Flashcards in Lipids lecture 6 Deck (66)
what is catalyst activity?
decrease in iodine number per unit of time during hydrogenation under a specific set of conditions
what is the iodine number?
-number of grams of iodine absorbed by 100 grams of fat
-iodine number indicates degree of unsat of the FA residues of the glycerides (b/c unsat FA reacts with iodine)
what is selectivity?
preferentially hydrogenating more highly unsaturated FA
what does SR= C(18:2)/C(18:1)-12.2 mean?
Selectivity ratio to produce C18:0
means that stearic acid is produced 12.2 times faster from linoleic acid than from oleic acid (b/c catalyst has a higher affinity for highly unsat FA)
2 types of hydrogenation?
partial and complete
what are factors that affect reaction rate of hydrogenation?
1. nature of substance to be hydrogenated
2. nature and conc of catalyst
3. rxn pressure
4. rxn temp
5. degreeeo f agitation
steps in hydrogenation of oils?
what are transfer/diffusion and adsorption critical for?
controlling the degree of isomerization and selectivity of rxns
what is transfer and diffusion?(hydrogenation)
what is it important for?
transfer: transferring reactants and products to and from liquid oil phase and outside surface of the catalyst
diffusion: diffusion of reactant into and out of the pores of the catalyst
both are important for controlling the degree of isomerization and selectivity of rxns
ratio to express selectivity?
K (lo) / K (o) = rate of hydrogenation of linleate relative to that of oleate
what determines selectivity for hydrogenation?
1. geometric configuration of the catalyst
2. chemical/physical characteristics of catalyst
calculate iodine number of linoleic acid, C17H31COOH.
Molecular weight of linoleic acid = 18(12) + 32(1) + 2(16) = 280 g /mol
Molecular weight of iodine = 2(127) = 254 g/mol
Linoleic acid has 2 double bonds per molecule (from last problem).
280 grams of fat reacts with 2 x 254 g of iodine = 508 g iodine
100 grams of fat reacts with 508/280 = 181
0.01 moles of linoleic acid reacts with 5.1 g of iodine. Determine the number of double bonds present in the fatty acid.
Moles iodine = (5.1 grams)(1 mole iodine / 254 grams of iodine) = 0.020 moles I2
This implies a ratio of 0.01 mol linoleic acid : 0.020 mole I2
in hydrogenation of soybean oil, what does linolenic become?
what starts as the highest percent before hydrogenation?
linolenic --> linoleic --> oleic --> stearic
linoleic is highest percent
(refer to chart)
describe copper catalyst
-copper-chromium (CuO 50% + Cr2O3 40% + BaO 10%)
-high selectivity for linolenic acid (KLn / KLO = 10)
-almost infinite selectivity for linoleate
hydrogenation of FA in TG is not a function of....
(whether the DB is in 1st, 2nd, or 3rd position doesn't matter)
what is the lifetime of a catalyst
how long a catalyst will remain active and useful
what is AOCS
what is their method of determining catalyst activity?
american oil chemists society
catalyst activity is determined by the time required to hydrogenate soybean oil to an IV of 80 from 120 at 350 deg F, 20psig, 0.05% catalyst conc compared to time needed using AOCS standard catalyst under the same conditions
does olive oil of hydrogenated soybean oil have lower IV?
olive oil has lower IV b/c has more monounsaturates
what are factors affecting hydrogenation?
4. catalyst concentration
1. trans FA
2. selectivity ratio
3. hydrogenation rate
how does increased pressure and temp effect trans unsaturation of soybean oil?
as pressure INCREASES, trans FA DECREASES
as temp INCREASES, trans FA INCREASES
how does pressure, temp and catalyst conc effect selectivity ratio?
as pressure INCREASES, selectivity ratio DECREASES
as temp INCREASES, selectivity ratio INCREASES
as catalyst conc INCREASES, sr INCREASES
how does agitation, pressure, temp affect selectivity ratio?
as agitation INCREASES, sr DECREASES
as pressure INCREASES, sr INCREASES
as temp INCREASES, sr INCREASES
how does agitation and catalyst conc affect rate of hydrogenation?
as catalyst conc increases, H rate increases
as agitation increases, H rate increases
another use for interesterification
production of monoglycerides used as emulsifiers
analytical methods for modified TG?
gas chromatographic analysis for FA
what is the saponification value?
number of milligrams (mg) of potassium hydroxide (KOH) to saponify 1 g of the fat/oil sample.
expressed by weight, not moles (b/c the substance is not always known or pure)
what is saponification?
hydrolysis of ester under alkaline conditions
how to determine saponification value?
1. Weigh 5 g of fat in 250-mL Erlenmeyer.
2. Add 50 ml KOH (0.5 N) to Erlenmeyer.
3. Boil to saponify fat.
4. Titrate with HCl (0.5 N) using phenolphthalein.
5. Conduct blank determination.
Saponification value = 56.1 × (B – S) × normality of HCl / g of sample
B = mL of HCl required by blank to reach phenolphthalein endpoint.
S = mL of HCl required by sample to reach phenolphthalein endpoint.
Molecular weight of KOH = 56.1