The invention relates to a process for the dry fractionation of edible oil. More particularly, although not exclusively, the invention relates to a process for the production of carotene rich crude palm olein. DESCRIPTION OF THE PRIOR ART

The oil palm produces two types of oils: crude palm oil from the fibrous mesocarp and crude palm kernel oil from the kernels. Although both oils originate from the same fruit, palm oil is chemically and nutritionally different from palm kernel oil.

Crude palm oil is deep orange red in colour due to the high content of natural carotenes. It is a rich source of carotenoids and vitamin E which confers natural stability against oxidative deterioration. However, without any processing, crude palm oil has limited usefulness. Crude palm oil can be refined and further fractionated to widen its application.

To produce a useful palm oil, crude palm oil is processed through three refining stages, namely degumming, bleaching and deodorising and then fractionated. In degumming, the gum and fatty acid in crude palm oil are separated together with other impurities such as trace minerals, copper and iron by the application of phosphoric acid. In bleaching, the oil is mixed with bleaching earth (bentonite calcium) in a vacuum room to remove impurities and colour pigments in the palm oil. In deodorising, the odour and taste of the oil are removed. This refined palm oil is known as RBD palm oil. Fractionation of RBD palm oil separates the oil into liquid (olein) and solid (stearin) fractions.

Dry fractionation is the simplest and most cost effective process in processing RBD palm oil. The adjective "dry" refers to the absence of any solvents, catalysts or chemical additives during the process. For that reason, dry fractionation is a zero-effluent modification technology, unlike solvent fractionation, hydrogenation, etc.

Palm olein is the liquid fraction obtained by fractionation of refined RBD palm oil after crystallization at controlled temperatures. It is fully liquid in warm climate and has a narrow range of glycerides. However, when the temperature drops below the "cloud point" of palm olein (approximately 20°C), palm olein molecules crystallize. The oil will appear cloudy. At even lower temperatures, the cloudy oil then becomes solid. The oil soon clears up when the temperature rises above the "cloud point". Palm olein is widely used as cooking oil. It also blends with other popular vegetable oils. Palm stearin is the more solid fraction obtained by fractionation of RBD palm oil after crystallization at controlled temperatures. It is commonly used to formulate trans-free fats such as margarine, shortening and vegetable ghee.

Dry fractionation generally involves the heating up of RBD palm oil to a temperature of between 50°C to 55°C, cooling the oil to between 30°C to 40°C followed by further cooling of the oil to the final fractionation temperature of between 20°C to 25°C. The crystallizer is then held at this temperature for a number of hours depending on the type and characteristics of the olein and stearin desired. The crystallized slurry is then filtered under a pressure to obtain the olein and stearin fractions. The filtration pressure is generally 3 to 5 bars. The purpose of heating the oil is for destroying the memory effect before it is cooled in crystallizer chamber. The presence of crystal memory can negatively affect the yield.

If the holding times, the number of fractionation steps or the filtration pressure is varied the characteristics of the olein and stearin obtained is altered.

The iodine value of the olein obtained is about 56 for a single fractionation of around 6-9 hours holding time. The yield of olein and stearin obtained is about 75% and 20% respectively where the remaining yield consists of palm fatty acid distillates and waste oil.

The iodine value of the olein obtained is about 58 for a single fractionation of around 18- 20 hours holding time. The yield of olein and stearin obtained is between 70% and 25% respectively where the remaining yield consists of palm fatty acid distillates and waste oil. The iodine value is a measure of the degree of unsaturation of fats and oils. It is one of the parameters commonly used to measure the quality of olein. The higher the iodine value, the better the quality of the olein.

Dry fractionation of crude palm oil using the conditions stated above is deemed to be difficult to control when dry fractionation is conducted on crude palm oil due to the presence of gums and other impurities which will interfere with the crystallization of the oil during the fractionation process, which is why dry fractionation is always conducted on RBD palm oil. Thus there are no known processes to produce olein with an iodine value of 56 or 58 without refining the crude palm oil first.

Further, it is difficult to produce carotene rich palm olein by way of dry fractionation only as the key for producing carotene rich palm oil is that the crude palm oil must be deodorized.

An example of a process is a modified physical refining process, which produces a refined palm oil of similar quality to that of RBD palm oil while retaining most of the carotenoids and the vitamin E originally present in crude palm oil, has been disclosed.

"Characteristics of Red Palm Oil, a Carotene- and Vitamin E-Rich Refined Oil for Food Uses" by B. Nagendran, U. R. Unnithan, Y. M. Choo, and Kalyana Sundram discloses a process involving pre-treatment of crude palm oil, followed by deacidification and deodorization using molecular distillation, to produce a carotene rich refined edible palm oil. The product is a refined red palm oil that meets standard refined edible oil specifications and retains up to 80% of the carotene and vitamin E originally present in the crude palm oil. The oil contains no less than 500 ppm carotene, 90% of which is present as a- and b-carotene. The vitamin E content is about 800 ppm, 70% of it in the form of tocotrienols (mainly as a-, b-, and g-tocotrienols). The process is also applicable for the production of other natural vitamin-rich palm fractions, such as stearin, olein, and palm mid-fraction.

US 9,051,533 B2 describes a continuous process for the dry fractionation of edible oils and fats using one or more crystallisers in series, the process comprising the steps of: (a) providing a molten fat; (b) continuously feeding the molten oil or fat to the first of the one or more crystallisers in series in which the fat is gradually cooled by using heat exchangers containing a cooling medium so that a crystal slurry is formed, each of the one or more crystallisers exhibiting a temperature gradient, the temperature at the point where the molten or partially crystallised fat enters one of the crystallisers being higher than that at the point where the slurry leaves that crystalliser; (c) continuously withdrawing said slurry from the last of the one or more crystallisers; (d) separating said crystal slurry by filtration in a filter cake and a filtrate, wherein said process further comprises the step of at least partially melting fat encrustations deposited on the heat exchangers. An oil fraction is produced by the continuous process.

Standard crystallisation vessels used to fractionate edible oils and fats incorporate an agitator that comprises a rotating shaft onto which agitator blades have been fitted in such a way that on rotation these blades exert a vertical force onto the surrounding slurry. However, there exist crystallisation vessels that do not have agitators.

US 8,133,519 B2 describes a crystallization process for edible oil and fats which is carried out in a crystallizer with stationary heat exchange elements, wherein the contents of the crystallizer are made to move along the heat exchange elements in an oscillatory manner without the use of an internal agitator.

Scraped surface heat exchangers (SSHEs) are commonly used in the food, chemical, and pharmaceutical industries for heat transfer, crystallization, and other continuous processes. They are ideally suited for products that are viscous, sticky, that contain particulate matter, or that need some degree of crystallization. During operation, the product is brought in contact with a heat transfer surface that is rapidly and continuously scraped, thereby exposing the surface to the passage of untreated product. In addition to maintaining high and uniform heat exchange, the scraper blades also provide simultaneous mixing and agitation. High heat transfer coefficients are achieved because the boundary layer is continuously replaced by fresh material. Moreover, the product is in contact with the heating surface for only a few seconds and high temperature gradients can be used without the danger of causing undesirable reactions. SSHEs are especially suited for making heavy salad dressings, margarine, chocolate, peanut butter, fondant, ice cream, and shortenings.

To the best knowledge of the applicant, no known art has disclosed the use of scraped surface heat exchangers for dry fractionation of crude palm oil.

US 8,962,874 B2 describes an improved process for fractionating triglyceride oil. The process attains a reproducible crystallization by introducing a controlled temperature profile and ensuing crystal development that reduces the amount of entrapped olein inside the crystals or crystal aggregates. The process can be used to fractionate vegetable oils such as palm oil or its blends with other palm oil products or edible vegetable oils. The disadvantage of this process is that it involves repeated heating and cooling of the crude triglyceride oil which increases the total processing time. Further, the crude palm olein produced in the process can be refined, bleached and deodorised without adversely affecting the iodine value of the olein.

This invention thus aims to alleviate some or all of the problems of the prior art.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a process for the dry fractionation of edible oil.

It has surprisingly been found that in an aspect of the present invention, the above objects can be realised by a dry fractionation of edible oil, the process including the steps of: a) pre-cooling the oil to a temperature between 30-38°C; b) subjecting the pre-cooled oil to pressure; c) passing the pre-cooled oil under pressure from step b) through one or more scraped surface heat exchanger in which the oil is cooled so that a crystal slurry is formed and the temperature of the crystal slurry is reduced to 10-18°C; and d) separating said crystal slurry by filtration to obtain an olein fraction and stearin fraction.

The process is advantageous in that the crude palm oil does not need to be pre-treated using chemicals and/or solvents and/or refined, bleached and deodorised, which results in the product of the process being safe for humans and animals to consume.

Further, the invention produces a crude palm olein of similar quality to that of fractioned RBD palm olein and retaining most of the carotenoids and the vitamin E originally present in crude palm oil. Since the crude palm olein does not to be refined, bleached and deodorised, operating costs are reduced which results in higher profit margin. It is a further advantage of the process of the present invention that a higher olein yield is obtained compared to conventional processes.

In an embodiment, the process is operated in batches where the process time is 4 hours per batch of 20-80 metric tonnes of edible oil. This processing time is faster than that of conventional processes. In a further embodiment, the process is operated continuously.

In another embodiment, the edible oil to be pre-cooled in step a) is at ambient temperature. In an additional embodiment, the oil in step a) is pre-cooled in a plate heat exchanger.

In a further embodiment, the pressure applied in step b) is in the range of 0.5 to 4 MPa.

In an embodiment, multiple scraped surface heat exchangers are connected in series.

In an additional embodiment, the separation in step d) is conducted using a press machine. In a further embodiment, the edible oil is palm oil, or other edible vegetable oil in its natural state.

In a preferred embodiment, the iodine value of the olein obtained from the process is between 56 to 58.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated, although not limited, by the following description of embodiments made with reference to the accompanying drawing in which:

Figure 1 is a diagram of a plant for carrying out the process of dry fractionation of crude palm oil in accordance to the present invention.

Figure 2 is a block diagram of a process for the dry fractionation of crude palm oil in accordance to the present invention.

Figure 3 is a block diagram of a conventional process for the attaining palm olein with an iodine value of about 56.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention relates to a process for the dry fractionation of edible oil.

The edible oil to be used in the process according to the invention can be of vegetable origin. Examples of vegetable oils are palm oil, various palm oil fractions, soybean oil, coconut oil, rapeseed oil (canola), olive oil, peanut oil, sunflower oil and corn oil.

In a preferred embodiment of the invention, the oil is crude palm oil or other vegetable oil in its natural state. The oil to be fractionated according to the invention should be in liquid form.

Referring to Figure 1, a plant for carrying out the process of dry fractionation of crude palm oil includes a holding tank 10 for receiving the oil to be processed, a heat exchanger 20 for pre-cooling the edible oil, a pump 30 for applying pressure to the pre-cooled oil, a set of scraped surface heat exchangers 40 for conducting crystallization of the oil, a temperature gauge 50 for measuring the temperature of the crystal slurry and a filtration machine 60 for filtering and separating the crystal slurry into an olein and stearin fraction. One way of introducing the oil into the heat exchanger 20 is to pump it from a tank or to pump the oil straight from the oil carrier. In the embodiment of Figure 1, the heat exchanger 20 is a plate heat exchanger.

The temperature of the coolant of the heat exchanger 20 is maintained at a temperature between -5°C and 5°C. The coolant can be water or an ethylene glycol-based water solution. The oil is pre-cooled to a temperature between 30°C and 38°C.

The pre-cooled oil is then subjected to pressure. The pressure source can be a rotary pump.

The pressurised pre-cooled oil is then passed through a scraped surface heat exchanger 40 in which the oil is cooled so that a crystal slurry is formed. The scraped surface heat exchanger 40 is maintained at a substantially uniform temperature throughout the entire vessel.

During operation of the scraped surface heat exchanger 40, the pressurised pre-cooled oil is introduced into the scraped surface heat exchanger 40. During its passage through the scraped surface heat exchanger 40 the viscosity of the pre-cooled oil changes due to changes in temperature, and therefore portions of the crystal slurry will stick to the inside wall of the scraped surface heat exchanger 40. This results in deteriorated heat transmission. When the shaft with the blades rotates the blades will scrape the crystal slurry which sticks to the inside wall of the scraped surface heat exchanger, thereby enhancing efficient heat transmission so as to allow cooling of the crystal slurry to be affected in a continuous heat exchange process. It also has the advantage that leads to the formation of a homogeneous crystal population. Following this the crystallised slurry leaves the heat exchanger.

One or more scraped surface heat exchangers are used in the process according to the invention. In a preferred embodiment, a set of scraped surface heat exchangers are used and are connected in series. Each scraped surface heat exchanger must show a temperature gradient i.e. the temperature of the second scraped surface heat exchanger is lower than the temperature of the first scraped surface heat exchanger.

The crystal slurry has to be transferred from one scraped surface heat exchanger to the next scraped surface heat exchanger. When more than one vertically oriented scraped surface heat exchangers are used in the process according to the invention, the crystal slurry is made to move along by the application of pressure.

The temperature of the crystal slurry leaving the last scraped surface heat exchanger should be in the range between 12°C and 15°C. Cooling the oil to below its cloud point is not recommended since this may lead to a deposit of fat crystals in the heat exchanger.

Preferably, rotation of the shaft of the scraped surface heat exchanger is performed at a speed between 50 and 400 rpm.

Although the scraped surface heat exchanger is designed so as to minimize encrustation, this often involves high liquid speeds. In the continuous dry fractionation process of oils according to the invention, these high speeds have to be avoided since they have been found to lead to secondary nucleation, non-uniform crystal sizes, slow filtration and high residual oil content in the stearin fraction.

A suitable temperature gauge 50 may be placed to measure the temperature of the crystal slurry that has passed through the scraped surface heat exchanger. The slurry leaving the scraped surface heat exchanger has to be separated by filtration 60 into a stearin fraction and an olein fraction. One way of introducing the crystal slurry into the press is to pump it from the scraped surface heat exchanger. The filtration can be done via a plate and frame filter press, chamber plate filter press or a membrane plate filter press.

Referring to Figure 2, the crude palm olein can be further refined 70 once dry fractionation has been completed, only if needed. Since the crude palm olein is used for animal feed additive, refining, bleaching and deodorising the crude palm olein which uses chemicals is not preferred. As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its scope or essential characteristics. The present embodiments are, therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and all changes which come within therefore intended to be embraced therein.

EXAMPLES

The following Examples illustrate the various aspects, methods and steps of the system and process of this invention. These Examples do not limit the invention, the scope of which is set out in the appended claims.

Example 1: Process using four scraped surface heat exchanger

The experiment conducted is a batch process of dry fractionation of crude palm oil. The iodine value of the crude palm oil is 51. Crude palm oil is pumped from a storage tank in which the oil temperature in the tank is between 50°C and 60°C, through a plate heat exchanger that cooled the oil to a temperature between 30°C and 38°C. The temperature of the coolant of the plate heat exchanger is maintained at a temperature between -5°C and 5°C. The coolant used is in the plate heat exchanger is water.

The pre-cooled oil is then subjected to pressure by way of a rotary pump. The pressure subjected to the pre-cooled oil is between 0.5 MPa and 1.5 MPa.

The pressurised pre-cooled oil is then passed through a scraped surface heat exchanger in which the oil is cooled so that a crystal slurry is formed. The scraped surface heat exchanger is filled at a rate between 5 and 20 metric ton per hour. The cooling rate of the scraped surface heat exchanger is between 10°C and 25°C per minute. The frequency of the rotation of the shaft of the scraped surface heat exchanger is between 50 rpm and 400 rpm.

The crystal slurry was allowed to flow from to the second to fourth scraped surface heat exchangers accordingly.

The temperature of the crystal slurry exiting the fourth scraped surface heat exchanger is between 15°C and 18°C.

The crystal slurry was allowed to flow from the scraped surface heat exchanger to a membrane filter press.

The experiment was continued for 4 hours. The olein yield was between 85% and 90% and its iodine value is 56. Table 1 illustrates the product properties obtained by the process according to the invention compared to the conventional process as described in Figure 3 where the crude palm oil must be refined, bleached and deodorized prior to dry fractionation.

Table 2 illustrates the properties of the crude palm olein obtained by the process according to the invention.

Example 2: Process using six scraped surface heat exchangers

The experiment conducted is a batch process of dry fractionation of crude palm oil. The iodine value of the crude palm oil is 51. Crude palm oil is pumped from a storage tank in which the oil temperature in the tank is between 50°C and 60°C, through a plate heat exchanger that cooled the oil to a temperature between 30°C and 38°C. The temperature of the coolant of the plate heat exchanger is maintained at a temperature between -5°C and 5°C. The coolant used is in the plate heat exchanger is water.

The pre-cooled oil is then subjected to pressure by way of a rotary pump. The pressure subjected to the pre-cooled oil is between 0.5 MPa to 1.5 MPa. The pressurised pre-cooled oil is then passed through a first scraped surface heat exchanger in which the oil is cooled so that a crystal slurry is formed. The scraped surface heat exchanger is filled at a rate of 5-20 tons per hour. The cooling rate of the scraped surface heat exchanger is 10-25°C per minute. The frequency of the rotation of the shaft of the scraped surface heat exchanger is 50-400 rpm. The crystal slurry was allowed to flow from to the second scraped surface heat exchanger. The cooling rate of the scraped surface heat exchanger is 15-30°C per minute. The frequency of the rotation of the shaft of the scraped surface heat exchanger is between 50 rpm and 400 rpm. The crystal slurry was allowed to flow from to the third to sixth scraped surface heat exchangers accordingly. The temperature of the crystal slurry exiting the sixth scraped surface heat exchanger is between 10°C and 13°C.

The crystal slurry was allowed to flow from the scraped surface heat exchanger to a membrane filter press. The experiment was continued for 4 hours. The olein yield was between 80% and 85% and its iodine value is 58.

Table 3 illustrates the product properties obtained by the process according to the invention.

Table 4 illustrates the properties of the crude palm olein obtained by the process according to the invention.