dissolved ni soaps - and how to minimize them
TRANSCRIPT
Gerard B. Hawkins Managing Director
C2PT Catalyst Process Technology
Hydrogenation Process
Crushing Refining
Filtration
Blending/ Packaging/Delivery
Ni catalyst in
Ni catalyst out
Oil Seeds
Hydrogenation
Product
Post bleaching/
Deodorization
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
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
Equilibrium is determined by hydrogen concentration !
Ni(fa)2 + H2
low pressure/ hydrogen shortage
high pressure/ abundance of hydrogen
Ni + 2 ffa
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
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)
Reversible reaction More H2 reaction goes Less H2
Concentration of Ni soaps will vary with conditions
and time!
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
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
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
“Prevention is better than cure” Reduce FFA even further!
Try to minimize the formation of Ni soaps by
making conditions for it unfavorable
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
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
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
Filter immediately after hydrogenation is finished Increasing filter area for faster filtration Minimizing problem-causing impurities (e.g. P,
wax) Optimize temperature of filtration
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
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
Reduce FFA in oil Prevent water or soap stock getting into reactor Minimize t1 Minimize t3 Find optimum filtration temperature