FAT & OIL SPLITTING

Process Principles

Fat Splitting is fundamental to efficient manufacturing of all downstream Oleo-Chemicals, fatty acids, fatty alcohols and soaps.

Oil enters from the bottom of the splitter and reacts with a countercurrent water stream input from the top. The reaction is endothermic, HP Steam is input at multiple points along the splitter to provide the required energy.

1. DOS.

The extent of reaction completion is defined as ‘Degree Of Split’ (DOS = AV/SV, ie Acid Value/Saponification Value, simply described as the % of split fatty acid in the Oil). The reaction mechanism is first water dissolves in fat and then reacts sequentially to split the fat, from tri to di-glyceride, di to mono-glyceride and finally from mono-glyceride to fatty acid. Therefore, at any given time, there is always partially reacted mono and di-glyceride present, which recombines with fatty acid to revert to tri-glyceride at distillation temperatures, reducing yields.

Reaction: C3H5(OOCR)3 + 3HOH = C3H5(OH)3 + 3HOOCR  (R is the fatty acid chain)

Triglyceride  +  Water =  Glycerine   + Fatty Acid (CFA or Crude Fatty Acid)

Targeted DOS should be in excess of 98.5%. A poor DOS has a multiplier effect in reducing distillation yield.

Splitting Temperatures range from 230 to 265°C, required for solubalisation of water in fat. Higher the water solubility, faster the reaction, with diminishing returns. Short chain fats require lower splitting temperature as they solubalise more water.

2. Plant Capacity: DOS achieved depends on the feed and through-put.

A higher molecular weight feed requires a longer residence time and therefore a larger splitting volume. By contrast a partially split feed, like PFAD, would require a much smaller residence time or splitter.

3. Yields / Effective DOS.

In actual practice, distillation yields reduce due to factors such as reaction reversal, polymerisation of unsaturated fatty acids, etc. The simulator provides an accurate estimate of the Distilled Fatty Acid (DFA) yield, accounting for these factors. The guiding parameter used is ‘Effective DOS’.

4. Water Usage:

In addition to water of reaction, water removes product glycerine, preventing reverse reaction, however any excess will eat into the splitting reaction time and increase energy consumption. The optimum water flow depends on, the Glycerine content of the input Oil, solubility of water in oil, and presence of impurities.

5. Crude Fatty Acid (CFA) Exit Temperature From Splitter:

Higher the temperature, higher the HP Steam consumption. Higher temperatures also increase the water dissolved in the CFA exiting, increasing the risk of Glycerine being carried out with CFA, which inevitably recombines with Fatty acid to reduce distillate yield.

6. HP Steam input guidance:

For best DOS, optimum distribution of HP Steam between Bottom, Middle and Top steam is critical. The addition logic as follows:

  • Bottom Steam: To bring input oil to splitter temperature, provide heat of reaction, and water solubalisation / minus heat from outgoing sweet water.
  • Middle Steam: Provide heat of reaction, maintain temperature.
  • Top Steam: To bring water to splitter temperature, netted against heat from outgoing CFA and heat of water de-solubalisation.

Simulator: Design Basis & Scope

The simulator designs and evaluates, both direct hp steam injection uni-towers as well as medium pressure splitting columns, with indirect Limpet Coil Heating.

The program evaluates, all oils, refined and crude, from C6:18 Laurics to C18:22 mustard, including PFAD and Distillation residues for all operating conditions.

Output:

  • PFD’S (Process Flow Diagrams) for splitting and distillation.
  • A complete material balance upto distilled products.
  • Equipment and line wise temperature profiles.
  • Moisture and Glycerine content of process streams.
  • Distillation Process Flow Diagrams in various configurations, 2 column, single column, re-boiler or candles.
  • DOS as measured in the plant and seen by the operator.
  • Distillation Yields / Effective DOS.
  • HP Steam and TF (Thermic Fluid) consumption / LP Steam Generation / Heat Exchanger duties in splitting and distillation.

Calculation Methodology:

  1. Input the Splitter Volume, Operating Temperature and Feed Thru-put and Specifications (AV, SV, UNSAP, MIV). In-built formulas, calculate Molecular Wt of Fatty Acid, % Fatty Acids, and % Glycerine.
  2. A reaction curve that plots DOS Vs Residence time is inbuilt in the program, developed through plant data, and batch autoclave data of Struzenegger & Strum for the initial reaction, up to 80% DOS.
  3. Reaction starting point feed AV/SV is placed on the curve. Reaction time in the splitter is added and a first cut DOS obtained from the reaction curve. Inbuilt Density Vs Temperature equations for oil and water, accurately determine volumetric flow.
  4. The reaction rate or DOS is adjusted for;
    • Splitter Temperature and Feed Molecular wt. These affect solubalisation of water in oil. Equations are input which relate rate of reaction to solubalisation. Solubility curves developed by Mills and McLain are used.
    • Reverse reaction due to Glycerine carry over in CFA.
    • Heat damaged feeds such as PFAD and Residues.
  5. ‘Effective DOS’ is calculated, factoring for Mono and Di Glycerides in CFA, and polymerisation of unsaturated fatty acids.
  6. Effective DOS and an ‘input AV of residue’ are used to calculate the yield of distilled products, and complete the material balance.

Example Simulations:

1. A 2 tph splitter operating at 6.6 tph. to illustrate the capacity available when processing a high AV -70:30 PFAD:CPS feed.

  • Operating at over 3 times design capacity, results in a relatively poor DOS of 97.42%. This is improved to a DOS of 98.09% by partly recycling the distillation residue. 3% of the total 6.52% residue generated is recycled.
  • CFA exit temperature is high at 175°С, resulting in a high HP Steam (10% Wetness) consumption of 182 Kg/T Feed or 205 Kg/T DFA. To improve overall steam efficiency. A Sweet Water preconcentrator utilizing flash vessel steam would be very effective.

Click to view Splitting 6.6 tph, cps.pfad feed (150 tons per day)

Splitting 6.6 tph, cps.pfad feed (150 tons per day)

Click to view 6.6 tph Single Column Distillation

6.6 tph Single Column Distillation

2. A 32 tph splitter, CPKO feed. (750 tons/day).

  • Probably the largest splitter in the world.
  • Designed for 98.5% at 32 tph, presently operating at 28 tph – 99% DOS
  • HPS consumption 110 KG / T FEED
  • HP Steam, design 113 Kg / T Feed 124 Kg / T DFA C8:18 wetness-10%

Click to view splittin 32 tph, pko feed (750 tons per day)

splittin 32 tph, pko feed (750 tons per day)

Click to view 32tph Two Column Distillation

32tph Two Column Distillation

Summary SPKO to C8:10 – column 1, C12:18 column 2

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16 thoughts on “FAT & OIL SPLITTING

  1. what is the reaction kinetics followed while calculating fatty acid generated during splitting??
    along with units… thank you!!

      • I am trying to model the process to design a control system but stuck with kinetics. Please provide the rate expression if possible with units. Thank You.

  2. Unfortunately, Nikhil, very little data is available. The paper referenced in the calculation methodology had limited value as it is only for batch reactions. The kinetics follows an exponential function, which had to be back fitted after observing innumerable splitting operations at different residence times and temperatures. Solubility of oil is the other driver, short chains are more soluble and split easier. For designing a control system, temperature, residence time, water input are the variables available. From a practical stand point, the objective is to maximise DOS. Once conditions are optimised, for a thruput, if operation constraints permit, thruput can be reduced.

    • Thank You for your expert comments. I managed to model the reaction but stuck with energy balance. I am not able to figure out heat of reaction. If possible please provide. Thank You

  3. Sir would you pls guide in fractionation what is Kcal /MT of feed CFA
    As per my calculation
    for Splilt crude refined palm steraine thermic fluid heat load required 190000Kcal/MT of feed

    can you pls expertise your value for various feed
    1) PKO
    2) RPS
    3) Mustard oil

    • Dear Mangesh,

      sorry for the delay. the main parameter which determines steam consumption is cfa exit T of the splitter. for an exit around 140C, PKO 70000 kcal/tfeed, rps 85000, and mustard 100,000. many plants however do consume 190000 if exit T is high, or if excess water is used.

      Rustom

      • Dear sir, i want to know that for which purpose level transmitter mount in bottom side of splitter. In bottom of splitter, level transmitter used for water level measurement or glycerol water? . We used capacitance type level transmitter for this. Float type lt not gives accurate measurement . Plz sir give any detail about which type n make of level trans. you used…

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