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(11) | EP 0 182 396 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Process for treating triglyceride oil |
| (57) Process for treating triglyceride oil including removing from the triglyceride oil
at least a part of particulate matter within the range of from 0.04pm to 25pm, preferably 0.2 to 15µm, and subsequently degumming the oil. Removal of
particulate matter can be by e.g. microfiltration. Degumming can be e.g. water degumming
or ultrafiltration. Cleaner lecithin and improved ultrafiltration flux can be achieved
due to process. |
[0001] The present invention relates to a process for treating triglyceride oil. In particular the present invention relates to a process for degumming triglyceride oil.
[0002] Triglyceride oils are valuable raw materials. They consist of triglycerides of fatty acids but usually contain minor components such as colouring materials, sugars, glucosides, waxes, free fatty acids, metals and phosphatides. Some of these minor components are preferably removed in smaller or larger amounts. A particularly important and valuable group of these minor components is formed by the phosphatides. "Degumming" is the name given to processes in which inter alia phosphatides are removed from triglyceride oil. The product obtained from the phosphatidecontaining composition that is separated from the oil is commonly called lecithin.
[0003] Two known ways of degumming a triglyceride oil are water degumming and ultrafiltration. In water degumming the oil is brought into contact with water and an aqueous phase separated from the oil containing phosphatides and other impurities. Various additives and procedures can be employed to improve the essential water degumming step. Examples of such are found in GB 1541017 and GB 1585166, each of whose contents are incorporated herein by reference.
[0004] In ultrafiltration the triglyceride oil is contacted under pressure with a semi-permeable membrane. In the oil the phosphatides form micelles whose size prevents the phosphatides passing through the membrane. Other impurities can be incorporated in the micelles.
[0005] Triglyceride oil passes through the membrane, providing a filtrate of refined oil. Further details of the process carried out in the presence of a solvent can be found in GB 1509543.
[0006] Water degumming and its many variations can be an efficient process. It can, however, suffer from the disadvantage that the aqueous residue formed cannot readily realise its value. It contains not only useful phosphatides, but also other impurities whose presence detracts from the inherent value of the lecithin.
[0007] Ultrafiltration can provide a way of refining triglyceride oil to a high level of purity. In practice, however, it has been found to suffer from a variety of operational problems.
[0008] We have now found a process for treating triglyceride oils which provides an improved process for degumming triglyceride oils.
[0009] According to the present invention there is provided a process for treating triglyceride oil including
(i) removing from the triglyceride oil at least a part of particulate matter within the range of from 0.04pm to 25pm and subsequently
(ii) degumming the oil.
[0010] Step (i) of the present process requires that at least a part of the particulate matter in the oil which falls somewhere within the range of 0.04 to 25pm, preferably 0.2 to 25pm, more preferably 0.2 to 15pm, is removed. Parficulate matter larger than 25pm can, of course, and normally will be removed as well, either as part of the present process or as part of a separate process. Advantages accruing to the present process are, however, believed to be due to the attention paid to the removal of a substantial part of particulate matter between 0.04um, particularly matter between 0.2pm and 15pm, prior to performing a specific degumming operation. Matter smaller than 0.04pm, in the preferred embodiment matter smaller than 0.2pm, is not removed in step (i), it is retained in the oil and where appropriate is removed from the oil during the degumming step; in particular phosphatides present in micelles of approximately 5-10 nm are removed from the oil in step (ii) of the process, not in step (i).
[0011] Preferably step (i) is directed to removal of particulate matter within the range of from 0.2pm to 15pm, more preferably matter within the range of from 0.2 to l.Opm.
[0012] The degumming step can, for example, be a water degumming operation or involve ultrafiltration. In the former, practice of the present invention can remove impurities such as iron-containing particles prior to water degumming so that a high quality, pale, transparent phosphatide phase having a low iron content can be obtained. If water degumming is to be performed, step (i) is preferably carried out in the absence of a solvent If desired, however, step (i) may be carried out in the presence of a solvent
[0013] If ultrafiltration is employed as the degumming step, improved flux rates can be obtained. In particular, removal of particulate matter within the range of 0.2 to 15pm is believed to reduce the amount of fouling to which the membrane employed in ultrafiltration is subjected. If ultrafiltration is intended to be used as the degumming procedure, step (i) is preferably carried out in the presence of a solvent, preferably a non- acidic, non-alcoholic, non-polar organic solvent Preferably the solvent has a molecular weight within the range 50-200, especially 60-150. Examples of suitable solvents include esters of lower fatty acids and lower monohydric alcohols, in which the total number of carbon atoms is at most 12, halogenated hydrocarbons and inert hydrocarbons, particularly alkanes, cycloalkanes and simple aromatic hydrocarbons, e.g. benzene and its homologues containing alkyl substituents having up to 4 carbon atoms. Suitably step (i) is performed on the miscella obtained direct from solvent extraction of the triglyceride oil. The solvent employed is preferably hexane. Ultrafiltration is preferably performed in the presence of the same solvent using a suitable semipermeable membrane of a cut-off limit between 1000 and 1,000,000, preferably between 10,000 and 100,000 at temperatures between 10°C and 80°C at pressures of 1.5-10 bar absolute. Membranes may be flat plate type, or tubular or capillary bundles or a combination of these types in parallel or series. The module construction is not of primary importance for good flux and all types of commercial modules of any geometry may be used, either alone or in combination with each other, parallel or in series. Further details for carrying out an ultrafiltration step are found in the above-mentioned GB 1509543.
[0014] Step (i) preferably includes microfiltration to remove insoluble particles down to 0.04pm, preferably down to 0.1pm, more preferably down to 0.2pm in dimension. Optionally step (i) can include one or more conditioning steps such as one or multiple heat treatment steps, an adsorbtive treatment with a suitable adsorbent (e.g. bleaching earth) or a pretreatment with alkali followed in each case by settling or microfiltration. Where more than one conditioning step is applied they can be employed in any order.
[0015] The present process can thus include the following sequence of steps: in a first step the oil to be degummed is subjected to a pre-treatment consisting of:
(a) microfiltration, preferably crossflowmicrofiltration with back-flushing, or,
(b) heat treatment followed by sedimentation or microfiltration as in (a), or
(c) addition of lye or an adsorbent (e.g. bleaching earth, active carbon etc.), followed by sedimentation or microfittration as in (a), or
(d) combination of heat treatment, addition of lye and/or an adsorbent in any order, followed by sedimentation and/or microfiltration as in (a),
and in the second step the purified oil obtained as a filtrate or supernatant from the pre-treatment operation is degummed.
(a) Crossflow-microfiltration with back-flushino
[0017] By crossflow-microfiltration is meant use of a microfiltration means in which the material being filtered flows along the surface of the microfiltration means. Preferably use is made of high flow speeds tangentially to the filter or membrane surface to eliminate the formation of deposit layers on the membrane. This same principle is used also in ultrafiltration. The main difference between crossflow microfiltration and ultrafiltration lies in the configuration of the pores in the membranes used for these two processes. Since microfiltration is concerned with suspended particles of micron size, the pores of the membrane are of a similar order of magnitude. Ideally these pores should be slightly smaller than the particles so as to avoid clogging of the pores by the particles on the one hand and ensure maximum filtrate flow on the other.
[0018] Additional features can be:
- intermittent application of back pressure, e.g. use of frequent short backflushing cycles, are applied during the filtration process (1 -2 s at 2 min. or longer invervals) to help reduce the deposit and/or clean the pores (self-supporting tube or capillary membranes are particularly suited);
- a homogeneous pore structure of the membrane whose average pore size is 0.2 or 0.4µm (distinctly higher quality of the filtrate, even sterile filtration possible);
- narrow pore size distribution (the average pore diameter is about half the diameter of the largest pore measured by bubble point method);
- high pore volume: 75-80%. This can give high filtrate flow;
- membrane polymer is polypropylene, a chemically very resistant material which, in addition, offers the possibility to clean to regenerate chemically the filter modules. Alternative preferred membrane materials which are resistant to solvents and other chemicals are steel and poly- tetrafluoroethyiene, e.g. Teflon;
- the pores should be cylindrical, preferably symmetrical, so as to allow backflushing without damage;
- the membranes may be tubular or a bundle of capillaries or a combination of both.
(b) Heat treatment
[0019] A heat treatment at 50-150°C, preferably at 70-120°C, more preferably at 85-100°C for a period of at least 1 second, preferably for a period of 1 second to 5 minutes, by passage through a heat exchanger (the duration of the treatment may easily be regulated by adjusting the throughput) causes the suspended matters to coagulate rapidly and the rate of sedimentation to increase. In a comparative trial employing one and the same crude soyabean oil miscella without heat treatment, it required about 4 days for more or less complete sedimentation of the suspended matters, whereas the heat-treated miscella (1 min., 100°C) deposited suspended matter in less than 1 hour. The sedimented matter of the heat-treated miscella was, moreover, somewhat slimy in consistence and did not whirl up when shaken, in contrast to the non-heated miscella. The amount of the sediments from the heat-treated miscella was about 50-100% higher than in the case of the non-heated miscella and could be separated from the miscella by decantation or by microfiltration. Alternative separation techniques, such as rotary decanters and clarifiers, could be employed.
(c) Addition of absorbent or Ive
[0020] In case of addition of an adsorbent, 0.1% of a mixture of a fitter aid Celite 535 (Trade-mark) and of an acid- activated bleaching earth Tonsil ACFF (Trade-mark) of Südchemie, Munich (ratio 15/85), can be added to the crude soyabean miscella containing 30% crude soyabean oil, stirred at a temperature of 50°C and then filtered through a Funda filter (Trade-mark) (manufactured by A.G. für Chemieapparatebau, Mannedorf, Zurich) with a built-in stainless steel filter of 75pm aperture. The rate of filtration was 4 m3/h per square metre of filter surface. The starting miscella contained 0.01% of suspended matter, whereas the filtrate was free of suspended matter. Additionally, water, chlorophyll and phospholipid contents were lowered by about 2% only, compared to the initial content of these components of the crude miscella. Other adsorbents such as active carbon, non-activated bleaching earths, e.g. Tonsil 13 (Trade-mark) (Sudchemie), or organic filter aids, e.g. Porvacel HB 150 and Highflow (Trade-marks) were effective. Other filtering equipments, e.g. Niagara Filter (Trade-mark) (of Messrs AMA Filter BV, Alkmaar, Netherlands) were also effective. The treatment could suitably be carried out at a temperature in the range of from 20 to 150°C.
[0021] It is worthwhile to note that suspended matters of the crude oild, of which 70% were of a particle size of less than 25µm, could now be separated in the presence of bleaching earths even by a filter gauze of 75pm aperture because of a precoat formation on the filter by recirculating the miscella. Use of Funda Filter, Niagara Filter type filters etc. are discontinuous operations, which necessitates the opening up of the filter to remove the accumulated dirt. Working with an inflammable liquid like hexane miscella, it is not very desirable. For that reason the crossflowmicrofiltration is a preferred alternative. See (a) above.
[0022] Addition of aqueous lye to the miscella neutralises the free fatty acids present and produces soaps in situ. A major part of the soaps form mixed micelles with the phospholipids present in the miscella and remain dissolved, but a minor part form double-salt type complexes with proteins, lipoproteins and phospholipids and separate out as finely divided particles, which, if present in the uftrafiltration stage, cause low flux and flux decline. These materials can effectively be removed by crossflowmicrofiltration.
[0023] The suspended particulate matter which can be removed by use of the present process is believed to comprise lipoproteins and other insoluble materials. From a typical soyabean crude extraction miscella the particulate matter was collected by using a 0.2p Teflon (Trade-mark) microfilter and analysed for the chemical composition. The analysis of the material recovered from a crude soyabean miscella obtained by extracting crushed soyabeans with industrial hexane is given below:
[0024] Apart from the inorganic dusty material and the crude fibres, the major part of the other components are present as lipoproteins. The particle size distribution of the suspended matter is shown in the following Table:
[0025] 75.9% of the particles are smaller than 24 µm and they are not easily separated by usual commercial 25 pm sieve-type filters. The rate of sedimentation can be very slow in a 30% oil-hexane miscella and it can take 3 to 7 days for the material to settle down more or less completely, although some finer particles can still remain in suspension after a week. Pumping the miscella using a centrifugal pump at a high linear velocity through a membrane module shifts the particle size distribution in favour of smaller particles. Storage for a longer period of time shows slow agglomeration in favour of the particles with bigger particle sizes.
[0026] Before for example an oil seed is extracted with hexane or other organic solvent, the seeds are usually crushed with various types of high speed mills (e.g. hammer mill) using a fine screen (e.g. 1/32 inch). Higher speed of the mills allows a better extraction of the oil, but at the same time promotes the formation of lipid-protein complexes by cell disruption. Deposition of lipid-protein complexes on the surface of the ultrafiltration membrane is, we believe, a reason for flux decline during ultrafiltration. By use of the present process the lipoproteins, whether soluble or insoluble, can be removed from the oil prior to degumming. The heat treatment for example can lead to accelerated decomposition of the lipoproteins rendering them to agglomerate and be separated readily by sedimentation or filtration. Addition of an adsorbent like bleaching earth leads to decomposition and adsorption of the lipoproteins with resulting easier separation by the following microfiltration or sedimentation. Addition of aqueous lye or other scavengers to the crude miscella prior to ultrafiltration can be effective too, leading to a better and more consistent flux rate in a subsequent ultrafiltration step.
[0027] The present pretreatment of triglyceride oil prior to ultrafiltration can thus not only improve the flux rate to a great extent, but also reduce the tendency for flux decline during operation of the ultrafiltration significantly.
[0028] The present invention is applicable to all triglyceride oils, but is of particular use in refining of soyabean oil, sunflower oil, safflower oil, cottonseed oil, rapeseed oil, corn oil, grapeseed oil, rice bran oil, tallow and fish oil. Embodiments of the present invention will now be described with reference to the following examples:
Examole 1
[0029] A crude soyabean oil miscella fresh from the extraction plant analysing
was subjected to a crossflow microfiltration using a Mycrodyn Filter (trade-mark) module HA 1124 H 22 of Messrs ENKA AG, Wuppertal, Germany, length 50 cm, total filter surface 0.05m2, pore diameter 0.2p, material polypropylene. The operational conditions were:
[0030] Temperature = 52.5°C, front pressure = 3.2 bar, hind pressure = 3 bar, linear velocity = 2 m/sec, backflush pressure = 4 bar, backflush duration = 5 sec, pulse time = 4 min.
[0031] The average flux was 2.82 m3/m2h. The flux diagram illustrating the backflushing is shown in Fig. 1. Total suspended matter (lipoproteins etc.) dropped after microfiltration to 5 ppm.
[0032] The filtered miscella was immediately ultrafiltered using a PCI-BX3 (Trade-mark) tubular polysulphone membrane at 45°C, 4.5 bar pressure and 3.7 m/sec linear velocity. The membrane was conditioned prior to use by soaking 2 hours each in isopropanol and hexane. The permeate leaving the ultrafiltration module was collected, whereas the retentate leaving the ultrafiltration unit was mixed with the miscella to be ultrafiltered.
[0033] The initial flux was 232 l/m2h of miscella (corresponding to 50 kg hexane-free oil/m2h), which dropped to 210 I/m2h miscella corresponding to 47 kg/m2h hexane-free oil after 8 hours run. Phosphorus content in the permeate oil was 7 ppm.
[0034] In a parallel experiment the same miscella without previous microfiltration was ultrafiltered as above using the same membrane and the same process conditions. This time the flux was 168 I/m2h at the start (corresponding to 35.8 kg hexane-free oil/m2h) which dropped to 90 l/m2h after 8 hours run (corresponding to 18 kg hexane-free oil/m2h).
[0035] Pretreatment by crossflow microfiitration not only led to higher absolute flux rates during the subsequent ultrafiltration, but also to higher flux constancy.
Example 2
[0036] A sample of crude extraction soyabean miscella from the same source as employed in Example 1 was ultrafiltered as above after having been heat-treated at 100°C for 1 minute, at a pressure higher than the vapour pressure of the miscella, and separated from the coagulated sediments. The initial and the final flux during ultrafiltration after 8 hours run was very similar to themicrofiftered miscella and showed the same constancy.
Example 3
[0037] A crude soyabean oil miscella, which was purified by crossflow microfiltration as described under Example 1, was immediately ultrafiftered as also described under Example 1. The initial rate of ultrafiltration was 165 l/m2h, which decreased to 122 l/m2h after 4 hours run. The total yield of permeate was 18.3 1 of 25 1 input ( = 73% of input). The P-contents of the permeate oil and of the retentate oil were 7 ppm and 3246 ppm, respectively.
[0038] In a parallel trial the same amount of the same crude soyabean oil miscella without pretreatment by crossflow microfiftration was subjected to ultrafiltration. The initial flux was 120 l/m2h, but it decreased to 50 l/m2h after 8 hours of run (total yield of permeate was 70.0% of input). The P-contents of the permeate oil and of the retentate oil were 8 ppm and 3133 ppm, respectively.
[0039] Figure 2 shows the flux diagrams of the microfiltered miscella as compared to the non-microfiltered miscella. The following Table shows the analytical data of the crude miscella, the microfiltered miscella and the ultrafiltered mis- cellas.
Miscella Analysis
[0041] The results show that the removal of the suspended matters including lipoproteins has a beneficial effect on the flux of the ultrafiltration stage.
Example 4
[0042] A crude rapeseed oil miscella containing 1.2% free fatty acids (based on oil) was neutralised by addition of the theoretical amount of 40% aq. KOH solution. The major part of the soap formed in situ went into micellar solution, but complexes of soaps, phospholipids, lipoproteins etc. remained suspended in the miscella.
[0043] The miscella was subjected to a pretreatment by heating at 90°C for 20 sec. and then crossflow microfiltered as described under Example 1. The microfiltered miscella was immediately cooled down to 45°C and ultrafiltered as described under Example 1. After 4.5 hours the total yield of permeate was 77% of the input; the P-content in the retentate oil was 1507 ppm. The flux rate in dependence on time is shown in Fig. 3. The analytical results of the crude miscella after addition of lye, after crossflow microfiltration, and ultrafiltration are shown in the Table below.
[0044] In a parallel trial the same amount of the same crude miscella with added lye was subjected to ultrafiltration without previous pretreatment by heat and without crossflow microfiltration. After 8 hours the total yield of permeate was only 37% of the input; the P-content in the retentate oil was 772 ppm. Fig. 3 shows the time dependent flux rate.
Analytical data of miscella
[0046] The above results show that a part of the phospholipids and K-soaps are removed by crossflow microfiltration as suspended matter together with the lipoproteins. Chlorophyll and other plant pigments form a complex with lipoproteins and are thus in part removed by the microfiltration step. The preliminary heat treatment and crossflow microfiltration lead to improved flux rates during ultrafiftration.
Example 5
[0047] Hexane-free crude extracted soyabean oil was passed through a crossflow microfiltration unit with back flushing and then water degummed. The water content of the aqueous phase obtained was reduced to yield a lecithin of high transparency and good quality.
[0048] Crossflow microfiltration was carried out on a Microdyn Filter Module HA 11 24 H 22 unit ex Enka AG, Wuppertal pore dia 0.2µ. The filtration was carried out at 45°C/2 bar. For the back flushing, a cycle time of 3.5 min. and a back flushing time of 2 sec. were used. The linear flow velocity was about 2 m/sec. The mean filtration rate was about 95 kg oil/m2h. The starting oil contained 230 ppm total suspended solids and 7.4 ppm Fe. The filtered oil contained 8 ppm total suspended solids and 0.6 ppm Fe. The filtrate was conventionally degummed with water at 85°C, the gum was centrifuged off, and water removed under vacuum at a temperature of 50°C. The lecithin contained 1.95% P and 15 ppm FE and was more than 90% transparent The same extraction oil without previous crossflow microfiltration yielded, following the same degumming step, a lecithin having about 30% transparency and 169 ppm Fe.
[0049] In a parallel test, instead of hexane-free crude oil, the hexane miscella was microfiltered, oil being obtained from the filtrate and lecithin from the oil. The transparency was more than 90% but the Fe content was 145 ppm.
Example 6
[0050] 40 1 crude soyabean oil miscella (oil content 30%, P-content 1000 ppm on oil) was heated batchwise to 100°C. After keeping the miscella at this temperature for 0.5 hours, the miscella was cooled down to 50°C. At this temperature 0.5%, calculated on the weight of the oil, of bleaching earth (Toncil ACFF) was added to the miscella. The temperature was then reduced to 20°C and kept at this temperature for 0.5 hours. During this pretreatment the miscella was stirred continuously. Subsequently the mixture was microfiftered at 20°C, using a microfilter with pore diameter 0.04µm. The permeate obtained was subjected to ultrafiltration at 50°C, 4.0 bar pressure and 3.0 m/sec. linear velocity. The ultrafiltration was carried out, using the same membranes as in Example 1. Contrary to the procedure used in Examples 1-4, in the present Example both the permeate and the retentate leaving the ultrafiltration module were mixed with the miscella to be ultrafiltered. In this manner the phosphatide content of the feed for the uftrafiltration unit was kept constant The P-content of the ultrafiltration permeate was less than 10 ppm (on oil) at all times during the experiment The permeate flux rates at various times during the experiment are listed in the Table below.
[0051] The experiment was repeated under the same conditions, but using organic fitter aid Highfiow instead of the bleaching earth.
1. Process for treating triglyceride oil including
(i) removing from the triglyceride oil at least a part of particulate matter within the range of from 0.04µm to 25µm and subsequently
(ii) degumming the oil.
2. Process according to Claim 1 wherein step (i) comprises removing from the triglyceride
oil at least a part of particulate matter within the range of from 0.2 µm to 25pm.
3. Process according to Claim 2 wherein step (i) comprises removing from the triglyceride
oil at least a part of particulate matter within the range of from 0.2 µm to 15µm.
4. Process according to any one of Claims 1 to 3 wherein step (i) includes bringing
the oil into contact with an adsorbent
5. Process according to any one of the preceding Claims wherein step (i) includes
bringing the oil into contact with an alkali.
6. Process according to any one of the preceding Claims wherein step (i) includes
heating the oil.
7. Process according to any one of Claims 4 to 6 wherein step (i) includes subsequently
allowing the oil to settle and separating an oil phase from the resulting sediment
8. Process according to any one of Claims 1 to 6 wherein step (i) includes subjecting
the oil to microfiltration.
9. Process according to Claim 8 wherein the oil is passed through microfilter means
having a pore size of at least 0.04pm.
10. Process according to Claim 9 wherein the pore size is at least 0.1pm.
11. Process according to Claim 10 wherein the pore size is at least 0.2pm.
12. Process according to any one of Claims 8 to 11 wherein the oil is arranged to
flow along a surface of a microfilter means.
13. Process according to any one of Claims 8 to 12 wherein back pressure is applied
intermittently during microfiltration.
14. Process for treating triglyceride oil including:
(i) subjecting the triglyceride oil to
(a) microfiftration, preferably crossflow microfiltration with backflushing; or
(b)heat treatment, followed by sedimentation or microfiltration; or
(c) addition of lye or an adsorbent, followed by sedimentation or microfiltration; or
(d) combination of heat treatment, addition of lye and/or an adsorbent in any order, followed by sedimentation and/or microfiltration, so as to remove at least a substantial part of particulate matter contained in the oil within the range of from 0.04 to 25µm, preferably within the range of from 0.2 to 25µm, more preferably within the range of from 0.2 to 15µm, and subsequently
(ii) degumming the oil.
15. Process according to any one of the preceding Claims performed at least in part
in the presence of a solvent
16. Process according to any one of the preceding Claims wherein step (ii) includes
bringing the oil into contact with an aqueous phase and separating an aqueous phase
containing phosphatides from the oil.
17. Process according to any one of Claims 1 to 15 wherein step (ii) includes subjecting
the oil to ultrafiltration.
18. Use of microfiltration to remove at least a substantial part of particulate matter
within the range of from 0.04pm to 25pm, preferably of from 0.2 µm to 25µm, more preferably
of from 0.2µm to 15µm from triglyceride oil prior to degumming.