FRACTIONATION OF TRIGLYCERIDE OILS

Abstract: Fractionation of palmkernel oil using stirred crystallisation with a separation efficiency of more than 70 % by employing a sucrose polyester as a crystallisation modifying substance.

Description: Fractionation of triglyceride oils The present invention is concerned with a process for fractionating triglyceride oils, particularly lauric oils. The fractionation (fractional crystallization) of triglyceride oils is described by Gunstone, Harwood and Padley in The Lipid Handbook, 1986 edition, pages 213-215. Generally triglyceride oils are mixtures of various triglycerides having different melting points. The present invention refers to a specific lauric oil: palmkemel oil. The composition of triglyceride oils may be modified e.g. by fractionation yielding a fraction having a different melting point or solubility. One fractionation method is the so-called dry fractionation process which comprises cooling the oil until a solid phase crystallises and separating the crystallised phase from the liquid phase. The liquid phase is denoted as olein fraction, while the solid phase is denoted as stearin fraction. The separation of the phases is usually carried out by filtration, optionally applying some kind of pressure. The major problem encountered with phase separation in the dry fractionation process is the inclusion of a lot of liquid olein fraction in the separated stearin fraction. The olein fraction is thereby included in the inter- and intracrystal spaces of the crystal mass of the stearin fraction. Therefore the separation of the solid from the liquid fraction is only partial. The solids content of the stearin fraction is denoted as the separation efficiency. In dry fractionation it seldom surpasses 50 to 60 wt.%. This is detrimental to the quality of the stearin as well as to the yield of the olein. For the related solvent fractionation process, where the fat to be fractionated is crystallised from e.g. a hexane or acetone solution, separation efficiencies may be up to 95%. Dry fractionation, however, is a process which is more economical and more environmentally friendly than solvent fractionation. An increase of separation efficiency for dry fractionation is therefore much desired, particularly for the commercially important palmkernel oil. It is known to interfere with the crystallization by adding to a crystallising oil a substance which will generally be indicated as a crystallization modifying substance. The presence of small quantities of such a substance in the cooling oil may accelerate, retard or inhibit crystallization. In certain situations the above substances are more precisely indicated as crystal habit modifiers. Known crystallization modifiers are e.g. fatty acid esters of sucrose, described in US 3,059,010, US 3,059,010, JP 05/125389 and JP 06/181686, fatty acid esters of glucose and derivatives, described in US 3,059,011. These crystallization modifiers are effective in speeding up the crystallization rate. Other crystallization modifiers, e.g. as described in US 3,158,490 when added to kitchen oils have the effect that solid fat crystallization is prevented or at least retarded. Other types of crystallization modifiers, particularly referred to as crystal habit modifiers, are widely used as an ingredient for mineral fuel oils in which waxes are prone to crystallize at low temperatures. US 3,536,461 teaches the addition of a crystal habit modifier to fuel oil with the effect that the cloud point (or pour point) temperature is lowered far enough to prevent crystal precipitation. Or, alternatively, the solids are induced to crystallize in a different habit so that the crystals when formed can pass fuel filters without clogging them. Other crystal habit modifiers are actually able to change the habit of the crystallized triglyceride fat crystals in a way such that after crystallization the crystals, the stearin phase, can be more effectively separated from the liquid phase, the olein phase. Publications describing such crystal habit modifiers are e.g. GB 1 015 354, US 2,610,915, co-pending PCT application WO 95/04122, US 3,059,008, US 3,059,009 and US 3,059,010. Separation efficiency also depends on the mode of crystallisation, either stagnant or stirred. Often good results are obtained with stagnant crystallisation rather than with stirred crystallisation. From the point of view of process economy, however, stirred crystallization is preferred. Palmkernel oil crystallizes in a needle-like morphology. The resulting crystal agglomerates (see Figure 1A) easily include olein. Fractionation by stirred crystallization is not possible because the hydrodynamic shear would crush the needles and produces crystal slurries which can not be separated in a stearin and an olein phase. Quiescent crystallization (the stagnant mode) produces large, flake¬ like crystallites which can be separated, provided a high pressure regime of 25-30 bar is applied. Therefore palmkernel oil fractionation is only possible in a stagnant mode which is a very labour intensive process. An effective crystallization modifying substance which enables stirred mode fractionation is badly needed. STATEMENT OF INVENTION It has been found that palmkernel oil can be crystallized in a stirred mode so that the stearin phase and the olein phase can be separated. By crystallization large and non- porous spherulites are formed which are easily separated and - also when working in stagnant mode - the separation efficiency is considerably increased. Accordingly the invention relates to a process for separating solid fatty material crystallised from palmkernel oil, which comprises the steps: a. heating the oil until no longer a substantial amount of solid triglyceride is present in the oil, b. cooling and crystallising the triglyceride oil resulting in a solid stearin phase besides a liquid olein phase and c. recovering the stearin phase by separating it from the olein phase, where before crystallization starts a crystallization modifying substance is added to said triglyceride oil or to a solution of said triglyceride oil in an inert solvent, characterized in that the crystallization proceeds in a stirred mode. DESCRIPTION OF THE FIGURE Figure 1A shows agglomerates of needle-like crystals of palmkernel oil obtained by quiescent crystallization without additive. Figure IB shows spherulite crystals of palmkernel oil obtained by stirred crystallization in the presence of sucrose polylaurate. DETAILS OF THE INVENTION The palmkernel oil to be fractionated is mixed with the crystallization modifying substance (the additive) before crystallization starts, preferably before the oil is heated or dissolved in the solvent so that all solid triglyceride fat and preferably also the modifying substance is liquefied. Then the oil or solution is cooled to the chosen crystallisation temperature. A suitable temperature range is 15-35°C. To each temperature belongs a specific composition of the olein and stearin phases. Crystallisation proceeds at the chosen temperature until the crystallised oil stabilises to a constant solid phase content. The crystallisation time increases when more solid phase is desired and the temperature is lowered. Usual times are in the range of 4-16 hours. During crystallisation the oil is stirred, e.g. with a gate stirrer. The additive is a sugar polyester of fatty acids. Preferred polyesters are chosen from the group consisting of sucrose polylaurate (100wt.% laurate) , sucrose polyester (75wt.% laurate, 25wt.% palmitate) , sucrose polyester (50wt.% laurate, 25wt.% palmitate, 25wt.% stearate) , sucrose polyester (25wt.% laurate, 35wt.% palmitate, 40wt.% stearate), sucrose polyester (75wt.% caprate, 25wt.% palmitate), sucrose polyester (75wt.% myristate, 25wt.% palmitate) and sucrose polypalmitate (100 wt.% palmitate) , where the ratios are denoted as weight percentages. Sucrose polyester in the context of this description denotes a sucrose ester of which on average at least four, preferably five to six of the eight hydroxyl groups have been esterified with one or more types of fatty acids. The ester can be obtained by well-known usual processes such as esterification of sucrose with fatty acids or a mixture of fatty acids or of reactive fatty acid derivatives. Sucrose with more than four free hydroxyl groups has an insufficient oil solubility. Sucrose polylaurate as mentioned in this specification is a highly esterified (50-100%) sucrose ester with a lauric- content of 95 wt.%. It is a readily available commercial product (e.g. Kyoto Sugar Ester L195 , ex MITSUBISHI) . The stearin and olein phases may be separated by filtration but for an effective separation of the solid from the liquid phase the higher pressures of a membrane filter press are used. Suitable pressures are 3-50 bar, exerted for about 20-200 minutes. However, the invention allows a low or moderate pressure. As a rule with a pressure of 6-12 bar it takes about 30-60 minutes to get a proper separation of the stearin phase from the olein phase. The solids content of the crystal slurry before separation and of the stearin phase obtained after separation is measured according to the known pulse NMR method (ref. Fette, Seifen, Anstrichmittel 1978, ___., nr. 5, pp. 180- 186) . The effect of the invention is believed to be caused by alteration of the crystal structure or crystal habit of the stearin under the influence of the additive. These might interfere in different ways with the growth of the various crystal faces. At microscopic inspection (see Figure IB) the effect of the additive is that the crystals and crystal aggregates formed in the oil are conspicuously different from the crystals obtained without the crystallization modifying substance (Figure IB) . Instead of brittle needle-like crystals, large and non-porous spherulites are formed. Since a stearin fraction with such crystals retains less of the olein fraction, even at low or moderate filtration pressure, the altered crystallization results in a considerable increase of the separation efficiency and facilitates stirred crystallization. Although the invention is useful for solvent fractionation or detergent fractionation, the process is carried out preferably as a dry fractionation process. The sucrose polyester is suitably applied in an amount of 0.005 - 2 wt.% on the total amount of oil. A useful amount is about 1 wt.%. The invention is illustrated by the following examples: Examples 1-2 A sample was prepared containing 1000 g of palmkernel oil (neutralised, bleached, deodorised) and 10 g (1%) of sucrose polylaurate. The sample was heated and stirred at 65°C until completely liquefied (no solid fat content) and then slowly cooled. Crystallization proceeded in a stagnant (0 rpm) mode at the chosen temperature of 23°C until a constant solid phase content was reached. The sample was filtered and pressed at 12 bar for 30 minutes. After filtration and pressing, the solid phase content (SE = separation efficiency) of the cake was measured by NMR. For comparison the fractionation was repeated with the only difference that no sucrose polylaurate was added. In example 2, palmkernel oil was fractionated following the same procedure as described above, but in a stirred mode (5 rpm) . Examples 3-8 The dry fractionation process of example 2 is repeated with various sucrose polyesters. Each experiment has been carried out with and without crystallization modifying substance. Table I indicates the SE and the relative improvements caused by the modifier. The used crystal habit modifiers are: #3 sucrose polyester (75% laurate, 25% palmitate) , #4 sucrose polyester (50% laurate, 25% palmitate, 25% stearate) , #5 sucrose polyester (25% laurate, 35% palmitate, 40% stearate) , #6 sucrose polyester (75% caprate, 25% palmitate) , #7 sucrose polyester (75% myristate, 25% palmitate) and #8 sucrose polypalmitate, where the ratios are denoted as weight percentages. The results of Table I show that the addition of various sucrose polyesters allow the stirred fractionation of palmkernel oil with a surprisingly high separation efficiency. TABLE I # CHI- rpm c SE δ 1 sucrose polylaurate 0 0.0 46 +59 1.0 73 2 sucrose polylaurate 5 0.0 n.d. ++ 1.0 71 3 sucrose polyester 5 0.0 n.d. (75% laurate, 25% palmitate) 1.0 69 ++ 4 sucrose polyester 5 0.0 n.d. (50% laurate, 25% palmitate 1.0 73 ++ 25% stearate) 5 sucrose polyester 5 0.0 n.d. (25% laurate, 35% palmitate 1.0 73 ++ 40% stearate) 6 sucrose polyester 5 0.0 n.d. (75% caprate, 25% palmitate) 1.0 60 ++ 7 sucrose polyester 5 0.0 n.d. (75% myristate 25% palmitate) 1.0 72 ++ 8 sucrose 5 0.0 n.d. polypalmitate ++ 1.0 48 c in wt% cone, of crystallization modifying substance rpm stirrer rotation speed SE in wt% separation efficiency δ in % enhancement SE relative to blank experiment n.d. not done: unable to separate solid/liquid phase.

Claims: CLAIMS 1. Process for separating solid fatty material from a partially crystallised palmkernel oil, which comprises the steps: a. heating palmkernel oil until no longer a substantial amount of solid triglyceride is present in the oil, b. cooling and crystallising the triglyceride oil resulting in a solid stearin phase besides a liquid olein phase and c. recovering the stearin phase by separating it from the olein phase, where before crystallization starts a crystallization modifying substance is added to said triglyceride oil or to a solution of said triglyceride oil in an inert solvent, characterized in that the crystallisation proceeds in a stirred mode. 2. Process according to claim 1, characterised in that the modifying substance is a sucrose polyester. 3. Process according to claim 2, characterised in that the sucrose polyester is chosen from the group consisting of sucrose polylaurate (100% laurate) , sucrose polyester (75% laurate, 25% palmitate) , sucrose polyester (50% laurate, 25% palmitate, 25% stearate) , sucrose polyester (25% laurate, 35% palmitate, 40% stearate) , sucrose polyester (75% caprate, 25% palmitate) , sucrose polyester (75% myristate, 25% palmitate) and sucrose polypalmitate (100% palmitate) , where the ratios are denoted as weight percentages. 4. Process according to claim 1 or 2, characterised in that the sucrose polyester has an average esterification degree of 50-100%. 5. Process according to claims 1 or 2, characterised in that the sucrose polyester is used in an amount of 0.005 ■ 2 wt.% on the total amount of oil. 6. Process according to anyone of claims 1-4, characterised in that the process is applied as a dry fractionation process.

Inventors: HOGERVORST WIM, KAMP FRANS, VAN DAM PETRUS HENRICUS J, HOGERVORST, WIM, KAMP, FRANS, VAN DAM, PETRUS, HENRICUS, J.
Applicants: DAM PETRUS HENRICUS J VAN, HOGERVORST WIM, KAMP FRANS, UNILEVER NV, UNILEVER PLC, HOGERVORST, WIM, KAMP, FRANS, UNILEVER N.V., VAN DAM, PETRUS, HENRICUS, J.
Application year: 1996
Main classification: C11B7
IPC codes: C11B7