DK158911B - Process for separating off fatty acids, and molecular sieve for use therein - Google Patents

Description

DK 158911B

The present invention relates to a process for separating oleic acid from linoleic acid as well as a molecular sieve for use therewith.

It is known in the art of separation that certain 5 crystalline aluminum silicates can be used to separate certain esters of fatty acids from mixtures thereof. For example, U.S. Patent Nos. 4,048,205, 4,049,688 and 4,066,677 disclose methods for separating esters of fatty acids with varying degrees of unsaturation from mixtures of esters of saturated and unsaturated fatty acids.

In these processes, adsorbents comprising an X or Y zeolite containing a selected cation are used at the interchangeable cationic sites. In U.S. Pat.

4,329,280 discloses a similar separation of fatty acid esters 15 and resin acid esters using a molecular sieve comprising silicalite as adsorbent. In contrast, the invention relates to the separation of fatty acids rather than fatty acid esters.

Major uses of fatty acids are in the field of plasticizers and surfactants. Derivatives of fatty acids are valuable for the composition of lubricating oils, as lubricants in the textile and molding industry, in special paints, as water repellents, in the cosmetic and pharmaceutical fields, and in biodegradable detergents.

It has now been found that a particular silica-containing molecular sieve exhibits selectivity for one unsaturated fatty acid (oleic acid) relative to another unsaturated fatty acid (linoleic acid), allowing effective separation of 30 such fatty acids by selective solid retention during use of inorganic adsorbents. Furthermore, it has been found that improved efficiency can be achieved in the separation process with particular displacement fluids under certain displacement conditions.

35 It has been found that silicalite, which is non-zeolitic hydrophobic crystalline molecular sieve of silica, is

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2 is particularly suitable for separating the components of tall oil in that it firstly accepts a fatty acid over a resinic acid, in particular using a special displacement fluid, and does not exhibit reactivity with the free acids, and secondly, accepts oleic acid rather than linoleic -acid. Furthermore, it has been found that improved results are obtained if the silicalite is present in a silica matrix and the overall material is substantially free of hydroxyl groups.

The invention relates to a process for separating oleic acid from linoleic acid in a feed mixture containing the acids, the process comprising contacting the feed mixture under separation conditions with a molecular sieve which is substantially free of hydroxyl groups and comprises silicalite in a silica matrix, whereby the oleic acid is selectively retained, the linoleic acid is removed from the oleic acid-containing molecular sieve, and the oleic acid is then recovered from the molecular sieve by displacement with a displacement fluid under displacement conditions.

The invention further relates to a molecular sieve for use in the process according to the invention, which molecular sieve consists of silicalite in a silica matrix and comprises from a precursor comprises silicalite powder dispersed in colloidal amorphous silica, the precursor having been subjected to gel formation and then treated in such manner. a substantially complete removal of hydroxyl groups on the molecular sieve.

According to a preferred embodiment, the method according to the invention comprises the following steps: a) maintaining a net liquid flow in a single direction through a column of the molecular sieve, which column contains at least three zones with each of its operating functions connected in series with the end zones of the column; b) maintaining a retention zone in the column where the zone is defined by the molecular sieve located between a feed mix inlet stream at a boundary of the zone up

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3 by the stream and a raf finate - outlet stream at a boundary of the downstream zone, c) maintaining a purification zone immediately upstream of the retention zone, where the purification zone is defined by the molecular sieve located between an extract outlet stream at a boundary of the purification zone upstream and feed mixture inlet stream at a downstream purification zone boundary, d) maintaining in the column of a displacement zone immediately upstream of the purification zone, where the displacement zone is defined by the molecular sieve located between a displacement fluid inlet stream e) conducting the feed mixture to the retention zone under separation conditions to effect selective retention of oleic acid by the molecular sieve in the retention zone, f) conducting a displacement fluid to the displacement zone during displacement conditions for causing displacement of the oleic acid from the molecular sieve in the displacement zone; - and the refinery outlet streams.

FIG. 1 of the drawing schematically shows the embodiment of the present invention comprising a simulated moving layer as described below and comprising an adsorption column 1, a branching system 3 and various connecting lines.

FIG. 2, 3 and 4 show graphically the results obtained according to the exemplary embodiments.

Initially, the various terms used in the description are defined for the purpose of clarifying the operation, purposes and benefits of the method of the present invention.

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A "food blend" is a blend containing one or more extract components and one or more refining components to be separated by the process of the present invention. The term "feed stream" refers to a stream 5 of a feed mixture fed to the molecular sieve used in the process of the present invention.

An "extract component" is a compound or compound type that is retained by the molecular sieve, while a "refine component" is a compound or compound type that is not retained. In this process, oleic acid is an extract component and linoleic acid is a raffinate component. The term "displacement fluid" generally refers to a fluid capable of displacing an extract component. The term "displacement fluid flow" or "displacement fluid inlet stream" means the stream in which displacement fluid is directed to the molecular sieve. The term "diluent" or "diluent stream" refers to the stream in which the diluent is passed to the molecular sieve. The term "refiner stream" or "refiner effluent stream" refers to the stream in which a refinery component is removed from the molecular sieve. "denotes the stream in which an extract material that has been displaced by a displacement fluid is removed from the molecular sieve. The composition of the extract stream may also vary from substantially 100% displacement fluid to substantially 100% extract components. of the extract stream and preferably at least a portion of the raffinate stream from the separation process is passed to separation devices, typically fractionators, where at least a portion of the displacement fluid and diluent are separated to form an extract product and a raffinate product. "refined

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5 night product "means products prepared by the process which contain, respectively, an extract component and a raffinate component at higher concentrations than those found in the extract stream and the raffinate stream. Although 5 in the process of the present invention, it is possible to produce a fatty acid product or a resin acid product (or both) with high purity in high yields, it will be understood that neither an extract component nor a raffinate component is ever completely retained by the molecular sieve. Therefore, varying amounts of a raffinate component may occur in the extract stream, and varying amounts may also occur. Therefore, the extract and raffinate stream differ further from each other and from the feed mixture at the ratio of the concentrations of an extract component to a raffinate component present in the stream in question. the ion of a fatty acid and the concentration of non-retained resin acid are lowest in the raffinate stream, second highest in the feed mixture and highest in the extract stream. Likewise, the ratio of the concentration of resin acid to the concentration of retained fatty acid will be highest in the raffinate stream, second highest in the feed mixture and lowest in the extract stream.

The term "selective pore volume" of the molecular sieve is defined as the volume of the molecular sieve that selectively retains an extract component from the feed mixture. The term "non-selective void volume" of the molecular sieve is the volume of the molecular sieve that does not selectively retain an extract component from the feed mixture. This volume comprises the cavities in the molecular sieve allowing access of raffinate components and the gaps between the particles of the molecular sieve. The selective pore volume and the non-selective pore volume are generally expressed at volumetric sizes and are of importance in determining appropriate flow rates for fluid to be directed.

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to an operating zone so that there is an efficient operation for a given amount of molecular sieve. When the molecular sieve is "directed" to an operating zone (defined and described below) used in one embodiment of the invention, its non-selective huir volume together with its selective pore volume of fluid leads to this zone. determining the amount of fluid that should be directed to the same zone countercurrent with the molecular sieve to displace the fluid present in the non-selective void volume. If the flow rate of a fluid to a zone is less than the rate of non-selective void volume applied to this zone of the molecular sieve, there is a net co-drag of liquid to the zone of the 15 sieve, since this net co-drag is a fluid present in the non-selective void volume of molecular sieve, in most cases it includes non-retained food components.

Before explaining the food compositions which can be applied to the process of the present invention, a brief explanation of the terminology of fatty acids and their general preparation is given. 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" of some has been restricted to saturated acids of the acetic acid series, both straight and branched, it is now generally used, and also in the present description, in that it also includes related unsaturated acids, certain sub - 30 stituated acids and even aliphatic acids containing alicyclic substituents. The naturally occurring fatty acids are, with a few exceptions, higher straight-chain unsubstituted acids containing an equal number of carbon atoms. The unsaturated fatty acids, on the basis of the number of 35 double bonds in the hydrocarbon chain, can be divided into monoethanoid, diethanoid, triethanoid, etc. (or monoethylene

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happen etc.). Thus, the term "unsaturated fatty acid" is a generic 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 liter. mole-5 kyle. Fatty acids are typically prepared from glyceride fats or oils by one of several cleavage or hydrolytic processes. In all cases, the hydrolysis reactions can be summarized as the reaction of a fat or oil with water to form 10 fatty acids and glycerol. In modern fatty acid plants, this process is carried out by continuous hydrolysis of the fat under high pressure and high temperature. Commonly used fatty acid starting materials include coconut oil, palm oil, animal fats unsuitable for human consumption, and the commonly used vegetable oils, soybean oil, cottonseed oil and corn oil.

The source of fatty acids to which the present invention relates primarily is tall oil, which is a by-product of the wood pulp industry and is usually extracted from pine black liquor from the sulphate or kraft paper process. Tall oil contains approx. 50-60% fatty acids and approx. 34--40% resin acids. The fatty acids include oleic acid, linoleic acid, palmitic acid and stearic acid. Linoleic acid and oleic acid make up over 90% of the fatty acids present in tall-25 oil. The resin acids, such as abiethic acid, are monocarboxylic acids having a molecular structure comprising carbon, hydrogen and oxygen with three condensed 6-membered carbon rings which produce the much larger molecular diameter of resin acids than of fatty acids.

Feed mixtures which can be fed to the process of this invention may contain, in addition to the components of tall oil, a diluent which is not adsorbed by the adsorbent and preferably separable from the extract and raffinate effluent streams by fractional distillation. When a diluent is used, the concentration of diluent in the mixture of

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thinner and acids are preferably from a few vol.% and up to approx. 75% by volume, with the remainder of fatty acids and resin acids. Although it has been previously described in US Patent No. 4,329,280 that silicalite is effective in separating esters of fatty acids and resin acids, separation of the free acids from each other has not been reported so far using silicalite.

The displacement fluids used in various known adsorption processes and molecular sieve separation processes may vary depending on such factors as the type of operation used. In separation processes that are generally continuously operated at substantially constant pressures and temperatures to ensure liquid phase, and where a molecular sieve is used, the displacement material must be carefully selected to meet many criteria. First, the displacement material should displace an extract component from the molecular sieve at reasonable mass flow rates, yet allow access of an extract component to the molecular sieve so that it does not overly prevent an extract component from displacing the displacement material in a subsequent separation cycle. In addition, displacement fluids should be substances that are readily separable from the food mixture that is fed to the process. Both the raffinate stream and the extract stream are removed from the molecular sieve in admixture with the displacement fluid, and without a method of separating at least a portion of the displacement fluid, the purity of the extract product and the refinate product will not be very high, nor will the displacement fluid be recovered. . Therefore, it is envisaged that any displacement fluid material used in the process will preferably have a substantially different average boiling point than the feed mixture, so as to allow separation of at least a portion of the displacement fluid from the feed components of the extract and raffinate streams by simple fractionation. the-

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9 DK 15891 1 station, which makes it possible to reuse the displacement fluid during the process. The term "substantially different" is understood to mean that the difference between the mean boiling points of the displacement fluid and the feed mixture must be at least approx. 5 ° C. The boiling range of the displacement fluid may be higher or lower than the boiling range of the feed mixture. Finally, displacement fluids should also be materials that are readily available and therefore have a reasonable price. In the process of the invention, which is preferably isothermally, isobarically and in liquid phase, it has been found, as will be further described below, that displacement fluid comprising a diluent soluble in the feed mixture and having a polarity index 15 of at least 3, 5, are the most desirable. A highly effective displacement fluid is an organic acid.

However, it has been observed that even silicite can be ineffective for separating fatty acids and resin acids by reusing the molecular sieve layer for separation after the displacement step. When displacement fluid is present in the layer, selective retention of the fatty acid may fail. It is believed that the displacement fluid, especially an organic acid, participates in or even catalyzes hydrogen bond dimerization reactions, in which there is a alignment between the molecules of fatty acid and resin acid and, perhaps, the molecules of the displacement fluid. These dimerization reactions can be represented by the formulas: 30 FA + FA s ......:: r · (FAFA) RA + RA, v ... _______ _ * · (RARA) FA + RA v- ..... .. (FARA) wherein FA and RA mean fatty acids and resin acids respectively. The molecules of the organic acid of the displacing fluid should probably also be considered reactants and product constituents in the above reactions. The dimers will prevent separation of the fatty acids and the resin acids

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10 o by blocking access of the former to the pores of the molecular sieve. This impediment to the separation caused by the presence of dimers does not appear to be a significant problem in the above-mentioned process 5 for separating esters of fatty acids.

It has been found that the above dimerization reactions can be minimized, at least to the extent that separation of resin acids and / or fatty acids is possible, by first rinsing the molecular sieve with a suitable diluent. The diluent serves to remove displacement fluid from at least the non-selective void volume in the molecular sieve. Proper selection requires first and foremost solubility of the feed stream components of the diluent as well as easy separation of the diluent by conventional methods, as is the case with the displacement fluid.

It has also been found that the aforementioned flush can even be avoided if the displacement fluid has a polarity index of at least 3.5. A preferred displacement fluid having a polarity index of at least 3.5 comprises a short chain organic acid having a chain length of 2-5 carbon atoms in solution in a diluent and having the property of minimizing dimerization. The measure of this property is the liquid polarity index.

The Polarity Index is described by L.J. Snyder, "Classification of the Solvent Properties of Common Liquids," J. Chromatography 92 ^ 223 (1974). The diluent should contain from approx. 50 to approx. 95% by volume of the displacement fluid. Polarity indices for some 30 selected diluents are as follows:

Solvent Polarity Index

Isooctane -0.4 n-Hexane 0.0

Toluene 2.3 p-xylene 2.4

Benzene 3.0 Methylethyl ketone 4.5

Acetone 5.4

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Acetone, methyl ethyl ketone and diethyl ketone are preferred diluents.

It should be noted that diluents having a polarity index of at least 3.5 are most particularly preferred as displacement fluids, especially when the temperature at which the displacement is carried out is from ca.

120 to approx. 150 ° C. Again, acetone, methyl ethyl ketone and diethyl ketone are preferred. This is an improvement over the practice of using a solution of such a diluent and an organic acid as a displacement fluid at a relatively low temperature. A primary disadvantage of using the latter solution is that the extraction of the organic acid from the extract product stream is relatively energy intensive and requires a high temperature to obtain distillation which causes some thermal degradation of the fatty acids. Another advantage is that the corrosive effects of short-chain organic acids are eliminated.

The molecular sieve to be used in the process of this invention comprises silicalite. As mentioned earlier, silicalite is a hydrophobic crystalline silicon dioxide molecular sieve. Silicalite is described and disclosed in U.S. Patent Nos. 4,061,724 and 4,104,294. Due to its aluminum-free structure, silicalite exhibits no ion exchange behavior and is hydrophobic and organophilic. Thus, silicalite is a molecular sieve, but not a zeolite. Silicalite is uniquely suited to the separation process according to the invention for the presumed reason that its pores have a size and shape that allows the silicalite to function as a molecular sieve, i.e. receive the fatty acid molecules in its channels or internal structure and reject the resin acid molecules. A more detailed mention of silicalite is found in the article "Silicalite, A New Hydrophobic Crystalline Silica Molecular Sieve", Nature 271, 9th February, 1978.

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Like other adsorbents or molecular sieves, silicalite is most advantageously used in connection with a suitable binder. The binder helps to form or agglomerate the crystalline particles of silicalite that would otherwise form a fine powder. All previously tested binders are not suitable for use in separating the components of tall oil due to the reactivity of the binder or interfering with the separation. In accordance with the invention, a binder has been discovered which, upon incorporation into silicalite, provides a novel molecular sieve which is unique for separating the components of tall oil.

The silicalite is bonded with silica, i.e. the silicalite is incorporated into a silica matrix.

The silicalite is incorporated into the silica by dispersing silicalite powder in colloidal amorphous silica to obtain a precursor, gelling the precursor and then treating the gel in such a manner as to effect a substantially complete removal of hydroxyl groups in the silicalite and silicon rich silica. -late. The colloidal amorphous silica comprises an aqueous colloidal dispersion of amorphous silica particles and the gelling is preferably accomplished by removing water from the dispersion, although other gelling methods can be used such as changing the pH or adding a salt or water miscible organic solvent. The silicalite should be present in the silica matrix in amounts ranging from about 75 to approx. 98% by weight of silicalite, based on a composition which is free of volatile components. Prior to the treatment of the hydroxyl group removal gel, it is preferably extruded while still in a plastic state and is then broken into single particles. The plastic state will occur for at least part of the period of time in which water is removed to achieve gelation. After treatment, the particles can be ground to a smaller size

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13 I DK 15891! which are more physically suitable for use in the particular separation process involved, typically 16-60 mesh (U.S. Standard). ^

The colloidal amorphous silica preferred for use in the present invention is that sold under the name "Ludox" (Du Pont). The colloidal silica "Ludox" is described as discrete uniform spheres of silica having no inner surface area or any detectable crystallinity, dispersed in a basic medium which reacts with the silica surface to form a negative charge. The pH of the basic medium is kept at approx. 8.5 to 11.0. The stabilizing cations in the basic medium may comprise sodium or ammonium ions. The concentration of silicon dioxide in the colloidal dispersion may be from ca. 30 to approx. 50% by weight, based on SiO 2 · In Du Ponts's description of the colloidal silica "Ludox" it is stated that the hydroxyl groups on the surface of the silica particles during drying condense by decomposition of water to form siloxane bonds (Si-O-Si ), which results in the waxing, forming of bonds and particles that are chemically inert and heat resistant. However, it has been found that the mere drying of the silica-bound silicalite under generally accepted drying conditions, i.e. heating in air at a temperature slightly above 100 ° C gives a molecular sieve which is unacceptable for use in separating the components of tall oil. Such a molecular sieve exhibits reactivity for the fatty acids and the resin acids, and the separation obtained is very poor, with large amounts of undesirable resin acid components present in the fatty acid components. It is believed that the reason for this behavior is that what is stated in Du Pont's literature regarding the formation of siloxane bonds during conventional drying is substantially correct, but that there is still a very small amount of hydroxyl

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14 groups (or ammonium groups if the stabilizing cations are ammonium ions) remain on the particles, which is unimportant in most practical applications, but render the adsorbent completely unsuitable for use in the process of the invention. It should also be mentioned here that other binders for silicalite have been tried, but with equally poor results. Organic binders, such as polyvinyl alcohol, are unsuitable, probably due to the presence of hydroxyl groups. Natural clay binders exhibit selectivity for various constituents of tall oil and therefore interfere with the effect of silicalite.

Therefore, it is necessary to treat the silica gel-bound silicalite as stated above to eliminate the hydroxyl groups and replace them with siloxane bonds.

The resulting molecular sieve of silicalite in a silica matrix is exceptionally suitable for separation of tall oil components as it provides excellent separation as pure silicalite and at the same time provides a physically strong and stable molecular sieve suitable for commercial separation applications.

There are several methods for treating the silica gel-bound silicalite to obtain a substantially complete elimination of hydroxyl groups. One method is heat treatment at a temperature of approx. 450 to approx. 1000 ° C for a period of at least approx. 3 to approx. 48 hours, and this heat treatment can take place in the presence of oxygen, nitrogen and / or hydrogen. Another method is to first contact the molecular sieve with an alcohol such as ethanol and then heat treat the molecular sieve at elevated temperature (above 350 ° C) in the presence of oxygen. A third method for removing hydroxyl groups is chlorination of the molecular sieve at elevated temperature, e.g. as described in U.S. Pat.

4,308,172 contacting the molecular sieve at elevated temperature with a chlorinating agent (e.g., CCll, COCl₂, Cl₂, C₂Cl₂, SO₂Cl₂ or SOCl₂), the resulting

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15 chlorinated molecular sieve is deactivated at elevated temperature and the dechlorinated molecular sieve is oxidized at elevated temperature. Another method of removing hydroxy groups by chlorination is to contact the molecular sieve with a mixture containing oxygen and silicon tetrachloride at elevated temperature.

The molecular sieve can be used in the form of a dense compact solid layer which is alternately contacted with food mixture and displacement fluid. In the simplest embodiment of the invention, the molecular sieve is used in the form of a single static layer, in which case the process is only semi-continuous. In another embodiment, a set of two or more static layers can be used for solid-layer contacting by appropriate valve connections, such that the feed mixture is passed through one or more layers of molecular sieve, while the displacement fluid can be passed through one or more layers. several of the other layers in the set. The flow of the feed mixture and displacement fluid can be either upward or downward through the molecular sieve. Any of the conventional apparatus used for contacting fluid and solid in static layer may be used.

However, systems with countercurrent movement of the layer or countercurrent systems with simulated movement of the layer have a much greater separation efficiency than systems with fixed layers and are therefore preferred. In the layer moving or simulated layer moving processes, the retention and displacement processes are continuous, allowing both continuous production of an extract stream and a refinery stream and continuous use of feed and displacement fluid streams and, if required by the present invention, spoon-flushing stream. In a preferred embodiment of this method, what is known as a countercurrent system with simulated movement of the layer is used. The operating principles and order of such a power system are described in U.S. Patent No. 2,985,589. In such a system, it is the gradual movement of several fluid pathways.

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aisles down a molecular sieve chamber simulating the upward motion of the molecular sieve found in the chamber. Only five of the access lines are active at a particular point in time, namely the feed mix 5 inlet stream, the displacement fluid inlet stream, the liquid rinse inlet stream, the raffinate outlet stream, and the extract outlet stream. Coinciding with this simulated upward motion of the solid molecular sieve, the movement of the liquid occupying the void volume of 10 is the packed layer of molecular sieve. To maintain countercurrent contact, a fluid stream can be provided down the molecular sieve chamber by means of a pump. While an active liquid access point moves through the cycle, i.e., moves from the top to the bottom of the chamber, the circulation pump of the chamber moves through different zones requiring different flow rates.

A programmed current controller can be provided for setting and controlling these flow rates.

The active liquid access points effectively divide the molecular sieve chamber into separate zones, each having different functions. In this embodiment of the process, it is generally necessary that three separate operating zones be present for the process to proceed, although in some cases a fourth zone may be used if desired.

There is a positive net flow of fluid through all parts of the column in the same direction, although the composition and flow rate of the fluid will of course vary from point to point. In FIG. 1, zones I, II, 30 III and IV are shown, as well as a branching system 3, a pump 2 which maintains the positive net flow of fluid and a conduit 4 connected to the pump 2. Inlet and outlet outlet lines leading to or from the process via the branching system 3.

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The retention zone, Zone X, is defined as the molecular sieve located between the feed inlet stream 5 and the raffinate outlet stream 7. In this zone, the feed mixture comes into contact with the molecular sieve, an extract 5 component is retained, and a raffinate stream is withdrawn.

Since the general flow through zone I is from the feed stream passing into the zone to the refinery stream passing out of the zone, the flow in this zone is considered to be downstream, passing from the feed inlet stream to raffinatudløbsstrømmen. The liquid rinse stream (diluent) may be introduced into zone I at a point slightly downstream of the feed inlet stream. If diluent is used, it will be supplied at a sufficient rate to displace the displacement fluid associated with at least a portion of the non-selective void volume of the packed layer of molecular sieve in simulated motion in zone I, thereby retaining the fatty acid is relieved.

Immediately upstream of the liquid stream in zone I is the purification zone, zone II. The purification zone is defined as the molecular sieve between the extract outlet stream and the feed inlet stream 5. The basic processes going on in Zone II are displacement of the non-selective void volume of the molecular sieve with a circulating stream of any refinery material introduced into zone II of molecular sieve to this zone. The purification is accomplished by passing a portion of extract stream material leaving zone III into zone II at the boundary of zone II upstream, the extract outlet stream, 30 to displace refinery material. The flow of material in zone II is in a direction downstream from the extract outlet stream to the feed inlet stream.

Immediately upstream of zone II flow with respect to zone II flow is the displacement zone or zone III. The displacement zone is defined as the molecular sieve between the displacement fluid inlet 13 and the extract outlet stream 11. The function of the displacement zone is to

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Fig. 18 allows a displacement fluid entering this zone to displace the extract component that has been retained in the molecular sieve during a previous contact with food mixture in zone I in a previous operating cycle.

5 The flow of fluid in zone III is substantially in the same direction as in zones I and II.

In some cases, an additional buffer zone, zone IV, may be used. This zone, which is defined as the molecular sieve between the refinery outlet stream 7 and the displacement 10 fluid inlet stream 13, if used, is located immediately upstream of the liquid flow into zone III. Zone IV will be used to preserve the amount of displacement fluid used in the displacement step, as a portion of the raffinate stream removed from zone I can be fed into zone IV to displace the molecular sieve present in this zone. of this zone and into the displacement zone. Zone IV will contain enough molecular sieve to allow refinery material present in the refinery stream passing out of zone I 20 and into zone IV to be prevented from passing into zone III, thereby contaminating the extract stream removed from zone III . In cases where a fourth operating zone is not used, the refinery stream that would have passed from zone I to zone IV must be carefully monitored so that the flow directly from zone I to zone II can be stopped when there is a significant amount of raffinate material present in the raffinate stream passing from zone I to zone III so that the extract effluent stream is not contaminated.

In the most preferred embodiment of the present invention, Zone IV will be used and, if used, the diluent liquid flow stream may not be introduced into Zone I but into Zone IV at the boundary of Zone IV upstream. In this way, the displacement fluid, which would otherwise move into zone IV from zone III as part of the simulated moving layer, will be kept in zone III, provided that the correct amount of rinsing fluid is used. This will also reduce the need for 19

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displacing fluid. Thus, when the molecular sieve enters zone I, it will be surrounded by a suitable minimum of displacement fluid.

A cyclic feeding of inlet and outlet flow.

5 through the solid layer of molecular sieve can be achieved by using a branching system in which the valves are operated in a certain order so that the inlet and outlet flows are displaced, thereby allowing a flow of fluid in the countercurrent with a solid molecular sieve. Another method capable of effecting solid molecular sieve flow in countercurrent fluid involves the use of a rotating plate valve in which the inlet and outlet streams are connected to the valve and conduits through which feed mix, extract outlet, displacement fluid, the inlet 15 and the refinate outlet streams are advanced in the same direction through the layer of molecular sieve. Both the branching arrangement and plate valves are known. Specifically, rotary plate valves that can be used for this process are described in U.S. Patent Nos. 3,040,777 and 3,422,848.

In both of these patents, a rotary-type connecting valve is described, with which the convenient feeding of the various inlet and outlet flows from solid sources can be achieved without difficulty.

In many cases, one operating zone will contain a much larger amount of molecular sieve than another operating zone.

For example, in some cases, the buffer zone may contain a smaller amount of molecular sieve compared to the amount of molecular sieve required in the detention and purification zones. It is also clear that in cases where displacement fluid is used which can easily displace extract material from the molecular sieve, a relatively small amount of molecular sieve will be required in a displacement zone in comparison with the amount of molecular sieve required in the buffer zone or retention zone or the purification zone or in all of these zones. Since it is not necessary-

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The molecular sieve is located in a single column / the use of several chambers or a series of columns lies within the scope of the invention.

It is not necessary that all inlet or outlet streams be used at the same time, and in many cases some of the streams may be interrupted while others are used for material inlets or outlets. The apparatus which can be used for carrying out the method according to the invention may also contain a series of individual layers connected by 10 connecting lines, on which are arranged inlet or outlet outlets, to which the various inlet or outlet streams can be connected and alternately and periodically can be connected. offset to carry on a continuous operation.

In some cases, the connecting wires may be connected to 15 transfer outlets which during normal operation do not function as a conduit through which material is fed to or from the process.

It is envisaged that at least a portion of the extract effluent will pass into a separation device wherein at least a portion of the diluent fluid containing diluent may be separated to form an extract product containing a decreased concentration of the displacement fluid. Preferably, but not necessary for the operation of the process, at least a portion of the refinery effluent stream will also be fed to a separation device wherein at least a portion of the diluent may be separated to form a recyclable diluent stream and a raffinate product containing a reduced diluent concentration. The separation device will typically be a fractionation column whose design and operation is well known in the art of separation.

Reference is made to U.S. Patent No. 2,985,589 and an article by D.B. Broughton, entitled: "Continuous 35 Adsorptive Processing - A New Separation Technique", 21

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was presented at the 34th Annual Meeting of the Society of Chemical Engineers in Tokyo, Japan, April 2, 1969. Both references provide a more detailed explanation of the countercurrent process with simulated moving layer.

With regard to the separation conditions, liquid phase operation is preferred in the present process, although both liquid and vapor phase operation can be used in many adsorptive separation processes because lower temperatures are required and higher yields of extract product can be obtained in liquid phase operation. vapor-phase operation. The separation conditions will comprise a temperature range of approx. 20 to approx. 200 ° C, with approx. 20-100 ° C is more preferred and a pressure sufficient to maintain liquid phase, with the proviso that when the displacement fluid 15 is diluent above, the temperature should be at least 120 ° C. Replacement conditions will include the same range of temperatures and pressures as those used as separation conditions.

The size of the units that can be used to carry out the process of the present invention may vary from experimental set-up size (see, e.g., U.S. Patent No. 3,706,812) to commercial scale, and flow rates may be from as little as a few cm per up to several thousand liters per hour. hour.

25 When the feed mixture for the process contains pitch acids, as is the case with tall oil, another step will be. necessary to first separate the resin acids from the food mixture. This can be accomplished by contacting the resin-acidic feed mixture with a first molecular sieve comprising silicalite, thereby selectively retaining the fatty acids, excluding the resin acid. The resin acid will then be removed from the fatty acid-containing first molecular sieve, the mixture of fatty acids will be recovered by displacement from the first molecular sieve, and the fatty acid mixture will then be brought

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22 in contact with another molecular sieve comprising the molecular sieve causing separation of the fatty acids from one another as described above and preferably associated with the simulated movement of the layer.

A dynamic test apparatus is used to test different molecular sieves with a particular feed mixture and a particular displacement fluid to measure the molecular sieve characteristics in terms of retention capacity and exchange rate. The apparatus consists of a helical molecular sieve chamber having a volume of approx. 70 cm having inlet and outlet portions at opposite ends of the chamber. The chamber is kept in a temperature control device, and furthermore, a pressure control device is used to drive the chamber at a constant predetermined pressure. Quantitative and qualitative analysis equipment such as refractometers, polarimeters and chromatographs can be connected to the chamber outlet line and used for quantitative or qualitative detection of one or more components in the outlet stream leaving the molecular sieve chamber. An impulse test conducted using this apparatus and the following general procedure is used to determine data for various molecular sieve systems. The molecular sieve is filled to equilibrium with a particular displacement fluid material by passing the displacement fluid through the molecular sieve chamber. At a convenient time, for a period of several minutes, a pulse of feed mixture containing known concentrations of a trace element and of a particular extract component or of a refinate component or both, each diluted in displacement fluid is injected. The displacement fluid flow is restarted and the tracer and extract component or refinate component (or both) are eluted as in a liquid / solid chromatographic process. The eluate can be analyzed continuously or alternatively, eluate samples can be taken periodically, after which the latter are analyzed separately with analysis equipment and curves for the tracers or similar component peaks are provided.

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From the information obtained in this sample, the function of the molecular sieve can be assessed in terms of void volume, retention volume of an extract or refinate component and the rate of displacement of an extract component of the molecular sieve. The retention volume of an extract or refinate component can be characterized by the distance between the center of the peak curve of the tracer component or some other known reference point.

3

It is expressed in the number of cm displacement fluid which is pumped 10 during this time and is represented by the distance between the top curves. The rate of exchange of an extract component with the displacement fluid can generally be characterized by the width of the peak curves at half intensity. The smaller the peak width, the greater the displacement rate. The displacement rate can also be characterized by the distance between the center of the tracer peak curve and the disappearance of an extract component that has just been displaced. This distance is again the volume of displacement fluid that has been pumped during this time interval.

The following examples are intended to illustrate the process of the invention.

Example 1

The pulse tester described above is used to obtain the results of this example. The liquid temperature is 60 ° C and the flow is upward through the column at a rate of 1.2 ml / min. The feed stream comprises 10 wt.% Fatty acid mixture and 90 wt.% Displacement fluid. The fatty acid mixture consists of linoleic acid and oleic acid in the ratio 50:50. The column is packed with 77 wt.% Silicalite bonded with 23 wt.% "Ludox" prepared as preferred by the practice of the present invention, including gelling by removal of water (drying) followed by treatment to remove hydroxyl groups, which the present case occurs by heating in air at 1000 ° C for 48 hours. The prepared molecular sieve is ground and sieved to 20-50 mesh. The displacement fluid used is

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80 liquid vol.% Methyl ethyl ketone and 20 liquid vol.% Propionic acid.

The results of this example are shown in FIG. 2 of the drawing. It can be seen from FIG. 2, that there is a clear and clear separation between the curves for oleic acid and linoleic acid, although the desorption rate is rather low which is reflected by the high gross retention volume / comprising the volume of displacement fluid needed to obtain displacement.

The curves also illustrate that there is no trace of the aforementioned reactivity between adsorbent and feed mix components, which has previously been found to occur with silicalite with an organic binder and silicite with a silica binder which is not heat treated according to the invention. .

Example 2

The above-described pulse tester is again used to obtain the results of the present example. The liquid temperature is 80 ° C and the flow is downward through the column at a rate of 1.2 ml / min. The feed stream comprises 10% by weight tall oil and 90% by weight displacement fluid. The column is packed with 77 wt% silicalite bonded with 23 wt% "Ludox" as in Example 1. The displacement fluid used is 100% acetone.

The results of this example are shown in FIG. Third

The figure shows that the separation of resin acid, oleic acid and linoleic acid is clear and clear, but again the rate of desorption is rather low.

30

Example 3

The sample described in Example 2 is repeated except that, in addition to the use of a displacement fluid having a polarity index greater than 3.5, a liquid temperature in the column of 120 ° C is used.

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The results of this example are shown in FIG. 4th

FIG. 4 shows a significant improvement (increase) in the rate of desorption, ie. gross retention volume is significantly reduced. An increased desorption rate is, of course, desirable in a commercial practice of the invention, especially in a simulated layer movement embodiment, in that it will have a direct effect (reduction) on the required volume of displacement fluid with consequent energy savings as less displacement fluid. -1Q dum should be distilled from the product streams.

15 20 25 30 35

Claims (13)

A process for separating oleic acid from linoleic acid in a feed mixture containing these acids, characterized in that the feed mixture is contacted under separation conditions with a molecular sieve which is essentially free of hydroxyl groups and comprises silicalite in a silicon dioxide matrix, whereby the oleic acid is retained. selectively, the linoleic acid is removed from the oleic acid-containing molecular sieve and the oleic acid is then recovered from the molecular sieve 10 by displacement with a displacement fluid under displacement conditions. The method according to claim 1, characterized in that the displacing fluid comprises a diluent which is soluble in the feed mixture and has a polarity index 15 of at least 3.5. The process according to claim 2, characterized in that the displacing fluid comprises a solution of an organic acid having 2-5 carbon atoms per minute. molecule and a diluent selected from acetone, methyl ethyl ketone and 2. diethyl ketone. The method according to claim 3, characterized in that the separation and displacement conditions comprise a temperature of from approx. 20 to approx. 200 ° C and a pressure sufficient to maintain liquid phase. Process according to claim 1, characterized in that the displacement fluid is selected from acetone, methyl ethyl ketone and diethyl ketone, and that the separation and displacement conditions comprise a temperature of from approx. 120 to approx. 150 ° C and a pressure sufficient to maintain liquid phase 30. Process according to claim 1, characterized in that the displacement fluid comprises an organic acid, the process is cyclic, that the molecular sieve is rinsed with a diluent under rinsing conditions before each contact of the feed mixture with the molecular sieve, and that the separation, rinsing and displacement conditions includes a tempera- ture from approx. 20 to approx. 200 ° C and a pressure sufficient to maintain liquid phase. Process according to any one of claims 1-6, characterized in that the feed mixture is obtained from a feed stream which further contains a resinic acid and which is first contacted with a first molecular sieve comprising silicalite, whereby oleic acid and linoleic acid are selectively retained. the resin acid being excluded, followed by removal of the resin acid and recovery of a mixture of oleic acid 10 and linoleic acid by displacement from the first molecular sieve. Method according to any one of claims 1-6, characterized in that it comprises the first step: a) maintaining a net liquid flow in a single direction through a column of the molecular sieve, which column contains at least three zones with each of its own operating function connected in series with the column end zones so as to obtain a cyclic connection; b) maintaining a retention zone in the column where the zone is defined by the molecular sieve located between a feed mix inlet stream at a boundary of the zone up c) maintaining a purification zone immediately upstream of the retention zone, wherein the purification zone 25 is defined by the molecular sieve located between an ex-funnel outlet stream at a boundary of the purification zone upstream of the stream and a refinery effluent stream at a boundary of the downstream zone; the stream and feed mixture inlet stream at a boundary of the downstream purification zone; d) maintaining in the column n of a displacement zone immediately upstream of the purification zone, wherein the displacement zone is defined by the molecular sieve located between a displacement fluid inlet stream at a boundary of the upstream zone and the extract outlet stream at a boundary of the downstream zone; the feeding mixture to the retention zone under separation conditions to effect selective retention of oleic acid by the molecular sieve in the retention zone; ) extracting an extract stream containing the oleic acid and displacement fluid from the displacement zone, and h) periodically passing through the column in a downstream direction with respect to the fluid flow in the retention zone of the feed inlet stream, the raffinate outlet stream, f the extraction fluid inlet stream and the extract outlet streams. Method according to claim 8, characterized in that a diluent stream is fed into the downstream retention zone from the feed mixture inlet stream to cause flushing of the molecular sieve in the retention zone, the diluent inlet stream being advanced with the other inlet and outlet streams as 8th Process according to claim 8 or 9, characterized in that a buffer zone is maintained immediately upstream of the displacement zone, wherein the buffer zone is defined as the molecular sieve located between the displacement fluid inlet stream at a boundary of the buffer zone 25 downstream of a refinery outlet stream. buffer zone upstream. A process according to any one of claims 1-10, characterized in that the molecular sieve is obtained from a precursor comprising silicalite powder dispersed in colloidal 30 amorphous silica, the precursor having been subjected to gel formation and then treated in such a way as to produce a substantially complete removal of hydroxyl groups on the molecular sieve. Process according to claim 11, characterized in that the pre-molecular sieve comprises an aqueous colloidal dispersion of amorphous silica particles and silicate lith powder and that the gel formation is effected by removal of water from the dispersion. Molecular sieve for use in the method of claim 1, characterized in that it consists of silica 5 in a silica matrix and obtained from a precursor comprises silicalite powder dispersed in colloidal amorphous silicon dioxide, wherein the precursor has been subjected to gel formation and then treated. in such a manner as to effect a substantially complete removal of hydroxyl groups 10 on the molecular sieve.