Dissolved Ni Soaps - and How To Minimize Them
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Transcript of Dissolved Ni Soaps - and How To Minimize Them
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Gerard B. Hawkins Managing Director
C2PT Catalyst Process Technology
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Hydrogenation Process
Crushing Refining
Filtration
Blending/ Packaging/Delivery
Ni catalyst in
Ni catalyst out
Oil Seeds
Hydrogenation
Product
Post bleaching/
Deodorization
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Reactor mix is 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
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Majority of residual 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
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Equilibrium is determined by hydrogen concentration !
Ni(fa)2 + H2
low pressure/ hydrogen shortage
high pressure/ abundance of hydrogen
Ni + 2 ffa
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Fate of nickel crystallites: 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
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0
5
10
15
20
25
0 0.1 0.2 0.3 0.4 0.5 0.6
1/H2 pressure (bar-1)
Dis
solv
ed N
i (pp
m)
2 bar 10 bar 30 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)
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Reversible reaction More H2 reaction goes Less H2
Concentration of Ni soaps will vary with conditions
and time!
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Concentration of Ni soaps will vary depending on ◦ H2 concentration (pressure/mixing) ◦ Ni content ◦ FFA content ◦ Temperature
These vary over the process ◦ Hence dissolved Ni content DYNAMIC
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A : heat-up, catalyst in FA but no H2
Ni content in oil
time
Ni c
onte
nt (p
pm)
0 t0 t1 t2 t3
Neq
Nmax
Nf
A B C
• B : H2 present; reaction occurring
• C : H2 valve closed; drop-tank & filtration
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Leads to higher residual Ni
Ni content in oil
time
Ni c
onte
nt (p
pm)
0 t0 t1 t2 actual t3 actual
Neq
Nmax
Nf
IV90
IV80
IV70
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“Prevention is better than cure” Reduce FFA even further!
Try to minimize the formation of Ni soaps by
making conditions for it unfavorable
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Shorten contact time in absence of H2 BEFORE reaction
Ni content in oil minimizing t1 (catalyst in oil without hydrogen before reaction)
time
Ni c
onte
nt (p
pm)
0 t0 t1 new t2 t3
Nmax
Nf
IV90
IV80
IV70Nf new
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Make addition of catalyst last possible operation before opening H2 valve
Dose to the reactor while under H2 pressure
Melt catalyst only in cover fat
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Shorten contact time 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
Ni c
onte
nt (p
pm)
0 t0 t1 t2 t3
Nmax
Nf
IV90
IV70Nf
Nf new
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Filter immediately after hydrogenation is finished Increasing filter area for faster filtration Minimizing problem-causing impurities (e.g. P,
wax) Optimize temperature of filtration
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Reactor mix is 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
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Dissolved Nickel removed 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
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Reduce FFA in oil Prevent water or soap stock getting into reactor Minimize t1 Minimize t3 Find optimum filtration temperature
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