FIELD OF THE INVENTION

The present invention relates to a process for degumming crude palm oil. More particularly, the invention relates to a process for degumming crude palm oil using polyvinylidene fluoride ultrafiltration membrane.

BACKGROUND OF THE INVENTION

Palm oil which derived from the fruits of palm trees is a common cooking ingredient in the tropical belt of Southeast Asia, Africa and parts of Brazil. Besides being used as cooking oil, palm oil can also be made into margarine, specialty fats and oleochemicals. Its increasing use in commercial food industry is mainly due to its many nutritional advantages such as being cholesterol free, rich in natural anti-oxidants and having high content of natural carotenoids.

Refining process in crude palm oil industry involves removal of undesirable constituents such as free fatty acid, phospholipids, colour pigments and trace metals from crude palm oil with an objective of achieving acceptable effects on colour, taste, odour and stability of the refined product. Industrially, the two most commonly used methods for crude palm oil refining are chemical and physical steam refining. Impurities can be removed or partially removed at different stages of these methods which include degumming, refining, bleaching and deodorizing. However, these methods have several significant drawbacks such as loss of neutral oil and nutrients, high energy consumption and huge usage of water and chemicals. Furthermore, water is often used for washing of oil in the chemical refining process and the washing could generate heavily polluted effluent which, in turn, requires additional efforts and time in treating the wastewater before the wastewater is allowed to be discharged into the environment. These drawbacks associated with the conventional refining processes are described in Bhosle, B.M., et al. (2005), "New approaches in deacidification of edible oils - a review", J. Food Eng, 69, 481-494. Asymmetric polymeric membrane has been widely used in various industrial applications since its development in the late 1950s. This membrane is one of the new approaches recommended to overcome the drawbacks in the conventional crude palm oil refining process. The feasibility of using membrane technology in oil industry has been widely reported in the literature. In 1985, attempt has been made to dewax, degum and deacidify undiluted crude sunflower oil using hollow fiber microfiltration membrane with pore size of 0.3 pm (US Patent no. 4,545,940). The results described in this publication show a significant reduction of the free fatty acid content in the refined oil. However, the removal of the free fatty acid from the crude oil is achieved with the use of phosphoric acid and sodium hydroxide.

Other than microfiltration membrane, Keurentjes et al. (1992), "Extraction and fractionation of fatty acids from oil using an ultrafiltration membrane", Ind. Eng. Chem. Res., 31 ,581-587 reported the feasibility of using ultrafiltration membrane in a liquid-liquid extraction of free fatty acid from oil using 1 ,2-butanediol as solvent. Results revealed that the losses of triglycerides could be minimized but a high mass transfer resistance resulted from the filtration might lead to a large membrane area requirement.

Besides microporous membranes, membranes which consist of densely structured active layer have also showed potential in removing phospholipids and pigments from oils (Subramanian et al. (1998), "Processing of vegetable oils using polymeric composite membranes", J. Food Eng., 38, 41-56). Removal of free fatty acid using such membrane however could not be completely achieved and the permeate needs to be further improved. Similar results were also reported in a more recent study in which non-porous membranes were found to be able to reduce phosphorus content in rice bran oil. The results however show a substantial reduction in color value of the rice bran oil (Manjula, S, et al. (2009), "Simultaneous degumming, dewaxing and decolorizing cure rice bran oil using non-porous membranes", Sep. Purif. Techno!., 66, 223-228). Consequently, there remains a need in the art to provide a process for degumming crude palm oil to address at least one of the above problems, or at least to provide an alternative.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a process for degumming crude palm oil. The process comprises the steps of providing a feed oil, the feed oil comprises a crude palm oil containing phosphorus; heating the feed oil; feeding the feed oil into a membrane processing module comprising polyvinylidene fluoride (PVDF) ultrafiltration membrane; and passing the feed oil through the PVDF ultrafiltration membrane at a pressure in the range of 2 x 10 ⁵ to 5 x 10 ⁵ Pa to obtain a permeate fraction having a phosphorus content which is less than the phosphorus content of the feed oil and a retentate fraction having an increased phosphorus content.

In accordance with an embodiment of this invention, the feed oil is heated to a temperature of 50°C.

In accordance with an embodiment of this invention, the permeate fraction having a phosphorus content of no more than 4 ppm.

In accordance with an embodiment of this invention, the PVDF ultrafiltration membrane is prepared using a polymer dope solution of PVDF pellets, N-methyl- 2-pyrrolidone and ethylene glycol.

In accordance with some embodiments of this invention, the PVDF ultrafiltration membrane is a hollow fiber membrane. The PVDF ultrafiltration membrane has a pore size of 24 nm to 37.5 nm.

In accordance with an embodiment of this invention, the feed oil is passed through the PVDF ultrafiltration membrane at a pressure of 2 x 10 ⁵ Pa. In accordance with an embodiment of this invention, the membrane processing module comprises 60 fibers with a length of 25 cm.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for degumming crude palm oil (CPO). More particularly, the invention relates to a process for degumming crude palm oil using polyvinylidene fluoride (PVDF) ultrafiltration membrane.

The process of the present invention comprises the steps of providing a crude palm oil and heating the crude palm oil prior to contacting the crude palm oil with a PVDF ultrafiltration membrane.

Crude palm oil is a semi-solid at ambient temperature. It needs to be heated prior to contacting it with the PVDF ultrafiltration membrane. Heating of the crude palm oil reduces the oil viscosity and this in turn helps to improve the oil flux rate of the membrane. In one embodiment of the present invention, the crude palm oil is heated to a temperature of about 50°C. Any temperature that goes beyond 50°C may soften the membrane material to an unacceptable degree in a long run. It may also result in an increase in energy usage. The PVDF membrane is operable at a temperature below 50°C. However, as the melting point of crude palm oil is around 33°C to 39°C, the operating temperature of PVDF membrane process should be higher than the melting point of crude palm oil so that the filtration process can be conducted easily.

The heated crude palm oil is then fed into a membrane processing module containing PVDF ultrafiltration membrane. In one embodiment of the present invention, the membrane processing module consists of 60 fibers and is about 25 cm in length. The module is able to provide a total filtration area of about 20 cm ² .

After the crude palm oil is fed into the membrane processing module, the crude palm oil passes through the PVDF ultrafiltration membrane at a pressure in the range of about 2 to 5 bar (about 2 x 10 ⁵ to 5 x 10 ⁵ Pa) to obtain a permeate fraction and a retentate fraction. In a preferred embodiment, the degumming process is conducted at a low operating pressure of 2 bar (2 x 10 ⁵ Pa).

The fibers of the PVDF ultrafiltration membrane act as semi-permeable membranes, preventing phospholipids from the crude palm oil from passing through the membrane. The permeate fraction which passes through the membrane is collected as a permeate oil and the retentate fraction which does not pass through the membrane is collected as a concentrated oil. In comparison, the permeate oil contains relatively less phospholipids than the crude palm oil. In proportion, the concentrated oil contains relatively more phospholipids than the permeate oil. In one embodiment, the oil that permeates through the PVDF ultrafiltration membrane is about 86% to 93% free of phospholipids content in comparison to the crude palm oil. In a preferred embodiment, the permeate oil contains no more than 4 ppm of phospholipids.

The PVDF ultrafiltration membrane used in the process of the present invention is preferably a hollow fiber membrane. 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 polymer dope solution is prepared by dissolving PVDF pellets into a mixture of N-methyl-2-pyrrolidone (NMP) and ethylene glycol (EG). Preferably, the polymer concentration of the dope solution is in the range of 12 to 20 wt%. More preferably, it is between 14 and 18 wt%. 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 - 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 has a pore size of 24 nm to 37.5 nm.

The PVDF membrane used in the process of the present invention shows 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 palm oil refining process

The process in accordance with the present invention has the advantage that 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 prior to subjecting the crude palm oil to subsequent refining steps. The membrane used in the present invention is able to remove the phospholipids to a minimal amount that meets the specification suitable for subsequent steps involved in the refining process. The present invention also does not require the use of any solvent (for example, hexane) to form oil miscella for removing phospholipids from the crude palm oil. The present invention thus reduces the usage of chemicals, and helps to improve the energy consumption of the process. This in turn helps to reduce operating cost.

There is also a possibility of recovering phospholipids from the concentrated oil for lecithin production. The invention may also be suitable for the treatment of other crude glyceride oils, for example, soy bean oil and sunflower oil.

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. EXAMPLES

Example 1

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 10 ⁵ 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. Results showed that 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%.

In comparison to the FFA content of feed crude palm oil, membranes were found to have little role in retaining FFA molecules. Both membranes tested showed less than 15% of FFA rejection. Given the fact that the molecular size of FFA (<300 Dalton) is much smaller than that of triglycerides (-800 Dalton), FFA in principle is very difficult to be separated using typical pressure-driven membrane process.

Table 1

Membrane FFA PV Phosphorous

*F P F P R F P R

(%) (%) (%) (ppm) (ppm) (%) (ppm) (ppm) (%)

14PVDF-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

18P VDF-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

5 ^a F= Feed, P=Permeate and R=Rejection

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

Example 2 0 Crude palm oil having phosphorus content of 15.49 ppm and free fatty acid of 5.39 % was treated in the permeation unit fitted with membrane modules in which the membranes were prepared from dope solution comprising 18% w/w polyvinylidene fluoride, 76% w/w N-methyl-2-pyrrolidone and 6% w/w ethylene glycol. The operating temperature was controlled at 50°C but the pressure was5 varied in the range between 2 and 5 bar (2 x 10 ⁵ Pa and 5 x 10 ⁵ Pa). The details of the experimental results are as shown in Table 2.

The test results show that increasing operating pressure from 2 to 5 bar (2 x 10 ⁵ Pa and 5 x 10 ⁵ Pa) resulted in significant decrease in phosphorus rejection, from

0 86.96% to 36.80%. With respect to FFA rejection, the membranes showed less than 8% rejection regardless of the operating pressure. Operating the membranes at pressure beyond 5 bar (5 x 10 ⁵ Pa) is not recommended as it would lead to a collapse in the membrane structure in a long run, leading to extraordinary high oil permeation.

5

Table 2

Pressure FFA PV Phosphorus

(bar) F P R F P R F P R

(%) (%) (%) (%) (%) (%) (ppm) (ppm) (%) 2 5.39 4.97 7.79 Nil Nil - 15.49 2.02 86.96

3 5.39 5.39 0.00 Nil Nil - 15.49 5.54 64.23

4 5.39 5.39 0.00 Nil Nil - 15.49 7.86 49.26

5 5.39 5.11 5.19 Nil Nil - 15.49 9.79 36.80

Example 3

Example 2 was repeated using the same type of membranes but under different 5 operating temperatures. Crude palm oil having phosphorus content of 15.4 ppm

- 16.72 ppm and free fatty acid of 4.68 % - 5.39 % was treated in the membrane permeation unit and operated at 2 bar (2 x 10 ⁵ Pa) pressure. The experiment results obtained were as shown in Table 3.

10 The increase in operating temperature in membrane CPO refining process is not

critical parameter affecting the quality of permeate with respect to phosphorus content. High operating temperature however may soften polymeric membrane material in a long run, deteriorating separation performance of membrane.

Preferably, temperature of 50°C is used during membrane CPO refining process

15 to minimize energy consumption.

Table 3

Temperature FFA PV Phosphorus

(°C) F P R F P R F P R

(%) (%) (%) (%) (%) (%) (ppm) (ppm) (%)

50 5.39 4.97 7.79 Nil Nil 15.49 2.02 86.96

60 4.77 4.46 6.50 Nil Nil - 16.11 1.87 88.39

70 4.89 4.72 3.48 Nil Nil - 16.72 1.42 91.51

80 4.68 4.68 0.00 Nil Nil - 16.72 2.48 85.17

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.