Basics of Alkali Refining of Vegetable Oils
Westfalia Separator Food Tec GmbH Mechanical Separation Division Basics of Alkali Refining of Vegetable Oils Renato Dorsa Klaus-Peter Eickhoff
Objectives of Refining 1. Removal of undesired products from crude oils • free fatty acids (FFA) • phospholipids (gums) • oxidised products • metal ions • colour pigments • others 2. Preservation of valuable vitamínes. (vitamina E or tocopherol – natural anti-oxidants) 3. Minimize oil losses 4. Protection of the oil against degradation
Steps of the chemical refining process 1. Degumming: Reduction of phospholipid (gum) content 2. Neutralisation: Removal of free fatty acids and residual gums 3. Bleaching: Removal of colour pigments and metal ions 4. Desodorization: Removal of odours
NEUTRALISATION Objective: Removal of free fatty acids Two different refining principles: 1. Chemical Refining: Removal by a chemical reaction with alkali (caustic soda). 2. Physical Refining: Removal by distillation at higher temperature and low vacuum
Structure of Triglycerides H H H H H H H H H H H H H H H H H H O O C C C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H H H H C O H H H H H H H H H H H H H H H H H H C C C C C C C C C C C C C C C C C C O C H H H H H H H H H H H H H H H H H H H C O H H H H H H H H H H H H H H H H H C C C C C C C C C C C C C C C C C C H H O H H H H H H H H H H H H H H H H H Stearic Glycerol acid
Structure of a free fatty acid molecule H H H H H H H H H H H H H H H H H O H C C C C C C C C C C C C C C C C C C O H H H H H H H H H H H H H H H H H H Functional group “acid” H+ Stearic acid (C18 H36 O2)
Chemical Neutralisation (after the reaction with caustic soda) Functional group “alkali” OH- Functional group “acid” H+ H H H H H H H H H H H H H H H H H O H C C C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H H O H H – O – Na fatty acid + caustic soda = soap + water
Alkali Refining Process steps: 1. Conditioning: Transformation of the non-hydratable phospholipids into their hydratable form by breaking down the metal/ phosphatide complexes with a strong acid. 2. Neutralisation Saponification of the free fatty acids by alkali (caustic soda). 3. Washing: Removal of residual soaps by hot water. 4. Drying: Removal of moisture under vacuum.
Steps of Alkali Refining 1. Conditioning to neutralisation mixing o 90 C Phosphoric Retention time acid Crude oil
Steps of Alkali Refining 2. Neutralisation centrifugation mixing to washing from conditioning caustic soda Retention time soap
Steps of Alkali Refining 3. Washing centrifugation mixing from neutralisation to drying 95oC water (~ 10%) water + soap
Steps of Alkali Refining 4. Drying water steam vacuum system from washing dryer neutral oil
Alkali Refining: Plant Design Crude oil dosation The capacity of the plant is adjusted by a speed controlled crude oil pump in Massflow combination with a Dual pre- meter strainer massflowmeter. A pre-strainer is installed to protect the pump and following equipment . The oil temperature is Crude oil Heat adjusted with a heat pump exchanger exchanger by means of steam.
Alkali Refining: Plant Design Acid Conditioning The acid is circulated with a certain pressure by a Reaction Dosing Flow tank circulating pump. meter valve The dosing is done by a magnetic flowmeter and a pneumatic dosing valve. The acid flow is controlled by Circulating the PLC in relation to the oil pump flow. acid mixer Acid and oil is mixed tank intensively by a dynamic mixer followed by a retention time (5min.)
Alkali Refining: Plant Design Details of the acid dosing system return Acid Pressure tank relief valve circulation strainer Circulating pump Magnetic flowmeter dosation Dosing valve Oil
Alkali Refining: Plant Design Neutralisation Concentrated caustic soda is Diluting circulated with a certain pressure water by a circulating pump. dosing retention Dosing of lye and diluting water is valves tank done with a magnetic flowmeters and a pneumatic dosing valves. flow meters The lye flow is controlled by the pressure relief PLC in relation to the oil flow and valve the FFA content. static The diluting water flow is mixer controlled in relation to the lye lye flow and the lye dilution degree. tank Conc. lye and diluting water is dynamic mixer mixed by a static mixer, the circulating diluted lye is mixed with the oil by pump a dynamic mixer, followed by a retention time (approx. 10 min.)
Alkali Refining: Plant Design Details of caustic soda retention tank Divided into several compartments oil out to ensure an even retention time. Smooth agitation to avoid baffles decantation of soap and emulsification. Separating disc Soap flocks are agglomerated to larger particles to improves Agitador separation efficiency in the centrifuge. compartment Hydration of phospholipids is improved. oil in
Alkali Refining: Plant Design Soapstock separation Soapstock is continuouly separator discharged by the separator to the soapstock tank. neutral oil Residual soap content in neutral oil < 500 ppm. Soapstock tank soapstock
Alkali Neutralisation: Plant Design Water washing Neutral oil is heated to flow meter optimal washing temperature (95 °C). hot water dosing Hot and soft water ist added valve separator to the oil and mixed intensively by a dynamic mixer. dynamic Washing water flow is mixer controlled by the PLC in relation to the oil flow. heat exchanger Wash water is separated immediately after mixing, no retention time.
Alkali Refining: Plant Design Vacuum drying Residual moisture is vacuum system removed by a dryer under a vacuum of < 50 mbar. Final moisture content vacuum dryer < 0,1 %. neutral oil clean oil pump
Alkali Refining: Plant Design Complete 3-stage plant Hot water Phosphoric Caustic soda circulation acid dosing dosing Vacuum drying Acid Neutralisation Wasching conditioning Soapstock
Alkali Refining: Chemicals Phosphoric acid .Converts the non-hydratable phospholipids into their hydratable form by breaking up the Ca- and Mg- complexes of phosphatitic acid (PA) and phosphadityl etholamine (PE). .Concentration: 75 – 85 % .Addition : 1 – 3 kg / t oil .Temperature: 80 – 90 °C
Alkali Refining: Chemicals Caustic soda . Neutralises the free fatty acids by saponifying them into sodium salts. . Saponifies and hydrates phospholipids . Removes colour pigments . Concentration: 12 – 24 °Bé . Addition: stochiometric amount to neutralise the phosphoric acid and the free fatty acids plus an excess of 0 – 40 % . Calculation: 0,142 kg NaOH (100%) per kg FFA + 0,816 kg NaOH (100%) per kg H3PO4 (100%)
Alkali Refining: Chemicals Caustic soda . Finding the optimal condition between: – Neutral oil saponification and emulsification NaOH contact time emulsion saponification temperature
Alkali Refining: Chemicals Water .To wash out residual soaps and to dilute the caustic soda .Quality: soft, demineralised water .Temperature: min. 90°C .Addition for washing: 5 – 10 %
Alkali Refining: Results .Typical neutral oil quality: – FFA: < 0,1 % – Phospolipids: < 10 ppm – Soaps: < 50 ppm – Moisture: < 0,1 % – Impurities: nil .Losses: – According to the Theoretical Loss (TL) • TL = FFA + Phospholipids + moisture + impurities + 0,3% – Neutralisation Loss: • TL < 3 %: Loss = 1,25 x TL + 0,3 • TL> 3 %: Loss = 1,35 TL
Alkali Refining: General Comments feed . A centrífuge or separator is an accelerator for the decantation of oil gums, soapstock or wash water soapstock from oil and is not changing anything in the chemical structure of the products. Important for the efficiency of the machines are the process conditions prior and during the separation (dosation of chemicals, mixing, reaction times, temperature). . For the optimal operation of the separator the ideal adjustments for the separating zone between the two phases to be separated (Fine Tuner diameter) and the outlet pressure of the oilphase (function of the hydrohermetic feed) have to be found.
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EtiketlerBasics of Alkali Refining of Vegetable Oils Bleaching degradation Degumming Desodorization Minimize oil losses Neutralisation