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Dissolved Ni Soaps - and How To Minimize Them
The document discusses the challenges of controlling residual nickel content in hydrogenation processes, focusing on dissolved and particulate nickel. It outlines strategies to minimize nickel soaps formation and improve filtration methods while highlighting the dynamic nature of nickel content based on processing conditions. Key recommendations include reducing free fatty acids (FFA), optimizing filtration temperature, and ensuring proper timing of catalyst addition relative to hydrogen presence.
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Dissolved Ni Soaps - and How To Minimize Them
- 1. Gerard B. Hawkins ManagingDirector C2PT Catalyst Process Technology
- 2. Hydrogenation Process Crushing Refining Filtration Blending/ Packaging /Delivery Nicatalyst in Ni catalyst out Oil Seeds Hydrogenation Product Post bleaching/ Deodorization
- 3. Reactor mixis filtered to remove the catalyst There is usually a maximum allowed residual nickel content in the product 2 types of residual nickel ◦ (a) Particulate nickel - small black particles ◦ (b) Dissolved nickel - soluble nickel soaps, salts, etc
- 4. Majority ofresidual Ni cases are due to this Ni tolerances have been coming down ………but Fatty Acid levels haven’t => Increasingly difficult to keep dissolved Ni soaps below detection
- 5. Equilibrium is determinedby hydrogen concentration ! Ni(fa)2 + H2 low pressure/ hydrogen shortage high pressure/ abundance of hydrogen Ni + 2 ffa
- 6. Fate of nickelcrystallites: Nickel dissolution is chemically reversible, but catalytic surface vanishes drastically thereby (loss of Nickel dispersion): + ffa - ffa + Ni-soaps fresh catalyst 100 m²/g Ni used catalyst 10-20 m²/g Ni
- 8. 0 5 10 15 20 25 0 0.1 0.20.3 0.4 0.5 0.6 1/H2 pressure (bar-1) DissolvedNi(ppm) 2 bar10 bar30 bar Ni2+ = K.(H+)2/H2 Ni + 2H+ = Ni2+ + H2 Note Ni dissolution decreases by factor 100 for every pH unit rise! (data based on fatty acid hydrogenation 180 C)
- 9. Reversible reaction More H2 reaction goes Less H2 Concentration of Ni soaps will vary with conditions and time!
- 10. Concentration ofNi soaps will vary depending on ◦ H2 concentration (pressure/mixing) ◦ Ni content ◦ FFA content ◦ Temperature These vary over the process ◦ Hence dissolved Ni content DYNAMIC
- 11. A :heat-up, catalyst in FA but no H2 Ni content in oil time Nicontent(ppm) 0 t0 t1 t2 t3 Neq Nmax Nf A B C • B : H2 present; reaction occurring • C : H2 valve closed; drop-tank & filtration
- 12. Leads tohigher residual Ni Ni content in oil time Nicontent(ppm) 0 t0 t1 t2 actual t3 actual Neq Nmax Nf IV90 IV80 IV70
- 13. “Prevention isbetter than cure” Reduce FFA even further! Try to minimize the formation of Ni soaps by making conditions for it unfavorable
- 14. Shorten contacttime in absence of H2 BEFORE reaction Ni content in oil minimizing t1 (catalyst in oil without hydrogen before reaction) time Nicontent(ppm) 0 t0 t1 new t2 t3 Nmax Nf IV90 IV80 IV70 Nf new
- 15. Make additionof catalyst last possible operation before opening H2 valve Dose to the reactor while under H2 pressure Melt catalyst only in cover fat
- 16. Shorten contacttime in absence of H2 AFTER reaction Ni content in oil (Green Line ) minimizing t1 & t3 (catalyst in oil without hydrogen before and after reaction) time Nicontent(ppm) 0 t0 t1 t2 t3 Nmax Nf IV90 IV70 Nf Nf new
- 17. Filter immediatelyafter hydrogenation is finished Increasing filter area for faster filtration Minimizing problem-causing impurities (e.g. P, wax) Optimize temperature of filtration
- 18. Reactor mixis filtered to remove the catalyst There is usually a maximum allowed residual nickel content in the product 2 types of residual nickel ◦ (a) Particulate nickel - small black particles ◦ (b) Dissolved nickel - soluble nickel soaps, salts, etc Identifying which type: ◦ Can check if it is (a) by using a filter paper check and particle analysis ◦ If no black dots on filter paper and still Ni in ICP reading it is probably dissolved nickel
- 19. Dissolved Nickelremoved with ◦ post bleaching with citric or phosphoric acid ◦ use of bleaching earth ◦ reduction in FFAs and/or water in feed oil ◦ reduction in contact time without hydrogen
- 20. Reduce FFAin oil Prevent water or soap stock getting into reactor Minimize t1 Minimize t3 Find optimum filtration temperature