Biofuel Industry Case Study: Refining of Vegetable Oils for Biofuels


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Find the solution for one of the toughest mixing applications in the chemical industry, refining vegetable oils for biofuels. Read this case study on the Process, the Problem and the Solution.

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Biofuel Industry Case Study: Refining of Vegetable Oils for Biofuels

  1. 1. Refining of Vegetable Oils for Biofuels The Advantages Introduction The Process The Problem The Solution HIGH SHEAR MIXERS/EMULSIFIERS CHEMICALS Solutions for Your TOUGHEST MIXING Applications in APPLICATION REPORT
  2. 2. There are therefore 4 processes carried out on oil used for this application. Although there are variations, and some processes may combine or eliminate certain stages (e.g. Bleaching), they can be summarized as follows: There is considerable growth in the use of vegetable oils such as palm, rape seed, soybean, sunflower etc. as an alternative to petroleum based diesels. Currently there are two options for this; Straight Vegetable Oil (SVO) and Biodiesel. In either case the untreated or “crude” oil has to be refined prior to use, in a series of stages; Degumming, Neutralizing and Bleaching. The resultant SVO can be used in diesel engines but it must first be heated to around 150˚F (65˚C) to reduce the viscosity. Separate fuel tanks and/or pre-heating systems are used to achieve this. Biodiesel offers the advantage that it can be used as a direct replacement for ordinary diesel without requiring preheating. It is produced by subjecting SVO to a further refining process called Transesterification. The properties of biodiesel are covered by legislation such as American ASTM standards and European Standard EN14214. CHEMICALS The Process Refining of Vegetable Oils for Biofuels untreated oil heat to 120 - 160˚F (50-70˚C) In-Line Mixer acid addition, typically phosphoric or citric acid at 0.1 - 1 % acid reacts with phosphatides (gums) in the oil, making them hydratable oil may pass straight to neutralizing or bleaching without removal of gums (“acid conditioning”) water may be added to hydrate the phosphatides before removal in the separator water separator gums degummed oil untreated, degummed or acid conditioned oil sodium hydroxide solution (caustic soda) a washing stage may be carried out to remove residual soap water separator neutralized oil soap stock spent water degummed and/or neutralized oil water removal oil/clay suspension formed impurities are adsorbed by the clay Straight Vegetable Oil (SVO) bleaching clay filter clay and adsorbed impurities separator SVO heat premixed to form “methoxide” methanol methoxide mixed with oil and reacts to form methyl ester (“biodiesel”), glycerine and residual soaps filter aid powder (e.g. magnesium silicate) filter aid powder (e.g. kieselguhr) biodiesel caustic soda (catalyst) 1. Degumming 2. Neutralizing 3. Bleaching 4.Transesterification In-Line Mixer sodium hydroxide neutralizes excess acid and saponifies fatty acids in the oil washing stage removes residual soaps water separator glycerine filter soap stock heat to around 200˚F (95˚C)
  3. 3. CHEMICALS A Silverson High Shear Mixer can overcome these problems and dramatically improve the process This is achieved by the 3 stage mixing/shearing action of the rotor/stator workhead as follows: The Solution The reagent additions were typically carried out using low shear static mixers or inline agitators in a high volume, continuous operation. The transesterification process is more varied in volume and the methanol premix may be prepared in a separate vessel prior to addition to the oil in a “reactor vessel.” Again, conventional agitators were often used. These processes are subject to a number of problems: • The acid and sodium hydroxide solutions make up only a small fraction of the total product, and must be reduced to the smallest possible droplet size to ensure intimate contact with the oil. Low shear devices with a relatively short dwell time cannot easily achieve this. • Where an emulsion is formed it must be easy to break during separation. • Conventional agitation cannot rapidly produce the agglomerate-free, homogeneous suspension required for the clays and filter aid powders. • Poor dispersion of reagents reduces process efficiency, leading to increased chemical consumption and waste. The Problem Further reduction in particle size follows as the mixture is forced out through the stator, increasing the surface area of reagent exposed to the oil. This accelerates the reaction, and maximizes the yield. Centrifugal force drives the materials to the periphery of the workhead where they are reduced to a fine droplet/ particle size in the gap between the rotor blades and the inner wall of the stator. The reagent is introduced to the oil just prior to the intake of the Silverson mixer. The ingredients are drawn into the rotor/stator workhead and vigorously mixed.
  4. 4. Silverson Machines,Inc. 355 Chestnut Street, East Longmeadow, MA 01028 Ph: (413) 525-4825 • Fax:(413) 525-5804 • Information contained in this report is believed to be correct and is included as a guide only. No warranty is expressed or implied as to fitness for use or freedom from patents. Silverson Machines reserve the right to change product specification without notice. Issue No. 63CA1 • Improved dispersion of reagents into the oil maximizes the surface area exposed to the oil, accelerating the reaction • Reduced chemical and energy consumption and less environmental impact • Rapid processing times • Easily interchangeable workheads and screens allow the Silverson mixer to be adapted to optimize performance for processing a range of oils, including those with a tendency to emulsify Silverson offers a range of machines suitable for the acid and sodium hydroxide additions, and the Silverson Flashblend for the clay and filter aid dispersions: The Advantages High Shear In-Line Mixers • Aeration free • Easily retro-fitted to existing plant • Ideal for continuous processes • Explosionproof units available. • Multistage units available offering greater degree of shear, resulting in finer particle size and faster processing times. Silverson Flashblend • Designed for high speed dispersion of powders into liquids • Minimized cleaning requirements • Minimum operator input required • Easily automated • Silverson should be consulted regarding systems involving flammable solvents Centrifugal Pump Venturi Assembly In-Line Mixer Powder Feed Hopper Liquid in Product out Reagent/water fed into line just prior to intake of In-Line mixer. untreated oil in Clay/filter aid powder feed hopper Feedstock oil in reagent/oil blend passes to next processing stage