5 FA distribution Flashcards
(42 cards)
what is hydrogenation and what are its applications?
addition of H2 in the presence of a catalyst to reduce level of unsaturation or convert cis/trans bonds; can make more plastic fats from oils
what is an IV?
iodine value; GRAMS of iodine absorbed by 100 g of fat.
degree of UNsaturation and IV have an direct or indirect relationship? therefore, a fat with a higher degree of unsaturation would have a (higher/lower) IV?
direct; higher
what ratio does I2 react with an unsaturated fat?
1:1 per double bond
what is selectivity?
the preference for hydrogenation to occur to more more highly unsaturated FAs
what are the factors that influence hydrogenation reaction rate?
- degree of unsaturation
- nature and concentration of catalyst
- rxn presure [H]
- temp
- degree of agitation
what are the steps of hydrogenation
1) transfer/diffusion
2) adsorption
3) hydrogenation/isomerization
4) desorption
5) transfer
what happens during the transfer/diffusion step of hydrogenation?
CRITICAL STEPS. controls degree of isomerization and selectivity
transfer: take reactants/products to and from liquid phase and surface of catalyst
diffusion: diffusion of reactant into pores/product out of pores of the catalyst
would oleic or linoleic acid be selectively preferred during hydrogenation?
linoleic
how is selectively expressed as?
Kln/Ko = rate of hydrogenation of linoleate relative to oleate
what is copper (CuO + Cr2O3) catalyst selective for?
linoleate. Kln/Ko=10
how is catalyst activity defined by the American Oil Chemist’s Society?
IV decrease per unit of time during a hydrogenation under a specific set of conditions
what are the conditions for determining catalyst activity of soybean oil?
IV: 120 to 80
temp: 350°F
pressure: 20 psig
[catalyst]: 0.05%
what is catalyst lifetime?
how long a catalyst remains active/useful
is hydrogenation stereoselective?
no, locations aren’t being altered.
what are the independent variables that influence the rate of hydrogenation?
- temp
- pressure
- agitation
- catalyst concentration
what are the dependent variables that influence hydrogenation?
- nature of FA (trans FAs)
- nature of catalyst (selectivity ratio)
- hydrogenation rate
as temp increases, the selectivity ratio:
increases
as temp increases, the trans content:
increases
as temp increases, the reaction rate:
increases
as pressure increases, the selectivity ratio:
decreases
as pressure increases, the trans content:
decreases
as pressure increases, the reaction rate:
increases
as agitation increases, the selectivity ratio:
decreases
