NO156455B - PROCEDURE FOR SEPARATING OIL ACID FROM LINOLIC ACID AND MEDICINE FOR CARRYING OUT THE PROCEDURE - Google Patents

Description

The invention relates to the separation of fatty acids by means of molecular sieves in the form of a solid layer. More specifically, the invention relates to a method for separating oleic acid from linoleic acid using silicalite as a molecular sieve.

State of the art

It is known in the separation technique that certain crystalline aluminum silicates can be used to separate certain esters of fatty acids from mixtures thereof. For example, in US Patents 4,048,205, 4,049,688 and 4,066,677 methods are claimed for the separation of esters of fatty acids with different degrees of unsaturation from mixtures of esters of saturated and unsaturated fatty acids. In the methods, adsorbents are used which comprise an X- or a Y-zeolite containing a selected cation on the exchangeable cation-active centers.

In contrast, the present invention relates to the separation of certain fatty acids instead of fatty acid esters. According to the invention, it has been shown that a special molecular sieve which exhibits selectivity towards one unsaturated fatty acid in relation to another unsaturated fatty acid thereby makes the separation of such fatty acids possible by means of selective retention on a solid layer. It has also been shown according to the invention that an improved efficiency is obtained by using special displacement fluids under certain displacement conditions. Fatty acids are used to a large extent in the area of emollients and surfactants. Derivatives of fatty acids are valuable when it comes to compounding lubricating oils, as lubricants for the textile and molding industry, in special varnishes, as waterproofing agents, in the cosmetic and pharmaceutical areas and in bio-chemically degradable surfactants.

It has been shown that silicalite which is a hydro-

fob, crystalline silicon dioxide molecular sieve of the non-zeolite type, is uniquely well suited for use in the separation process according to the invention, in that it does not show reactivity towards the free acids and that it accepts oleic acid rather than linoleic acid.

Brief description of the drawings

From the drawing shows

fig. 1 schematically an embodiment of the invention with a simulated, movable layer which is described in more detail below, comprising an adsorption column 1, a distribution system 3 and various interconnecting lines, and

fig. 2, 3 and 4 graphically show data obtained according to

to the following examples.

Summary of the invention

The invention relates to a method for separation

of oleic acid from linoleic acid in a feed mixture comprising the aforementioned acids, where the feed mixture is brought into contact with a molecular sieve under separation conditions to thereby selectively retain the oleic acid, linoleic acid is removed from the oleic acid-containing molecular sieve, and the oleic acid is then recovered from the molecular sieve by displacement under displacement conditions with a displacement liquid, and the method is characterized by the fact that silicalite is used as a molecular sieve and that an organic acid with 2-5 C atoms is used as the displacement liquid, and a dilution liquid consisting of acetone, methyl ethyl ketone or diethyl ketone, using a temperature of 120- 150°C and a pressure sufficient for a liquid phase to be maintained.

The invention further relates to a molecular sieve for carrying out the present method, and the molecular sieve is characterized by the fact that it consists of silicalite dispersed in a silicon dioxide matrix, the starting material for the molecular sieve comprising silicalite powder which is dispersed in colloidal, amorphous silicon dioxide, and the starting material has been converted into a gel and then treated in a manner known per se for essentially complete removal of hydroxyl groups on the molecular sieve. The procedure may include the steps that

(a) a net liquid flow is maintained through a column of the molecular sieve in a single direction, using a column containing at least three zones with separate working functions occurring therein, and interconnected in series with the end zones of the column connected to provide a continuous connection between the zones, (b) a retention zone is maintained in the column, the zone being bounded by the molecular sieve arranged between an inlet feed stream at an upstream boundary of the zone and a raffinate outlet stream at a downstream boundary of the zones, (c) a purification zone is maintained immediately upstream of the retention zone, the purification zone being delimited by the molecular sieve arranged between an extract outlet stream at an upstream boundary of the purification zone and the inlet feed stream at a downstream boundary of the purification zone, (d) a displacement zone is maintained immediately upstream of the purification zone, the displacement zone being delimited by the molecular sieve ano rdnet between a displacement fluid inlet stream at an upstream interface of the zone and the extract outlet stream at a downstream interface of the zone, (e) the inlet feed stream is directed into the retention zone under separation conditions to effect selective retention of oleic acid by means of the molecular sieve in the retention zone and to remove a raffinate outlet stream from the retention zone, (f) a displacement fluid is passed into the displacement zone under displacement conditions to effect displacement of the oleic acid from the adsorbent in the displacement zone, (g) an extract stream is removed comprising the oleic acid and displacement fluid from the displacement zone, and (h) the feed inlet stream, the raffinate outlet stream, the displacement fluid inlet stream and the extract outlet and raffinate outlet streams are periodically passed through the molecular sieve column in a downstream direction relative to the liquid stream in the retention zone.

Description of the invention

First, it is believed that definitions of various terms used in the present description will be useful in clarifying the embodiments, purposes and advantages of the present method.

A "feed mixture" is a mixture containing one or more extract components and one or more raffinate components to be separated using the present method. The term "feed stream" refers to a stream of a feed mixture which is directed to the molecular sieve used in the execution of the present method.

An "extract component" is a compound or type of compound that is retained by the molecular sieve, while a "raffinate component" is a compound or type of compound that is not retained. In the present method, oleic acid is an extract component and linoleic acid is a raffinate component. The term "displacement fluid" shall generally apply to a fluid capable of displacing an extract component. The term "displacement fluid flow" or "displacement fluid inlet flow" indicates the flow by means of which the displacement fluid is directed to the molecular sieve. The term "diluent" or "diluent flow" indicates the flow that carries the diluent to the molecular sieve. The term "raffinate stream" or "raffinate outlet stream" refers to a stream with which a raffinate component is removed from the molecular sieve. The composition of the raffinate stream can vary from essentially consisting of 100% displacement fluid to essentially consisting of 100% raffinate components. The term "extract stream" or "extract outlet stream" denotes a stream by which an extract material displaced by a displacement fluid is removed from the molecular sieve. The composition of the extract stream can likewise vary from essentially consisting of 100% displacement fluid to essentially consisting of 100% extract components. At least a portion of the extract stream and preferably at least a portion of the raffinate stream from the separation process is transferred to a separation device, typically fractionation devices, in which at least a portion of displacement fluid and diluent are separated while obtaining the extract and a raffinate product. The terms "extract product" and "raffinate product" indicate products produced by the method and containing respectively an extract component and a raffinate component in a higher concentration than the concentrations occurring in the extract stream and the raffinate stream. Although by means of the present method it is possible to produce a highly pure oleic acid product or linoleic acid product (or both) in high yields,

it will be understood that an extract component will never be completely retained by the molecular sieve, nor will a raffinate component be completely not retained by the molecular sieve. Varying amounts of raffinate component can therefore occur in the extract stream, and likewise varying amounts of an extract component can occur in the raffinate stream. Between the extract stream and the raffinate stream and also the feed mixture, it can be further distinguished by means of the ratio between the concentrations of an extract component and a raffinate component occurring in the particular stream. More specifically, the ratio between the concentration of oleic acid and the concentration of unretained linoleic acid will be lowest in the raffinate stream, second highest in the feed mixture and highest in the extract stream. Likewise, the relationship between the concentration of linoleic

acid and the concentration of the retained oleic acid 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 refers to the volume of the molecular sieve which selectively retains an extract component from the feed mixture. The term "non-selective void volume" for the molecular sieve refers to the volume of the molecular sieve which does not selectively retain an extract component from the feed mixture. This volume includes voids in the molecular sieves that let in raffinate components, and the void between molecular sieve particles. The selective pore volume and the non-selective void volume can generally be expressed using volumetric units and are of importance in determining the correct flow rates for fluid to be directed into a working zone in order for an effective effect to be achieved for a given quantity of molecular sieve. When molecular sieve "flows" into a working zone (which is further described below) used according to an embodiment of the present method, its non-selective void volume together with its selective pore volume will carry fluid into that zone. The non-selective void volume is utilized to determine the amount of fluid that should flow into the same zone countercurrently to the molecular sieve to displace the fluid present in the non-selective void volume. If the speed of the fluid flow that flows into a zone is less than the non-selective void volume amount of the molecular sieve material which per unit of time flows into this zone, a net collection of liquid in the zone is obtained using the molecular sieve. As this net capture is made up of a fluid that is present in the non-selective void volume of the molecular sieve, it will in most cases include non-retained fed components.

Before the feed mixtures that can be supplied in the execution of the present method are evaluated in more detail, a brief reference must first be made to the terminology used in connection with fatty acids and to the general production of fatty acids. Fatty acids are a large group of aliphatic monocarboxylic acids, and several of these occur as glycerides (esters of glycerol) in natural fats and oils. Although the term "fatty acids" has been restricted by some to apply to the saturated acids of the acetic acid series, both with normal and branched chains, the term is generally used, and it is used here in this way, to also include related unsaturated acids, certain substituted acids and even aliphatic acids containing alicyclic substituents. The naturally occurring fatty acids are, with a few exceptions, made up of higher straight-chain, unsubstituted acids containing an even number of carbon atoms. On the basis of the number of double bonds in the hydrocarbon chain, the unsaturated fatty acids can be divided into monoethanoids.).; diethanoid or triethanoid fatty acids etc. (or monoethylenic fatty acids etc). The term "unsaturated fatty acid" is therefore a generic term for a fatty acid with at least one double bond, and the term "polyethanoid fatty acid" applies to a fatty acid with more than one double bond per molecule. Fatty acids are typically prepared from glyceride fats or oils by one of many "cracking" or hydrolytic processes. In all cases, the hydrolysis reaction can be simply described as the reaction between a fat or oil and water with the formation of fatty acids plus glycerol. In modern fatty acid plants, this process is carried out by continuous high-pressure, high-temperature hydrolysis of fat. The starting materials that are commonly used for the production of fatty acids include coconut oil, palm oil, inedible animal fats or the commonly used vegetable oils, soybean oil, cottonseed oil or corn oil.

The starting material for fatty acids for the purpose of the present invention is mainly tall oil which is a by-product of the wood pulp industry and which is usually extracted from "black liquor" by the sulphate or kraft paper process using pine as firewood. Tall oil contains 50 - 60% fatty acids and 30 - 40% rosin acids. The fatty acids include oleic, linoleic, palmitic and stearic acids. linoleic

and oleic acids make up over 90% of the fatty acids present in tallow oil. Rosin acids, such as abietic acid, are monocarboxylic acids with a molecular structure comprising carbon, hydrogen and oxygen together with three fused six-rings of carbon, and this explains the much larger molecular diameter of rosin acids compared to the molecular diameter of fatty acids.

Feed mixtures that can be used in the execution of the present method can, in addition to the components of tallow oil, contain a dilution material which is not adsorbed by the adsorbent and which can preferably be separated from the extract and raffinate outlet streams by means of fractional distillation. When a diluent is used, the concentration of diluent in the mixture of diluent and acids will preferably be from a few volume% up to 75% by volume, the remainder being made up of fatty acids and rosin acids. Although it has previously been discovered that silicalite can be effectively used for the separation of esters of fatty acids and rosin acids, separation of free acids from each other using silicalite has not been carried out so far.

Displacement fluids, which are used for the various known adsorption and molecular sieve separation processes,

will vary depending on such variables as the working method used. In separation processes which are generally operated continuously at essentially constant pressure and temperature to ensure a liquid phase and where a molecular sieve is used, the roå dilution material is chosen critically so that it satisfies a number of conditions. Firstly, the displacement material should displace an extract component from the molecular sieve while obtaining reasonable mass flow rates, but it should still allow an extract component to enter the molecular sieve so that an extract component is not too strongly prevented from displacing the displacement material during a subsequent separation cycle. Displacement fluids should also be materials that are light

can be separated from the feed mixture supplied to the process. Both the raffinate stream and the extract stream are removed from the molecular sieve in admixture with displacement fluid, and without a method of separating at least a portion of the displacement fluid, the purity of the extract product and the raffinate product would not have been very high, nor would the displacement fluid have been available for renewed use in the execution of the process. It is therefore intended that any displacement fluid material used in the present method will preferably have a significantly different average boiling point in relation to the boiling point of the feed mixture, so that at least a portion of displacement fluid can be separated from feed components in the extract and raffinate streams using of simple fractional distillation, whereby the displacement fluid can be used again for the process. The term "substantially different" shall here indicate that the difference between the average boiling points of the displacement fluid and the feed mixture shall be at least

5° C. The boiling point range of the displacement fluid may be higher or lower than the boiling point range of the feed mixture. Finally, displacement fluids must also be materials that are easily available and can therefore be obtained at a reasonable price. In the preferred isothermal, isobaric liquid phase embodiment of the present method, it has been shown, and this will be described in more detail below, that displacement liquids comprising a diluent which is soluble in the feed mixture and has a polarity index of at least 3.5, are the most favorable .

A very effective displacement fluid is an organic acid. However, it has been shown that even silicalite can be ineffective in terms of separating fatty acids and rosin acids or fatty acids from each other by renewed use of the molecular sieve layer for separation after the displacement step. When displacement fluid is present in the layer, selective retention of a fatty acid may not occur. It can be hypothesized that the displacement fluid, especially an organic acid, takes part in or even catalyzes hydrogen bonding dimerization reactions where the molecules of fatty acids and rosin acids are brought into line with each other and, if possible, with the molecules of the displacement fluid. These dimerization reactions can be represented using the equations

FA + FA (FAFA)

RA + RA (RARA)

FA + RA (HAZARD)

in which FA and RA stand for respectively fatty acids and rosin acids. The molecules for the displacement liquid of organic acid should presumably also be considered as reactants and product components in the above equations. The dimers will exclude the separation of fatty acids and rosin acids by blocking access for the former in the pores of the molecular sieve. This obstacle to separation caused by the presence of dimers does not seem to constitute a significant problem in the above-mentioned method for separating esters of fatty acids.

According to the invention, it has been shown that the above dimerization reactions can be reduced to a minimum, at least to the extent necessary to make it possible to separate oleic acid from linoleic acid, by first flushing the molecular sieves with a suitable diluent. The diluent removes displacement fluid at least from the non-selective void volume in the molecular sieves. A correct choice first requires that the feed stream components must be soluble in the diluent and, furthermore, that the diluent can be easily separated using common means, such as e.g. with the displacement fluid.

According to the invention, it has also been shown that even the above-mentioned pre-flushing can be avoided if the displacement liquid has a minimum polarity index of 3.5. A preferred displacement liquid with a minimum polarity index of 3.5 comprises a short-chain organic acid with a chain length of 2-5 carbon atoms dissolved together with a diluent which exhibits the property of reducing dimerization to a minimum. The measure of this property is the liquid's polarity index.

Polarity index is described in the article "Classification of the Solvent Properties of Common Liquids", Snyder, L., J. Chromatography, 92, 223 (1974). The diluent should make up 50 - 95% by volume, in the form of liquid, of the displacement liquid. Polarity indices for certain diluents are as follows:

Acetone, methyl ethyl ketone and diethyl ketone are diluents with a polarity index of at least 3.5 and are very suitable as displacement liquids, especially when the temperature at which the displacement is carried out is 120 - 150°C. This represents an improvement compared to the practice where a solution of such a diluent and an organic acid is used as displacement fluid for use at a relatively low temperature. A main disadvantage of using this solution is that recovery of the organic acid from the extract product stream becomes relatively energy-intensive and requires a significantly higher temperature to achieve distillation, and this causes a certain thermal breakdown of the fatty acids. Another advantage is that the corrosive effect of short-chain organic acids is eliminated.

The molecular sieve to be used in carrying out the present method comprises silicalite. As mentioned above, silicalite is a hydrophobic, crystalline silicon dioxide molecular sieve. Silicalite is described in US Patents 4,061,724 and 4,104,294. Because of its aluminum-free structure, silicalite does not exhibit ion exchange properties and is hydrophobic and organophilic. Silicalite thus comprises a molecular sieve, but not a zeolite. Silicalite is particularly suitable for the separation process according to the invention for the presumed reason that its pores have such a size and shape that the silicalite can function as a molecular sieve, i.e. accept the molecules of oleic acid in its channels or internal structure, while the molecules of linoleic acid are rejected. A more detailed discussion of silicalite can be found in the article "Silicalite, A New Hydrophobic Crystalline Silica Molecular Sieve"; Nature, Vol. 271, 9 February 1978.

In a similar way to known adsorbents or molecular sieves, silicalite can be used with the greatest advantage when used in conjunction with a suitable binding material. The binding material helps to form or agglomerate the crystalline particles of the silicalites which would otherwise have consisted of a finely divided powder. All binding materials that have been tried so far are not suitable for use in separating the components of tall oil due to the binding material's reactivity or impact on the separation. According to the invention, a binding material has been found which, when incorporated together with the silicalite, provides a

new molecular sieve that is uniquely suitable for separating oleic acid from linoleic acid.

The silicalite is bound by silicon dioxide, i.e. that the silicalite has been incorporated into a silicon dioxide ground mass. The silicalite is incorporated into the silicon dioxide by dispersing silicalite powder in colloidal, amorphous silicon dioxide to obtain a starting material which is subjected to gel formation, after which the gel is treated in a manner that effectively and substantially completely removes hydroxyl groups on the silicalite and the silicon dioxide matrix. The colloidal, amorphous silicon dioxide consists of an aqueous, colloidal dispersion of amorphous silicon dioxide particles, and the gel formation is preferably carried out by removing water from the dispersion, although other agents for gel formation can be used, such as e.g. change of pH or addition of salt or a water-miscible organic solvent. The silicalite should be. present in the silicon dioxide matrix

in an amount of 75 - 98% by weight of silicalite, based on the material free of volatile constituents. Before the gel is treated to remove hydroxyl groups, it is preferably extruded while still in a plastic state,

and it is then broken into separate particles. The plastic state will occur during at least part of the time during which water is removed to achieve gelation. After this treatment, the particles can be further ground to a smaller size that is better physically suited for use in the particular separation system used, and this size is typically 0.25 - 1.19 mm.

The colloidal amorphous silicon dioxide which is preferred for use in the practice of the present process is that sold under the trade name "Ludox". This colloidal silicon dioxide is described as discrete, uniform spheres of silicon dioxide having no internal surface area or detectable crystallinity, dispersed in an alkaline medium which reacts with the silicon dioxide surface to form a negative charge. '. The alkaline medium's pH is kept at 8.5 - 11.0. The stabilizing cations in the alkaline medium can be made up of sodium or ammonium ions. The concentration of silicon dioxide in the colloidal dispersion can be from 30 - 50% by weight, calculated as SiC>2 •

In the manufacturer's literature where the colloidal silicon dioxide "Ludox" is described, it is stated that under

drying, the hydroxyl groups on the surface of the silicon dioxide particles will condense by splitting off water to form siloxane bonds (Si - 0 - Si) which lead to coalescence, mutual bonding and particles that are chemically inert and heat resistant. However, it turned out that by simply drying the silicon dioxide-bound silicalite under conditions which are accepted as drying conditions within the relevant technology, i.e. heating in air in an oven vsd a temperature slightly above 100° C, a molecular sieve is obtained which is not applicable for the separation of the components of tall oil. Such a molecular sieve exhibits a reactivity towards the fatty acids and rosin acids, and the separation achieved is very poor in that there are serious traces of the rosin acid components in the fatty acid components. The reason for this theory is that even if what the manufacturer states in its literature regarding the formation of siloxane bonds during normal drying is essentially correct, there is still a very small amount of hydroxyl groups (or ammonium groups if the stabilizing cations are ammonium ions) that remain. on the particles and which for most practical purposes is of no importance, but which makes the adsorbent completely unsuitable for use when carrying out the present method. 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, presumably because of the presence of hydroxyl groups. Binders of natural clay show selectivity towards different components of tall oil and therefore influence the action of the silicalite.

It is therefore necessary to treat the gel-like, silicon dioxide-bound silicalite as mentioned above to remove the hydroxyl groups and replace these with siloxane bonds. The silicalite obtained in a silicon dioxide matrix - molecular sieve is particularly suitable for the separation of oleic acid from linoleic acid as it provides excellent separation for pure silicalite and at the same time a physically strong and stable molecular sieve which is suitable for separations on a technical scale.

The gelled silica-bound silicate can be treated in a number of ways to effect substantially complete removal of hydroxyl groups. One way to treat the silicate is by thermal treatment at a temperature of 450 - 1000° C for a period of 3 - 48 hours, and this treatment can be carried out in the presence of oxygen, nitrogen and/or hydrogen. Another way to treat the silicate is to first contact the molecular sieve with an alcohol, such as methanol, and then to heat treat the molecular sieve at an elevated temperature (above approx. 35 0° C) in the presence of oxygen. A third way to remove hydroxyl groups is by chlorination of the molecular sieve at an elevated temperature, as described in US Patent 4,308,172, whereby the molecular sieve is brought into contact at an elevated temperature with a chlorinating agent (e.g. CCI4, COC12»Cl2> <C> 2C14, SO2C12 or SOCl2)# and the obtained chlorinated molecular sieve. is dechlorinated at elevated temperature, and the dechlorinated molecular sieve is oxidized at elevated temperature. Another way to remove hydroxyl groups during chlorination is by bringing the molecular sieve at elevated temperature into contact with a mixture containing oxygen and silicon tetrachloride.

The molecular sieve can be used in the form of a dense, compact, solid layer which is alternately brought into contact with the feed mixture and displacement fluid. According to the simplest embodiment of the present method, the molecular sieve is used in the form of a single static layer, and in this case the method is only semi-continuous. According to another embodiment, a set of two or more static layers can be used to, in the form of a fixed layer and using a suitable valve device, be brought into contact with the feed mixture which is passed through one or more molecular sieve layers, while the displacement fluid can be passed through one or several of the other teams in the set. The flow of feed mixture and displacement fluid can be upward or downward through the molecular sieve. Any of the usual devices used to achieve contact in static layers for fluid-solids can be used.

However, systems with a moving bed in counterflow or simulated moving bed in counterflow give a much higher separation yield than fixed bed systems and are therefore preferred. In processes with a moving bed or simulated moving bed, the retention and displacement take place continuously, and this enables both the continuous production of an extract and a raffinate stream as well as the continuous use of feed and displacement fluid streams and, if necessary according to the invention, a liquid flushing stream. In a preferred embodiment of this method, what is known within the relevant technique as the counter-flow system with simulated moving layer is used. The working principles and procedures for such a flow system are described in US Patent 2,985,589. In such a system, it is the increasing movement of several liquid access points downwards in a molecular sieve chamber that simulates the upward movement of molecular sieves contained in the chamber. Only five of the access lines are active at the same time, ie the lines for the feed stream, the displacement fluid inlet stream, the liquid purge inlet stream, the raffinate inlet stream and the extract outlet stream. Simultaneously with this simulated upward movement of the solid molecular sieve, there is movement of the liquid occupying the void volume in the packed layer of molecular sieve. In order for countercurrent contact to be maintained, a liquid flow directed downwards through the molecular sieve chamber can be provided by means of a pump. As an active fluid access point moves through a cycle, ie from the top of the chamber to the bottom of the chamber, the chamber circulation pump will move through different zones requiring different flow rates.

A programmed flow control device can be used for

to set and regulate these flow rates.

The access points for active fluid effectively divide the molecular sieve chamber into separate zones, each of which has a different function. According to this embodiment of the present method, it is generally necessary that three separate working zones are present for the process to take place, although an optional fourth zone can be used in some cases.

A net positive fluid flow is obtained through all parts of the column in the same direction, even though the composition and speed of the fluid will of course vary from point to point. In fig. 1, zones I, II, III and IV and also a distribution system 3, a pump 2 which maintains net positive fluid flow, and a line 4 associated with the pump 2 are shown. Also, the inlet and outlet lines for the process and which open into or leave the distribution system 3 are shown.

The residence zone, i.e. zone I, is defined as the molecular sieve located between the feed inflow stream 5 and the raffinate outlet stream 7. In this zone, the fed material comes into contact with the molecular sieve, an extract component is retained, and a raffinate stream is removed. As the general flow through zone I takes place from the feed stream which is led into the zone, to the raffinate stream which flows out of the zone, the flow in this zone will be considered as downstream from the feed inlet stream to the raffinate outlet stream. The liquid flush stream (diluent) may be introduced into zone I at a location somewhat downstream of the feed inlet stream. If the diluent is used, it will be added in an amount per unit of time sufficient to displace the displacement fluid associated with at least the non-selective void volume in the packed layer of molecular sieve by simulated movement in zone I, thereby facilitating retention of the fatty acid.

Immediately upstream in relation to the fluid flow in zone I, the cleaning zone, zone II, is located. The purification zone is defined by the molecular sieve located between the extract outlet stream and the feed inlet stream 5. The basic operations that take place in zone II are the displacement from the non-selective void volume in the molecular sieve by means of a circulating stream of any raffinate material that is carried into zone II by replacing the molecular sieve into this zone. The purification is achieved by a part of the extract stream material leaving zone III being led into zone II at its upstream boundary, i.e. the extract outlet stream, in order to displace raffinate material. Material flow in zone II is downstream from the extract outlet stream to the feed inlet stream.

Immediately upstream of zone II and the fluid flowing in zone II, the displacement zone, zone III, is located. The displacement zone is defined by the molecular sieve located between the displacement fluid inlet 13 and the extract outlet stream 11. In the displacement zone, a displacement fluid flowing into this zone must displace the extract component that was retained in the molecular sieve during a previous contact with fed material in zone I at a previous operating cycle. The fluid flow in zone III is essentially in the same direction as in zones I and II.

In some cases, an optional buffer zone, zone IV, can be used. This zone, which is defined by the molecular sieve between the raffinate outlet stream 7 and the displacement fluid inlet stream 13, will then be arranged immediately upstream in relation to the fluid stream of zone III. Zone IV will be used to conserve the amount of displacement fluid used during the displacement step, as a portion of the raffinate stream removed from Zone I may flow into Zone IV to displace molecular sieves present in this zone and out of this zone into the displacement zone. Zone IV will contain sufficient molecular sieve so that raffinate material present in the raffinate flowing out of zone I and into zone IV can be prevented from flowing into zone III and thereby contaminating the extract stream which is removed from zone III. In those cases where the fourth working zone is not used, the raffinate stream which would have flowed from zone I to zone IV must be carefully monitored so that a flow directly from zone I to zone III can be stopped when a significant amount of raffinate material occurs in the raffinate stream which flows from zone I into zone III, so that the extract outlet stream will not be contaminated.

It is preferable to use zone IV, if any

<7 box flush dilution current can be introduced, not in zone I

but in zone IV at the upstream boundary of zone IV. In this way, displacement fluid that would otherwise have moved into zone IV from zone III as part of the simulated moving bed will be held in zone III, assuming the correct fluid flush amount is used. This will also reduce the requirement for displacement fluid. Thus, when the molecular sieve enters zone I, it will have the correct minimum surrounding of displacement fluid.

A cyclic routing of the input and output flows through the fixed layer of molecular sieve can be achieved by using a distribution system where the valves in the distribution device are operated sequentially to effect a shift of the input and output flows, so that a countercurrent fluid flow is obtained in relation to the fixed molecular sieve. Another working method which can provide a counterflow of fixed molecular sieve in relation to the fluid, includes the use of a disk valve in which the input and output flows are in connection with the valves and lines through which introduced feed material, extract outlet, introduced displacement fluid and raffinate outlet are moved in same direction through the molecular sieve layer. Both the distribution device and the disc valve are known within the relevant technology. More specifically, rotary disc valves that can be used for this work operation are described in US patent documents 3,040,777 and 3,422,848. In both of these patent documents, a connection valve of the rotary type is described in which a suitable routing of the different input and output flows from fixed supplies can be obtained without difficulty.

In a number of cases, one work zone will contain a far greater amount of molecular sieve than another work zone. For example, for certain work operations, the buffer zone may contain a smaller amount of molecular sieve compared to the molecular sieve required for the retention and cleaning zones. It will also appear 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 necessary in a displacement zone compared to the amount of molecular sieve which is necessary in the buffer zone or the retention zone or in the purification zone or all of these. As it is not necessary for the molecular sieve to be located in a single column, several other or a number of columns can also be used according to the invention

It is not necessary that the complete input or output streams be used simultaneously, and in fact in a number of cases some of the streams can be shut off while others provide for the supply or depletion of material. The apparatus which can be used to carry out the present method can also contain a number of separate layers which are connected to each other by means of connection lines on which input or output taps are placed to which the different input and output streams can be connected and alternately and periodically change to

achieve a continuous work operation. In some cases, the connection lines can be connected to transfer taps which, during normal operation, do not act as a line through which the material flows into or out of the process.

It is intended that at least part of the extract output stream will flow into a separation device in which at least part of the displacement fluid, including diluent, can be separated to obtain an extract product containing a reduced concentration of displacement fluid. Preferably, at least part of the raffinate output stream will then also be transferred to a separation device in which at least part of the diluent can be separated, obtaining a diluent stream that can be used again in the process, and a raffinate product that contains a reduced concentration of diluent . The separation device will typically consist of a fractionation column, the construction and operation of which is well known in the relevant art.

Reference may be made to US Patent 2,985,589 and to an article entitled "Continuous Adsorptive Process-ing — A New Separation Technique" by D.B. Broughton presented at the 34th Annual Meeting of the Society of Chemical Engineers in Tokyo, Japan, April 2, 1969, for further explanation of the flow chart of the simulated moving bed countercurrent process.

The present adsorptive separation process is a liquid phase operation because it requires a lower temperature and because of the higher yields of the extract product that can be obtained by the liquid phase operation compared to those that can be obtained by the vapor phase operation. The separation conditions include a temperature range of 120-150°C and a sufficient pressure to maintain the liquid phase. The displacement conditions will include the same temperature range and the same pressure range as for separation conditions.

The size of the units in which the present method can be carried out can vary from pilot plant scale (see e.g. US patent 3 7 96 812) to technical scale and can have flow quantities per unit of time which can vary from as little as a few cm per hour up to several thousand liters per hour.

If the feed material for the process contains rosin acids, in the same way as with tallow oil,

a further step may be necessary to first separate the rosin acids from the feed material. This can be carried out by bringing the feed mixture containing rosin acid into contact with a first molecular sieve comprising silicalite, thereby selectively retaining the fatty acids at the expense of the rosin acid. The rosin acid will then be removed from the first molecular sieve containing the fatty acids, and the mixture of fatty acids will be recovered by displacement from the first molecular sieve, and the fatty acid mixture will then be contacted with another molecular sieve comprising the molecular sieve which causes the separation of oleic acid from linoleic acid, as mentioned above, and which is preferably associated with the embodiment with simulated movable layer.

A dynamic testing apparatus is used to test different molecular sieves together with a special feed mixture and a special displacement fluid to measure the molecular sieve properties in terms of retention capacity and exchange rate. The apparatus consists of a spiral molecular sieve chamber with a volume of approx. 70 cm^ and with inlet and outlet parts at opposite ends of the chamber. The chamber is kept in a temperature control device, and in addition pressure-regulating equipment is used to operate the chamber at a constant pre-determined pressure. Quantitative and qualitative analysis equipment, such as refractometers, polarimeters or chromatographs, can be attached to the chamber outlet line and used to quantitatively detect or qualitatively determine one or more components of the effluent stream leaving the molecular sieve chamber. A pulsation assay designed using this apparatus and using the general method below is used to determine data for various molecular sieve systems. The molecular sieve is filled to equilibrium with a special displacement fluid material by passing this through the molecular sieve chamber. At a suitable time, a dose of feed material containing known concentrations of a tracer and of a particular extract component or of a raffinate component or of both, all diluted in displacement fluid, is injected over a period of several minutes. The flow of displacement fluid is resumed and the tracer and the extract component or the raffinate component (or both) are eluted, e.g. by liquid-solid chromatography. The effluent can be analyzed as it flows out or effluent samples can be collected periodically and later analyzed separately using analytical equipment and traces of the casings or correspondingly developed component tops.

Based on information obtained during the test, the properties of the molecular sieve can be determined in terms of void volume, the retention volume for an extract or a raffinate component and the displacement rate for an extract component from the molecular sieve. The retention volume for an extract or a raffinate component can be expressed by the distance between the center of the peak envelope for the tracer component or some known reference point. It is expressed by the volume in cm of displacement fluid that has been pumped in during this time interval which is represented by the distance between the top envelopes. The exchange rate of an extract component with the displacement fluid can generally be expressed by the width of the peak envelopes at half intensity. The narrower the peak width, the faster the displacement rate. The rate of displacement can also be expressed by the distance between the center of the tracer peak envelopment and the disappearance of an extract component that has just been displaced. This distance is again equal to the volume of displacement fluid that has been pumped during this time interval -.

Example 1

The above-described shock dosing test apparatus was used to obtain the data of this example. The liquid temperature was 60° C, and the flow proceeded up through the column in a quantity per time unit of 1.2 ml/min. The feed stream consisted of 10% by weight fatty acid mixture and 90% by weight displacement fluid. The fatty acid mixture consisted of linoleic acid and oleic acid in a ratio of 50:50. The column was packed with 23 wt% "Ludox" bonded silicalite (77 wt% silicalite) which had been prepared according to the

preferred form of execution/extensive gelation by removal of water (drying), followed by treatment to remove hydroxyl groups, and in this case this was carried out by heating in air for 48 hours at 1000° C. The molecular sieve obtained was then ground and sieved to 0.297 -0.841 mm. The displacement liquid used consisted of 80 volumes* of methyl ethyl ketone and 20 volumes of proDionic acid.

The results of this example are shown in fig. 2. It appears from the figure that the separation curves for the oleic acid from the linoleic acid are clear and distinct, but that the desorption kinetics is somewhat slow, which is evident in the high total retention volume that includes the volume of displacement liquid that is necessary to achieve displacement.

The curves also show that there is no trace of the above-mentioned reactivity between adsorbent and fed components that has previously been observed when using silicalite with an organic binder and silicalite with a silicon dioxide binder that has not been heat-treated.

Example 2

The above-described shock dosing test apparatus was again used to obtain the data for this example. The liquid temperature was 80° C, and the flow proceeded down the column in a quantity per time unit of 1.2 ml/min. The feed stream consisted of 10% by weight tallow oil and 90% by weight* displacement fluid. the column was packed with 23 wt* "Ludox" bound silicalite (77 wt* silicalite), in the same manner as described in Example 1. The displacement fluid used was 100% acetone.

The results for this example are shown in fig. 3. It is clear from the figure that the separation of the rosin acid, oleic acid and linoleic acid is clear and distinct, but that the desorption kinetics is again quite slow.

Example 3

The test according to Example 2 was repeated, except that in accordance with the present invention, in addition to a displacement liquid with a polarity index of over 3.5, a liquid temperature in the column of 120° C was used.

The results for this example are shown in fig. 4.

This shows a clear improvement (increase) in the desorption kinetics, i.e. that the overall retention volume has been considerably reduced. An increased desorption kinetics is of course desirable for a commercial embodiment of the invention, especially an embodiment with the simulated movable layer, as it will exert a direct effect (reduction) on the necessary volume of displacement liquid with consequent energy savings due to a smaller amount of displacement liquid will have to be distilled off from the product streams.

Claims (3)

1. Process for separating oleic acid from linoleic acid in a feed mixture comprising the aforementioned acids, where the feed mixture is brought into contact with a molecular sieve under separation conditions to thereby selectively retain the oleic acid, linoleic acid is removed from the oleic acid-containing molecular sieve, and the oleic acid is then recovered from the molecular sieve by displacement under displacement conditions with a displacement fluid, characterized in that silicalite is used as the molecular sieve and that an organic acid with 2-5 C atoms is used as the displacement liquid, and a dilution liquid consisting of acetone, methyl ethyl ketone or diethyl ketone, using a temperature of 120-150°C and a pressure which is sufficient for a liquid phase to be maintained. 2. Method according to claim 1, characterized in that the method is carried out cyclically and that the molecular sieve is flushed with a dilution agent before each contact between the feed mixture and the molecular sieve. 3. Molecular sieve for use in the method according to claim 1 or 2, characterized in that the molecular sieve consists of silicalite dispersed in a silicon dioxide matrix, the starting material for the molecular sieve comprising silicalite powder which is dispersed in colloidal, amorphous silicon dioxide, and the starting material has been converted into a gel and then processed in a manner known per se for essentially complete removal of hydroxyl groups on the molecular sieve.