Partial Hydrogenation of Vegetable Oil using Membrane

Reactor Technology

Devinder Singh, Brent Dringenberg, Dr. Peter Pfromm, Dr. Mary Rezac

Department of Chemical EngineeringKansas State University

Manhattan, Kansas

Trans-Fatty Acids

• "..there is a direct, proven relationship between diets high in trans fat content and LDL (“bad”) cholesterol levels and, therefore, an increased risk of coronary heart disease..." from FDA web site 10-3-2005, FDA fact sheet dated July 9, 2003

• By January, 2006 trans fat content will be shown on the Nutrition Facts Panel.Note: <0.5 g trans fat/14 g serving = label "zero"

• ChE Freshmen class (9-2005): the vast majority knew trans fats were "bad" for you.

• Switch to butter?

USDA/CFSANhttp://www.cfsan.fda.gov/~dms/transfat.html10-4-05

Trans-Fatty Acids

Origin of trans-fatty acids

• Except for some animal fats (beef, mutton), natural oils/fats are cis.

• Trans-fatty acids: by partial hydrogenation (in the rumen: vaccenic acid; or in technical hydrogenation of plant oils: elaidic acid; C18:1 9t )

• Why technical partial hydrogenation: optimize physical parameters (melting point), improve stability, reduce peroxidation

cis (C18:1 9c) trans (C18:1 9t)

oleic acid MP 16C elaidic acid MP 52Cstearic acid MP 70C

(C18:0)

Strategies to avoid/minimize trans-fatty acid intake

• Use trans fatty acid free fats and oils• Avoid partial hydrogenation by

changing the composition (Example: "Crisco® 0 trans fat": sunflower andsoybean oil+waxy fully hydrogenated cotton seed oil)

• Minimize/avoid formation of trans fatty acids during hydrogenation

Standard hydrogenation process• 1809 Sir Humphrey Davy coins the term "hydrogenation"

W. Normann, 1902: liquid/solid/gas for fat hardening• Generally batch, 5-20 tons of oil. Parameters: pressure, temperature,

agitation, catalyst, catalyst/oil ratio. 15 MM tons/year world wide.

H2

steam120-190C1-6 atm

catalyst: Ni0.05-0.1 wt% Ni on oilsupported catalyst

"selective" conditions:hydrogenate most highlyunsaturated fatty acids first (160-205C, low H2 pressure,

more catalyst, less agitation): ~50% more transhttp://www.thesoydailyclub.com/SFC/MSPproducts501.asp

Soyfoods Center, from unpublished manuscript by Shurtleff, W., Aoyagi, A.,

Alleviating mass transfer limitations of hydrogenation

Conventional Here: Membrane based

H2(dissolved)

solubility islow in oils

boundary layer

H2 suppliedby diffusion

Membrane

ΔP ΔpH2

H2 flux can be adjustedself-controlled H2 transport

boundary layers can be controlledshear can be introduced at the membrane

Oil

H2

Defect-free integral-asymmetricpolymeric membrane withmetal sputtered surface

Catalyst

H2 starvedcatalyst

hydrogenporous substructure(polymeric)

integral skin 100-500 nm

Pt Layer

metal layerdefects

Oil

Pt layer

"skin"(defect-freepolymer layer)

H-H H-HH-H

H+ H+ H+ H+

200-300µm

(10-20 nm)

H HH HH-H

100µm

Approach: supply hydrogenwhere catalysis takes place

Baker, R. W., Louie, J., Pfromm, P. H., Wijmans, J. G., "Ultrathin Metal Composite Membranes for Gas Separation", U.S. Patent 4,857,080,

Gas Flux (GPU), RT[10-6 cm3 (STP)cm-2

s-1 (cm Hg)-1 ]

Selectivity (H2/N2)

Before Pt Coating

Hydrogen 11.7 66

Nitrogen 0.18

After Pt Coating, before hydrogenation

Hydrogen 8 46

Nitrogen 0.18

After hydrogenation and washing in hexane

Hydrogen 0.5 12

Nitrogen 0.04

Peinemann et. al., 1987

Hydrogen 68 49

Nitrogen 1.4

Integral-Asymmetric Polyetherimide membrane: QA/QC[casting after US Patent: 4,673,418, Peinemann et. al., 1987]

basemembraneOK(fluxcould be optimized)

Integral-asymmetric membranes: bridging the gap from nanomaterials to

the macroscopic world

• The selective polymer layer:– 100-500 nanometers

thick– absolutely defect-free– made on a scale of– square centimeters

to square meters

• The porous support:– enables usefulness of the

nanomaterial

100µm

If membrane-based hydrogenation shows benefits, can it be done on a

technical scale? When?

• H2 pressure will be low while maintaining high H2 availability: existing H2 equipment is perhaps OK.

• Sputtering of technical membranes is relatively simple (flat sheet, hollow fiber)

• Technical scale gas permeation membranes are available (Air Liquide/Medal and others)

Iodine value, IV• Measure of the degree of unsaturation of a fat (one

I2/DB, "g Iodine reacting with double bonds/100 g of fat")

• High IV: less stable to oxidative attack

• Soybean Oil IV130, margerine stock soybean oil IV65 (40%TFA), shortening stock IV80 (32%TFA)

• If the fat composition is resolved chromatographically, IV can be calculated

FAME,potassium salt ofglycerol , water

centrifuge

potassium salt of glycerol, water

0.2 g Oil

add 2 ml hexane

add 0.1 mL methanolic KOH

K+MeO-

shake

(30 sec.)

GC w/FIDCP Sill88, 100m x0.25 mm)

170C

FAME, hexane

add 2 drops FAME/hexaneto 2 ml hexane

Inject 1µl

Analytical: preparation of Fatty Acid Methyl Ester (FAME) AOCS method Ce 2-66

50 min

3

4

5

6

30 35 40 45Time [min]

FID Response [pA]

MeE

MeE

MeE

MeE

MeE

MeE MeE MeE

MeE

Gas Chromatogram of Unhydrogenated Soybean Oil (Iodine Value = 126)(oil supplied by MP Biomedicals, LLC, Irvine, CA; analysis FAME, AOCS method Ce 2-66

C18:0

C18:1 9c

C18:1 11cC18:2 t

C18:2 9c12c

C20:0C18:3t

C20:1

C18:3 9c12c15c

Methyl stearate

Methyl Oleate

Methyl linoleate

Methyl linoleneate

DataAcquisition

Nitrogen

Hydrogen

P

T

C

P

P TC

Oil

Oil

Oil, 70 °C

Parr reactor(160 ml)

1/8” SS

1/8” SS

1/4” SS

1/8” SS1/8” SS

Membrane Reactor(Membrane area

12.6 cm2)

60-62 psig

50-52 psig

Reactor system

~13 ml/min

0

10

20

30

40

50

60

80 90 100 110 120 130 140

220°C, 2.5 atm H2, 0.18 wt % Ni **

0 hrs8 hrs

16 hrs

64 hrs

108 hrs

125 hrs

Trans FattyAcid [wt%]

**Karabulut, I. Kayahan, M.Yaprak, S. , Determination of changes in some physical and chemical properties of soybean oil during hydrogenation , Food Chemistry, 81, 453, 2003.

Iodine Value IV [g iodine/100 g oil]]

Membrane-facilitated hydrogenation

Membrane Reactor70°C, pH2=3.4 atmPt/polyimide membrane

3

4

5

6

30 35 40 45

C18:3 t

C18:2 tC18:1 t

C18:3 9c12c15c

C20:1C20:0

C18:1 11c

C18:1 12c

C18:1 9c C18:2 9c12c

FID Response [pA]

C18:0

Non-hydrogenated vs. Partially Hydrogenated Soybean Oil

Time [min]

0

10

20

30

40

50

60

80 90 100 110 120 130

Iodine Value, g Iodine/ 100 g Oil

Trans Fatty Acid, wt. %

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0 20 40 60 80 100 120 140

Max. H2 supplied by membrane (virgin characteristics before hydrog.experiment)

H2 consumed(from experiment)

Max. H2 supplied by membrane (characteristics after hydrog.experiment)

process upset(power outage)

Compare H2 consumed vs. supply through the membrane

Time [h]

molH2

Conclusions• Hydrogenation was observed with platinum-

coated integral-asymmetric gas permeation membranes

• The membranes appeared physically stable over 120 hours

• Formation of trans fatty acids was observed, but perhaps can be further reduced

Acknowledgements

• United States Department of Agriculture

From GC we obtain the relative amount of Fatty Acid in the mixture of their methyl esters. For free fatty acids the factors for IV can be calculated as

IVfree= (Mol. Wt. of Iodine/Mol. Wt. of Fatty acid)*nwhere n=no. unsaturated bonds

In oil we have to take into account the extra molecular weight due to glycerol and we find

IVoil=(Mol Wt. of Iodine/Mol. Wt. of Fatty Acid+12.68 )*nwhere 12.68 takes into account the additional molecular weight.

So for example for C18:1 = (253.8/(282.47+12.68))= 0.8598 (see above)

IV = 0.8598*(weight % C18:1)+1.7315*(weight % C18:2)+2.6152*(weight % C18:3) +0.8173*(weight % C20:1)

Note: weight% is relative to combined detected analytes

Discussion

Iodine Value (IV) calculation based on gas chromatographic resolution of oil