vol. % of palmitic acid, 2 vol. % stearic acid, 51 vol. ~ oleic acid, 45 vol. % linoleic acid and 4 vol. % others. Feed mixtures which can be charged to our process may contain, in addition to fatty ac;ds, a diluent material that is not adsorbed by the adsor-bent and which is preferably separable from the extract and raffinate output streams by fractional d;stillat;on. When a diluent is employed the concentrat;on of d;luent in the mixture of diluent and fatty acids may be from a few vol. % up to about 90 vol. X.
Desorbent materials used in various prior art a~sorptive separat;on processes vary depending upon such factors as ~he type of operation employed. In the swing bed system in which ~he select;vely adsorbed ~eed component is removed from the adsorbent by a purge stream desorbent selection is not as critical and desorbent mat~rials compris;ng gaseous hydrocarbons such as methane; ethane, e~c., or other types of ~3ases such as nitrogen or hydrogen may be used at elevated temperatures or reduced pressures or both to effectively purge the adsorbed feed component from the adsorbent. However, in adsorptive separation processes which are generally operated contin-uously at substantially constant pressures and temperatures to insure liquid phase, the desorbent material must be judic;ously selected to satisfy many criteria. First, the desorbent material should displace an extract component from the adsorbent with reasonable mass flow rates withuut itself being so strongly adsorbed as to unduly prevent an extract component from displacing the desorbent material in a following adsorption cycle. Expressed in tenms of the selectiYity ~hereinafter discussed in more detail)9 it is preferred that the adsorbent be more selective for all of the extract components with respect to a raffinate , _ ___.___ '7 component than it is for the desorbent material with respect ~o a raffinate component. Secondly, desorbent materials must be compati-ble with the particular adsorbent and the particular feed mixture.
More specifically, they must not reduce or destroy the critical sel-ectivity of the adsorbent for an extract component with respect to a raffinate component. Desorbent materials should addi~ionally be substances which are easily separable from the feed mixture that is passed into the process. Both the raffinate stream and the extract stream are removed from the adsorbent in admixture with desorbent material and without a method of separating at least a portion of the desorbent material the purity of the extract product and the raff;-nate product would no~ be very high, nor would the desorbent material be available for reuse in the process. It is therefore contemplated that any desorbent material used in th;s process will preferably have a substantially different average boiling point than that of the feed mixture to allow separation of at least a por~ion of desorbent mate-rial from feed components in the extract and raffinate streams by sim-ple fractional distillation ~hereby permitting reuse of desorbent material in the process. The term "substantially different" as used herein shall mean that the difference between the average boiling points between the desorbent material and the feed mixture shall be at least about 5C. The boiling range of the desorbent material may be higher or lower than that of the feed mixture. Finally, desorbent materials should also be materials which are readily available and therefore reasonable in cost. In the preferred isothermal, ;sobaric, liquid phase operation of the process of our invention? we ha~e found parti-cular1y effective desorbent materials compr~sing one o~ the mixtures 176~
in the group of mixtures comprising acetonitrile and methanol;
acetonitrile, tetrahydrofuran and water; acetone and water; dimethyl acetamide and water; methanol and water; dimethyl formamide and water;
quarternary methyl ammonium hydroxide, water and methanol; and quarter-nary propyl ammonium hydroxide.
The prior art has also recognized that certain characteristics of adsorbents are highly desirable, if not absolutely necessary, to the successful operation of a selective adsorption process. Such characteristics are equally important ~o this process. Among such characteristics are: adsorptive capacity for some volume of an extract component per volume of adsorbent; the selective adsorption of an extract componen~ with respect to a raffinate component and the desorbent materialj and sufficiently fast rates of adsorption and desorp~ion o~ an extract component to and from the adsorbent. Capa-city of the adsorbent for adsorbing a specific volume of an extract component is, of course, a necessity; without such capac;ty the adsorbent is useless for adsorptive separation. Furthermore, the higher the adsorbent's capacity for an extract component the better is the adsorbent. Increased capacity of a particular adsorbent makes it possible to reduce the amount of adsorbent needed to separate an extract component of known concentration contained in a particular charge rate of feed m;xture. A reduction in the amount of adsorbent requ;red for a specific adsorptive separation reduces the cost of the scparation process. It is important that the good initial capacity of
BACKGROUND OF THE INVENTION
Field of the Invention The field of art to which this invention pertains is the sol;d bed adsorptive separation oF Fatty acids. More specifically, the invention relates to a process for separating fatty acids which process employs an adsorbent comprising particular polymers which selectively adsorb one fatty acid from a feed mixture containing more than one fatty acid.
Descript _n of the Prior Art It is known in the separation art that cer~ain crys~al-line aluminosilicates can be used to separate certa;n esters of fatty acids from mixtures thereof. For example, in U.S. Patent Nos.
4,048,205; 4,049,688 and 4,066,6779 there are claimed processes ~or the separation of esters of fatty acids of various degrees of unsat-urat;on from mixtures of esters of saturated and unsaturated fatty acids. These processes use adsorbents comprising an X or a Y zeolite conta;n;ng a selected cation at the exchangeable cationic sites.
In contrast, this invention relates to the separation o-f certain fatty acids rather than fatty acid esters. We have discovered that adsorbents comprising nonionic hydrophobic insoluble crosslinked polystyrene polymers exhibit adsorptive selectivity for one fatty acid with respect to another fatty acid, thereby making separation of such fatty acids by solid bed selective hdsorption possible.
In one specific embodiment, our process is a process for separating stearic acid from palmitic acid. In another specific embodiment, our process is a process for separating oleic acid from linoleic acid. Substantial uses of fatty acids are in the plasticizer ancl surface active agent fields. uel~v~ s or ral~y a~as ar~ ul Y~IU~ in compounding lubri-cating oil~ as a lubricant ~or the tex~ile and molding trade, in special lacquers, as a water-proofing agent, in the cosmetic and pharmaceutical fields, and in biodegradable detergents.
SUMMARY OF THE INVENTION
-In brief summary, our invention is in one embodiment a process for separating a first fatty acid selected from the group consisting of stearic acid and oleic acid from a mix~ure comprising the first fatty acid and a second fatty acid selected from the group consisting of palmitic acid and linoleic acid, which process comprises contacting at adsorption conditions that mixture with an adsorbent comprising a non-ionic hydrophobic insoluble crosslinked polystyrene polymer having adsorp-tive selectivity for the f;rst fatty acid, thereby selectively adsorbing the first fatty acid, wherein when the first ac;d is stearic acid then the second acid is palmitic acid and wherein when the first acid is oleic acid then the second acid is linoleic actd, In yet another embodlment, our ;nvention is a process for separat-ing a first fatl;y acid selected from the group consisting of stearic acid and oleic acid frûm a mixture comprising the first fatty acid and a second fatty acid selected from the group consistlng of palmitic acid and linoleic acid, wherein, wb~n, the first acid is stearic acid then the second acid is palmitic acid and wherein when the first acid is oleic acid ^then the second acid is linoleic ~cid, which process employs an adsorbent fomprising a non~onic hydrophobic insoluble cross-linked polystryene polymer, which process cbmprises the steps of: (a) main~aining net fluid flow through a column of the adsorbent in a sinyle direction, which column contains at least three zones having separate operat;onal functions occurring therein and being serially interconnected with the terminal zones of said column connected to provide a continuous connection of the zones; (b) maintaining an adsorption zone in the column, the zone defined by the adsorbent located bet~een a feed inputstream at an upstream boundary of the ~one and a raffinate output stream at a downstream boundary of the zone; k) maintaining a purification zone i~nediately upstream from the adsorp-tion zone, the purification zone defined by the adsorbent located between an ex~ract output stream at an upstream boundary of the purification ~one and the feed input stream at a downs~ream boundary of the purification zone; (d) maintaining a desorpt;on zone immedi-ately upstream from the purification zone, the desorption zone defined by the adsorbent located between a desorbent input stream at an upstream boundary of the zone and the extract output stream at a downstream boundary of ~he zone; (e) pass;ng the ~eed mixture into the adsorption zone at adsorption conditions to effect the selective adsorption of the first fatty acid by the adsorbent in the adsorption zone and withdrawing a raffinate output stream com~
prising the second fatty acid from the adsorption zone;
(f) passing a desorbent material into the desorption zone at desorp-: tion conditions to effect the displacement of the first fatty acid from the adsorbent in the desorption zone; (g) withdrawing an extract ou~put stream comprising the first fatty acid and desorbent material from the desorption zone; (h) passing at least a portion of the extract output stream to a separation means and therein separating at separation conditions at least a portion of the desorbent material; and (i) periodically advancing through the column of adsorbent in a downstream direction with respect to fluid flow in the adsorption zone the feed ;nput stream, raffinate output stream, desorbent input stream, and extract output stream to effect the shift-ing of zones through the adsorbent and the production of extract out-put and raffinate output streams.
Other embodiments of our invention encompass details about 7~i7 feed mixtures, adsorbents, desorbents, desorbent materials and operating conditions, all of which are hereinafter disclosed in the following discussion of each of the facets of the prPsent invention.
DESCRIPTION OF THE INVENTION
At the outset the defin;t;ons of various ~er~s used through-out the specification will be useful in making clear the operation, objects and advantages of our process.
A "feed m;xture" is a mixture containing one or more extract components and one or rnore ra~finate components to be separated by our process. The term "feed stream" indicates a stream of a feed mixture which passes to the adsorbent used in the process.
An "extract component" is a compound or type of compound that is more selectively adsorbed by the adsorbent while a "raffinate csmponen'L" is a compound or type of rompound that is less selectively adsorbed. In this process a first fatty acid is an extract com-ponent and a second fatty acid is a raffinate component. The term "desorbent material" shall mean generally a material capable of desorb-~ ~ ~ ...................................... . .
ing an extract component. The term "desorbent stream" or "desorbent input stream" indicates the stream through which desorbent material passes to the adsorbent. The term "raffinate stream" or "raffinate output stream" means a stream ~hrough which a raffinate component is removed from the adsorbent. The composition of the raffinate stream can vary from essentially 100~ desorbent material to essentially 100%
raffinate components. The term "extract stream" or "extract output stream" shall mean a stream through which an extract material which has been desorbed by a desorbent material is removed from the adsor-bent. The composition of the extract stream, likewise, can vary from essentially 100% desorbent material to essentially 100% extract com-ponents. At least a portion of the extract stream and preferably at least a portion of the raffinate stream from the separation process are passed ts separation means, typically fractiona~ors? where at least a portion of desorbent material is separated to produce an ex-tract product and a raffinate product. The terms "extract product"
and "raffinate product" mean products produced by the process contain-;ng, respectively, an extract component and a raffinate component in higher concentrations than those found in the extract stream and the raffinate stream. Although it is possible by the process of this inven-tion to produce a high purity, first fatty acid product or a second fatty acid product (or both) at high recoveries, it will be appreciated that an extract component is never completely adsorbed by the adsorbent, nor is a raffinate component completely non-adsorbed by the adsorbent. Therefore, varying amounts of a raffinate component can appear in the extract stream and, likewise, varying amounts of an extract component can appear in the raffinate stream. The extract and raffinate streams then are further distinguished from each uther and from the feed ~i~17~;~
m;xture by the ratio of the concentrations of an extract component and a raffinate component appeariny in the particular stream. More specifically, the ra~io of the concentration of a first fatty acid to ~hat of a less selectively adsorbed second fatty acid will be lowest in the raffinate stream, next hi~hest in the feed mixture, and the highest in the extract stream. Likewise, the ratio of the concentration of a less selectively adsorbed first fatty acid to that of a more selectively adsorbed second fatty acid will be highest in the raffinate stream, next highest in the feed mixture, and the lowest in the extract stream.
The -term "selective pore volume" of the adsorbent is de-fined as the volume of the adsorbent which select;vely adsorbs an extract component from the feed mixture. The term "non-selective void volume" of ~he adsorbent is the volume of the adsorbent whioh does not selectively retain an extract component from the feed mix-ture. This volume includes the cavities of the adsorbent which con-tain no adsorptive sites and the interstitial void spaces between adsorbent particles. The selective pore volume and the non-selective void volume are generally expressed in volumetric quantities and are of importance in determinin~ the proper flow rates of fluid required to be passed into an operational zone for efficient operations to take place for a given quantity of adsorbent. When adsorbent "passes" into an operational zone (hereinafter defined and described) employed in - one embodiment of this process its non-selective void volume together with its selective pore volume carries fluid into that zone. The non-selective ~oid volume is utilized in determining the amount of fluid which should pass into the same zone in a countercurrent direction to the adsorbent to displa~e the fluid present in the non-selectiYe void ~ !L76~
volume. If the fluid flow rate passing into a zone is smaller than the non-selective void volume rate of adsorbent material passing into that zone, there is a net entrainment of liquid intn the zone by the adsorbent. Since this net entrainmen~ is a fluid present in non-selective void volume of the adsorbent, it in most instances comprises less selectively retained feed components. The selective pore volume of an adsorbent can in certain instances adsorb portions of raffinate material from the fluid surrounding the adsorbent since in certain instances there is competi$ion between extract material and raffinate material for adsorptive sites within the selective pore volume. If a large quantity of raf~inate material with respect to extract material surrounds the adsorbent, raffinate material can be competitive enough to be adsorbed by the adsorbent.
Before considering feed mixtures which can be charged to the process of our invention brief reference is first made to the terminology and to the general production of fatty acids. The fatty acids are a large group of aliphatic monocarboxylic acids, many of which occur as glycerides (esters of glycerol) in natural fats and oils. Although the term "fatty acids" has been restricted by some to the saturated acids of the acetic acid series, both normal and branched chain, it is now generally used, and is so used herein, to include also related unsaturated acids, certain substituted acids, and e~en aliphatic acids containing al;cyclic substituents. The naturally occurring fatty acids with a few exceptions are higher straight chain unsubstituted ~5 acids containing an even number of carbon atoms. The unsaturated fatty acids can be divided, on the basis of the number of double bonds in the hydrocarbon chain, into monoethanoid, diethanoid, triethanoid, etc. (or monoethylenic, etc.) Thus the term "unsaturated fatty acid" is a ~eneric 7~i7 term for a fatty acid having at least one double bond, and the term "polyethanoid fatty acid" means a fatty acid having more than one double bond per molecule. Fatty acids are typically prepared from glyceride fats or oils by one of several "splitting" or hydrolytic processes. In all cases the hydrolysis reaction may be summarized as the reaction of a fat or oil with water to yield fatty acids plus glycerol. In modern fatty acid plants this process is carried out by continuous high pressure, high temperature hydrolysis of the fat.
Starting materials most commonly used for the production of fatty acids include coconut oil, palm oil, inedible animal fats, and the commonly used vegetable oils, soybean oil~ cottonseed oil and corn oil.
The composition of the fatty acids obtained from the "spl;tter" is dependent on the fat or oil from which they were made. As detailed data for ~he fatty acid composition of fats have accumulated over a wide range of rnaterial, it has become more and more apparent that natural fats tend to align themselves, by their component acids, in groups according to their biological origin. Moreover, it has become clear that the fats of the simplest and most primitive organisms are usually made up from a very complex mixture of fatty acids whereas as biological development has proceeded, the chief romponent acids of the fats of the higher organisms have become fewer in number. In the animal kingdom this change in type is remarkably consistent and culmin-ates, in the fats of the higher land animals, in fats in which oleic, palmitic and stearic acids are the only major components. All fats of aquatic origin contain a wide range of combined fatty acids, mainly of the unsaturated series. On passing from fats of aquatic to those of land animals there is also a marked simplification in the composition of the mixed fatty acids, most of the unsaturated acids, except oleic '7~7 acid. disappear. The final result is that in most of the higher land animals the major componen~ acids of the fats are restr;cted to oleic, palmitic and stearic and, morPover, that about 60-65% of the acids belong to the C18 series, saturated or unsaturated. Thus the compo-sition cf the fatty acids obta;ned from the "splitter" can vary widely depending upon the fat or oil charged to the "spl;tter". Rarely will the composition of the fatty acid mixture nbtained from the "splitter"
be ideal or even satisfactory for most uses. Hence fractionation is used almost universally to prepare prsducts more desirable for spec;fic end uses than the mixtures obtained from the "splitter". Fractionation according to molecular weight is usually accomplished in fractional dis-i tillation. ~here is somewhat of a di ff erence in.the volatility of any two fatty acids ofdifferentchainlength~ andin practice,theutility sf fractional distillation is enhaneed by the absence of odd-membered 1~ acids in the natural fats, so that 2 carbon atoms is nearly always the minimum difference in chain ~ength of the fatty acids present in a mixture. Fract'ionating columns in such operation are sometimes ~apable of producing fatty acids of 95% purity or better from the viewpoin~ of chain length depending on the chain length in question. It is not pos-sible~ however, to separate unsaturated fatty acids from each other or . froms~t~r~ted fatty acids or to separate certain saturated fatty ac;ds ; from each other by commercial fractional distillation when all have the same cha~n length or minimum differen~e in chain length.
Our process is directed to separating certain mixtures of these , fatty acids; more specifically, it is directed to separating a f;rst fatty acid from a mixture comprising a first fatty acid and a second fatty acid, wherein when the first fatty acid is stearic acid then the second fatty acid is palmitic acid and where~n when the first fatty acid is oleic acid then the second fatty acid is linoleic acid.
~ . ..... .
An example of a typical feed mixture is known as "tall oil fatty acids"
and comprises abnut 1 vol. % of palmitic acid, 2 vol. % stearic acid, 51 vol. ~ oleic acid, 45 vol. % linoleic acid and 4 vol. % others. Feed mixtures which can be charged to our process may contain, in addition to fatty ac;ds, a diluent material that is not adsorbed by the adsor-bent and which is preferably separable from the extract and raffinate output streams by fractional d;stillat;on. When a diluent is employed the concentrat;on of d;luent in the mixture of diluent and fatty acids may be from a few vol. % up to about 90 vol. X.
Desorbent materials used in various prior art a~sorptive separat;on processes vary depending upon such factors as ~he type of operation employed. In the swing bed system in which ~he select;vely adsorbed ~eed component is removed from the adsorbent by a purge stream desorbent selection is not as critical and desorbent mat~rials compris;ng gaseous hydrocarbons such as methane; ethane, e~c., or other types of ~3ases such as nitrogen or hydrogen may be used at elevated temperatures or reduced pressures or both to effectively purge the adsorbed feed component from the adsorbent. However, in adsorptive separation processes which are generally operated contin-uously at substantially constant pressures and temperatures to insure liquid phase, the desorbent material must be judic;ously selected to satisfy many criteria. First, the desorbent material should displace an extract component from the adsorbent with reasonable mass flow rates withuut itself being so strongly adsorbed as to unduly prevent an extract component from displacing the desorbent material in a following adsorption cycle. Expressed in tenms of the selectiYity ~hereinafter discussed in more detail)9 it is preferred that the adsorbent be more selective for all of the extract components with respect to a raffinate , _ ___.___ '7 component than it is for the desorbent material with respect ~o a raffinate component. Secondly, desorbent materials must be compati-ble with the particular adsorbent and the particular feed mixture.
More specifically, they must not reduce or destroy the critical sel-ectivity of the adsorbent for an extract component with respect to a raffinate component. Desorbent materials should addi~ionally be substances which are easily separable from the feed mixture that is passed into the process. Both the raffinate stream and the extract stream are removed from the adsorbent in admixture with desorbent material and without a method of separating at least a portion of the desorbent material the purity of the extract product and the raff;-nate product would no~ be very high, nor would the desorbent material be available for reuse in the process. It is therefore contemplated that any desorbent material used in th;s process will preferably have a substantially different average boiling point than that of the feed mixture to allow separation of at least a por~ion of desorbent mate-rial from feed components in the extract and raffinate streams by sim-ple fractional distillation ~hereby permitting reuse of desorbent material in the process. The term "substantially different" as used herein shall mean that the difference between the average boiling points between the desorbent material and the feed mixture shall be at least about 5C. The boiling range of the desorbent material may be higher or lower than that of the feed mixture. Finally, desorbent materials should also be materials which are readily available and therefore reasonable in cost. In the preferred isothermal, ;sobaric, liquid phase operation of the process of our invention? we ha~e found parti-cular1y effective desorbent materials compr~sing one o~ the mixtures 176~
in the group of mixtures comprising acetonitrile and methanol;
acetonitrile, tetrahydrofuran and water; acetone and water; dimethyl acetamide and water; methanol and water; dimethyl formamide and water;
quarternary methyl ammonium hydroxide, water and methanol; and quarter-nary propyl ammonium hydroxide.
The prior art has also recognized that certain characteristics of adsorbents are highly desirable, if not absolutely necessary, to the successful operation of a selective adsorption process. Such characteristics are equally important ~o this process. Among such characteristics are: adsorptive capacity for some volume of an extract component per volume of adsorbent; the selective adsorption of an extract componen~ with respect to a raffinate component and the desorbent materialj and sufficiently fast rates of adsorption and desorp~ion o~ an extract component to and from the adsorbent. Capa-city of the adsorbent for adsorbing a specific volume of an extract component is, of course, a necessity; without such capac;ty the adsorbent is useless for adsorptive separation. Furthermore, the higher the adsorbent's capacity for an extract component the better is the adsorbent. Increased capacity of a particular adsorbent makes it possible to reduce the amount of adsorbent needed to separate an extract component of known concentration contained in a particular charge rate of feed m;xture. A reduction in the amount of adsorbent requ;red for a specific adsorptive separation reduces the cost of the scparation process. It is important that the good initial capacity of
2~ the adsorbent be maintained during actual use in the separation pro-cess over some economically desirable life. The second necessary ad-sorbent characteristic is the ability of the adsorbent to separate components of the feed, or, in other words, that the adsorbent possess adsorptive selectivity, (B), ~or one component as compared to another component. Relative selectivity can be expressed not only for one feed component as compared to another but can also be expressed be-tween any feed mixture component and the desorbent material. The selectivity, (B), as used throughout th;s spec;fication is defined as the ratio of the two components of the adsorbed phase over the ratio of the same two components in ~he unadsorbed phase at equilibrium conditions. Relative selectivity is shown as Equation 1 below:
Equation 1 Selectivity = (B) = Evl- percent C!vol. percent vol. percent Clvol. percent D U
where C and D are two components of the feed represented in volume percent and the subscr;p~s A and U represent the adsorbed and unadsorbed phases respectively. The equ;librium conditions were detenm;ned when the feed passing over a bed of adsorbent did not change compos;tion after contacting the bed of adsorbent. In other words, there was no net transfer of material occurring between the unadsorbed and adsorbed phases. Where select;v;ty of two components approaches 1.0 there is no preferential adsorption of one component by the adsorbent with respect to the other; they are both adsorbed ~or non-adsorbed) to about the same degree with respect to each o~her. As the (B) becomes less than or greater than 1.0 there is a preferent;al adsorption by the adsorbent for one component with respect to the other. When comparing the selectivity by the adsorbent of one component C over component D, a (B) larger than 1.0 indicates preferential adsorption of component C within the adsorbent.
~5 A (B) less than 1.0 would ;ndicate that component D is preferentially adsorbed leav;ng an unadsorbed phase richer in component C and an adsorbed phase r;cher in component D. Ideally desorbent mater;als should have a select;v;ty equal to about 1 or slightly less than 1 with respect to all extract components so that all of the ex~ract components can be desorbed as a class with reasonable flow rates of desorbent ma~erial and so that extract components can displace desorbent material in a subsequent adsorption step. Wh;le separation of an extract component from a raffinate component is theoretically possible when the selec-tivity of the adsorbent for the extract component with respect to the raffinate component is greater than 1, it ;s preferred that such selectiv;ty approach a value of 2. Like relative volat;l;ty, the higher the selectivity the easier the separation is to perform.
Higher select;v;ties penmit a smaller amount of adsorbent to be used.
The third ;mportant characteristic is the ra~e of exchange of the extract component of the feed m;xture mater;al or, in other words~
the relative rate of desorption of the extract component. Th;s char-acterist;c relates directly to the amount of desorbent material that must be employed in the process to recover the extract component from the adsorbent; faster rates of exchange reduce the amount of desorbent material needed to remove the extract component and therefore permit a reduction in the operating cost of the process. ~lith faster rates of exchange, less desorbent material has to be pumped through the process and separated from the extract stream for reuse in the process.
A dynamic testing apparatus is employed to test various adsorbents with a particular feed mixture and desorbent material to measure the adsorbent characteristics of adsorptive capacity, selecti-vity and exchange rate. The apparatus consists of an adsorbent chamber comprising a helical column of approximately 70 cc volume havlng inlet and outlet portions at opposite ends of the chamber. The chamber is contained within a temperature control means and, in addition, pressure ~81~76~7 control equipment ;s used to operate the chamber at a constant pre-determined pressure. Quantitative and qualitative analytical equip-ment such as refractometers, polarimeters and chromatographs can be attached to the outlet line of the chamber and used to detect quanti-tati~ely or determ;ne qualitatively one or more components in the effluent stream leaYing the adsorbent chamber. A pulse test, performed using this apparatus and the following general procedure, is used to determine selectivities and other data for various adsorbent systems.
The adsorbent is filled to equ;librium with a particular desorbent material by passing the desorbent material through the adsorbent cham-ber. At a convenient time, a pulse of feed containing known concentra-tions of a tracer and of a particular extract component or of a raffinate component or both all diluted in desorbent is injected for a duration of several minutes. Desorbent flow is resumed, and the tracer and the extract component or the raffinate component (or both) are eluted as in a liguid-solid chromatographic operation. The effluent can be analyzed onstream or alternatively eFfluent samples can be col-lected periodically and la~er analyzed separately by analytical equip-~ent and traces of the envelopes of corresponding component peaks developed.
-- From information derived from the test adsorbent performance can be rated in terms of void volume, retention volume for an extract or a raffinate component, selectivity for one component with respect to the other, and the rate of desorption of an extract component by the desorbent. The retention volume of an extract or a raffinate component may be characterized by the distance between the center of the peak envelope of an extract or a raffinate compon~nt and the peak envelope of the tracer component or some o~her known reference point. It is '76~
expressed in terms of the volume in cubic cent;meters of desorbent pumped during this time interval represented by the distance between the peak envelopes. Selectivity, (B), for an extract component w;th respect to a raff;nate component may be characterized by the ratio of the distance between the center of the extract camponent peak envelope and the tracer peak envelope ~or other reference point) to the corresponding distance between lthe center of the raffinate compo-nent peak envelope and the tracer peak envelope. The rate of exchange of an extract component with the desorbent can generally be charac-terized by the width of the peak envelopes at half intensity. The narrower the peak width the faster the desorption rate. The desorp-tion rate can also be characteri~ed by the distance between the center of the ~tracer peak envelope and ~he disappearance of an extract component which has just been desorbed. This distance is again the volume of desorbent pumped during this time interval.
To further evalua~te promising adsorbent systems and ~o translate this type of data into a practical separation process requires actual testing of the best system in a continuous counter-current liquid-solid contacting device. The general operating opera-ting principles of such a device have been previously described and are found in Broughton U.S. Patent 2,985,589. A specific laboratory size apparatus utilizing these principles is described in deRosset etal.,U.S.Patent 3,706,812. The equipment romprjSes multiple adsorbent beds with a number of access lines attached to dis-tributors within the beds and terminating at a rotary distributing valve. At a given valve position. feed and desorbent are being introduced through two of the lines and the raffinate and extract streams are being withdrawn through two more. All rema~ning access ~i81~6~
lines are inactive and when the position of the distributing valve is advanced by one index all active positions will be advanced by one bed. This simulates a condition in which the adsorbent physically moves in a direction countercurrent to the liquid flow.
Additional details on the above-mentioned nonionic adsorbent testing apparatus and adsorbent evaluation tPchn;ques may be found in the paper "Separation of C~ Aromatics by Adsorption" by A.J. deRosset9 R.W.
Neuzil, D.J. Korous, and D.H. Rosback presented at the American Chemical Society, Los Angeles9 California, March 28 through April 2, 1971.
Adsorbents to be used in the process of this invention will comprise nonionic hydrophobic insoluble crosslinked polystyrene polymers, preferably ~hose manufactured by the Rohm and Haas Company and sold under the trade name l'Amberlite". The types of Amberlite polymers known to be eFfective for use by this invention are referred to in Rohm and ~laas Company literature as Amberlite XAD-2 and Amberlite XAD-4, and described in the literature as "hard, insoluble spheres of high surface, porous polymer". The various types of Amberlite polymeric adsorbents differ in physical properties such as porosity volume, surface area, average pore d;ameter, skeletal density and nominal mesh sizes. Applications for Amberlite polymer;c adsorbents suggested in the Rohm and Haas Company literature include decolorizing pulp mill bleaching effluent, decolorizing dye wastes and pesticide removal from waste effluent. There is, of course, no hint in the 2~ literature to our surprising discovery of the effectiv2ness of Amberlite polymeric adsorbents in the separation of monoethanoid fatty acids from diethanoid fatty acids.
A fundamental superiority of the Amberlite polymeric adsor-6i~
bents over crystalline aluminosilicates is that the former, unlike the latter, may be used for the direct separation of fa~ty acids without first converting the fatty acids to their corresponding esters. The processes of the aforementioned prior art patents are applicable only to esters of fat~y acids because the free carboxylic group of a fatty ac;d chemically reacts with the crystalline alumino-s;licates used by those processes. The adsorbent of this invention exhibits no such reactivity and, therefore, the process of this invention is uniquely suitable for the separation of fatty acids.
The adsorbent may b~ employed in the form of a dense compact fixed bed which is alternatively contacted w;th the feed mix-ture and desorbent materials. In the simplest embodiment of the invention the adsorbent is employed in the fcrm of a single static bed in which case the process is only semi-oontinuous. In ano~her embod;ment a set of two or more static beds may be employed in fixed bed contacting with appropriate valving so that ~he feed mixture is passed through one or more adsorbent beds while the desorbent materials can be passed through one or more of the other beds in the set. The flow of feed mixture and desorben~ materials may be either up or down through the desorbent. Any of the conventional apparatus employed in static bed fluid-solid oontacting may be used.
Countercurrent moving bed or simulated movin~ bed counter-current flow systems, however, have a much greater separation efficiency than fixed adsorbent bed systems and are therefore preferred.
In the moving bed or simulated moving bed processes the adsorption and desorption operations are continuously taking place which allows both continuous production of an extract and a raffinate stream and the continual use of feed and desorbent streams. One preferred embodiment L'76~
of this process utilizes what is known in the art as the simulated moving bed countercurrent flow system. The operating principles and sequence of such a flow system are described in U.S. Patent 2,98~,589 incorporated herein by reference thereto. In such a system it is the progressive movement of multiple liquid access points down an adsorbent chamber that simulates the upward movement of adsorbent contained in the chamber. Only four of the access lines are active at any one timei the feed input stream, desorbent inlet stream, raf-finate owtlet stream, and extract outlet stream access lines.
~oincident with this simulated upward movement of the solid adsorbent is the movement of the liquid occupying the void volume of the packed bed of adsorbent. So that countercurrent contact is maintained, a liquid flow down the adsorbent chamber may be provided by a pump. As an ac~ive liquid access point moves through a cycle, that is, from the top of the chamber to the bottom, the chamber circulation pump moves through different zones which requ;re different flow rates. A
programmed flow controller may be provided to set and regulate these flow rates.
The active liqu;d access points effectively divided the adsorbent chamber into separate zunes, each of which has a different function. In this embodiment of our process it is generally necessary that three separate operational zones be present in order for the process to take place although in some instances an optional fourth zone may be used.
The adsorption zone, 7one 1, is defined as the adsorbent located between the feed ;nlet stream and the raffinate outlet stream.
In this zone, the feedstock contacts the adsorbent, an extract compo-nent is adsorbed, and a raffinate stream is withdrawn. Since the 76'~
general flow through zone 1 is from the feed stream which passes into the zone to the raffinate stream which passes out of the zone, the flow in this zone is considered to be a downstream direction when pro-ceeding from the feed inlet to the raffinate outlet streams.
I~mediately upstream with respect to fluid flow in zone 1 ;s the puri~ication zone, zone 2. The purification zone ;s defined as the adsorbent between the extract outlet stream and the feed inlet stream. The basic operations tak;ng place in zone 2 are ~he displace-ment from the non-selective void volume of the adsorbent of any raffinate material carried into zone 2 by the shift;ng of adsorbent into this zone and the desorption of any raffinate material adsorbed within the selective pore volume of the adsorbent or adsorbed on the surfaces of the adsorben~ particles. Purification is achieved by passing a portion of extract stream material leaving zone 3 into zone 2 at zone 2's upstream boundary, the extract outlet stream, to effect the displacement of raffinate material. The flow of material in zone 2 is in a downstream direction from the extract outlet stream to the feed inlet stream.
mediately upstream of zone 2 wi~h respect to the fluid flowing in zone 2 is the desorption zone or zone 3. The desorption zone is defined as the adsorbent between the desorbent inlet and the extract outlet stream. The function of the desorption zone is to allow a desorbent material which passes into this zone to displace the extract component wh;ch was adsorbed upon the adsorbent during a previous contact with feed in zone 1 in a prior cycle of operation.
The flow of fluid in zone 3 is essentially in the same direction as that of zones 1 and 2.
In some instances an optional buffer zone, zone 4, may be 1181 ~
utilized. This zone, defined as the adsorbent between the raffinate outlet stream and the desorbent inle~ stream, if used, is located immediately upstream with respect to the fluid flow to zone 3. Zone 4 would be utilized to conserve the amount of desorbent utilized in the desorption s~ep since a portion of the raffinate stream which ls removed from zone 1 can be passed into zone 4 ~o displace desorbent material present in that zone out of that zone into the~ desorption zone. Zone 4 will contain enough adsorbent so that raffinate mate-rial present in the raffinate stream passing out of zone 1 and into æone 4 can be prevented from passing into zone 3 thereby contaminating extract stream rcmoved from zone 3. In the ;nstances which the fourth operational zone is not utilized the raffina~e stream passed from 70ne 1 to zone 4 must be carefully monitored in order that the flow directly from zone 1 to zone 3 can be stopped when ~here is an appre-1B ciable quantity of raffinate material present in the raffinate stream passing from zone 1 into zone 3 so that the extract outlet stream is not contaminatled.
A cyclic advancement of the input and output streams through the fixed bed Df adsorbent can be accomplished by utilizing a manifold system in which the valves ~n the manifold are operated in a sequential manner to effect the shifting of the input and output streams thereby allowing a flow of fluid with respect to solid adsorbent in a counter-current manner. Another mode of operation whish can effect the counter-current flow of solid adsorbent with respect to fluid involves the use 2~ of a rotating disc valve in which the input and output streams are con-nected to the valve and the lines through which feed input~ extract output, desorbent input and raffinate output streams pass are advanced in the same direction through the adsorbent bed. Both the manifold ~81i767 arrangement and disc valve are known in the art. Specifically rotary disc valves which can be ut;l ked in this operation can be found in U.S. Patents 3,040,777 and 3,422,848. Both of the aforementioned patents disclose a rotary type connection valve in which the suitable advancement of the various input and output streams from fixed sources can be achieved without difficulty.
In many instances, one operational zone will contain a much larger quantity of adsorbent than some other operational zone.
For instances, in some operations the buffer zone can contain a minor amount of adsorbent as compared to the adsorbent required for the adsorption and purification zones. It can also be seen that ;n instances in which desorbent is used which can easily desorb extract material from the adsorbent that a relatively small amount of adsor-bent will be needed in a desorption zone as compared to the adsorbent needed in the buffer zone or adsorption zone or purification zone or all of them. Since it is not required that the adsorbent be located in a single column, the use of multiple chambers or a series of col-umns is within the scope of the invention.
It is not necessary that all of the input or output streams be simultaneously used, and in fact, in many instances some of the streams can be shut off while others effect an ;nput or output of mate-rial. The apparatus which can be utili7ed to e ffect ~he process of this invention can also contain a series of individual beds connected by connecting conduits upon which are placed input or output taps to which the various input or output streams can be attached and alternately and periodically shifted to effect continuous operation. In some in-stances, the connecting conduits can be connected to transfer taps which during the normal operations do not function as a conduit through which ~L~ '7 material passes into or out of the process.
It is contemplated that at least a port;on of the extract output stream will pass into a separation means wherein at least a portion of the desorbent material can be separated to produce an ex-tract product containing a reduced concentration of desorbent material. Preferably, but not necessary to the operat;on of the pro-cess, at least a portion of the raffinate output stream will also be passed to a separation means where;n at least a portion of the desorbent material can be separated to produce a desorbent stream which can be reused in the process and a raffinate product containing a reduced concentration o~ desorbent material. The separa~ion means will typically be a fract;onation column, the design and operation of which is well-known to the separation art.
Reference can be made to D.B. Broughton U.S. Patent 2,985,589, and to a paper entitled "Continuous Adsorpt;ve Processing--A New Separation Technique" by D.B. Broughton presented at the 34th Annual Meeting of the Society of Chemical Engineers at Tokyo~ Japan on April 2, 1969, both incorporated herein by reference, for further explana~ion of the simulated mo~ing bed countercurrent process flow scheme.
Although both liquid and vapor phase operations can be used in many adsorptive separation processes, liquid-phase operation is preferred for this process because of the lower temperature requirements and because of the higher yields of extract product than can be obtained with liquid-phase operation over those obtained with vapor-phase operation. Adsorption conditions will include a temperature range of from about 20C. to about 200~C. with about 20C. to about 100C.
being more preferred and a pressure range of from about atmospheric to 7~-7 about 500 psig ~345n kPa gauge) w~th from about a~mospheric to about 250 psig (1725 kPa gauge) being more preferred to ensure liquid phase.
Desorption conditions will include the same range of tempera~ures and pressures as used for adsorption conditions.
The size of the units which can util ke the process of this invention can vary anywhere from those of pilot plant scale (see for example our assignee's U.S. Patent 3,706,~12, ineorporated herein by reference) to those of commercial scale and can range in flow rates fron as little as a few cc an hour up to ~any thousands of gallons per hour.
The ~ollowing examplearépresented to illustrate 1:he selectivity relationsh;p that makes the process o~ our in~ention pos-sible. The example is not ~ntended to unduly res~rict the scope and spirit o~ claims attached hereto.
1~ ~, .
Thi5 example presents selectivities ~or two Amberlite polymeric adsorbents, comprising Amberlite XAD-2 and Amberlite XAD-4, for oleic acid with respect to a linoleic acid.
The feed mixture comprised the desorbent used in the pulse test in ques-tion and Tall-oil fatty acids in a ratio of desbrbent to Tall-oil fatty ~cids of 90:10. The Tall-~il fatty acids had the following composition:
Fatt~ Acids Palmitic (C160) S Stearic (Cl8~) 2 Ole;c (C181) 5~
Linoleic ~C182) 45 All others 4 Retention volumes and selectivities were obtained using ~ 1 ~3il~7~i~7 the pulse test apparatus and procedure previously described. Spec-ifically, the adsorbents were tested in a 70 cc helical coiled column using the following sequence of operations for each pulse test.
Desorbent material was continuously run through ~he column containing the adsorbent at a nominal liquid hourly space veloc;ty (LHSV) of about 1Ø A void volume was determined by observing the volume of desorbent reguired to fill the packed dry column. At a convenient time the flow of desorbent material was stopped, and a 10 cc sample of feed mixture was injected into the column via a sample loop and the flow of desorben~ material was resumed. Samples of the effluent were automatically collected in an automatic sample collector and later analyzed by chromatographic analysis. From the analysis of these samples peak envelope concentrations were developed for ~he feed mixture components. The retention volume for the fatty acids werP
calculated by measuring the distances from time zero on the reference po;nt to the respective midpoints of the fatty acids and subtracting the distance representing the void volume of the adsorbent. The selectivities of an adsorbent for oleic ac;d with respect to linoleic acid in the presence of a desorbent material are in the quotients obtained by divid;ng the retention volume for the oleic acid by the retention volume for the linoleic acid. The results for these pulse tests are shown in Table No. 1.
~ C~l ~ C~ C ~ O ~
., ~ ~ I ~ C~J ~ t~ ~1 _I ei' N -1 al ~ ~ I r I ~ r-i r~ C_~
-~ N ) Lt U') I~ ~ O
~ Et~ ~1 ~ 1 N C~ ~ ~ t~ ~I 1~ et , ~S I 1~ d` N C~J N Ll O ~D 1~ N '* _I
O --'CO
~_1 O 1~ N 1~ _1 1~ 0 0` ~O O cr~ O
Z ~ ~ ~ CO D et CO 1~ et ~ el~ Cl~
C~
~ ~1 ~ O
c~ . ~D ~D ~ ~ æ o o ~ cn ~L
_I c~ E
O~ U~
Z:~ T T
11.1 t~ O O O
~:~ I ~
ClL~ O C~ ~ ~
O CU I U~ I I
O ~e u)a) Ln ~r) o o O --~ ~ ~ O O
~1 O I _ I I I I C`J C~
clC ~ IaJ -- O E ~ _ O CO I T X X
~ ~ ~ 52 F N S- E E ~ J i_~--LLJ L OL~ I ~ jS5L ~ ~ O ~ O O ~, ~, O ~ I tU ~ O O O ~
C~: _1 11L~ o o z z E E
O t~O 1-) ~J I ~IJal ~11 2 Z O O
T~ I~ a ~ O ~ Y' ~ d ~! ~ ~a ~ ~ ~ ~ ~5 E E
O u~ U~ ~ O ~ Ln u~ l O O ~ n:s O
E Q
N C~ C~ J ~ N ~ ~I C~ r~, XXXXXXX~ XX XX .Q~ ~
O , ,_ 1~7 S_ = = = = = = = = a ~ = -- c ~' -~:1 O U
L'76''~
Figure 1 is an example of a graphical presentation of the results of one of the pulse tests the data from which is also set forth in Table 1. This pulse test was conducted at 90C. with Amberlite XAD-2 adsorbent and 85% dimethylformamide-15~ water desorbent. As shown in Figure 1 linoleic acid was eluted first and then oleic acid.
Table 1 and Figure 1 show that oleic acid is more strongly adsorbed than lino7eic acid, particularly for certain desorbent mixture combinations when used for the separation of fatty acids having 18 carbon atoms per molecule. Furthermore, the separations achieved for many of these combinations are substantial, as exempli~ied in Figure 1, and clearly o~ commercial feasibility.
~7-EXAMPLE II
This example presents the results of using Amberlite XAD-2 for separating stear;c acid from about a 50-50 mlxture of stearic and palmitic acids diluted in desorbent in a ratio of desor-bent ~o acid mixture of 90 10. The desorbent used was 85 wt. %
dimethyl formamide and 15 wt. ~ water.
Data was obtained using the pulse te t appara~us and procedure previously described at a temperature of 90C. Specifi-cally, the adsorbent was placed in a 70 cc helical coiled column and the following sequence of operations was used. Desorbent mate-rial was continuously run upflow through the column containing the adsorbent at a flow rate of 1.2 ml/min. At a convenient time the flow of desorben~ material was stopped, and a 10 cc sample of feed mixture was injec~ed into the column via a sample loop and the flow of desorbent material was resumed. Samples of the effluent were automatically collected in an automatic sample collector and later analyzed by chromatographic analysis.
Figure 2 is a graphical presentation of the results of the pulse tests. Figure 2 shows that stearic acid is more strongly adsorbed than palmitic acid, particularly for the desorbent mixture used. Furthermore, the separation achieved for this combination was - substantial and clearly of commercial feasibility.
-2~-
Equation 1 Selectivity = (B) = Evl- percent C!vol. percent vol. percent Clvol. percent D U
where C and D are two components of the feed represented in volume percent and the subscr;p~s A and U represent the adsorbed and unadsorbed phases respectively. The equ;librium conditions were detenm;ned when the feed passing over a bed of adsorbent did not change compos;tion after contacting the bed of adsorbent. In other words, there was no net transfer of material occurring between the unadsorbed and adsorbed phases. Where select;v;ty of two components approaches 1.0 there is no preferential adsorption of one component by the adsorbent with respect to the other; they are both adsorbed ~or non-adsorbed) to about the same degree with respect to each o~her. As the (B) becomes less than or greater than 1.0 there is a preferent;al adsorption by the adsorbent for one component with respect to the other. When comparing the selectivity by the adsorbent of one component C over component D, a (B) larger than 1.0 indicates preferential adsorption of component C within the adsorbent.
~5 A (B) less than 1.0 would ;ndicate that component D is preferentially adsorbed leav;ng an unadsorbed phase richer in component C and an adsorbed phase r;cher in component D. Ideally desorbent mater;als should have a select;v;ty equal to about 1 or slightly less than 1 with respect to all extract components so that all of the ex~ract components can be desorbed as a class with reasonable flow rates of desorbent ma~erial and so that extract components can displace desorbent material in a subsequent adsorption step. Wh;le separation of an extract component from a raffinate component is theoretically possible when the selec-tivity of the adsorbent for the extract component with respect to the raffinate component is greater than 1, it ;s preferred that such selectiv;ty approach a value of 2. Like relative volat;l;ty, the higher the selectivity the easier the separation is to perform.
Higher select;v;ties penmit a smaller amount of adsorbent to be used.
The third ;mportant characteristic is the ra~e of exchange of the extract component of the feed m;xture mater;al or, in other words~
the relative rate of desorption of the extract component. Th;s char-acterist;c relates directly to the amount of desorbent material that must be employed in the process to recover the extract component from the adsorbent; faster rates of exchange reduce the amount of desorbent material needed to remove the extract component and therefore permit a reduction in the operating cost of the process. ~lith faster rates of exchange, less desorbent material has to be pumped through the process and separated from the extract stream for reuse in the process.
A dynamic testing apparatus is employed to test various adsorbents with a particular feed mixture and desorbent material to measure the adsorbent characteristics of adsorptive capacity, selecti-vity and exchange rate. The apparatus consists of an adsorbent chamber comprising a helical column of approximately 70 cc volume havlng inlet and outlet portions at opposite ends of the chamber. The chamber is contained within a temperature control means and, in addition, pressure ~81~76~7 control equipment ;s used to operate the chamber at a constant pre-determined pressure. Quantitative and qualitative analytical equip-ment such as refractometers, polarimeters and chromatographs can be attached to the outlet line of the chamber and used to detect quanti-tati~ely or determ;ne qualitatively one or more components in the effluent stream leaYing the adsorbent chamber. A pulse test, performed using this apparatus and the following general procedure, is used to determine selectivities and other data for various adsorbent systems.
The adsorbent is filled to equ;librium with a particular desorbent material by passing the desorbent material through the adsorbent cham-ber. At a convenient time, a pulse of feed containing known concentra-tions of a tracer and of a particular extract component or of a raffinate component or both all diluted in desorbent is injected for a duration of several minutes. Desorbent flow is resumed, and the tracer and the extract component or the raffinate component (or both) are eluted as in a liguid-solid chromatographic operation. The effluent can be analyzed onstream or alternatively eFfluent samples can be col-lected periodically and la~er analyzed separately by analytical equip-~ent and traces of the envelopes of corresponding component peaks developed.
-- From information derived from the test adsorbent performance can be rated in terms of void volume, retention volume for an extract or a raffinate component, selectivity for one component with respect to the other, and the rate of desorption of an extract component by the desorbent. The retention volume of an extract or a raffinate component may be characterized by the distance between the center of the peak envelope of an extract or a raffinate compon~nt and the peak envelope of the tracer component or some o~her known reference point. It is '76~
expressed in terms of the volume in cubic cent;meters of desorbent pumped during this time interval represented by the distance between the peak envelopes. Selectivity, (B), for an extract component w;th respect to a raff;nate component may be characterized by the ratio of the distance between the center of the extract camponent peak envelope and the tracer peak envelope ~or other reference point) to the corresponding distance between lthe center of the raffinate compo-nent peak envelope and the tracer peak envelope. The rate of exchange of an extract component with the desorbent can generally be charac-terized by the width of the peak envelopes at half intensity. The narrower the peak width the faster the desorption rate. The desorp-tion rate can also be characteri~ed by the distance between the center of the ~tracer peak envelope and ~he disappearance of an extract component which has just been desorbed. This distance is again the volume of desorbent pumped during this time interval.
To further evalua~te promising adsorbent systems and ~o translate this type of data into a practical separation process requires actual testing of the best system in a continuous counter-current liquid-solid contacting device. The general operating opera-ting principles of such a device have been previously described and are found in Broughton U.S. Patent 2,985,589. A specific laboratory size apparatus utilizing these principles is described in deRosset etal.,U.S.Patent 3,706,812. The equipment romprjSes multiple adsorbent beds with a number of access lines attached to dis-tributors within the beds and terminating at a rotary distributing valve. At a given valve position. feed and desorbent are being introduced through two of the lines and the raffinate and extract streams are being withdrawn through two more. All rema~ning access ~i81~6~
lines are inactive and when the position of the distributing valve is advanced by one index all active positions will be advanced by one bed. This simulates a condition in which the adsorbent physically moves in a direction countercurrent to the liquid flow.
Additional details on the above-mentioned nonionic adsorbent testing apparatus and adsorbent evaluation tPchn;ques may be found in the paper "Separation of C~ Aromatics by Adsorption" by A.J. deRosset9 R.W.
Neuzil, D.J. Korous, and D.H. Rosback presented at the American Chemical Society, Los Angeles9 California, March 28 through April 2, 1971.
Adsorbents to be used in the process of this invention will comprise nonionic hydrophobic insoluble crosslinked polystyrene polymers, preferably ~hose manufactured by the Rohm and Haas Company and sold under the trade name l'Amberlite". The types of Amberlite polymers known to be eFfective for use by this invention are referred to in Rohm and ~laas Company literature as Amberlite XAD-2 and Amberlite XAD-4, and described in the literature as "hard, insoluble spheres of high surface, porous polymer". The various types of Amberlite polymeric adsorbents differ in physical properties such as porosity volume, surface area, average pore d;ameter, skeletal density and nominal mesh sizes. Applications for Amberlite polymer;c adsorbents suggested in the Rohm and Haas Company literature include decolorizing pulp mill bleaching effluent, decolorizing dye wastes and pesticide removal from waste effluent. There is, of course, no hint in the 2~ literature to our surprising discovery of the effectiv2ness of Amberlite polymeric adsorbents in the separation of monoethanoid fatty acids from diethanoid fatty acids.
A fundamental superiority of the Amberlite polymeric adsor-6i~
bents over crystalline aluminosilicates is that the former, unlike the latter, may be used for the direct separation of fa~ty acids without first converting the fatty acids to their corresponding esters. The processes of the aforementioned prior art patents are applicable only to esters of fat~y acids because the free carboxylic group of a fatty ac;d chemically reacts with the crystalline alumino-s;licates used by those processes. The adsorbent of this invention exhibits no such reactivity and, therefore, the process of this invention is uniquely suitable for the separation of fatty acids.
The adsorbent may b~ employed in the form of a dense compact fixed bed which is alternatively contacted w;th the feed mix-ture and desorbent materials. In the simplest embodiment of the invention the adsorbent is employed in the fcrm of a single static bed in which case the process is only semi-oontinuous. In ano~her embod;ment a set of two or more static beds may be employed in fixed bed contacting with appropriate valving so that ~he feed mixture is passed through one or more adsorbent beds while the desorbent materials can be passed through one or more of the other beds in the set. The flow of feed mixture and desorben~ materials may be either up or down through the desorbent. Any of the conventional apparatus employed in static bed fluid-solid oontacting may be used.
Countercurrent moving bed or simulated movin~ bed counter-current flow systems, however, have a much greater separation efficiency than fixed adsorbent bed systems and are therefore preferred.
In the moving bed or simulated moving bed processes the adsorption and desorption operations are continuously taking place which allows both continuous production of an extract and a raffinate stream and the continual use of feed and desorbent streams. One preferred embodiment L'76~
of this process utilizes what is known in the art as the simulated moving bed countercurrent flow system. The operating principles and sequence of such a flow system are described in U.S. Patent 2,98~,589 incorporated herein by reference thereto. In such a system it is the progressive movement of multiple liquid access points down an adsorbent chamber that simulates the upward movement of adsorbent contained in the chamber. Only four of the access lines are active at any one timei the feed input stream, desorbent inlet stream, raf-finate owtlet stream, and extract outlet stream access lines.
~oincident with this simulated upward movement of the solid adsorbent is the movement of the liquid occupying the void volume of the packed bed of adsorbent. So that countercurrent contact is maintained, a liquid flow down the adsorbent chamber may be provided by a pump. As an ac~ive liquid access point moves through a cycle, that is, from the top of the chamber to the bottom, the chamber circulation pump moves through different zones which requ;re different flow rates. A
programmed flow controller may be provided to set and regulate these flow rates.
The active liqu;d access points effectively divided the adsorbent chamber into separate zunes, each of which has a different function. In this embodiment of our process it is generally necessary that three separate operational zones be present in order for the process to take place although in some instances an optional fourth zone may be used.
The adsorption zone, 7one 1, is defined as the adsorbent located between the feed ;nlet stream and the raffinate outlet stream.
In this zone, the feedstock contacts the adsorbent, an extract compo-nent is adsorbed, and a raffinate stream is withdrawn. Since the 76'~
general flow through zone 1 is from the feed stream which passes into the zone to the raffinate stream which passes out of the zone, the flow in this zone is considered to be a downstream direction when pro-ceeding from the feed inlet to the raffinate outlet streams.
I~mediately upstream with respect to fluid flow in zone 1 ;s the puri~ication zone, zone 2. The purification zone ;s defined as the adsorbent between the extract outlet stream and the feed inlet stream. The basic operations tak;ng place in zone 2 are ~he displace-ment from the non-selective void volume of the adsorbent of any raffinate material carried into zone 2 by the shift;ng of adsorbent into this zone and the desorption of any raffinate material adsorbed within the selective pore volume of the adsorbent or adsorbed on the surfaces of the adsorben~ particles. Purification is achieved by passing a portion of extract stream material leaving zone 3 into zone 2 at zone 2's upstream boundary, the extract outlet stream, to effect the displacement of raffinate material. The flow of material in zone 2 is in a downstream direction from the extract outlet stream to the feed inlet stream.
mediately upstream of zone 2 wi~h respect to the fluid flowing in zone 2 is the desorption zone or zone 3. The desorption zone is defined as the adsorbent between the desorbent inlet and the extract outlet stream. The function of the desorption zone is to allow a desorbent material which passes into this zone to displace the extract component wh;ch was adsorbed upon the adsorbent during a previous contact with feed in zone 1 in a prior cycle of operation.
The flow of fluid in zone 3 is essentially in the same direction as that of zones 1 and 2.
In some instances an optional buffer zone, zone 4, may be 1181 ~
utilized. This zone, defined as the adsorbent between the raffinate outlet stream and the desorbent inle~ stream, if used, is located immediately upstream with respect to the fluid flow to zone 3. Zone 4 would be utilized to conserve the amount of desorbent utilized in the desorption s~ep since a portion of the raffinate stream which ls removed from zone 1 can be passed into zone 4 ~o displace desorbent material present in that zone out of that zone into the~ desorption zone. Zone 4 will contain enough adsorbent so that raffinate mate-rial present in the raffinate stream passing out of zone 1 and into æone 4 can be prevented from passing into zone 3 thereby contaminating extract stream rcmoved from zone 3. In the ;nstances which the fourth operational zone is not utilized the raffina~e stream passed from 70ne 1 to zone 4 must be carefully monitored in order that the flow directly from zone 1 to zone 3 can be stopped when ~here is an appre-1B ciable quantity of raffinate material present in the raffinate stream passing from zone 1 into zone 3 so that the extract outlet stream is not contaminatled.
A cyclic advancement of the input and output streams through the fixed bed Df adsorbent can be accomplished by utilizing a manifold system in which the valves ~n the manifold are operated in a sequential manner to effect the shifting of the input and output streams thereby allowing a flow of fluid with respect to solid adsorbent in a counter-current manner. Another mode of operation whish can effect the counter-current flow of solid adsorbent with respect to fluid involves the use 2~ of a rotating disc valve in which the input and output streams are con-nected to the valve and the lines through which feed input~ extract output, desorbent input and raffinate output streams pass are advanced in the same direction through the adsorbent bed. Both the manifold ~81i767 arrangement and disc valve are known in the art. Specifically rotary disc valves which can be ut;l ked in this operation can be found in U.S. Patents 3,040,777 and 3,422,848. Both of the aforementioned patents disclose a rotary type connection valve in which the suitable advancement of the various input and output streams from fixed sources can be achieved without difficulty.
In many instances, one operational zone will contain a much larger quantity of adsorbent than some other operational zone.
For instances, in some operations the buffer zone can contain a minor amount of adsorbent as compared to the adsorbent required for the adsorption and purification zones. It can also be seen that ;n instances in which desorbent is used which can easily desorb extract material from the adsorbent that a relatively small amount of adsor-bent will be needed in a desorption zone as compared to the adsorbent needed in the buffer zone or adsorption zone or purification zone or all of them. Since it is not required that the adsorbent be located in a single column, the use of multiple chambers or a series of col-umns is within the scope of the invention.
It is not necessary that all of the input or output streams be simultaneously used, and in fact, in many instances some of the streams can be shut off while others effect an ;nput or output of mate-rial. The apparatus which can be utili7ed to e ffect ~he process of this invention can also contain a series of individual beds connected by connecting conduits upon which are placed input or output taps to which the various input or output streams can be attached and alternately and periodically shifted to effect continuous operation. In some in-stances, the connecting conduits can be connected to transfer taps which during the normal operations do not function as a conduit through which ~L~ '7 material passes into or out of the process.
It is contemplated that at least a port;on of the extract output stream will pass into a separation means wherein at least a portion of the desorbent material can be separated to produce an ex-tract product containing a reduced concentration of desorbent material. Preferably, but not necessary to the operat;on of the pro-cess, at least a portion of the raffinate output stream will also be passed to a separation means where;n at least a portion of the desorbent material can be separated to produce a desorbent stream which can be reused in the process and a raffinate product containing a reduced concentration o~ desorbent material. The separa~ion means will typically be a fract;onation column, the design and operation of which is well-known to the separation art.
Reference can be made to D.B. Broughton U.S. Patent 2,985,589, and to a paper entitled "Continuous Adsorpt;ve Processing--A New Separation Technique" by D.B. Broughton presented at the 34th Annual Meeting of the Society of Chemical Engineers at Tokyo~ Japan on April 2, 1969, both incorporated herein by reference, for further explana~ion of the simulated mo~ing bed countercurrent process flow scheme.
Although both liquid and vapor phase operations can be used in many adsorptive separation processes, liquid-phase operation is preferred for this process because of the lower temperature requirements and because of the higher yields of extract product than can be obtained with liquid-phase operation over those obtained with vapor-phase operation. Adsorption conditions will include a temperature range of from about 20C. to about 200~C. with about 20C. to about 100C.
being more preferred and a pressure range of from about atmospheric to 7~-7 about 500 psig ~345n kPa gauge) w~th from about a~mospheric to about 250 psig (1725 kPa gauge) being more preferred to ensure liquid phase.
Desorption conditions will include the same range of tempera~ures and pressures as used for adsorption conditions.
The size of the units which can util ke the process of this invention can vary anywhere from those of pilot plant scale (see for example our assignee's U.S. Patent 3,706,~12, ineorporated herein by reference) to those of commercial scale and can range in flow rates fron as little as a few cc an hour up to ~any thousands of gallons per hour.
The ~ollowing examplearépresented to illustrate 1:he selectivity relationsh;p that makes the process o~ our in~ention pos-sible. The example is not ~ntended to unduly res~rict the scope and spirit o~ claims attached hereto.
1~ ~, .
Thi5 example presents selectivities ~or two Amberlite polymeric adsorbents, comprising Amberlite XAD-2 and Amberlite XAD-4, for oleic acid with respect to a linoleic acid.
The feed mixture comprised the desorbent used in the pulse test in ques-tion and Tall-oil fatty acids in a ratio of desbrbent to Tall-oil fatty ~cids of 90:10. The Tall-~il fatty acids had the following composition:
Fatt~ Acids Palmitic (C160) S Stearic (Cl8~) 2 Ole;c (C181) 5~
Linoleic ~C182) 45 All others 4 Retention volumes and selectivities were obtained using ~ 1 ~3il~7~i~7 the pulse test apparatus and procedure previously described. Spec-ifically, the adsorbents were tested in a 70 cc helical coiled column using the following sequence of operations for each pulse test.
Desorbent material was continuously run through ~he column containing the adsorbent at a nominal liquid hourly space veloc;ty (LHSV) of about 1Ø A void volume was determined by observing the volume of desorbent reguired to fill the packed dry column. At a convenient time the flow of desorbent material was stopped, and a 10 cc sample of feed mixture was injected into the column via a sample loop and the flow of desorben~ material was resumed. Samples of the effluent were automatically collected in an automatic sample collector and later analyzed by chromatographic analysis. From the analysis of these samples peak envelope concentrations were developed for ~he feed mixture components. The retention volume for the fatty acids werP
calculated by measuring the distances from time zero on the reference po;nt to the respective midpoints of the fatty acids and subtracting the distance representing the void volume of the adsorbent. The selectivities of an adsorbent for oleic ac;d with respect to linoleic acid in the presence of a desorbent material are in the quotients obtained by divid;ng the retention volume for the oleic acid by the retention volume for the linoleic acid. The results for these pulse tests are shown in Table No. 1.
~ C~l ~ C~ C ~ O ~
., ~ ~ I ~ C~J ~ t~ ~1 _I ei' N -1 al ~ ~ I r I ~ r-i r~ C_~
-~ N ) Lt U') I~ ~ O
~ Et~ ~1 ~ 1 N C~ ~ ~ t~ ~I 1~ et , ~S I 1~ d` N C~J N Ll O ~D 1~ N '* _I
O --'CO
~_1 O 1~ N 1~ _1 1~ 0 0` ~O O cr~ O
Z ~ ~ ~ CO D et CO 1~ et ~ el~ Cl~
C~
~ ~1 ~ O
c~ . ~D ~D ~ ~ æ o o ~ cn ~L
_I c~ E
O~ U~
Z:~ T T
11.1 t~ O O O
~:~ I ~
ClL~ O C~ ~ ~
O CU I U~ I I
O ~e u)a) Ln ~r) o o O --~ ~ ~ O O
~1 O I _ I I I I C`J C~
clC ~ IaJ -- O E ~ _ O CO I T X X
~ ~ ~ 52 F N S- E E ~ J i_~--LLJ L OL~ I ~ jS5L ~ ~ O ~ O O ~, ~, O ~ I tU ~ O O O ~
C~: _1 11L~ o o z z E E
O t~O 1-) ~J I ~IJal ~11 2 Z O O
T~ I~ a ~ O ~ Y' ~ d ~! ~ ~a ~ ~ ~ ~ ~5 E E
O u~ U~ ~ O ~ Ln u~ l O O ~ n:s O
E Q
N C~ C~ J ~ N ~ ~I C~ r~, XXXXXXX~ XX XX .Q~ ~
O , ,_ 1~7 S_ = = = = = = = = a ~ = -- c ~' -~:1 O U
L'76''~
Figure 1 is an example of a graphical presentation of the results of one of the pulse tests the data from which is also set forth in Table 1. This pulse test was conducted at 90C. with Amberlite XAD-2 adsorbent and 85% dimethylformamide-15~ water desorbent. As shown in Figure 1 linoleic acid was eluted first and then oleic acid.
Table 1 and Figure 1 show that oleic acid is more strongly adsorbed than lino7eic acid, particularly for certain desorbent mixture combinations when used for the separation of fatty acids having 18 carbon atoms per molecule. Furthermore, the separations achieved for many of these combinations are substantial, as exempli~ied in Figure 1, and clearly o~ commercial feasibility.
~7-EXAMPLE II
This example presents the results of using Amberlite XAD-2 for separating stear;c acid from about a 50-50 mlxture of stearic and palmitic acids diluted in desorbent in a ratio of desor-bent ~o acid mixture of 90 10. The desorbent used was 85 wt. %
dimethyl formamide and 15 wt. ~ water.
Data was obtained using the pulse te t appara~us and procedure previously described at a temperature of 90C. Specifi-cally, the adsorbent was placed in a 70 cc helical coiled column and the following sequence of operations was used. Desorbent mate-rial was continuously run upflow through the column containing the adsorbent at a flow rate of 1.2 ml/min. At a convenient time the flow of desorben~ material was stopped, and a 10 cc sample of feed mixture was injec~ed into the column via a sample loop and the flow of desorbent material was resumed. Samples of the effluent were automatically collected in an automatic sample collector and later analyzed by chromatographic analysis.
Figure 2 is a graphical presentation of the results of the pulse tests. Figure 2 shows that stearic acid is more strongly adsorbed than palmitic acid, particularly for the desorbent mixture used. Furthermore, the separation achieved for this combination was - substantial and clearly of commercial feasibility.
-2~-
Claims (10)
1. A process for separating a first fatty acid selected from the group consisting of stearic acid and oleic acid from a mixture of this first fatty acid and a second fatty acid selected from the group consisting of palmitic acid and linoleic acid comprising contact-ing said mixture with an adsorbent comprising a nonionic hydrophobic insoluble cross-linked polystyrene polymer at adsorption conditions selected to selectively adsorb said first acid in preference to said second acid, wherein when said first acid is stearic acid then said second acid is palmitic acid and wherein when said first acid is oleic acid when said second acid is linoleic acid.
2. The process of Claim 1 further characterized in that said first fatty acid is recovered by desorption with a desorbent at desorption conditions.
3. The process of Claim 2 further characterized in that said adsorption and desorption conditions include a temperature within the range of from about 20°C to about 200°C and a pressure within the range of from about atmospheric to about 500 psig (3450 kPa gauge).
4. The process of Claim 3 further characterized in that it is effected in the liquid phase.
5. The process of Claim 1 further characterized in that said desorbent comprises one of the mixtures in the group of mixtures compris-ing acetonitrile and methanol; acetonitrile, tetrahydrofuran and water;
acetone and water; diemthyl acetamide and water; methanol and water;
dimethyl formamide and water, quaternary methyl ammonium hydroxide, water and methanol; and quaternary propyl ammonium hydroxide.
acetone and water; diemthyl acetamide and water; methanol and water;
dimethyl formamide and water, quaternary methyl ammonium hydroxide, water and methanol; and quaternary propyl ammonium hydroxide.
6. A process for separating a first fatty acid selected from the group consisting of stearic acid and oleic acid from a mixture of this first fatty acid and a second fatty acid selected from the group consisting of palmitic acid and linoleic acid, wherein when said first acid is stearic acid then said second acid is palmitic acid and wherein when said first acid is oleic acid then said second acid is linoleic acid, which process employs an adsorbent comprising a nonionic hydrophobic insoluble cross-linked polystyrene polymer, which process comprises the steps of:
(a) maintaining net fluid flow through a column of said adsorbent in a single direction, which column contains at least three zones having separate operational functions occurring therein and being serially interconnected with the terminal zones of said column connected to provide a continuous connection of said zones;
(b) maintaining an adsorption zone in said column, said zone defined by the adsorbent located between a feed input stream at an upstream boundary of said zone and a raffinate output stream at a downstream boundary of said zone;
(c) maintaining a purification zone immediately upstream from said adsorption zone, said purification zone defined by the adsorbent located between an extract output stream at an upstream boundary of said purification zone and said feed input stream at a downstream boundary of said purification zone;
(d) maintaining a desorption zone immediately upstream from said purification zone, said desorption zone defined by the adsorbent located between a desorbent input stream at an upstream boundary of said zone and said extract output stream at a downstream boundary of said zone;
(e) passing said feed mixture into said adsorption zone at adsorption conditions to effect the selective adsorption of said first fatty acid by said adsorbent in said adsorption zone and withdrawing a raffinate output stream comprising said second fatty acid from said adsorption zone;
(f) passing a desorbent material into said desorption zone at desorption conditions to effect the displacement of said first fatty acid from the adsorbent in said desorption zone;
(g) withdrawing an extract output stream comprising said first fatty acid and desorbent material from said desorption zone;
(h) passing at least a portion of said extract out-put stream to a separation means and therein separating at separation conditions at least a portion of said desorbent material; and, (i) periodically advancing through said column of adsorbent in a downstream direction with respect to fluid flow in said adsorption zone the feed input stream, raffinate output stream, desorbent input stream, and extract output stream to effect the shifting of zones through said adsorbent and the production of extract output and raffinate output streams.
(a) maintaining net fluid flow through a column of said adsorbent in a single direction, which column contains at least three zones having separate operational functions occurring therein and being serially interconnected with the terminal zones of said column connected to provide a continuous connection of said zones;
(b) maintaining an adsorption zone in said column, said zone defined by the adsorbent located between a feed input stream at an upstream boundary of said zone and a raffinate output stream at a downstream boundary of said zone;
(c) maintaining a purification zone immediately upstream from said adsorption zone, said purification zone defined by the adsorbent located between an extract output stream at an upstream boundary of said purification zone and said feed input stream at a downstream boundary of said purification zone;
(d) maintaining a desorption zone immediately upstream from said purification zone, said desorption zone defined by the adsorbent located between a desorbent input stream at an upstream boundary of said zone and said extract output stream at a downstream boundary of said zone;
(e) passing said feed mixture into said adsorption zone at adsorption conditions to effect the selective adsorption of said first fatty acid by said adsorbent in said adsorption zone and withdrawing a raffinate output stream comprising said second fatty acid from said adsorption zone;
(f) passing a desorbent material into said desorption zone at desorption conditions to effect the displacement of said first fatty acid from the adsorbent in said desorption zone;
(g) withdrawing an extract output stream comprising said first fatty acid and desorbent material from said desorption zone;
(h) passing at least a portion of said extract out-put stream to a separation means and therein separating at separation conditions at least a portion of said desorbent material; and, (i) periodically advancing through said column of adsorbent in a downstream direction with respect to fluid flow in said adsorption zone the feed input stream, raffinate output stream, desorbent input stream, and extract output stream to effect the shifting of zones through said adsorbent and the production of extract output and raffinate output streams.
7. The process of Claim 6 further characterized in that it includes the step of passing at least a portion of said raffinate output stream to a separation means and therein separating at separa-tion conditions at least a portion of said desorbent material to produce a raffinate product having a reduced concentration of desorbent material.
8. The process of Claim 6 further characterized in that it includes the step of maintaining a buffer zone immediately upstream from said desorption zone, said buffer zone defined as the adsorbent located between the desorbent input stream at a downstream boundary of said buffer zone and the raffinate output stream at an upstream boundary of said buffer zone.
9. The process of Claim 6 further characterized in that said adsorption conditions and desorption conditions include a tempera-ture within the range of from about 20°C to about 200°C and a pressure within the range of from about atmospheric to about 500 psig (3450 kPa gauge) to ensure liquid phase.
10. The process of Claim 6 further characterized in that said desorbent comprises one of the mixtures in the group of mixtures comprising acetonitrile and methanol; acetonitrile, tetrahydrofuran and water; acetone and water; dimethyl acetamide and water; methanol and water; dimethyl formamide and water, quaternary methyl ammonium hydroxide, water and methanol; and quaternary propyl ammonium hydroxide.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000413100A CA1181767A (en) | 1982-10-08 | 1982-10-08 | Fatty acid separation |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000413100A CA1181767A (en) | 1982-10-08 | 1982-10-08 | Fatty acid separation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1181767A true CA1181767A (en) | 1985-01-29 |
Family
ID=4123744
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000413100A Expired CA1181767A (en) | 1982-10-08 | 1982-10-08 | Fatty acid separation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1181767A (en) |
-
1982
- 1982-10-08 CA CA000413100A patent/CA1181767A/en not_active Expired
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