Refinery of Palm Oil

Introduction to Palm Oil: From dust to dawn

The economical history of the oil palm (Elaeis guineensis) began in the rain forests of western Africa in the late 19th century. Since its introduction into Malaysia in the early 20th century until the early sixties its impact on the economy was marginal. For many years the economy of Malaysia had depended for its wealth and prosperity upon rubber. In 1961, Malaysia embarked on an intensive agricultural diversification program, and the crop that has achieved the most notable success since then is palm oil. Within a relatively short period, Malaysia became the world’s largest commercial producer and exporter of palm oil in 1966. Diversification into oil palm means that the country is now less dependent on the fortunes of rubber as a plantation crop.

Palm Oil a Cost Effective Product

Palm oil is obtained from the flesh of the palm fruit. Each palm tree produces approximately one fruit bunch, containing as many as 3000 fruitlets, per month. In addition, each palm tree continues producing fruit economically for up to 25 years. This ensures a constant stable supply, as compared with other annual crops.

            Naturally, palm oil is characterized as stabilized oil due to its chemical composition. As such, it can be used in most food applications without hydrogenation, thus, reducing production cost by as much as 30%. Palm oil also is priced competitively and can represent a saving of upto several cents per pound, compared to other edible oils.

            Palm oil is available in a variety of forms: crude palm oil, palm olein, palm stearin, RBD palm oil, fractionated palm olein and pal mid-fraction. While most of the oil Malaysia exports is RBD palm oil and RBD palm olein, the range of products is available to suit a variety of manufacturing needs and in forms that are ready-to-use and require no further processing.

Palm Oil Composition 

Palm oil is extracted from the mesocarp of the fruit of the palm Elaeis guineensis. There are a few varieties of this plant but Tenera, which is a hybrid of the Dura and the Pisifera, present abundantly through out the whole Peninsular.

            The mesocarp comprises about 70 – 80% by weight of the fruit and about 45 -50% of this mesocarp is oil. The rest of the fruit comprises the shell, kernel, moisture and other non fatty fiber.The extracted oil is known as crude palm oil (CPO) which until quite recently was known as the golden commodity.

            Palm oil like all natural fats and oils comprises mainly Triglyceries, mono and diglycerides. Free fatty acids, moisture, dirt and minor components of non oil fatty matter referred to collectively as unsaponifiable matter.

1. Tryglyceride

            It is a chemical compound of one molecule of glycerol bound to three molecules of Fatty Acid.

            CH2 – OH        +          R1-COOH                   CH2 – COOR1

            CH – OH         +          R2-COOH                   CH – COOR2      +   3H2O

            CH2 – OH        +          R3-COOH                   CH2 – COOR3

            Glycerol                       Fatty Acid                    Triglyceride                  Water

The fatty acids could be of the same type or they could be different. The property of a triglyceride will depend on the different fatty acids that combine to form the triglyceride.

            The fatty acids themselves are different depending on their chain length and degree of saturation. The short chain fatty acids are of lower melting point and are more soluble in water. Whereas, the longer chain fatty acids have higher melting points. The melting point is also dependent on degree of non-saturation. Unsaturated acids will have a lower melting point compared to saturated fatty acids of similar chain length.

            The 2 most predominant fatty acids in palm oil are C16:0(saturated) palmitic acid and C18:1 (unsaturated) oleic acid. Typical fatty acid composition of palm oil is given as:

            C12:0   Lauric               –   0.2%

            C14:0   Myrstic             –   1.1%

            C16:0   Palmitic            – 44.0%

            C18:0   Stearic              –   4.5%

            C18:1   Oleic                – 39.2%

            C18:2   Linoleic            – 10.1%

            Others                          –   0.9%

2. Mono and di-glycerides and FFA

            In the presence of heat and water the triglycerides break up by a process known as hydrolysis to form free fatty acids thus yielding mono and di-glycerides and FFA which is of crucial importance to the refiners.

Hydrolysis can be represented as below:

CH2 – COOR1            +                                              CH2 – OH

CH – COOR2             +          H2O                            CH – COOR2             +          R1COOH

CH2 – COOR3            +                                              CH2 – COOR3

Triglyceride                              Water                           Diglyceride                               FFA

            Mono and diglycerides account for about 3 to 6% by weight of the glycerides in the oil. Good oils having lower amount of mono and diglycerides is said to be of great importance in the fractionation process because they act as emulsifying agents inhibiting crystal formation and making filtration difficult.

            The amount of mono and diglycerides and FFA is reduced in the process of refining as can be seen from their concentration in the DFA(Distillate Fatty Acid).

3. Moisture and Dirt

            This is a result of milling practice. Good milling will reduce moisture and dirt in palm oil but normally it is in the range of 0.25%.

4. Minor Component

 These are classified into one category because they are fatty in nature but are not really oils. They are referred to as unsaponifiable matter and they include the following:

  1. Carotineoids
  2. Tocopherols
  3. Sterols
  4. Polar Lipids
  5. Impurities

            As a conclusion, palm oil is one of the most widely consumed edible oils in the world today. Beside, it contains more monounsaturated fatty acids than many other vegetable oils. Recent scientific studies indicate that consumption of monounsaturated has some beneficial effects in order to maintain a healthy life style. In addition, compared with other vegetable oils, palm oil is a rich source of the anti-oxidant vitamin E containing about 360 – 600 ppm in its refined form. There are certain reports show that:

  • Palm oil did not increase baseline serum cholesterol
  • Palm oil did not affect LDL/HDL ratio.
  • The vitamin E found in palm oil behaved as an anti-oxidant.

Physical Refinery: The first step toward edibility  

Palm oils consist mainly of glycerides and, like other oils in their crude form, small and variable portions of non-glyceride components as well. In order to render the oils to an edible form, some of these non-glycerides need to be either removed or reduced to acceptable levels.

            In term of solubility study – glycerides are of two broad types: oil insoluble and oil soluble. The insoluble impurities consisting of fruit fibres, nut shells and free moisture mainly, are readily removed. The oil soluble non-glycerides which include free fatty acids, phospholipids, trace metals, carotenoids, tocopherols or tocotrienols, oxidation products and sterols are more difficult to remove and thus, the oil needs to undergo various stages of refining.

            Not all of the above non-glyceride components are undesirable. The tocopherols and tocotrienols not only help to protect the oil from oxidation, which is detrimental to flavour and keep ability of the finished oil, but also have nutritional attributes, a- and b-carotene, the major constituents of carotenoids, are precursors of vitamin A. The other impurities generally are detrimental to the oil’s flavour, odour, colour and keep ability and thus influence the oil’s usefulness.

            The aim of refining is therefore to convert the crude oil to quality edible oil by removing objectionable impurities to the desired levels in the most efficient manner. This also means that, where possible, losses in the desirable component are kept minimal. The impurities which are contained in the crude palm oil (CPO) is shown in table 1.0:

Substances

Content

Free Fatty Acid (FFA)

3 – 5%

Gums (phospholipids, phosphotides)

300 ppm

Dirt

0.01%

Shell

Trace

Moisture and Impurities

0.15%

Trace metal

0.50%

Oxidation Products

Trace

Total Carotenoids

500 – 1000 mg/ke

Table 1.0 Composition of CPO

General speaking, the refining routes of palm oil is quite identical. There are two routes are taken to process crude oil into refined oil; which are chemical (basic) refining and physical refining. The methods differ basically in the way the fatty acids are removed from the oil. Physical refining, which eliminates the need for an effluent plant for the soap stock, involves subjecting the oil to steam distillation under higher temperature and vacuum for removal of the free fatty acids. The physical refining is used to remove the free fatty acids. The refining of physical plant is practiced to subject the oil to steam distillation. The typical refining process is shown in Figure 1.0.

Physical Refinery Process Description

            The raw material which is used by physical plant is crude palm oil (CPO) from the CPO storage tank. CPO is feed at the flow rate about 35-60 tons/hour. The initial temperature of CPO is at 40 – 60°C. The feed is pumped through the heat recovery system, that is plate heat exchanger to increase the temperature around 60 – 90°C.

            After that, there is about 20% of the CPO feed to into the slurry and mix with the bleaching earth (6 – 12kg/ton CPO) to form slurry (CPO + Bleaching earth). The agitator inside the slurry tank will mixed the CPO and bleaching earth completely. Then, the slurry will go into the bleacher.

            At the same time, another 80% of the CPO is pumped through another plate heat exchanger (PHE) and steam heater to increase the CPO temperature to 90 – 130°C (it is a desired temperature for the reaction between CPO and phosphoric acid). Then, the CPO feed is pumped to static mixers and the phosphoric acid is dosed at 0.35 – 0.45 kg/ton. Inside there, the intensive mixing is carried out with the crude oil for precipitation up the gums. The precipitation of gums will ease the later filtration process, avoid the scale formation in deodorizer and heating surface. The degumming CPO then will go into bleacher.

            In the bleacher, there are 20% slurry and 80% degummed CPO will mix together and the bleaching process occur. The practice of bleaching involves the addition of bleaching earth to remove  any undesirable impurities (all pigments, trace metals, oxidation products) from CPO and this improves the initial taste, final flavor and  oxidative stability of product. It also helps to overcome problems in subsequent processing by adsorption of soap traces, pro-oxidant metal ions, decomposes peroxides, colour reduction, and adsorbs other minor impurities. The temperature inside the bleacher must be around 100°C – 130°C to get the optimum bleaching process for 30 minutes of bleaching period. The low pressure steam is purged into bleacher to agitate the concentrated slurry for a better bleaching condition.

            The slurry containing the oil and bleaching earth is then passed through the Niagara filter to give a clean, free from bleaching earth particles oil. The temperature must be maintain at around 80 – 120°C for good filtration process. In the Niagara filter, the slurry passes through the filter leaves and the bleaching earth is trapped on the filter leaves. Actually, the bleaching earth must be clear from Niagara filter after45minutes in operation to get a good filtration. Bleached palm oil (BPO) from Niagara filter is then pumped into buffer tank as a temporary storage before further processing.

            Usually, a second check filter, trap filter is used in series with the Niagara filter to double ensure that no bleaching earth slips occur. The presence of bleaching earth fouls deodorizer, reduces the oxidative stability of the product oil and acts as a catalyst for dimerizaition and polymerization activities. So, the “blue test” is carried out for each batch of filtration to ensure the perfect filtration process. This test indicates whether any leaking is occurring in Niagara filter or trap filter. Hence, any corrective actions can be taken intermediately.

            The BPO comes out from the filter and passes through another series of heat recovery system, Schmidt plate heat exchanger and spiral (thermal oil: 250 – 305°C) heat exchanger to heat up the BPO from 80 – 120°C until 210 – 250°C.

            The hot BPO from spiral heat exchanger then proceeds to the next stage where the free fatty acid content and the color are further reduced and more important, it is deodorized to produce a product which is stable and bland in flavor.

            In the pre-stripping and deodorizing column, deacidification and deodorization process happen concurently. Deodorization is a high temperature, high vacuum and steam distillation process. A deodorizer operates in the following manner: (1) dearates the oil, (2) heat up the oil, (3) steam strips the oil and (4)cools the oil before it leaves the system. All materials if contact are stainless steel.

            In the column, the oil is generally heated to approximately 240 – 280°C under vacuum. A vacuum of less than 10 torr is usually maintained by the use of ejectors and boosters. Heat bleaching of the oil occurs at this temperature through the thermal destruction of the carotenoid pigments. The use of direct steam ensures readily removal of residue free fatty acids, aldehydes and ketones which are responsible for unacceptable odor and flavors. The lower molecular weight of vaporized fatty acids rises up the column and pulls out by the vacuum system. The fatty acid vapor leaving the deodorizer are condensed and collected in the fatty acid condenser as fatty acid. The fatty acids then is cooled in the fatty acid cooler and discharged to the fatty acid storage tank with temperature around 60 – 80°C as palm fatty acid distillate (PFAD), a by-product from refinery process.

            The bottom product of the pre-stripper and deodorizer is Refined, Bleached, Deodorized Palm Oil (RBDPO). The hot RBDPO (250 – 280°C) is pumped through Schmidt PHE to transfer its heat to incoming BPO with lower temperature. Then, it passes through another trap filters to have the final oil polishing (120 – 140°C) to prevent the earth traces from reaching the product tank. After that, the RBDPO will pass through the RBDPO cooler and plate heat exchanger to transfer the heat to the CPO feed. The RBDPO then is pumped to the storage with temperature 50 – 80°C.

Palm Fatty Acid Distillation Plant

            The separation of liquid mixture into their several components is one of the major process of the chemical industries, and distillation is the most widely used method of achieving this end: it is the key operation of the oil refinery. Though out the chemical industry the demand for pure products, coupled with a relentless pursuit of greater efficiency, has necessitated continued research into techniques of distillation. The distillation column is used in this purpose.

            The distillation column which have to be designed with a larger range in capacity than any other types of chemical engineering equipment, with single columns from 0.3 to 10m in diameter and from 3m to upwards of 75m in height. The purpose of designing is to achieve the desired product quality at minimum cost, but also to provide constant purity of product even though there may be some variation in feed composition. The vertical cylindrical column provides in a compact form, with the minimum of ground utilization, a large number of separate stages of vaporization and condensation.

            In practice, distillation may be carried out by either of two principal methods. The first method is based on the production of a vapor by boiling the liquid mixture to be separated and condensing the vapors without allowing any liquid to return to the still. There is then no reflux. The second method is based on the return of part of condensate to the still under such condition that this returning liquid is brought into intimate contact with the vapor on their way to the condenser. Either of these methods may be conducted as a continuous process or as a batch process.

PFAD Plant Description

a) Feed Raw Material                           – Palm Fatty Acid Distillate (PFAD)

b) i) Major Product Produced               – Distillate Fatty Acids (DFA)

   ii) By Product Produced                    – Precut-Lighter Fatty Acid Component

– Residue

PFAD Process Description

The feed Palm Fatty Acid Distillate (PFAD) from storage tank with temperature around 50 – 100°C will first passes through a heat exchanger network.

The temperature of PFAD will increase to approximately 200 –220°C. Then the hot feed will enters to the Degasifier for separating some impurities and light fatty acid presented in the feed under vacuum system.

            After that, the heavy components of fatty acid (C10, C12, C14, C16 & C18) come out from the bottom of Degasifier will go into column C for more separation between light and heavy components of fatty acids. Before that, there are three distillation column are used in distillation process. The products of these 3 columns are as follow:

                        1. Column A: Precut

                        2. Column B: Distillate Fatty Acid (DFA)

                        3. Column C: Residue

            In column C, the feed with temperature 220 – 255°C will further heating by thermal oil boiler until temperature become 240 – 300°C under vacuum system. The fatty acids will evaporate under the vacuum condition and separation of light fatty acid and heavy fatty acid will occur. At the top of column C, the light fatty acid (precut with lower carbon number <C16) from the evaporation become vapor is continuously pulled out by the vacuum system. The precut then passed through the heat exchangers and cooled down by the soft water and PFAD feed before going to storage.

            At the same time, the heavy fatty acid from the bottom of Column C (C16 & C18) is pumped to Column B for further separation. There is high temperature inside the column B which is supplied by thermal oil reboiler (290 – 310°C) will contribute to the vaporization of fatty acids. Therefore the temperature will increase (220 – 250°C) during the distillation process because of the higher boiling point of the fatty acids feed. The light fatty acid (DFA) from the vaporization of fatty acid is pulled out by the vacuum system into a reflux holder. When the refluks is overflow, the excess DFA is pumped to the heat exchangers and cooled down by the soft water and the PFAD feed. The DFA then is further cooled down in spiral heat exchanger (hot water/DFA) and plate heat exchanger (Cooling tower water/DFA) before sending to storage at 60 – 90°C.

            On the other hand, the bottom product of column B is residue, the heavy fatty acids component is pumped to the heat exchanger (Residue/PFAD feed and Residue/Hot Water) before going to storage tank. The uncompleted distillate will recycles back to column B for further separation.

Fractionation: Value added process?

The demand for liquid oils has increased in recent years, mainly for salad and cooking uses and an important property for such oils is low cloud point, which is the temperature at which turbidity appears when the oil is cooled under standard conditions. Liquids oils with a low cloud point are desirable because of the widespread use of household refrigeration.

            In order to cater for a wide range of markets, the Malaysian refiners start to offer product which are “harder”(Stearin) and “more liquid”(olein) than palm oil. These are accomplished trough a simple process of fractionation which is based on two fundamental operations:

1)      Crystallization

2)      Filtration

Fractionation of palm oil can be described as follow. The triglycerides found in the oil have different melting points. At certain temperature, the lower melting temperature triglycerides will crystallize into solid separating the oils into both liquid (Olein) and solid (Stearin) fraction. The fraction can then be separated by filtration.

            It is worth mentioning that in palm oil fractionation, palm olein is the premium product and the palm stearin is the discount product. In Malaysia, fractionation of palm oil into palm olein and palm stearin is accomplished using two types of processes which are “Viz Dry” and “Detergent Fractionation”.

Fractionation Plant Description

a)   Feed Raw Material                         –  Refined Bleached deodorised Palm Oil (RBDPO)

b)   i)    Major Product Produced          –  Refined Bleached Deodorised Palm Olein (Olein)

      ii)  By Product Produced               –  Refined Bleached Deodorised Stearin (Stearin)

 

Fractionation Process Description

          The dry fractionation is used to separate the palm olein and palm stearin from the RBDPO produced by physical treatment. The RBDPO is passed through the further fractionation process to get various grade of palm olein and palm stearin. Usually, there are three types of olein are produced: (1) normal grade olein, (2) super grade olein and (3) olein with cloud point 7 – 8°C.

Crystallization Process

            Firstly, the RBDPO feed must pass the quality specification, colour<2.6R and FFA< 0.075 is fed into the heat exchanger. The RBDPO feed is heated up by hot waters around 75°C. After that the oil is kept homogenized at about 70°C in homogenizes before the start of crystallization. The idea is to destroy any crystals present and to induce crystallization in a controlled manner in the crystallizer.

            After that, the oil is pumped to the crystallizer. The crystallization system is a batch type and is equipped with special crystallizers operating alternatively. These crystallizers are made up of vertical cylindrical vessel full of thermo-regulated water which submerged barrels containing the oil to be fractionated: each of these barrels is fitted with a mechanical agitator. An automatic station controls the temerature in the various crystallizers.

            The crystallization process is carried out to remove the higher melting glycerides which cause liquid oils to become cloudy and more viscous at low temperature. There are 3 factors (temperature, time and agitation), have a fundamental importance on the formation and character of the crystal:

  1. The lowering of temperature causes, because of supersaturating the higher melting component to separate from a solution.
  2. Agitation facilitates the formation of small crystals.
  3. Time with a gradual decrease in temperature and stillness, promotes the formation of longer crystals.

The solution is pumped batch-wise into the crystallizer according to a pre-established programme. In the crystallizer, the crystal formation and growth occurs as the oil is agitated and cooled sing chilled water and cool water filled in the jackets or cooling coils of the crystallizer. Cooling can be governed by controlling either the oil or water temperature.

Filtration Process

            After the crystallization process, the slurry from buffer tank passses through the filtration process for the physical separation between RBD palm stearin and RBD palm olein. Presently, the membrane filter is used for this filtration. Another alternative for this purpose is by employing drum filter for separation.

            The membrane filter is pressure filter where the filter pack comprising alternatively plates and frames, or a series of chamber is compressed between one fixed and one movable cover or bulk-head. The filter media are located between each individual element. Cake will build up in the hollow space between the elements and fall out of the press when the filter pack is opened. Composition of the filter pack is by means of electrically driven hydraulic system (75 bar), which controls the entire mechanical parts of units, head plates, filter plates, plate shifting device with the built in panel board.

Hydrogenation

            Hydrogenation is the most widely used method of all the oil modification processes, to reduce the degree of unsaturated in the fatty acid groups of the glycerides. It is a catalytic process whereby the number of double bonds are reduced and by the same time isomerization of the residual fatty acids is promoted. Liquid oils with unsaturated triglycerides are thus transformed into fats containing a higher % age of saturated triglycerides: Hydrogenation is often called hardening of oils and soft fats.

            Catalytic hydrogenation, which has been known in fat technology since the beginning of this century, is used increasingly for the preparation of ‘tailor-made’ fats. Depend on the condition of the reaction, the basic reaction can be shown as follows:

        H    H                                                         H   H

                         R – C = C – R + H2                                     R- C – C – R       Hydrogenation

                                                                                                   H  H

            The complex system consists of three phases: liquid oil, gaseous hydrogen and solid catalyst. Hence there are many different internal surfaces through which the hydrogen molecules have to pass until they reach the double bonds of the unsaturated triglycerides adsorbed on the catalyst surface. As soon as the unsaturated bonds are saturated, the triglyceride moves off the catalyst surface, thus enabling the next unsaturated molecule to be adsorbed and processed.

            The overall hydrogenation rage depends on the quality of the reactant involved, the degree of refining of the oil to be hydrogenated, the activity and nature of the catalyst. In addition reaction parameters such as hydrogen pressure, catalyst concentration, reaction temperature, stirring, etc have an influence. In spite of these numerous reaction parameters that affecting the quality of the desired product, fat-technologist have resolved the operating conditions required for the preparation of tailor-made fats. This process is established mainly to add value to by byproducts from the refinery. The raw materials are from refinery: Palm Fatty Acid Distillate (PFAD) and Refined Bleached Deodorized (RBD). Basically, stearin is the main raw material for this plant.

Hydrogenation Process Description

There are various kind of oils used as the feed of this plant depends on the market demands, there are DFA, PFAD, RBDSt, precut and split residue. Firstly, the fatty acid feed from the storage tank (60 – 70°C) is pumped to the feed preheater. In the feed preheater, the fatty acid feed is heated up by the hot hydrogenated FA from plant until 140 – 170°C, before entering the reactor for hydrogenation process.

            Then, the hot feed is transferred to the reactor autoclave for reaction. The reactor consisted of the nickel catalyst which play an important role in the reaction as follow:

  1. To avoid modifiers, such as sulphur, likely to give higher “trans” acid contents.
  2. Comparatively high temperature to accelerate reduction of poly-unsaturated without formation of saturates.
  3. Reduced the hydrogen gas pressure.
  4. Lowering the iodine value to improve stability and good yield of liquid oil when winterized.
  5. To remove materials responsible for clouding and solidification at low temperatures.

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