GB2458709A

GB2458709A - Centrifugal separation process for refining triglyceride oils

Info

Publication number: GB2458709A
Application number: GB0809065A
Authority: GB
Inventors: Marc Kellens; Bart Schols
Original assignee: Desmet Ballestra Engineering NV SA
Current assignee: Desmet Ballestra Engineering NV SA
Priority date: 2008-05-19
Filing date: 2008-05-19
Publication date: 2009-09-30
Also published as: GB0809065D0

Abstract

A process is described for separating a mixture 5 of a polar phase that is dispersed in a fatty phase 6 into its constituent phases by employing one or more centrifugal separators 3, in which part of the polar phase leaving one of said separators is recycled by being incorporated into the stream feeding one of said separators. The dielectric constant of the feed going into the centrifuge is measured by a sensor 7 to calculate the amount of polar phase present in the feed. A part of the separated polar phase is recycled back via control valve 12 through the centrifuge to ensure that the feed stream contains a relatively constant amount of polar phase. The centrifugal separator can then be optimized to run at this polar phase content. The process can be used in the production and refining of triglyceride oils.

Description

CENTRIFUGAL SEPARATION PROCESS

FIELD OF THE INVENTION

The invention relates to methods for the separation of a polar phase from a fatty phase employing one or more centrifugal separators.

BACKGROUND OF THE INVENTION

In the production, refining and modification processes of triglyceride oils such as vegetable oils, fats and butters and animal oils and fats, separation steps involving the use of centrifugal separators are quite common because said oils and fats are immiscible with water. Accordingly, when palm oil and olive oil are produced from their respective fruits and fish oil is isolated from macerated and cooked fish, this production involves the use of centrifugal separators. During refining, mucilaginous matter present in crude oil can be removed from this oil in a degumming process that causes said matter to be concentrated in an aqueous phase, which is then separated from the oil.

Similarly, free fatty acids present in said oils and fats can be removed by adding an aqueous solution of a base such as caustic soda to the oil. This base reacts with the free fatty acids and forms soaps that are concentrated in the aqueous phase, which can then be separated from the oil while using a centrifugal separator as disclosed in US Patent No 2,879,282. After this removal, residual soaps can be removed by adding washing water to the oil and separating the soapy water from the oil. As disclosed in US Patent No 3,994,943, vegetable oils such as sunflower seed oil that contain waxes can : 25 be dewaxed by using centrifugal separators after an aqueous solution of a detergent has been added to the oil and the oil has been cooled. This cooling causes the waxes to crystallise and the resulting wax crystals to move into the aqueous phase where they are kept in suspension by the detergent; separating this aqueous phase from the oil leads to a decrease of the wax content of the oil.

During modification processes of triglyceride oils such as for instance the interesterification, the interesterified oil can be washed with water to remove any soaps formed on inactivation of the interesterification catalyst.

In related domains such as the production of fatty acid methyl esters to be used as an intermediate in the oleochemjcal industry or as biodiesel, centrifugal separators can also play an important role. They can be used to separate the glycerol formed during the transesterification of the triglyceride oil with methanol from the fatty acid methyl esters formed. They can also be used when washing the fatty acid methyl esters with water to remove traces of glycerol, methanol and other water-soluble impurities.

The centrifugal separators used in the processes mentioned above are standard pieces of equipment that are also used in other industrial sectors.

They can be used to skim milk and produce skimmed milk and cream. They can be used to clean lubrication oil in motor vessels, in the chemical industry and many other sectors. However, this does not mean that each piece of equipment can be used for every application. Separating a relatively small amount of heavy phase from a large amount of light phase as for instance when washing triglyceride oil with water, requires a different type of centrifugal separator from the type used to skim milk, where the light phase is less than the heavy, skimmed milk phase.

Moreover, the separation achieved by industrial centrifugal separators is not perfect. When soap is removed from triglyceride oil during the alkali :.:: 20 refining process, the aqueous soap phase will contain some neutral oil and the neutralised oil will contain some free water. To some extent changing the settings of the centrifugal separator can reduce the neutral oil content of the soapstock but as with swings and roundabouts, this will lead to an increased water content of the oil. A higher water content means more residual soap and necessitates further washing or adsorptive treatment to lower the residual soap * content and thus increases oil treatment costs. These costs may exceed the savings resulting from the lower loss of neutral oil in the soapstock.

A method to attain both a low oil content in the aqueous phase and a low water content in the oil phase has been disclosed in EP 0 507 363. It discloses a degumming process that requires the use of two centrifugal separators in series. The settings of the first separator have been adjusted to ensure a minimal oil content of the aqueous gum phase and consequently, the oil leaving the first separator has an unacceptably high residual gum content.

Washing water is mixed into the oil leaving the first separator and the resulting mixture is fed to a second centrifugal separator the settings of which ensure a minimal gum content of the oil phase. As a consequence, the gum phase leaving this second separator contains substantial amounts of oil but by recycling the entire gum phase leaving the second separator to the stream feeding the first separator, this oil is effectively recuperated. Accordingly, the oil leaving the second separator has a low gum content and the gum phase leaving the first separator has a low oil content. In addition, the process disclosed in EP 0 507 363 has the advantage that the washing water passes through both separators and thereby retards the encrustation of the discs and thus reduces the frequency with which they have to be cleaned.

Such a cleaning operation involves a shutdown of the degumming or neutralisation line and it is also labour intensive; it is therefore preferably avoided. However, some adjustments to the centrifugal separator such as for instance replacing the centripetal pump that extracts the water phase, also necessitate a shutdown. A pump with a given size can cope effectively with variable gum contents and gum viscosities as long as they remain within a certain range but once they move outside this range, a pump with a different size is needed for optimal performance of the separator.

In industrial practice, the composition of the separator feed can change within wide limits. Oil may be stored in non-agitated tanks in which some stratification can take place. Mucilaginous matter can agglomerate by hydration and form particles that are no longer kept in suspension by the . : 25 Brownian movement. Accordingly, processing the tank bottoms causes the * separator feed to have a higher gum content than when oil is drawn from the top and consequently, the separator performance may vary when processing a given lot of oil. Changing from on lot to another lot and especially changing from one oil type to another may also lead to non-optimal separator performance.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a means for controlling and especially optimising the performance of centrifugal separators while they keep running and thus avoid the need for modifications requiring a temporary shutdown.

The above objective is accomplished by a method according to the present invention.

It has surprisingly been found that the above object can be realised by a process for separating a mixture of a polar phase that is dispersed in a fatty phase into its constituent phases by employing one or more centrifugal separators, in which part of the polar phase leaving one of said separators is recycled by being incorporated into the stream feeding one of said separators, as such or after adjustment of the pH of said polar phase.

In a first aspect, the present invention relates to a process for separating a mixture of a polar phase and a fatty phase (e.g. a polar phase dispersed in a fatty phase) into its constituent phases, the process comprising: -Separating said mixture into one or more polar phase streams and one or more fatty phase streams by means of one or more centrifugal i,.., separations, and -Incorporating part of at least one of the one or more polar phase streams into the feed of at least one of the centrifugal separations, said part of at least one of the polar phase streams being either obtained as such from at least one of the centrifugal separations or after acidity regulation within a pre-set acidity range.

. : 25 * In other words, the first aspect of the present invention relates to a process for separating a mixture of a polar phase that is dispersed in a fatty phase into its constituent phases by employing one or more centrifugal separators, in which part of the polar phase leaving one of said separators is recycled by being incorporated into the stream feeding one of said separators, as such or after adjustment of the pH of said polar phase.

In an embodiment of the first aspect of the present invention, a single centrifugal separation step may be used, e.g. the process may be employing a single centrifugal separator.

In an embodiment of the first aspect of the present invention the process may comprise: -separating the mixture into a first polar phase stream and a first fatty phase stream by means of a first centrifugal separation, -incorporating part of the first polar phase stream into the first fatty phase stream, forming thereby a combination and -separating said combination into a second polar phase stream and a second fatty phase stream by means of a second centrifugal separation.

For instance, in an embodiment of the present invention, the process may employ two centrifugal separators in series whereby part of the polar phase leaving the first separator is mixed into the stream being fed to the second separator.

In an embodiment of the first aspect of the present invention, the process may comprise: -separating said mixture into a first polar phase stream and a first fatty :.:: 20 phase stream by means of a first centrifugal separation, * S*S -separating said first fatty phase stream into a second polar phase stream and a second fatty phase stream by means of a second centrifugal separation, and *. : -incorporating part of the second polar phase stream into the feed of at least one of the centrifugal separations.

For instance, in an embodiment of the present invention, the process may be employing two centrifugal separators in series whereby part of the polar phase leaving the second separator is mixed into the stream being fed to the first separator.

In an embodiment of the first aspect of the present invention, said polar phase may represent 3 % by weight to 10 % by weight of said mixture. For instance, the polar phase content of the mixture being separated may be controlled at a value between 3 % by weight and 10 % by weight.

In an embodiment of the present invention, part of the polar phase may mean 99% or less, 95% or less, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, 5% or less or I % or less. Preferably, the part of the polar phase recycled is adapted to obtain a constant polar phase content, preferably a value between 3% by weight and 10% by weight, in the mixture to be separated, i.e. in the mixture comprising said recycled polar phase and the fluid to which the recycled polar feed has been incorporated.

In an embodiment of the first aspect of the present invention, said mixture may result from a degumming process of crude glyceride oils. In other words, an embodiment of the present invention, the mixture being separated results from a degumming process of crude glyceride oils.

In an embodiment of the first aspect of the present invention, said mixture may result from a chemical neutralisation process of triglyceride oils. In other words, in an embodiment of the first aspect of the present invention, the mixture being separated may result from a chemical neutralisation process of *..... triglyceride oils. S...

*** 20 In an embodiment of the first aspect of the present invention, the pH of * * the polar phase may be adjusted by the addition of water.

In an embodiment of the first aspect of the present invention, the pH of *SS the polar phase may be adjusted by the addition of an aqueous acid.

*:*. In an embodiment of the first aspect of the present invention, the pH of *.: 25 the polar phase may be adjusted by the addition of an aqueous base.

In an embodiment of the first aspect of the present invention, said aqueous base may be an alkali hydroxide.

In an embodiment of the first aspect of the present invention, the process may further comprise the step of washing said fatty phase with water. In other words, in an embodiment of the first aspect of the present invention, the fatty phase having been separated from the polar phase may be washed with water.

In an embodiment of the first aspect of the present invention, the water used to adjust the pH of the polar phase or to prepare the aqueous acid or aqueous alkali or to wash the fatty phase may originate from the condensers of a multi-stage steam jet ejector system used for the vacuum steam stripping of triglyceride oils.

In an embodiment of the first aspect of the present invention, said part may be controlled by a measurement of a property of said feed of at least one of the centrifugal separations.

In an embodiment of the first aspect of the present invention, said property may be the dielectric constant of said mixture.

In an embodiment of the first aspect of the present invention, the fatty phase may comprise fatty acid esters of C1-4 alcohols. For instance, this can be the case when only one centrifugal separation is performed.

In a second aspect, the present invention relates to an installation for separating a mixture of a polar phase that is dispersed in a fatty phase into its constituent phases, the installation comprising one or more centrifugal separators, each of the one or more separators having an inflow for receiving fluid to be separated, a first outflow for evacuating polar phase and a second *:*::* outflow for evacuating a stream of fluid, the installation comprising a recycling *::::* 20 means for providing part of the polar phase flowing out of at least one of the * outflows of the one or more separators back to the feed of one or more separators. The installation optionally comprises a regulating means for *** regulating the acidity of the at least part of the polar phase to be recycled.

*:*. In an embodiment of the second aspect of the present invention, the *:*. 25 recycling means comprise a valve for recycling only part of the polar phase flowing out of at least one of the oufflows of the one or more separators.

In an embodiment of the second aspect of the present invention, the installation may comprise only one centrifugal separator.

In an embodiment of the second aspect of the present invention, the installation may comprise two centrifugal separators coupled to each other in series. In this embodiment, the recycling means may be adapted to provide at least part of the polar phase from the outflow of the second separator to the inflow of the first separator.

in an embodiment of the second aspect of the present invention, the installation may comprise a mean to control the content of polar phase in the mixture of a polar phase that is dispersed in a fatty phase at a value between 3% by weight and 10% by weight.

Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

Although there has been constant improvement, change and evolution of devices in this field, the present concepts are believed to represent substantial new and novel improvements, including departures from prior practices, resulting in the provision of more efficient, stable and reliable devices of this nature.

The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way S... . . . . . . . 20 of example, the principles of the invention. This description is given for the * ** sake of example only, without limiting the scope of the invention. The :.:. reference figures quoted below refer to the attached drawings.

S

*:*. IEF DESCRIPTION OF THE DRAWINGS

**.: 25 FIG. 1 depicts a single separator system in which part of the heavy phase is recycled according to an embodiment of the present invention.

FIG. 2 depicts a two-separator system in which part of the polar phase separated by the first separator is recycled into the stream entering the second separator according to an embodiment of the present invention.

FIG. 3 depicts a line comprising two centrifugal separators and pH adjustment of the aqueous phase according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVEN1]ON

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that *. . . . . . the embodiments of the invention described herein are capable of operation in * other orientations than described or illustrated herein.

It is to be noticed that the term "comprisJp", used in the claims, should * not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the **.: 25 presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this *:*::* invention.

*. 20 Furthermore, while some embodiments described herein include some **1s but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, * and form different embodiments, as would be understood by those in the art.

*:*. For example, in the following claims, any of the claimed embodiments can be *..: 25 used in any combination.

Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function.

Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not

to obscure an understanding of this description.

The invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the true spirit or technical teaching of the invention, the invention being limited only by the terms of the appended claims.

In an embodiment of the process according to the invention, a mixture comprising a polar phase and a fatty phase is separated in the constituent phases by using a centrifugal separator. The main constituent of the polar phase may be water and it may contain various non-aqueous constituents that may either be dissolved in the water such as but not limited to sugars, soaps and/or some inorganic salts, or dispersed in the water such as but not limited to soaps, phosphatides (gums), water-insoluble inorganic salts or emulsified *:::: 20 oil. The polar phase may also comprise or be a monohydric alcohol such as * but not limited to C1-C4 alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, isobutanol and tert-butanol or a polyhydric *..

* alcohol such as but not limited to glycerol.

*. : The fatty phase can be a triglyceride oil that may also contain some partial glycerides, a fatty acid ester of monohydric alcohols, a fatty alcohol, etc. In its widest sense, the fatty phase in the embodiments of the process according to the invention comprises or consists of compounds or a mixture of compounds containing fatty acid or fatty alcohol moieties, which compounds are substantially immiscible with the polar phase. When the polar phase is a monohydric alcohol, some of this alcohol may dissolve in the fatty phase but to attain a phase separation in the process according to the invention, its concentration should preferably exceed its solubility in the fatty phase.

Moreover, to accentuate the density difference between the polar phase and the fatty phase, the alcohol may be diluted with water, the presence of which also decreases its solubility in the fatty phase.

The mixture comprising a polar phase and a fatty phase may be the result of a chemical reaction such as for instance the neutralisation of free fatty acids. The neutralisation may be, for example by an aqueous alkali solution. It may also be the result of a physical mixing of for instance a washing liquid and a fatty material to be washed. Various means of forming the mixture may be used such as but not limited to high shear mixers, rotary mixers and static mixers. In general, the process according to the invention does not require the upstream mixer to be replaced by a different one.

In one embodiment of the process according to the invention, part of the polar phase 2 emerging from the centrifugal separator 3 is recycled (see recycled polar phase 4 in Fig. 1) and mixed with the feed (i.e. the mixture to be separated 5) of said separator 3. This is illustrated in FIG. 1. The execution of the particular embodiment of fig. 1 therefore advantageously makes use of a mixer 13. If the pH of the heavy phase (here, the polar phase) to be recycled is to be adjusted, proper distribution of the acid or base in the heavy phase also advantageously makes use of a mixer 13. In general, the mixer 13 that can be used for these purposes preferably does not aim at a very fine dispersion but * rather at a gentle distribution of the polar phase 2 into the fatty phase 6.

:.: Preferably, the formation of a double emulsion whereby some fatty phase 6 is dispersed in the polar phase 2 droplets, is to be avoided since this may lead to loss of fatty phase 6. In general, static mixers 13 have been found to be :..: 25 effective in distributing the recycled heavy phase 4 into the fatty phase of the mixture to be separated. If the heavy phase 4 is rather viscous as happens with some degumming processes, a rotary mixer may be used instead of the static mixer.

In an embodiment of the process according to the present invention, the recycling of the heavy phase (see recycled polar phase 4 in Fig. 1) is controlled in such a way as to ensure a near-constant ratio between the polar phase 2 and the fatty phase 6 in the feed stream 5 entering the separator 3.

This enables optimal separator performance. In doing so, the process according to an embodiment of the invention counteracts fluctuations in this ratio caused by changes in raw material properties or type changes. Because of the recycling, the near-constant ratio between the polar phase 2 and the fatty phase 6 will be higher than when no polar phase is recycled. This means that the centrifugal separator 3 is preferably adjusted or constructed or adapted to deal with the high ratio but afterwards, it does not require further adjustment even when the ratio in the raw material is much lower and/or fluctuates.

The value of the ratio between the polar phase 2 and the fatty phase 6 in the stream 5 fed to the centrifugal separator 3 may be set at different levels. In practice values between 3 % by weight and 10 % by weight have been found to be optimal. Higher values unduly decrease the capacity of the separator 3 and lower values hardly contribute towards improved separator performance.

Besides, they might be exceeded by fluctuations in feed stream 5 composition.

To maintain a constant ratio between the polar phase 2 and the fatty phase 6 in the stream 5 fed to the centrifugal separator 3, a control valve 12 is provided in the polar phase outlet stream of the separator 3 as illustrated by *.... FIG. 1. This valve may be actuated by a sensor 7 that is fitted in the line **** connecting the mixer 13 with the separator 3. Several types of sensor 7 can be :.: used in embodiments of the process according to the invention. Because the * dielectric constant of the mixture 5 fed to the separator 3 varies with its polar : phase 2 content, a sensor 7 measuring this dielectric constant is a suitable means of controlling the polar phase content 2 of the mixture 5 fed to the * 25 separator 3; it has the advantage that its signal does not depend on the flow rate of said mixture 5.

Other ways of controlling re known to those skilled in the art. Maintaining constant the polar phase 2 content of the mixture 5 being fed to the centrifugal separator 3 implies that the rate of supp!y of the polar phase entering the system as part of the mixture 5 to be separated preferably equals the rate at which it has to leave the system as non-recycled polar phase 8. Sensors 7 on the line supplying the mixture to be separated 5 and the line for the excess polar waste 8 can therefore also form the basis of a control system.

In addition to a sensor 7 measuring the ratio of the polar phase 2 and the fatty phase 6 in the product stream 5 fed to the centrifugal separator 3, another sensor measuring the pH of said product stream 5 can be incorporated in the line connecting the mixer 13 with the separator 3. This pH-sensor output value can then be used as a control input to actuate a dosing system 9 controlling the pH of said product stream 5. The control system can be adapted to add either a controlled amount of acid and/or base. Fig.1 also shows a pump 16.

The presence of this pump 16 feeding the recycled polar phase into the mixture to be separated is optional, for instance when the separator comprises a centripetal pump providing enough pressure to overcome the supply pressure in the main stream line.

Adding a base has been found to be very useful in the acid refining process. In a degumming process, crude or water-degummed triglyceride oil is first of all mixed with a food-grade degumming acid such as weak acid, e.g. phosphoric acid or citric acid to decompose the so-called non-hydratable phosphatides, which consist predominantly of calcium and magnesium salts of phosphatidic acid. The degumniing acid decomposes said salts. Phosphatidic *S..

acid is liberated. In an acid environment, this phosphatidic acid is not dissociated and thus oil soluble. To remove this acid from the oil, the pH can be raised so that the acid dissociates and migrates to the water phase.

However, raising the pH will also convert free fatty acids present in the crude or water-degunimed oil to soaps. Accordingly, the amount of base added in the acid refining process is preferably limited to such an extent that hardly any soaps are formed while at the same time, the dissociation of phosphatidic acid is sufficiently well advanced to make this phosphatide hydratable. However, the resulting gums tend to be so viscous that they can hardly be pumped but raising the pH of the gums causes them to become much more fluid.

Accordingly, raising the pH of the gums produced by the acid refining process makes them more fluid and when they are recycled they become easier to transport in the centrifugal separator 3. Because of this increased fluidity, they also retain less triglyceride oil. However, if these gums were to react with the free fatty acids in the oil, soaps would be formed and the pH of the gums would again decrease, making them less fluid. Consequently, the gums being recycled in embodiments of the process according to the invention should preferably be distributed in the oil stream rather than being dispersed into the oil.

The pH can be raised in two ways. Addition of water will dilute the slightly acid gums but water on its own will not raise the pH above 7. If a higher pH is required, some basic compound, e.g. caustic compound must be added. This can be very dilute caustic of 5°Bé or even lower since soap formation should be avoided for yield reasons.

In other instances, a lowering of the pH may be advantageous. When washing a neutralised oil or an interesterification product, it may be advantageous to acidify residual soaps so that they can be removed as free acids during a subsequent step such as a subsequent deodorisation step. In such instances, it has been found to be advantageous to acidify the stream being recycled rather than the raw material itself. Because the acidified recycle stream has to acidify soaps present in said raw material, the two streams are preferably properly mixed, for instance by using a rotary mixer.

A further embodiment of the process according to the invention involving two centrifugal separators in series, can advantageously be used during the acid degumming process as shown in FIG. 2. The first of these separators is used for water degumming crude oil while the second one is used for the acid *:*. degumming of the water degummed oil provided by the first centrifugal separator.

An acid degumming process of the prior art has for instance been disclosed in US Patent No 4,049,6864. It involves a two-stage process, in which in the first step a substantially concentrated solution of an acid or an acid anhydride having a pH of at least 0.5 as measured at 20°C in a one molar solution, is dispersed in the oil, and in a second step 0.2 to 5 wt% of water is dispersed in the mixture obtained and an aqueous sludge is separated from the oil after the water has been in contact with the oil-acid-mixture for at least 5 minutes at a temperature below 40°C.

In a subsequent patent (US Patent No. 4,162,260), an improvement is disclosed involving the increase of the level of hydratable phosphatides before the removal of the impurities from triglyceride oils. Before these hydratable phosphatides are added to the oil to be refined they are preferably dried under reduced pressure so that they are added as lecithin; partially hydrolysed lecithin, hydroxylated lecithin and/or acylated lecithin can also be used.

In an embodiment of a process according to the present invention involving two separators in series, part 4 of the polar phase leaving the first separator 3 is mixed into the oil stream being acid degummed (via the degumming acid 18) and is fed to the second separator 3' either before the acid is mixed into the oil or preferably after the acid has been mixed into the oil (apparatus and method shown schematically in Fig. 2). Again, a ratio of the polar phase to the fatty phase of 3% to 10% is preferably aimed for but because the polar phase entering the second separator 3' now comprises both the gums that are generated by the acid degumming process and the gums *:*::* originating from the polar phase leaving the first separator, there is no need to improve the performance of the second separator by also recycling part of the : 20 polar phase leaving said second separator. Moreover, as soon as the polar phase content in the second separator has reached the desired value within a..

* the range of 3% to 10%, a steady state is preferably aimed for in which the rate at which the total amount of polar phase enters the separator equals the rate at which it leaves said separator.

FIG. 2 is a shematic representation of an apparatus and a method according to an embodiment of the present invention. The oil stream 6 leaving a first centrifugal separator 3 is fed to a second separator 3'. The mixture to be separated 5 (e.g. crude oil with hydrated gum) enters the fist separator 3 wherein it is separated into a polar phase 2 and a fatty phase 6. The polar phase 2 is directed to a control valve 12 wherein part of it is recycled as a recycled polar phase 4 while another part 8 of it is not recycled. This excess polar phase can for instance be used for lecithin production. The fatty phase 6 leaving the first separator 3 can be mixed with a degumming acid 18 via a mixer 13. The recycled polar phase 4 and the acid-treated fatty phase are then recombined and fed to the second separator 3' wherein it is separated in a fatty phase 6 and a polar phase (combined polar phase 14). A system comprising a water degumming line producing water degummed oil and gums (polar phase) that can be dried to produce lecithin and a second acid degumming or acid refining line whereby part of the polar phase produced by the water degumming line is mixed with oil being acid degummed or acid refined falls also within the scope of the process according to an embodiment of the present invention.

As shown in FIG. 3, yet another embodiment of process according to the invention entails the use of two centrifugal separators 3 and 3' in series, which embodiment enables a counter-current treatment of the fatty phase 6. This embodiment can profitably be used when treating a fatty material 5 with a liquid adsorbent. If the adsorbent present in the polar phase 2 emerging from the second centrifugal separator 3' still has some adsorption capacity left, this can be recycled as a recycled polar phase 4 to the mixture 5 being fed to the first separator 3. The polar phase 2 leaving the first separator 3 will have .* hardly any adsorption capacity left and can be discarded (spent adsorbent 8).

: 20 Fresh adsorbent 15 is then mixed into the fatty stream leaving the first separator 3 and being fed to the second separator 3' whereby part 17 of the polar phase leaving the second separator 3' is also recycled to the stream : being fed to the second separator 3' to maintain its polar phase content at the required level. Fig.3 also shows a sensor 7 and a mixer 13 in the line leading to the first separator 3 as well as a sensor 7' and a mixer 13' in the line leading to the second separator 3'. The function and the nature of sensors 7 and 7' and mixers 13 and 13' are as indicated above for sensor 7 and mixer 13 in the discussion of Fig. 1. The sensors 7 and/or 7' can be used to control the valve 12.

EXAM PL ES

Water-degummed rapeseed oil with a free fatty acid content of 0.50 % by weight (expressed as oleic acid) and with a residual phosphorus content of 93 ppm and still containing 21 ppm of calcium and 11 ppm of magnesium was subjected to an acid refining process to eliminate most of the non-hydratable phosphatides still present in the water-degummed oil. To this end, the oil was pumped through a heat exchanger raising the oil temperature to 95°C at a rate of 12.5 tonne/hour and an amount of 2 kg/tonne of phosphoric acid (expressed as 100%) was dispersed into the oil as a solution of 26 % by weight.

Accordingly, 1.5 L/tonne of the acid, which was supplied at8l % by weight strength and had a density of 1.645 was diluted with 5.2 L/tonne of water.

The water used for this purpose originated from a nearby deodorisation or vacuum steam-stripping unit. In such units, triglyceride oil is heated to elevated temperatures (200-250°C) and striping steam is sparged through the oil while a vacuum of 2-10 hPa absolute is maintained. The sparging steam entrains volatile constituents that are subsequently condensed in a scrubber positioned between the deodoriser vessel and the vacuum system. To create and maintain such a deep vacuum, most industrial installations use multi-stage steam ejector systems comprising for instance two boosters in series leading * **.

to a main mixing condenser followed by smaller ejectors and condensers or a :. small mechanical pump compressing the non-condensables for discharge into the atmosphere. In the condensers, motive steam and sparge steam are . : condensed by using cooling water but since the upstream vapour scrubbing system does not condense all organic vapours, this cooling water becomes seriously polluted and its disposal requires prior treatment. However, this polluted cooling water can be used as such to dilute the phosphoric acid after having been heated to a temperature of approximately 95°C. Accordingly, the use of said cooling water in the process according to the invention reduces the ultimate effluent treatment requirements of the combined processes.

The phosphoric acid was diluted with said heated cooling water and the diluted acid was finely dispersed in the preheated oil while using a high shear mixer (IKA DISPAXDR2000/1o 6F/6F/6F, IKA Werke GmbH & Co KG, Staufen, Germany) that had an installed capacity of 2 kW/tonne. After the diluted acid had been dispersed in the oil, the dispersion was fed to a holding vessel that provided a reaction time of 15 minutes. Subsequently, the phosphoric acid was partially neutralised by the addition of 0.6 kg/tonne caustic soda.(100%). This caustic soda was supplied at 45 % by weight strength and it was diluted with 12 kg/tonne water to a final strength of 2.1 % by weight. The water used for this dilution was again the cooling water originating from the nearby deodoriser vacuum system. A Silverson mixer (450 LS, Silverson Machines Ltd., Chesham, Bucks. UK) with an installed capacity of 7.5 kW was used to disperse the caustic in the medium.

Subsequently, the oil stream was cooled to 42°C in a heat exchanger and passed to a retention vessel with a residence time of 80 minutes. Thereafter the stream was heated again to some 80°C and fed to a self-cleaning centrifugal separator RSE1 10 (Westfalia Separator AG, Oelde, Germany) and split into an oil stream and a gum stream. However, the relatively small gum stream consisting of approximately 30 kg/hours of gums and 10-15 kg/hour of triglyceride oil in just over 200 L/hour of water was discharged irregularly and the risk of oil breakthrough leading to unacceptably high oil losses was permanently imminent. Therefore, in the process according to the invention, * ** gums were recirculated as shown in Figure 1 until a much more steady 0S*.

operation of the separator was observed. At that point in time, the total gum stream leaving the separator amounted to 500 kg/hour or 4% by weight of the product stream being separated. When this level had been reached, a steady state was aimed for by allowing part of the aqueous gum stream leaving the **: 25 separator to go to the waste water treatment plant and recycling the other part * to the oil stream.

The oil leaving the separator was washed by the addition of 64 kg/tonne washing water that had been acidified with 150 g/tonne citric acid; it was mixed into the oil with a Silverson 435LS mixer. For the separation an RTCI 50 (Westfalia Separator) was used. The water used was again the cooling water originating from the deodoriser vacuum system. Because the water had been acidified, the washing water did not contain any soaps. It contained some residual gums but as soon as gums were being recycled to the first separator in the process according to the invention, the gum content of the washing water was noticeably reduced.

Accordingly, recycling the gum phase and maintaining a higher aqueous phase content in the mixture being fed to the first separator not only improves the stability of the performance of the separator, it also improves the separating efficiency in that it reduces the residual gum content of the oil phase.

It is to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope and spirit of this invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention. * ** * . S * S. S... * S * S.. * S. * S * **. S S.. S. * * SS * S.

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Claims

CLAIMS1. A process for separating a mixture of a polar phase dispersed in a fatty phase into its constituent phases, the process comprising: -Separating said mixture into one or more polar phase streams and one or more fatty phase stream by means of one or more centrifugal separations, and -Incorporating part of at least one of the one or more polar phase streams into the feed of at least one of the centrifugal separations, said part of at least one of the polar phase streams being either obtained as such from at least one of the centrifugal separations or after acidity regulation within a pre-set acidity range.
2. A process according to claim 1 wherein a single centrifugal separation step is used.
3. A process according to claim 1, the process comprising: -separating said mixture into a first polar phase stream and a first fatty phase stream by means of a first centrifugal separation, -incorporating part of the first polar phase stream into the first fatty phase stream, forming thereby a combination and * ,* -separating said combination into a second polar phase stream and a second fatty phase stream by means of a second centrifugal separation.
4. A process according to claim 1, the process comprising: -separating said mixture into a first polar phase stream and a first fatty phase stream by means of a first centrifugal separation, -separating said first fatty phase stream into a second polar phase stream and a second fatty phase stream by means of a second centrifugal separation, and -incorporating part of the second polar phase stream into the feed of at least one of the centrifugal separations.
5. A process according to any of claims 1 to 4 wherein said polar phase represents 3 % by weight to 10 % by weight of said mixture.
6. A process according to any of claims 1 to 5 wherein said mixture results from a degumming process of crude glyceride oils.
L A process according to any of claims 1 to 5 wherein said mixture results from a chemical neutralisation process of triglyceride oils.
8. A process according to any of claims 1 to 7 wherein the pH of the polar phase is adjusted by the addition of water.
9. A process according to any of claims 1 to 7 wherein the pH of the polar phase is adjusted by the addition of an aqueous acid.
10.A process according to any of claims 1 to 7 wherein the pH of the polar phase is adjusted by the addition of an aqueous base.flA process according to claim 10 wherein said aqueous base is an alkali hydroxide.12.A process according to any of claims 1 to 11 further comprising the step of washing said fatty phase with water.13.A process according to any of claims 8 to 12 wherein the water used to adjust the pH of the polar phase or to prepare the aqueous acid or aqueous alkali or to wash the fatty phase originates from the condensers of a multi-stage steam jet ejector system used for the vacuum steam stripping of triglyceride oils.14.A process according to any of claims Ito 13 wherein said part is controlled by a measurement of a property of said feed of at least one of :.: 20 the centrifugal separation.15.A process according to claim 14, wherein said property is the dielectric constant of said mixture.16.A process according to claim 1 or claim 2 in which the fatty phase . : comprises fatty acid esters of C1..4 alcohols. * 25 *. . * S* * S.