A PROCESS OF REMOVING FREE FATTY ACIDS FROM CRUDE VEGETABLE OIL

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a process of removing free fatty acids (FFA) from crude vegetable oil. More particularly, the present invention provides a process of removing FFA from crude vegetable oil by mixing crude vegetable oil with a biologically treated aqueous discharge from oil milling process, and separating the mixture into treated vegetable oil and soap-containing aqueous liquor.

The invention also relates to a vegetable oil obtained by the aforementioned refining process.

BACKGROUND OF THE INVENTION

All crude vegetable oils are extracted from fruits or seeds. The oil extraction process takes place in oil mills.

Most crude vegetable oils tend to be unpalatable and, therefore, need to be purified before they can be incorporated in food products and/or sold to consumers. The various steps involved in this purification are referred to as "refining". The series of steps that typically lead to a fully refined or RBD (refined, bleached and deodorised) oil, comprises:

• Removal of gums. This step is commonly referred to as 'degumming' and aims to remove

phospholipids from the crude vegetable oil. Their removal is imperative for both subsequent processing and final product quality.

• Removal of free fatty acids (FFA). FFA can be removed chemically by allowing these acids to react with an alkali to form soaps and separating the soaps from the oil; this is called "alkali refining'. They can also be removed physically by volatilisation in what is called "physical refining". The physical refining process is also called "steam refining" since the volatilisation of the free fatty acids is achieved by a steam stripping process at reduced pressure and elevated temperature; it must be preceded by an adsorptive treatment.

• Removal of adsorbable compounds. This step is commonly referred to as "bleaching," but it does more than just decrease the absorbance of the oil. When acid-activated bleaching earth is used, this adsorbent also catalyses the decomposition of peroxides and removes all kinds of polar compounds.

• Removal of malodorous compounds. These compounds are removed by steam stripping, the process that is also used in steam refining. However, the free fatty acids removed during steam refining are already present in the feedstock, whereas the malodorous compounds removed during deodorisation are also generated as a direct result of the deodorisation treatment and its elevated temperature in particular. Alkali refining (or neutralisation) refers to a refining step in which crude oil is treated with an alkali such as caustic soda (sodium hydroxide). The feed can be crude oil, but the oil may also have been degummed before being alkali refined. The purpose of the alkali refining process is manifold. If there are still phosphatides present in the oil, the alkali refining process should remove them. The process should remove free fatty acids present by converting them into soaps that are oil-insoluble and can be separated from the oil by settling or centrifugal separation. In addition, the process should remove colouring compounds and/or their precursors so that bleaching the alkali-refined oil requires less bleaching earth and colour fixation during subsequent high temperature treatments is avoided.

Palm oil is an edible oil that is widely used in the food industry. Palm trees bear fruit in the third year after planting and continue producing for about 25 years. Fruit bunches of 4 to 20 kg contain 200 to 2000 individual fruits and are harvested throughout the year. The fruit bunches are transported to palm oil mills where crude palm oil (20 to 24%) is produced by mechanical and physical extraction processes along with palm kernels from which a further 2 to 4% of palm kernel oil (based on weight of palm fruits) can be produced. Crude palm oil is obtained from palm fruits by steaming at 95°C to loosen the fruits in the fruit bunch and to deactivate the lipase present in the fruits, followed by centrifugation or hydraulic pressing to release the oil. So called neutralised, bleached and deodorised (NBD) palm oil is produced from this crude palm oil by successively subjecting the oil to degumming, alkali refining, bleaching and deodorising.

The production of palm oil is accompanied by the generation of considerable quantities of polluted wastewater commonly referred to as palm oil mill effluent (POME). Typically, 1 t of crude palm oil production requires 5-7.5 1 of water; over 50% of which ends up as POME. This wastewater is a viscous, brownish liquid containing about 95-96% water, 0.6-0.7% oil and 4-5% total solids. It is acidic (pH 4-5), hot (80-90°C), nontoxic and has a high organic content (COD 50,000 mg/l, BOD 25,000 mg/l).

Efforts have been made to utilize wastewater from palm oil mills. US 2012/0040442 describes a method for use in treating palm oil mill effluents (POME) to generate a biogas with high methane content, the method comprising the steps of:

• treating the palm oil mill effluents with concentrated butyrate;

• introducing the treated palm oil mill effluents into an reaction tank with an loading rate of at least 1.5 g COD/L d and hydraulic retention time of at least 4 days; and

· providing microorganism biomass at the reaction tank so that anaerobic degradation of the palm oil mill effluents treated with butyrate can be performed.

WO 2013/169091 describes a zero discharge treatment technology in handling a palm oil milling waste; comprises the following steps:

(i) pre-treatment to recover waste oil; (ii) biological treatment to generate biogas and compound fertilizer; and

(iii) membrane separation to generate clean effluent and excess liquid potash which can be used a biofertililizer. Chan et I. (Optimization of palm oil mill effluent treatment in an integrated anaerobic-aerobic bioreactor, Sustain. Environ. Res., (2013), 23(3), 153-170) report the outcome of an optimization study on the simultaneous anaerobic and aerobic processes in an integrated anaerobic-aerobic bioreactor (IAAB) treatment system for palm oil mill effluent. The IAAB achieved highest overall Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD) and total suspended solids removal efficiencies of > 99% at optimum organic loading rates (OLR) of 12.8 g COD L ^'1 d ^"1 , mixed liquor volatile suspended solids in anaerobic compartments (MLVSS _an ) of 40,600 mg L ^"1 , and mixed liquor volatile suspended solids in aerobic compartments (MLVSS _a ) of 18,700 mg L ^"1 . In Table 2 the operating conditions of the IAAB are summarized. The pH of the aerobic effluent is specified as being in the range of 8.4 to 8.9.

SUMMARY OF THE INVENTION

The inventors have discovered that a particular biologically treated aqueous discharge from an oil milling process can suitably be used to reduce the FFA content of crude vegetable oils. This particular aqueous discharge has been biologically treated to reduce suspended and dissolved solids and has a total alkalinity of at least 1 ,000 mg CaC0 ₃ per litre.

By simply mixing the crude vegetable oil with the alkaline biologically treated aqueous discharge a mixture is obtained in which at least a fraction of the free fatty acids in the crude oil is saponified. This mixture can be separated using well-known separation techniques into a soap containing liquor and a vegetable oil having a reduced free fatty acid (FFA) content.

Thus, the present invention provides a process of treating crude vegetable oil, said process comprising the steps of:

• providing crude vegetable oil having a FFA content of at least 0.5%,

• providing biologically treated aqueous discharge from an oil milling process, said biologically treated aqueous discharge having a water content of at least 80 wt.% and a total alkalinity of at least 1 ,000 mg CaC0 ₃ per litre;

• mixing the crude vegetable oil with the biologically treated aqueous discharge in a weight ratio of crude vegetable oil to biologically treated aqueous discharge in the range of 1 : 10 to 10: 1 to produce a neutralization mixture; and

• separating the neutralization mixture into treated vegetable oil and soap-containing aqueous liquor. The present process can suitably be employed in oil mills to produce crude vegetable oils with a reduced FFA content. These crude vegetable oils may subsequently be refined by means of ordinary oil refining processes. The present process can advantageously be used to reduce the FFA content of various crude vegetable oils, including crude palm oil and crude palm kernel oil.

The present process offers the advantage that it enables the preparation of a crude vegetable oil with reduced FFA content without using chemicals such as caustic soda. Furthermore, the process can be used to improve the Deterioration of Bleachability Index (DOBI) of crude vegetable oil. Finally, the present process also reduces the amount of oil mill effluent.

The present invention also pertains to a treated vegetable oil that is obtained by the present process.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, a first aspect of the invention relates to a process of treating crude vegetable oil, said process comprising the steps of.

• providing crude vegetable oil having a free fatty acid (FFA) content of at least 0.5%;

• providing biologically treated aqueous discharge from an oil milling process, said biologically treated aqueous discharge having a water content of at least 80 wt.% and a total alkalinity of at least 1 ,000 mg CaC0 ₃ per litre;

• mixing the crude vegetable oil with the biologically treated aqueous discharge in a weight ratio of crude vegetable oil to biologically treated aqueous discharge in the range of 1 :10 to 10:1 to produce a neutralization mixture; and

· separating the neutralization mixture into treated vegetable oil and soap-containing aqueous liquor.

The term "oil" as used herein refers to glyceride oil that may be liquid, semi-solid or solid at ambient temperature (20°C).

The term "glyceride oil" as used herein refers to an oil that is composed of esters of glycerol and one or more fatty acids.

The term "vegetable oil" as used herein refers to an oil that has been isolated from a plant material.

The term "crude vegetable oil" as used herein refers to a vegetable oil that has not been bleached or deodorised. The term "crude vegetable oil', unless indicated otherwise, encompasses both degummed and non-degummed vegetable oils. The free fatty acid (FFA) content of a vegetable oil can suitably be determined by titration method with the use of potassium hydroxide (Ainie, K.et al. (2004) MPOB Test Methods - A Compendium of Test on Palm Oil Products, Palm Kernel Products, Fatty Acids, Food Related Products and Others.

Malaysian Palm Oil Board, Selangor, Malaysia).

The DOBI index of a vegetable oil is defined as the absorbance ratio Αφ,β _nm / A ₂₆ g _n m of around 0.1 g oil dissolved in 25 mL of hexane or 2,2,4Trimethylpentane (iso-octane). The higher the DOBI, the better the quality of the oil. The terminology "biologically treated aqueous discharge" as used herein, unless indicated otherwise, refers to an aqueous discharge that has undergone a treatment in which micro-organisms degrade organic components contained in the aqueous discharge. The biological treatment employed may include aerobic and/or anaerobic biological treatment. The present process is particularly suitable for treating crude vegetable oil having an FFA content of at least 0.5%, more preferably of 1-12%, even more preferably of 1.2-8% and most preferably of 1.3-6%.

The crude vegetable oil used in the present process typically has a DOBI index of at least 2, more preferably of a DOBI index of at least 2.5, and most preferably a DOBI index in the range of 3.0 to 4.0.

The crude vegetable oil that is treated in the present process preferably is a non-degummed vegetable oil.

According to one embodiment of the present process, the biologically treated aqueous discharge has undergone aerobic biological treatment. Aerobic treatment processes take place in the presence of air and utilize microorganisms (also called aerobes), which use molecular/free oxygen to assimilate organic impurities i.e. convert them into carbon dioxide, water and biomass. The biologically treated aqueous discharge is preferably produced by subjecting aqueous discharge from an oil milling plant to aerobic biological treatment (optionally after anaerobic biological treatment), followed by removal of suspended solids from the aqueous discharge by static settling, filtration and/or centrifugation.

According to another preferred embodiment, the treated aqueous discharge has undergone anaerobic biological treatment. Anaerobic treatment processes take place in the absence of air (and thus molecular/free oxygen) by microorganisms (also called anaerobes) which do not require air

(molecular/free oxygen) to assimilate organic impurities. The final products of organic assimilation in anaerobic treatment are methane and carbon dioxide gas and biomass. Preferably, the biologically treated aqueous discharge is produced by subjecting aqueous discharge from an oil milling plant to an anaerobic biological treatment. According to a particularly preferred embodiment, the treated aqueous discharge employed in the present process has undergone both aerobic and anaerobic biological treatment. Preferably, the treated aqueous discharge has first undergone anaerobic biological treatment, followed by aerobic biological treatment.

The biologically treated aqueous discharge that is employed in the present process is preferably obtained from a vegetable oil mill. Most preferably, the treated aqueous discharge is obtained from an oil mill that produces one or more vegetable oils selected from palm oil, palm kernel oil, coconut oil and combinations thereof. Even more preferably, the treated aqueous discharge is obtained from an oil mill that produces palm oil and/or palm kernel, most preferably, it is obtained from a palm oil mill.

The biologically treated aqueous discharge typically contains at least 1 ,000 ppm of potassium ions (K ⁺ ). More preferably, the treated aqueous discharge contains 2,000-10,000 ppm of potassium ions, most preferably 2,500-8,000 ppm of potassium ions.

The biologically treated aqueous discharge has a pH at 25°C in the range of 7.5 to 10.0, more preferably in the range of 8.0 to 9.8 and most preferably of 8.5 to 9.5.

Total alkalinity of the biologically treated aqueous discharge typically is in the range of 1 ,000-10,000 mg CaC0 ₃ per litre. More preferably, total alkalinity is in the range of 2,000-6,000 mg CaC0 ₃ per litre and most preferably of 3,000-5,000 mg CaC0 ₃ per litre.

The biologically treated aqueous discharge preferably contains no more than limited amounts of dissolved solids, oil and other suspended material. The biologically treated aqueous discharge typically contains at least 95 wt % water, most preferably 98.00-99.50 wt.% water.

As a result of the biological treatment the dry matter content of the biologically treated aqueous discharge preferably has been reduced to less than 5 g/l. More preferably, the biologically treated aqueous discharge has a dry matter content of 0.3-4 g /I and most preferably of 1-3 g/l.

Also suspended solids are preferably reduced considerably in the biologically treated aqueous discharge that is employed in the present process. According to a particularly preferred embodiment, the biologically treated aqueous discharge contains less than 5 g/l of suspended solids, more preferably less than 4g/l of suspended solids and most preferably less than 2 g/l of suspended solids. The suspended solids content of the biologically treated aqueous discharge can suitable be reduced by subjecting the biologically treated aqueous discharge to e.g. static settling or filtration, before mixing it with the crude vegetable oil.

The biologically treated aqueous discharge employed in the present process advantageously has a biological oxygen demand (BOD) of less than 500 mg/l and a chemical oxygen demand (COD) of less than 5,000 mg/l. More preferably, the BOD of the biologically treated aqueous discharge is less than 300 mg/l, most preferably less than 200 mg/l. The COD of the biological treated aqueous discharge is more preferably less than 3,000 mg/l, most preferably less than 2,000 mg/l. Examples of vegetable oils that may be treated in the present process include palm oil, palm kernel oil, coconut oil, soybean oil, sunflower oil, rapeseed oil, cottonseed oil, maize oil, linseed oil and combinations thereof. Preferably, the crude vegetable oil that is treated in the present process is selected from palm oil, palm kernel oil, coconut oil and combinations thereof. Even more preferably, the vegetable oil is selected from palm oil, palm kernel oil and combinations thereof. Most preferably, the vegetable oil is palm oil.

In the present process the crude vegetable oil and the biologically treated aqueous discharge are typically mixed in a weight ratio of crude vegetable oil to biologically treated aqueous discharge in the range of 1 :10 to 10:1. More preferably, the latter ratio is in the range of 1 :3 to 3:1 , most preferably in the range of 1:2 to 2:1.

In order to allow sufficient saponification of the free fatty acids in the crude vegetable oil, said crude vegetable oil and the biologically treated aqueous discharge are preferably mixed for at least 1 minute to maintain the neutralization mixture in the form of an oil-and-water emulsion, preferably an oil-in- water emulsion.

The neutralization mixture is preferably kept at a temperature of at least 50°C, more particularly of 50- 00 °C for at least 1 minute, more preferably for at least 2 minutes, most preferably for 3-180 minutes. The soap-containing biological aqueous liquor that is obtained from the separation of the neutralization mixture typically contains at least 0.1 g/l soap. More preferably, the soap content of the aqueous liquor is at least 0.5 g/l, most preferably 1-10 g/l.

The neutralization mixture may suitably separated into treated vegetable oil and soap-containing aqueous liquor by means of centrifugation and/or decanting and/or static settling. Most preferably, this separation is done by means of centrifugation.

The present process typically yields a treated vegetable oil having an FFA content that is at least 5% lower than the FFA content of the crude vegetable oil. More preferably, the FFA content of the treated vegetable oil is at least 10% lower, even more preferably at least 20% lower, and most preferably at least 30% lower than the FFA content of the crude vegetable oil. Another aspect of the present invention relates to treated vegetable oil obtained by a process as described herein. According to a particularly preferred embodiment, this treated vegetable oil is a treated palm oil, more particularly a non-bleached, non-deodorized palm oil. Typically, the non-bleached, non-deodorized palm oil obtained by the present process has an FFA content below 5%. The DOBI index of said non-bleached, non-deodorized palm oil is preferably in the range of 3.3-4.8, more preferably in the range of 3.5-4.5 most preferably in the range of 3.6-4.2.

The invention is further illustrated by the following non-limiting examples.

EXAMPLES Example 1

Raw effluent was subjected to anaerobic biological treatment, followed by aerobic biological treatment. The biologically treated aqueous discharge was pre-treated (by filtration) to remove suspended solids. The characteristics of treated effluent so obtained are described in Table 1.

Table 1

Experiments were carried out in which a crude palm oil having a relatively low FFA-content (below 2%) was mixed in different weight ratios with the aforementioned treated effluent to remove free fatty acids.

The treatment of the crude palm oil with the biologically treated aqueous discharge was carried out as follows:

i. The crude oil and the biological treated aqueous discharge were heated to 80 degree Celsius. ii. The hot crude oil was mixed with the hot biological treated aqueous discharge in different weight ratios and the mixture was stirred for 5 to 10 minutes whilst maintaining the temperature of the mixture at 80 degree Celsius.

iii. The mixtures were separated through centrifugation.

iv. FFA content of original crude palm oil and of the separated oils was measured.

The characteristics of the crude palm oil and of the treated palm oils obtained after separation of the aqueous soap-containing liquor are summarized in Table 2. Table 2

Example 2

Example 1 was repeated, again using biologically treated aqueous discharge from a palm oil mill's effluent treatment plant that had been subjected to anaerobic and aerobic biological treatment This time a crude palm oil having an FFA-content of below 3% was mixed in different weight ratios with the aforementioned biologically treated aqueous discharge to remove free fatty acids.

The characteristics of the crude palm oil and of the treated palm oils obtained after separation of the aqueous soap-containing liquor are summarized in Table 3.

Table 3

Example 3

Example 1 was repeated, again using biologically treated aqueous discharge from a palm oil mill that had been subjected to anaerobic and aerobic biological treatment.

This time a crude palm oil having an FFA-content of below 4% was mixed in different weight ratios with the aforementioned biologically treated aqueous discharge to remove free fatty acids.

The characteristics of the crude palm oil and of the treated palm oils obtained after separation of the aqueous soap-containing liquor are summarized in Table 4.

Table 4 T/MY2016/000007

Example 4

Example 1 was repeated, again using biologically treated aqueous discharge from a palm oil mill that had been subjected to anaerobic and aerobic biological treatment.

This time a crude palm oil having an FFA-content of above 6% was mixed in different weight ratios with the aforementioned biologically treated aqueous discharge to remove free fatty acids.

The characteristics of the crude palm oil and of the treated palm oils obtained after separation of the aqueous soap-containing liquor are summarized in Table 5.

Table 5

Weight ratio treated

FFA (%) DOBI

effluent : crude palm oil

0:1 5.93 2.45

1 :4 5.52 2.62

1 :2 5.32 2.70

3:4 5.07 n.a.

1 :1 4.92 n.a.

2:1 4.26 n.a.

5:2 3.92 n.a.

3:1 3.60 n.a.