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1

what is catalyst activity?

decrease in iodine number per unit of time during hydrogenation under a specific set of conditions

2

what is the iodine number?

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)

3

what is selectivity?

preferentially hydrogenating more highly unsaturated FA

4

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)

5

2 types of hydrogenation?

partial and complete

6

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

7

steps in hydrogenation of oils?

1 transfer/diffusion
2 absorption
3 hydrogenation/isomerization
4 desorption
5 transfer

8

what are transfer/diffusion and adsorption critical for?

controlling the degree of isomerization and selectivity of rxns

9

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

10

ratio to express selectivity?

K (lo) / K (o) = rate of hydrogenation of linleate relative to that of oleate

11

what determines selectivity for hydrogenation?

1. geometric configuration of the catalyst

2. chemical/physical characteristics of catalyst

12

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

13

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

14

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)

15

describe copper catalyst

-copper-chromium (CuO 50% + Cr2O3 40% + BaO 10%)

-high selectivity for linolenic acid (KLn / KLO = 10)

-almost infinite selectivity for linoleate

16

hydrogenation of FA in TG is not a function of....

their location

(whether the DB is in 1st, 2nd, or 3rd position doesn't matter)

17

what is the lifetime of a catalyst

how long a catalyst will remain active and useful

18

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

19

does olive oil of hydrogenated soybean oil have lower IV?

olive oil has lower IV b/c has more monounsaturates

20

what are factors affecting hydrogenation?

independent variables
1. pressure
2. temp
3. agitation
4. catalyst concentration

dependent
1. trans FA
2. selectivity ratio
3. hydrogenation rate

21

how does increased pressure and temp effect trans unsaturation of soybean oil?

as pressure INCREASES, trans FA DECREASES

as temp INCREASES, trans FA INCREASES

22

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

23

how does agitation, pressure, temp affect selectivity ratio?

as agitation INCREASES, sr DECREASES

as pressure INCREASES, sr INCREASES

as temp INCREASES, sr INCREASES

24

how does agitation and catalyst conc affect rate of hydrogenation?

as catalyst conc increases, H rate increases

as agitation increases, H rate increases

25

another use for interesterification

production of monoglycerides used as emulsifiers

26

analytical methods for modified TG?

saponification value

iodine value

gas chromatographic analysis for FA

liquid chromatography

27

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)

28

what is saponification?

hydrolysis of ester under alkaline conditions

29

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

30

how to calculate AMW of a simple TG?

AMW = 41 + 3 x (MWFA -1)