WO2015053609A1

WO2015053609A1 - A membrane pre-treatment system and process for producing refined oils and fats

Info

Publication number: WO2015053609A1
Application number: PCT/MY2014/000214
Authority: WO
Inventors: Noor Hidayu BINTI OTHMAN; Ahmadilfitri MD NOOR; Razam ABDUL LATIP; Mohd Suria Affandi Yusoff; Sofiyaton IBRAHIM; Ahmad Fauzi Ismail; Woei Jye LAU; Pei Sean GOH; Be Cheer NG; Mohammad Abdul Razis BIN SAIDIN; Mohd Sohaimi BIN ABDULLAH
Original assignee: Sime Darby Malaysia Berhad
Priority date: 2013-10-08
Filing date: 2014-07-23
Publication date: 2015-04-16
Also published as: MY163330A

Abstract

The present invention relates to a system and process for producing refined oils and fats using a membrane system. The process involves pre-treating a crude oil or and fat using a series of membrane units to remove undesirable constituents with the view of improving the quality and stability of the refined oil and fat. Each series of the membrane units comprises a plurality of membrane modules, with each membrane module containing 1,000 to 3,000 fibers, and wherein the plurality of membrane modules in at least one of the series of the membrane units are polyvinylidene fluoride (PVDF) ultrafiltration membrane modules. The membrane- treated oils and fats are further refined by subjecting the oils and fats to bleaching and deodorization processes to produce the desired refined oils and fats.

Description

A MEMBRANE PRE-TREATMENT SYSTEM AND PROCESS FOR

PRODUCING REFINED OILS AND FATS

FIELD OF THE INVENTION

The present invention relates to a system and process for producing refined oils and fats. More particularly, the invention relates to a pre-treatment system and process for producing refined oils and fats using membrane system. BACKGROUND OF THE INVENTION

Over the last 15 years, there were quite a number of research works reporting on alternative methods for refining vegetable oil (Rafe, A, et al. (2009), "Water and hexane permeate flux through UF polysulfone amide membrane", Desalination, 236: 39-45; Bhosle, B M, et al. (2005), "New approaches in deacidification of edible oils: A review", J. Food Eng., 69: 481-494; Dunford, N T, et al. (2001), "Thermal gradient deacidification of crude rice bran oil utilizing supercritical carbon dioxide", J. Am. Oil. Chem. Soc, 78: 121-125; Sengupta, R, et al. (1996), "Enzymatic deacidification of rice bran oils of varying acidity", Journal of the Oil Technologists Association of India, 28: 17-21 ; and Subramanian, R, er a/. (1998), "Processing of vegetable oils using polymeric composite membranes", J. Food Eng., 38: 41-56).

Among the methods evaluated as alternative process, membrane-based separation is found to be the most suitable solution to overcome the drawbacks associated with conventional refining process. Such method also shows great potential in commercialization (Manjula, S, et al. (2009), "Simultaneous degumming, dewaxing and decolorizing crude rice bran oil using nonporous membranes", Sep. Purif. Techno!., 66: 223-228; De Morais Coutinho, C, et al. (2009), "State of art of the application of membrane technology to vegetable oils:A review. Food Res. Int., 42: 536-550; Hafidi, A, et al. (2005), "Membrane-based simultaneous degumming and deacidification of vegetable oils", Innov. Food Sci. Emerg. Techno!. , 6: 203-212; Lin, L, et al. (1997), "Bench-scale membrane degumming of crude vegetable oil: Process optimization", J. Membr. Sci., 134: 101-108; and Ochoa, N., et al. (2001 ), "Ultrafiltration of vegetable oils Degumming by polymeric membranes", Sep. Purif. Technol., 22-23: 417-422).

US 6,797,172 B2 describes a process for refining and degumming crude corn oil using ultrafiltration (tubular) membrane. The process produces a permeate fraction with reduced phosphatide content and a retentate with increased phosphatide content. The ultrafiltration membrane used in this process comprised of a polymeric polymer of vinylidene difluoride monomer. US 2008/0135482 describes a polyamide nanofiltration membrane and a process for the preparation thereof. This publication further provides a process for removal of phospholipids from rice bran oil using novel nanofiltration membrane. Flat sheet nanofiltration membranes were developed and studied. In this process, high operating pressure was required (600 psi) and flux was relatively low (0.8-5 gal/ft².day). The oil permeated through the membrane was 90-95% free from phospholipids in comparison to feed oil.

US 5,310,487 describes a method for refining domestic edible oils using lab-scale ultrafiltration membrane separation technology. The method involves treating crude soybean oils and solvent mixture in a membrane module system that provides optimal separation performance and service life. The described process simplifies edible oil processing and permits the attainment of the desired product in an essentially single step operation. However, hexane was used to form oil miscella (mixture of oil and solvent) and phosphoric acid was added to remove gums.

US 6,207,209 B1 describes a method for removing phospholipids from vegetable oil miscella, a method for conditioning a polymeric microfiltration membrane, and a membrane. The method includes the steps of feeding vegetable oil miscella to a conditioned polymeric microfiltration membrane; and recovering a permeate stream having a decreased weight percent of phospholipids provided in the miscella. The vegetable oil miscella is described to contain between 45% by weight and 90% by weight of extraction solvent, and more preferably, between 70% by weight and 80% by weight of extraction solvent. The preferred extraction solvent is hexane.

US 4,414,157 describes a process for purification of crude soybean oil compositions. The process comprises bringing a miscella of a crude glyceride oil composition containing a glyceride oil and phospholipid into contact with a semipermeable membrane (capillary) to concentrate the miscella to a predetermined level, and thereafter, bringing the preliminarily concentrated miscella into contact with a tubular semipermeable membrane to concentrate the miscella to a higher level. Solvent was used in the process in which soybean oil miscella comprised of 30 parts by weight of crude soybean oil and the remaining was hexane, which was treated by tubular membrane module.

US 4,062,882 describes a method for refining crude soybean oils using membrane filtration (flat membrane) under pressure in organic solvents, particularly to separate phosphatides. The solvents used are non-acidic, non- hydroxy solvent and halogenated hydrocarbons. Micelles were formed due to the addition of solvent. Up to 97.7% phospholipids were rejected by the membrane. Many researchers have continued to make new attempts to prove the feasibility of membrane technology as an alternative solution for existing refining technology. Although membrane technology has showed great potential in refining process, the complete implementation of this technology on an industrial scale still requires further efforts and improvements in many aspects, including operation, yields of the product. (Badan Ribeiro, et a/, (2008), "The optimisation of soybean oil degumming on a pilot plant scale using a ceramic membrane", J. Food Eng., 87: 514-521 ).

It is generally agreed that resistance to oxidative degradation during storage is an important issue for the successful development of an alternative refining process. The occurrence of oxidation of unsaturated esters as a function of time in refined edible oil, for example palm oil, is a main concern to many people as it may impair oil quality and subsequently possess a threat to human health. Consequently, in view of the above, there remains a need in the art to provide an alternative refining system and process for improving the quality and stability of refined edible oils and fats, and further extending its shelf life. SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a process for producing refined oils and fats. The process comprises providing a feed oil or fat; heating the feed oil or fat; passing the feed oil or fat through at least two series of membrane units at a pressure in the range of 0.2 to 3.0 bar (20 to 300 kPa) to obtain a retentate fraction and a permeate fraction, the permeate fraction having a phosphorus content which is less than that of the feed oil or fat, wherein each series of the membrane units comprises a plurality of membrane modules, with each membrane module containing 1 ,000 to 3,000 fibers; and wherein the plurality of membrane modules in at least one of the series of the membrane units are polyvinylidene fluoride (PVDF) ultrafiltration membrane modules; and treating the permeate fraction to obtain a refined oil or fat.

In accordance with an embodiment of this invention, each series of the membrane units comprises four membrane modules.

In accordance with an embodiment of this invention, the plurality of membrane modules in all the series of the membrane units are polyvinylidene fluoride (PVDF) ultrafiltration membrane modules.

In accordance with an embodiment of this invention, each membrane module comprises 1 ,250 to 2,750 fibers. In accordance with other embodiment of this invention, each membrane module comprises 1 ,500 to 2,500 fibers. In accordance with an embodiment of this invention, the total filtration area for each membrane module is in the range of 0.45 to 1.4 m². In accordance with an embodiment of this invention, each of the membrane modules has an outer pore size of 10 to 40 nm. In accordance with an embodiment of this invention, each of the membrane modules is a hollow fiber membrane and prepared using a dry-jet wet spinning method. In accordance with a second aspect of the present invention, a membrane pre- treatment system for producing refined oils and fats is provided. The system comprises at feed tank for receiving and heating a feed oil or fat; at least two series of membrane units for receiving the feed oil or fat and separating the feed oil or fat into a retentate fraction and a permeate fraction, each series of the membrane units comprises a plurality of membrane modules, with each membrane module containing 1 ,000 to 3,000 fibers, wherein the plurality of membrane modules in at least one of the series of the membrane units are polyvinylidene fluoride (PVDF) ultrafiltration membrane modules; a permeate tank for receiving the permeate fraction from the membrane units; and a recirculation line for circulating the retentate fraction from the membrane units back to the feed tank.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other features and advantages of the present invention will more clearly understood from the following detailed description taken in conjunction with the accompanying drawings:

Figure 1 shows the conventional refining process and the refining process of the present invention.

Figure 2 shows the schematic diagram of the membrane system for pre-treating crude oils and fats in accordance with the process of the present invention. Figure 3 shows the schematic drawing of a single membrane module. The module is depicted by a side, a top (with and without housing end cap) and a bottom (with and without housing end cap) views. Figure 4 shows a graph comparing the free fatty acids stability of the refined oil and fat as a function of day produced using the conventional refining process and the process of the present invention. Figure 5 shows a graph illustrating that the initial PV of the oil samples was the same irrespective of the refining process employed.

Figure 6 shows the AnV of oil samples determined at initial day and at Day 5. Figure 7 shows the colour change in the refined oil and fat produced from using the conventional refining process and the refining process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a system and process for producing refined oils and fats. More particularly, the invention relates to a pre-treatment system and process for producing refined oils and fats using membrane system. The process comprises three main refining steps, that is, degumming using membrane pre- treatment system, followed by bleaching and deodorization of the oil and fat obtained from the degumming process.

In an embodiment of the present invention, the process comprises providing a feed oil or fat, and heating the feed oil or fat prior to passing the feed oil or fat through at least two series of membrane units to obtain a retentate fraction and a permeate fraction. The permeate fraction having a phosphorus content which is less than that of the feed oil or fat. Each series of the membrane units comprises a plurality of membrane modules, with each membrane module containing 1 ,000 to 3,000 fibers. In one embodiment of the invention, the plurality of membrane modules in at least one of the series of the membrane units is polyvinylidene fluoride (PVDF) ultrafiltration membrane modules. The process further comprises treating the permeate fraction to obtain the refined oil or fat. The present invention will be described in further detail with reference to the drawings.

Figure 1 is a flow diagram showing (a) a typical prior art process for refining edible oil or fat; and (b) the refining process in accordance with the present invention. Examples of oil and fat that can be applied to the process of the present invention includes palm oil, soybean oil, corn oil, rice bran oil, sunflower oil, rapeseed oil, canola oil, peanut oil and the like. Generally, crude edible oil and fat are semi-solid at ambient temperature. They need to be heated prior to contacting them with a membrane system. Heating of the crude oil and fat reduces the oil viscosity and this in turns improves the permeation rate of the oil and fat through the membrane system. In the process of the present invention, the fat and oil are heated to a temperature in the range of 40°C to 70°C, preferably 45°C to 65°C, and more preferably 50°C to 60°C. The heated oil and fat is then pre-treated by passing the oil and fat through a membrane system. In one embodiment of the present invention, the membrane system comprises at least two series of membrane units. The series of the membrane units can be of the same or different types, arranged in any desired configurations, such as in parallel or in sequence, depending on the requirements. Such requirements may include, but not limited to, the properties of the feed oil or fat used and the quality of the permeate oil required to achieve, etc. Each series of the membrane units comprises a plurality of processing membrane modules. Any suitable number of processing membrane modules may be employed without departing from the scope of this invention. The higher the number of processing membrane modules provided in the membrane unit, the greater is the surface contact area of the membrane modules with the oil or fat, and greater is the production rate. In a preferred embodiment of the invention, each series of the membrane units comprises four processing membrane modules. The processing membrane module of the present invention includes any polymeric membrane that is circular in shape, for example, hollow fibers. The hollow fibers can be made of, for example, polyvinylidene fluoride, polysulfone, polyethersulfone, cellulose acetate and the like. Each processing membrane module comprises 1 ,000 to 3,000 fibers, preferably 1 ,250 to 2,750 fibers and more preferably 1 ,500 to 2,500 fibers. Each processing membrane module may comprise the same or different number of fibers as the processing membrane modules provided within the same or different membrane unit. In one embodiment of the invention, each of the processing membrane module in the series of membrane units comprises hollow fibers made of polyvinylidene fluoride (PVDF). In another embodiment of the invention, at least one of the series of the membrane units comprises processing membrane modules having hollow fibers made of polyvinylidene fluoride (PVDF). Preferably, the length of the processing membrane module is between 0.22 to 0.455 m.

The total filtration area for each processing membrane module is 0.45 to 1 .4 m², preferably 0.65 to 1.2 m² and more preferably 0.85 to 1.0 m².

In one embodiment of the invention, the crude oil and fat pass through the series of membrane units at a pressure of 0.2 to 3.0 bar (20 to 300 kPa) to obtain a permeate fraction and a retentate fraction. In other embodiments of the invention, the crude oil and fat pass through the series of membrane units at a pressure of 0.5 to 2.5 bar (50 to 250 KPa), and preferably 1.0 to 2.0 bar (100 to 200 KPa). The series of the membrane units may be operated under the same or different pressure.

One of the advantages of using at least two series of membrane units in the process is that it will further improve the quality of the permeate oil produced from the process. If the series of the membrane units are of a different type, the first series will have a bigger pore size than the following series, and it will play a role in minimizing fouling of the subsequent series. Each membrane unit has a molecular weight cut-off (MWCO) of between 5,000 and 10,000 dalton. Preferably, the process in accordance with the present invention is conducted using cross flow filtration mode. This means that the feed oil or fat is passed across the ultrafiltration membrane at positive pressure relative to the permeate side. Those compounds in the feed oil and fat which are smaller than the ultrafiltration membrane pore size will pass through the membrane as permeate. Everything else is retained on the feed side of the membrane as retentate. The permeate fraction that passes through the membrane system is collected as a permeate oil and the retentate fraction which does not pass through the membrane system is recycled back to feed tank. In comparison, the permeate oil contains relatively less phospholipids than the feed oil.

The membrane modules used in the process of the present invention is preferably a hollow-fiber membrane. The hollow-fiber membrane may operate in an "inside- out" or "outside-in" mode. In a preferred embodiment of the present invention, the membrane operates in an outside-in mode which requires the feed oil or fat to pass from outside the fibers to the inside, where the permeate fraction is collected in the center of the fibers. The hollow-fibre membrane is preferably fabricated using a dry-wet phase separation method known in the art, by spinning a polymer dope solution that is extruded through a spinneret having an annular orifice together with a bore-forming fluid.

The PVDF ultrafiltration membrane modules of the present invention are prepared using a dope solution comprising PVDF pallets, solvent and non-solvent additive. In an embodiment of the invention, the dope solution comprises 14 to 22 wt% PVDF pellets, 72 to 80 wt% solvent and 6 wt% non-solvent additive. In another embodiment of the invention, the dope solution comprises 15 to 20 wt% PVDF pellets, 74 to 79 wt% solvent and 6 wt% non-solvent additive. In yet another embodiment of the invention, the dope solution comprises 16 to 18 wt% PVDF pellets, 76 to 78 wt% solvent and 6 wt% non-solvent additive.

The solvent used for preparing the dope solution includes, but not limited to, N- methyl-2-pyrrolidone and dimethylacetamide. The additive used for preparing the dope solution as a pore forming agent includes, but not limited to, methanol, polyvinylpyrrolidone and ethylene glycol. Hollow fiber membranes are spun according to the dry-wet phase separation method. The polymer dope solution is smoothly conveyed to the spinneret having OD/ID 1.3/0.6 (mm). A pulse-free bore fluid consisting of distilled water is fed into the inner tube of the spinneret by a syringe pump. Preferably, the bore fluid is controlled at a rate of 1.8 to 2.0 ml/min. Once the dope solution and the bore fluid meet at the tip of the spinneret, they go through a 10 cm air gap and into an external coagulation water bath. A wind-up drum is used to properly collect the hollow fibers. Preferably, the as-spun fibers are stored in a water bath for 1 day before they are post-treated by ethanol solution of various concentrations. Preferably, water in the membrane pores is gradually replaced with water/ethanol (1 :1 ) solution, followed by pure ethanol solution before the hollow fibers are dried in air for 1 day.

The resulting PVDF membrane module has a pore size of 10 to 40 nm, preferably 15 to 35 nm and more preferably 20 to 30 nm.

After the crude oil and fat are pre-treated by the membrane units, the oil is collected and subjected to bleaching. Preferably, 0.8 to 1.2% bleaching earth is used as an adsorbent for decolourization process. The temperature is controlled at about 95 to 110°C and the process is operated under vacuum condition for about 30 min. The final step of the refining process involves deodorization in which odoriferous matters and free fatty acid are removed to produce odourless and bland refined oil and fat. The final product produced is known as membrane refined oil and fat. In an exemplary embodiment, the operating temperature and pressure of the deodorization process are controlled within a range of 240 to 260°C and under vacuum condition of 2 to 4 mmHg respectively. This process is operated for about 90 min.

Figure 2 is a schematic diagram illustrating the refining process of the present invention using a membrane system. This figure also shows the apparatus for carrying out the process of the present invention.

Referring to Figure 2, the membrane system is designed to pre-treat crude oil and fat in a single stage. Prior to the refining process, crude vegetable oils and fats are stored in two identical reservoir tanks 1 & 1 '. The reservoir tanks can be of any suitable capacity. In one embodiment, each reservoir tank has a capacity of 50L. Each reservoir tank is equipped with heating element which is installed on the outer wall of the tank. An overhead mechanical stirrer 2 & 2' is used to ensure that the crude oil and fat is consistently and uniformly heated before the crude oil and fat are delivered to a membrane module. The crude oil and fat can be delivered to the membrane module by any suitable means. In this exemplary embodiment, the crude oil and fat are delivered to the membrane module by a rotary lobe pump 3 & 3'.

Feed crude oil and fat 4 & 4' are delivered to a series of membrane units comprising a plurality of membrane modules. In this exemplary embodiment, the crude oil and fat are delivered to eight membrane modules 5-8 & 5'-8' which are arranged in two series. One skilled in the art will recognise that other arrangements may be employed without departing from this invention. Each series consists of four membrane modules completed with pressure gauge. The cross flow velocity of the membrane module is determined using a portable ultrasonic flow meter. The cross flow velocity can be manipulated by controlling the needle valve installed at the feed stream of each module. Each membrane module 5-8 & 5'-8' is jacketed to minimize significant temperature drop that occurs during refining process. The refined oil and fat produced from each series of the membrane units is then delivered to 9 & 9' while the rejected stream (also known as retentate stream) 10 & 10' is recycled back to feed tank 1 & 1 ' for further refining. The refined oil and fat produced is collected as 1 1 before it is sent to a permeate tank 13 by rotary lobe pump 12. Permeate tank is also equipped with a mechanical stirrer 14. Additional permeate tanks 15 and 16 can be used if higher production rate is required.

Figure 3 shows a schematic drawing of a single membrane module. The membrane module is depicted by a side, a top (with and without housing end cap) and a bottom (with and without housing end cap) views.

The membrane module has a housing 17, a top housing end cap 18 and a bottom housing end cap 19, all of which are made of stainless steel material so that they are resistance against thermal and chemical exposure. The top housing end cap 18 is designed to have a single outlet 20 which acts as a retentate stream while the bottom housing end cap is designed to have two outlets, one for feed stream 21 and another for permeate stream 22. The length of the cylindrical module is in the range of 0.22 to 0.455 m. The diameter of the cylindrical module is in the range of 0.04 to 0.085 m. Each membrane module is packed with 1 ,000 to 3,000 fibers, preferably 1 ,250 to 2,750 fibers and more preferably 1 ,500 to 2,500 fibers, which correspond with approximately 0.45 to 1 .4 m², preferably 0.65 to 1.2 m² and more preferably 0.85 to 1.0 m² filtration areas respectively.

The inner diameter of the pipe used for the retentate stream 20, the feed stream 21 and the permeate stream 22 is identical, at approximately 0.020 m.

The PVDF membrane modules of the present invention show outstanding properties such as high thermal stability, chemical resistance and high hydrophilicity as compared to other polymeric materials used in the art, making it suitable for use in oil refining process.

The process in accordance with the present invention has several advantages. Firstly, it can be operated at a relatively low pressure and temperature. The process does not require any chemicals, such as phosphoric acid and sulphuric acid to be added for removing phospholipids and impurities prior to subjecting the crude oil and fat to subsequent refining steps. Moreover, the membrane used in the present invention is able to remove the phospholipids to a minimal amount (for example, less than 4 ppm phosphorus) that meets the specification suitable for subsequent steps involved in the refining process, i.e. bleaching and deodorization processes. The membrane units of the present invention allows refined oil and fat to be produced at a relatively higher production rate, for example, at 5kg/hr or 0.5kg/hr per membrane module. This is attributed to the use of unique number of fibers in the processing membrane modules and the number of processing membrane modules used in each series of the membrane units, as well as the number of membrane units used in the process of the present invention. The following examples are provided to further illustrate and describe particular embodiments of the present invention, and are in no way to be construed to limit the invention to the specific procedures, conditions or compositions described therein.

EXAMPLE

Example 1 Crude palm oil having 3.31 % free fatty acid (FFA), phosphorus content of 7.07 ppm, peroxide value of 5.82 meq/kg and anisidine value (AnV) of 7.76 were used as feed source for producing refined palm oil based on two different refining routes, i.e. the conventional refining process and the refining process in accordance with the present invention with the use of membrane system.

Heat stability test was carried out using accelerated test method (industrially acceptable) by adding each sample into a beaker with 1 % distilled water, covered with aluminium foil and kept the sample in an oven at 90°C. The properties of each refined oil and fat sample produced were determined daily for 5 consecutive days. The properties of the refined oil and fat that were determined for 5 consecutive days include the free fatty acid (FFA) content, phosphorus, peroxide value (PV), and colour. Anisidine value (AnV) was measured only on day 5 and the value was assessed according to the American Oil Chemists' Society (AOCS) method - Cd 3d-63, Ca 12-55 and Cd 8b-90 and Cd 18-19. The colour of the refined oil and fat produced was determined using Lovibond Tintometer (model F). The colour of the oil and fat was matched using colour racks of red (R) and yellow (Y).

The accelerated heat stability of the membrane refined oil and fat was obtained and compared with the refined oil and fat produced using the conventional physical refining technique.

The results obtained are as shown in Figure 4. Figure 4 compares the FFA stability of the refined oil and fat as a function of day produced from the two different refining processes. The refined oil and fat produced from the two refining processes are referred to as refined, bleached and deodorized palm oil (RBDPO) and membrane refined, bleached and deodorized palm oil (M-RBDPO) respectively.

It can be seen from figure 4 that both the refined oil and fat displayed less than 0.05% FFA right after they were produced. Comparing the FFA stability of M- RBDPO sample with the standard RBDPO sample, it is found that the FFA content of RBDPO increased steadily whereas the FFA content in M-RBDPO remained almost the same within the period studied. At day 5, RBDPO sample showed 0.81 % FFA in comparison to only 0.06% FFA found in M-RBDPO sample. This indicates the significant improvement on the heat stability of the refined oil produced by the refining process of the present invention which integrates with the membrane technology.

Figure 5 shows the initial PV of the refined oil and fat produced using the two refining processes. As shown in Figure 5, the initial PV of oil samples was the same irrespective of the refining process that was employed. Though PV is not one of the criteria under Palm Oil Refiners Association of Malaysia (PORAM)'s standard specification of processed palm oil, a refined oil of good quality usually needs to have less than 1.0 meq/kg PV after refining. In this experiment, both oil samples produced met the standard of PORAM and displayed zero PV right after the refining process and the following day. The PV of both samples however increased significantly from zero to 6.14 and 7.57 meq/kg for RBDPO and MRBDPO respectively when they were evaluated on Day 2. At the end of Day 5, it is recorded that the PV for M-RBDPO (20.43 meq/kg) was slightly higher than that of RBDPO (16.28 meq/kg). It is fair to say that M-RBDPO has shown no significant difference in terms of PV for the first two days of experiment, though it displayed slightly higher PV at the end of experiment.

Compared to PV which measures current oxidation of oil sample, AnV reflects how an oil sample has been handled and stored. For both AnV and PV, a lower number is better. Figure 6 shows the AnV of the refined oil and fat samples determined at initial day and at Day 5. From the figure, M-RBDPO sample showed better heat stability with respect to AnV at the initial day, but it was the RBDPO sample which demonstrated better quality (lower AnV) after the 5-day experiment.

Figure 7 presents the colour change in the refined oil and fat produced from the two different refining routes. Industrially, the standard colour of RBDPO must be maximum of 3.0 Red right after the refining process. In comparison to the colour of RBDPO sample which increased from initial day of 2.4R to 4. OR at Day 5, the sample of MRBDPO has shown great resistance against colour change. There was less than 24% colour change found in M-RBDPO sample as compared to more than 65% change observed in RBDPO sample. Furthermore, the colour index of M-RBDPO sample was found to be lower than the standard required even though it was kept under 90°C in oven for 5 days. These interesting results showed that the refining process of the present invention which uses membrane technology could produce refined palm oil that not only meets the standard of the industry but also displays higher colour resistance than the oil and fat produced using the conventional methods. Example 2

In this example, hollow fiber membranes are spun from two different dope solutions comprising (1) 14% w/w polyvinylidene fluoride, 80% w/w N-methyl-2- pyrrolidone and 6% w/w ethylene glycol; and (2) 18% w/w polyvinylidene fluoride, 76% w/w N-methyl-2-pyrrolidone and 6% w/w ethylene glycol. The polyvinylidene fluoride used (Kynar^® 740) is commercially available from Arkema Inc., USA.

Crude palm oil having phosphorus content varied between 10.83 and 24.80 ppm, free fatty acid (FFA) less than 4% was treated in a membrane permeation unit fitted with PVDF membrane at 2 bar (2 x 10⁵ Pa) pressure and 50°C temperature. The operating pressure of the process was controlled at desired value using pure nitrogen gas while the temperature of crude palm oil was maintained by immersing the permeation unit into a water bath fitted with immersion coiled heater. Membranes prepared from different polymer concentrations were studied and the results of the refining experiments are shown in Table 1. From Table 1 , we can see that the membrane of lower polymer concentration (i.e. 14PVDF-80NMP-6EG) exhibited relatively low selectivity against phosphorus (79.88 to 83.44%) in comparison to the membrane prepared from higher polymer concentration (i.e. 18PVDF-76NMP-6EG which shows a range of 86.08 to 93.43%). This is mainly due to the decrease in membrane pore size upon addition of higher amount of polymer. The pore size of the membrane has been reduced from 37.5 nm to 24 nm with increasing polymer concentration from 14 wt% to 18 wt%. The results also show that the permeate fraction obtained by using the membrane system of the present invention has a phosphorus content which is less than that of the feed oil or fat.

Table 1

Membrane FFA PV Phosphorous

*F P R F P R F P R

(%) (%) (%) (ppm) (ppm) (%) (ppm) (ppm) (%)PVDF-80NMP-6EG "3.32 3.31 0.30 Trace Nil - 10.83 1.75 83.84

3.87 3.58 7.49 Trace Nil - 18.39 3.70 79.88 PVDF-76NMP-6EG 3.42 3.12 8.77 Trace Nil _ 26.36 1.91 92.75

3.87 3.30 14.73 Trace Nil - 24.80 1.63 93.43

3.13 3.04 9.27 Trace Nil — 18.10 2.52 86.08

F= Feed, P=Permeate and R=Rejection

Feed properties of CPO were varied due to different batch of CPO used.

The above is a description of the subject matter the inventors regard as the invention and is believed that others can and will design alternative systems that include this invention based on the above disclosure.

Claims

1 . A process for producing refined oil or fat comprising:

providing a feed oil or fat;

heating the feed oil or fat;

passing the feed oil or fat through at least two series of membrane units at a pressure in the range of 0.2 to 3.0 bar (20 to 300 kPa) to obtain a retentate fraction and a permeate fraction, the permeate fraction having a phosphorus content which is less than that of the feed oil or fat, wherein each series of the membrane units comprises a plurality of membrane modules, with each membrane module containing 1 ,000 to 3,000 fibers; and wherein the plurality of membrane modules in at least one of the series of the membrane units are polyvinylidene fluoride (PVDF) ultrafiltration membrane modules; and

treating the permeate fraction to obtain a refined oil or fat.

2. The process according to claim 1 , wherein each series of the membrane units comprises four membrane modules.

3. The process according to claim 1 , wherein the plurality of membrane modules in all the series of the membrane units are polyvinylidene fluoride (PVDF) ultrafiltration membrane modules.

4. The process according to claim 1 , wherein each membrane module comprises 1 ,250 to 2,750 fibers.

5. The process according to claim 1 , wherein each membrane module comprises 1 ,500 to 2,500 fibers.

6. The process according to claim 1 , wherein each membrane module having a length in the range of 0.22 to 0.455m.

7. The process according to claim 1 , wherein the pressure is in the range of 0.5 to 2.5 bar (50 to 250 KPa).

8. The process according to claim 1 , wherein the pressure is in the range of 1 .0 to 2.0 bar (100 to 200 kPa).

9. The process according to claim 1 , wherein the total filtration area for each membrane module is in the range of 0.45 to 1 .4 m².

10. The process according to claim 4, wherein the total filtration area for each membrane module is in the range of 0.65 to 1 .2 m².

1 1 . The process according to claim 5, wherein the total filtration area for each membrane module is in the range of 0.85 to 1 .0 m².

12. The process according to claim 1 , wherein the feed oil or fat is heated to a temperature of 40°C to 70°C.

13. The process according to claim 1 , wherein each of the membrane modules has an outer pore size of 10 to 40 nm.

14. The process according to claim 1 , wherein each of the membrane modules has an outer pore size of 15 to 35 nm.

15. The process according to claim 1 , wherein each of the membrane modules has an outer pore size of 20 to 30 nm.

16. The process according to claim 1 , wherein each of the PVDF ultrafiltration membrane modules is a hollow fiber membrane and prepared using a dry-jet wet spinning method.

17. The process according to claim 16, wherein the PVDF ultrafiltration membrane modules are prepared using a dope solution comprising 14 to 22 wt% PVDF pellets, 80 - 72wt% solvent and 6 wt% non-solvent additive.

18. The process according to claim 16, wherein the PVDF ultrafiltration membrane modules are prepared using a dope solution comprising 15 to 20 wt% PVDF pellets, 79 to 74 wt% solvent and 6 wt% non-solvent additive.

19. The process according to claim 16, wherein the PVDF ultrafiltration membrane modules are prepared using a dope solution comprising 16 to 18 wt% PVDF pellets, 78 to 76 wt% solvent and 6 wt% non-solvent additive.

20. The process according to any one of claims 17 to 19, wherein the solvent is N-methyl-2-pyrrolidone or dimethylacetamide.

21. The process according to any one of claims 17 to 19, wherein the solvent is N-methyl-2-pyrrolidone.

22. The process according to any one of claims 17 to 19, wherein the additive used as pore forming agents is selected from the group consisting of methanol, polyvinylpyrrolidone and ethylene glycol.

23. The process according to any one of claims 17 to 19, wherein the additive is ethylene glycol.

24. The process according to claim 1 , wherein the filtration mode of the heated oil or fat is outside-in.

25. The process according to claim 1 , wherein the feed oil or fat is selected from the group consisting of palm oil, soybean oil, corn oil, rice bran oil, sunflower oil, rapeseed oil, canola oil and peanut oil.

26. The process according to claim 1 , wherein the step of treating the permeate fraction comprises the steps of deacidification and decolourization of the permeate fraction.

27. A membrane pre-treatment system for producing refined oil or fat, comprising: a feed tank for receiving and heating a feed oil or fat;

at least two series of membrane units for receiving the feed oil or fat and separating the feed oil or fat into a retentate fraction and a permeate fraction, each series of the membrane units comprises a plurality of membrane modules, with each membrane module containing 1 ,000 to 3,000 fibers, wherein the plurality of membrane modules in at least one of the series of the membrane units are polyvinylidene fluoride (PVDF) ultrafiltration membrane modules;

a permeate tank for receiving the permeate fraction from the membrane units; and

a recirculation line for circulating the retentate fraction from the membrane units back to the feed tank.

28. The system according to claim 27, wherein each series of the membrane units comprises four membrane modules.

29. The system according to claim 27, wherein the plurality of membrane modules in all the series of the membrane units are polyvinylidene fluoride (PVDF) ultrafiltration membrane modules.

30. The system according to claim 27, wherein each of the membrane modules is a hollow fiber membrane and prepared using a dry-jet wet spinning method.

31 . The system according to claim 27, wherein each of the membrane modules has an outer pore size of 10 to 40 nm.

32. The system according to claim 27, wherein each of the membrane modules has an outer pore size of 15 to 35 nm.

33. The system according to claim 27, wherein each of the membrane modules has an outer pore size of 20 to 30 nm.