Hydrogenation of Canola Oil: Influence of Catalyst Concentration

Can. Inst. Food Sei. Teehnol. J. Vo!. 14. No. I, pp. 53-58. January 1981 pergamon Press Ltd. Printed in Canada.

Hydrogenation of Canola Oil: Influence of Catalyst Concentration Y. El-Shattoryl, L deMan 2 and J.M. deMan Department of Food Science University of Guelph Guelph, Ontario NI G 2W I

the hydrogenation of Canola oil, a study was conducted on the effect of catalyst concentration on the progress of the hydrogenation reaction and the composition and properties of the hydrogenated products. It is generally known (Coenen, 1976) that increasing catalyst concentration results in a higher rate of hydrogenation and increase in selectivity, but no published data exist for Canola oiL

Abstract Canola oil (Tower) was hydrogenated with the standard American Oil Chemists' Society catalyst and a commercial catalyst at concentrations of 0.2,0.4 and 0.6% by weight. Selective and nonselective hydrogenation conditions were used. Fatty acid composition of the hydrogenated oils was determined and selectivity ratios were calculated. Solid fat content was determined by wide-line nuclear magnetic resonance (NM R). Canola oil was hydrogenated without difficulty with 0.2% by weight of catalyst. Comparison of Tower oil with Zephyr oil demonstrated a lower content of sulfur in the Tower oil.

Materials and Methods The oil used in this study was refined and bleached oil of Brassica napus cultivar Tower. Hydrogenations were carried out in a Parr pressure reaction apparatus series 4500, using a 2 L bomb and a charge of I L of oiL Catalysts used were the standard hydrogenation catalyst of the American Oil Chemists' Society (AOCS) and a commercial nickel catalyst (catalyst D). Hydrogenation time was40 min and after each 10 min interval samples were withdrawn from the reactor for analysis. Selective hydrogenation was carried out at 200°C and a hydrogen pressure of 48 kPa (7 psig 3). N on-selective conditions used were 176° C and 303 kPa (44 psig). Iodine values were determined by the Wijs method (AOCS Cd 1-25) and refractive index was measured at 60°C with a Zeiss refractometer. Trans fatty acids were determined by the infra-red spectrophotometric method (AOCS Cd 14-61). Fatty acid composition was determined by gas-liquid chromatography of the methyl esters on a 125 cm column packed with 15% DEGS on Chromosorb RZ-60/80 mesh operated at 185°C, using a model 402 Hewlett Packard instrument with dual flame ionization detectors. Dropping point of the hydrogenated fat was determined with a Mettler FP3 automatic dropping point apparatus as described by Mertens and deMan (1972a). Solid fat content was determined by wide-line nuclear magnetic resonance (NMR) using a Newport

Resume De l'huile Canola (Tower) fut hydrogene avec le catalyseur standard AOCS et avec un catalyseur commercial, aux concentrations de 0,2, 0,4 et 0,6%, base poids. On a utilise des conditions d'hydrogenation selectives et non selectives. La composition en acides gras des huiles hydrogenees fut determinee et on a calcule les rapports de selectivite. La teneur en graisse concrete fut determinee a l'aide d'un N M R aspectre large. 11 a ete facile d'hydrogener l'huile Canola avec 0,2% (base poids) de catalyseur. En comparant l'huile Tower a l'huile Zephyr. on a observe que l'huile Tower etait plus pauvre en soufre que l'huile Zephyr.

Introduction Rapeseed has become the most important oilseed crop in Canada and the oil is used widely in the production of margarine, shortening and salad oiL The name Canola was adopted by the rapeseed industry in 1978 to identify cultivars which yield oil low in erucic acid and glucosinolates. Because of the steady improvement in Canola oil properties over the years, there are now no difficulties in processing the oil (Teasdale, 1980). In the hydrogenation of oils several variables are important in influencing composition and physical properties of the hydrogenated product. These include temperature, agitation, hydrogen pressure, catalyst type and catalyst concentration (Coenen, 1976). As part of a series of investigations on IPermanent address: Fats and Oils Lab.• National Research Centre. Dokki. Cairo. Egypt. 2Permanent address: Gay Lea Foods Co-op Ltd., Guelph. Ontario NI H 6J6.

Copyright

©

3Pounds per square inch on the gauge.

0315-5463/81/010053-06$2.00/0 1981 Canadian Institute of Food Science and Technology

53

Analyzer Mk 3 with temp. controlled magnet assembly. Samples were kept at 60°C for 30 min, then immersed in a O°C bath for 15 min, tempered in a 25°C bath for 30 min and again kept in a O°C bath for 15 min. Readings were then taken in the analyzer at 0,5, 10, 15, 20, 25 and 60° C. Percent solid fat was calculated as described by Mertens and de Man (1972b). The sulfur content of Canola oil was determined by using several methods: (a) Sosulski's method as described by Embong and Jelen (1977), (b) the method of Baltes (1967), (c) the Raney nickel method as described by Daun and Hougen (1976), and (d) a method using normal hydrogenation catalyst. The catalysts were filtered off after selective or non-selective hydrogenation. The sulfide in the catalyst was released with acid and the released hydrogen sulfide trapped in sodium hydroxide solution and measured as in method (c), and (e) the combustion method of Hoffmann (personal communication).

The overall reaction rate (r) of the hydrogenation can be described by the relation: d(lV)/dt = k' (IV)

in the region where a plot of iodine value against time yields a straight line. k' is the overall first order reaction rate constant (Albright and Wisniak, 1962). A linear relationship exists between the catalyst concentration and the rate constant for non-selective hydrogenation (Figure I). It is to be ex pected that the dropping point (D P) of the hydrogenated oils will increase as iodine values decrease. A plot of these two parameters is presented in Figure 2. Linear regression analysis yielded the following relationship: OP = -0.734 IV + 88.9

The progress of the hydrogenation of oils is characterized by a decrease in iodine value (IV). The iodine values of the hydrogenated Tower oil sampled at 10 min intervals using selective and non-selective hydrogenation conditions are presented in Table I. Since iodine value is directly related to refractive index it is advantageous to use the latter for monitoring a hydrogenation reaction. The relationship between iodine value and refractive index, N~ using the two digits following 1.45 was:

=0.774 N~ + 34.16

(r

2>

=0.9997)

1.0

"'C"

for selective hydrogenation conditions and IV = 0.902 N~ + 22.73

= 0.9402)

The relatively low correlation between these two parameters is probably due to the formation of transisomers during the course of hydrogenation. The trans-isomers are included as unsaturated fatty acids

Results and Discussion

IV

(r

10

c;; C

(r

0

= 0.9935)

0

Ql

<;;

for non-selective conditions. There was no difference in activity of the two catalysts at the 0.2% level or under selective conditions. Under non-selective conditions and at the 0.2% level catalyst D was more active than the AOCS standard catalyst. Increasing the catalyst concentration resulted in slightly increased activity under selective conditions and practically no difference in activity under nonselective conditions with the exception of the 40 min hydrogenation time.

a:

0.5

0.2

0.4

0.6

Catalyst Concn. % Fig. I.

Hydrogenation rate constant for non-selective hydrogenation of Canola oil as a function of catalyst concentration.

Table I. Iodine value of hydrogenated Tower oil (initial IV = 113.0). Hyd rogenation time (min)

10 20 30 40

Non-selective conditions 2

Selective conditions' Standard catalyst

Catalyst 0

Catalyst 0

Standard catalyst

0.2%

0.2%

0.4%

0.6%

0.2%

0.2%

0.4%

0.6%

102.4 94.8 83.6 73.3

102.0 90.2 82.3 73.1

99.2 87.5 78.5 70.9

98.6 87.2 78.8 67.4

91.0 72.0 53.1 34.3

90.4 69.1 48.2 27.0

89.3 70.9 47.2 23.4

93.0 70.1 47.1 22.6

'200°C; 48 kPa (7 psig). 2176°C; 303 kPa (44 psig).

54/ EI-Shattory, deMan and deMan

J. Inst. Can. Sci. Technol. Aliment. Vo!. 14. No. I, Janvier 1981

70,----------------------,

60,-------------------

°° 60

50

° C 50 '0 a.

40

()

'"<:

.~ 40

e

o

20

30

°° 20 '--_---'_ _-'-_ _-'--_-.J'---_----'-_ _--'--o'-'o'---......J 70 20 40 50 60 80 90 30

10

Iodine Value 0'--_----'-_ _-'--_-..l_ _--l...-_ _L-_---L_---..1

Fig. 2.

120

Relationship between dropping point and iodine value of hydrogenated Canola oil.

90

100

80

70

60

Iodine Value Fig. 3.

in the iodine value, but their higher melting point should result in an increase in the dropping point. The fatty acid composition ofthe selectively hydrogenated Tower oils is presented in Table 2 and the formation of trans-isomers is shown in Figure 3. The corresponding data for the non-selective hydrogenation conditions are presented in Table 3 and Figure 4. Under selective conditions trans-isomer content increased steadily up to the 40 min time limit. The trans-isomer levels obtained with the two catalysts at the 0.2% level were almost identical, and reached levels of over 50% at the 0.4 and 0.6% concentrations of catalyst D. These levels of trans-isomers under selective conditions were obtained in the iodine value range of about 67-73. The non-selectively hydrogenated oil reached maximum levels of trans-isomers in the 3845% range and this occurred at iodine values close to 70. After this point continuing hydrogenation resulted in progressively decreasing levels of trans-isomers, as trans-isomers were being saturated. These data indi-

110

Relationship of iodine value and lrans-isomer content of selectively hydrogenated Canola oil. S = 0.2% standard catalyst, 1 = 0.2% catalyst D, 2 =0.4% catalyst D. 3 = 0.6% catalyst D.

cate that selective hydrogenation conditions favour the formation of trans-isomers in Canola oil and this has been observed with other oils (Alien, 1978). For hydrogenation under selective conditions the selectivity ratios were determined by using the method of Alien (1978) and listed in Table 4. The selectivity ratio is defined as K2 / KJ , where K2 = I - LILo

and K}=S-So

Lo and So represent the linoleic and stearic acid contents in the original oil, and Land S the same in the hydrogenated sample. At theO.2% catalyst concentration catalyst D was more selective than the AOCS

Table 2. Fatty acid composition of hydrogenated Tower oil (selective conditions). Hydrogenation time (min)

Catalyst

Fatty acid composition (wt %) 16:0

18:0

18: 1

18:2

18:3

20:0

0.2 0.2 0.4 0.6

4.9 5.0 4.9 4.7 5.4

2.3 3.2 3.7 3.1 4.8

55.6 64.7 63.5 66.7 70.9

24.0 22.5 20.0 19.6 16.7

12.5 3.8 6.1 5.7 1.9

1.1 0.9 1.8 0.3 0.4

Standard D D D

0.2 0.2 0.4 0.6

4.7 5.0 5.4 5.4

3.7 3.6 4.3 5.7

71.8 73.2 69.9 72.3

17.2 14.8 14.0 13.8

2.2 1.8 4.2 2.4

0.4 1.6 1.8 0.3

30 30 30 30

Standard D D D

0.2 0.2 0.4 0.6

4.7 4.9 5.1 5.9

4.5 4.3 6.7 6.7

73.6 78.5 77.9 72.6

11.8 8.5 6.6 8.4

2.8 2.6 2.3 4.3

2.2 1.2 1.3 2.1

40 40 40 40

Standard D D D

0.2 0.2 0.4 0.6

4.5 4.7 4.7 5.1

10.8 11.3 12.8 16.4

75.9 78.3 69.1 68.9

5.4 3.9 6.0 5.6

2.1 1.2 1.4 1.8

1.3 0.6 2.0 2.1

Type

Concentration %

0 10 10 10 10

Standard D D D

20 20 20 20

Can. Inst. Food Se;. Technol. J. Vol. 14. No. I. January 1981

El-Shattory, deMan and deMan/55

Table 3. Fatty acid composition of hydrogenated Tower oil (non-selective conditions). Hydrogenation time (min)

Catalyst

Fatty acid composition (wt %) 16:0

18:0

18: I

18:2

18:3

20:0

0.2 0.2 0.4 0.6

4.9 4.9 4.9 4.8 5.0

2.3 3.9 3.7 4.2 5.1

55.6 72.2 68.7 71.8 71.5

24.0 15.6 17.2 16.1 14.9

12.5 2.6 4.1 2.4 2.8

1.1 0.7 1.4 0.6 0.7

Standard D D D

0.2 0.2 0.4 0.6

4.8 4.8 4.8 5.3

14.3 15.7 15.0 14.2

70.5 73.4 70.3 68.8

6.1 3.9 5.9 5.3

2.5 1.5 2.5 4.4

1.8 0.6 1.5 2.1

30 30 30 30

Standard D D D

0.2 0.2 0.4 0.6

4.9 4.8 4.9 5.3

33.5 37.6 40.3 38.4

56.2 5 1.4 50.7 51.5

1.9 2.8 2.7 3.6

1.7 1.6 0.5 0.5

1.8 1.8 0.9 0.9

40 40 40 40

Standard D D D

0.2 0.2 0.4 0.6

5.2 5.0 5.1 4.9

51.0 57.4 63.4 63.0

39.5 32.7 26.3 26.3

1.5 1.4 2.5 3.3

1.3 1.2 0.8

1.6 2.2 2.1 2.4

Type

Concentration %

10 10

Standard D D D

20 20 20 20

0 10

10

standard catalyst. Increasing catalyst concentration generally resulted in decreasing selectivity. The relationship between dropping point and transcontent of selectively hydrogenated Canola oil is pre-

50 r - - - - - - - - - - - - - - - - - - - ,

sented in Figure 5 and for non-selective conditions in Figure 6. The plot for selective conditions shows a somewhat irregular increase in dropping point as trans-level increased. Under non-selective conditions the maximum trans-content was reached at a dropping point of about 40°C. Thereafter the dropping point increased sharply at first and more slowly later as the trans-content continued to decrease.

40 60 r - - - - - - - - - - - - - - - - - - - - ,

~c

30

~

20

50 10 Non-Selective

120

100

80

40

60

20

Iodine Value

Fig. 4.

40

Relationship of iodine value and trans-isomer content of non-selectively hydrogenated Canola oil. S = 0.2% standard catalyst. I =0.2% catalyst D. 2 =0.4% catalyst D. 3 = 0.6% catalyst D.

30 Table 4. Selectivity ratios for selective hydrogenation of Canola oil. Selectivity ratio Hydrogenation time (min) 10 20 30 40

Standard catalyst 0.2% 29.2 27.6 34.3 10.7

Selective

Catalyst D 0.2% 19.9 41.7 40.0 10.4

56/ El-Shattory, deMan and de Man

0.4% 28.6 20.8 19.3 8.2

0.6% 12.2 17.6 16.3 6.7

20

30

40

50

Dropping Point 0 C

Fig. 5.

Relationship of trans-isomer content and dropping point of selectively hydrogenated Ca no la oil. J. InST. Can. Sci. Technol. Alimenr. Vo!' 14. No. I. Janvier 1981

50 r - - - - - - - - - - - - - - - - - - - ,

40

~

Table 6. Solid fat content of non-selectively hydrogenated Canola oil.

Catalyst

Standard, 0.2% Standard, 0.2% Standard,0.2% Cat. D,0.2% Cat. D, 0.2% Cat. D, 0.2% Cat. D. 0.4% Cat. D,O.4% Cat. D, 0.4% Cat. D,0.6% Cat. D,O.6% Cat. D.0.6%

30

(/)

c

~

20

10 Non-Selective

20

30

Hydrogenation Solid fat content (%) time OCC 5CC lOCC 15 c C 20 c C 25 c C (min)

40

50

60

20 30 40 20 30 40 20 30 40 20 30 40

56.3 87.9 94.0 69.1 91.9 93.8 68.0 91.2 94.4 69.7 92.0 93.9

45.1 83.5 92.1 59.9 89.2 93.1 58.0 89.2 92.7 60.2 90.1 92.7

52.6 86.5 93.8 66.2 90.6 93.3 64.6 91.1 93.5 66.5 91.3 93.1

35.0 79.2 90.9 49.2 86.0 92.9 48.0 87.0 92.2 50.0 88.0 92.2

25.8 75.4 89.8 38.8 84.1 92.6 38.0 84.9 91.6 39.8 85.6 91.7

20.3 72.8 89.3 32.0 81.5 91.9 31.1 83.2 90.7 33.3 83.0 91.4

70

Dropping Point QC

Fig. 6.

Relationship of Irans-isomer content and dropping point of non-selectively hydrogenated Canola oil.

Table 7. Sulfur content of Zephyr and Tower oils as determined by different methods. Sulfur (mgj kg) Method

Solid fat contents of the oils hydrogenated under selective and non-selective conditions are presented in Tables 5 and 6, respectively. Using 0.2% of the standard catalyst solid fat levels obtained after 40 min selective hydrogenation were greater than those obtained after 20 min non-selective hydrogenation but less than those after 30 min. With 0.2% of catalyst D the solid fat contents after 40 min selective hydrogenation were nearly equal to those obtained after 20 min of nonselective hydrogenation. The solid fat contents of the oil hydrogenated under non-selective conditions for 30 and 40 min differed only slightly. During this period trans-isomers are hydrogenated and since both transisomer and the stearic acid formed are solid in the range of solid fat measurement, no major change in solid fat content was observed. The results obtained in this study show that Canola oil of the Tower cultivar was hydrogenated without difficulty with a catalyst concentration of 0.2%, and that increasing the level of catalyst did not result in any appreciable improvement in activity. The improved hydrogenation performance of the present low glucosinolate cultivars as compared with earlier ones, such as Zephyr, is related to the lower sulfur content of the former. This is suggested by the analyses of the sulfur content of Zephyr and Tower oils (Table 7). It is Table 5. Solid fat content of selectively hydrogenated Ca no la oil.

Catalyst

Hydrogenation Solid fat content (%) time OCC 5c C 10cC 15 c C 20 c C 25°C (min)

Standard, 0.2% Standard, 0-.2% Cat. D, 0.2% Cat. D,0.2% Cat. D,0.4% Cat. D,O.4% Cat. D,0.6% Cat. D,O.6%

30 40 30 40 30 40 30 40

35.0 69.4 36.1 71.3 56.6 78.9 51.7 84.3

30.9 65.6 31.7 67.1 51.6 76.8 48.4 82.4

22.3 54.1 23.8 60.7 44.2 71.3 41.4 77.9

Can. Inst. Food Sci. Technol. J. vo!. 14, No. I, January 19H1

14.0 47.6 14.3 49.4 32.2 61.8 28.3 70.2

6.5 33.5 6.8 37.5 20.3 50.5 18.4 60.9

3.5 26.5 3.9 28.3 13.0 42.1 10.4 53.8

Sosulski Baltes Raney nickel Hydrogenation non-selective Hydrogenation selective Hoffmann

Zephyr

Tower

2.0 2.2 4.1 4.5 3.3 7.5

Trace Trace 1.0 1.3 0.9 4.1

well known that various methods of analysis yield different results. The Sosulski (Embong and Jelen, 1977) and Baltes (1967) methods yield values about half of those found with hydrogenation methods. The combustion method of Hoffmann (personal communication) yields the highest values. It is not yet clear whether all of the sulfur determined by the latter method has the ability to poison hydrogenation catalysts. This method recovers all of the sulfur in the oil, including sulfates and these mayor may not be catalyst poisons. It is evident from these results that the sulfur content of Tower oil is very low and this ex plains the ease of hydrogenation of this oil which is comparable to that of soybean oil.

Acknowledgements Financial support for this work was received from the Natural Sciences and Engineering Research Council of Canada and the Ontario Ministry of Agriculture and Food. Mr. Prem Maheshwari of this Department and Mrs. L Hoffmann of Margarinbolaget, Helsingborg, Sweden, carried out some ofthe sulfur analyses.

References Albright, L.F. and Wisniak, J. 1962. Selectivity and isomerization during partial hydrogenation of cottonseed oil and methyl oleate: effect of operating variables. J. Am. Oil Chemists' Soc. 39: 14. Alien. R. R. 1978. Principles and catalysts for hydrogenation offats and oils. J. Am. Oil Chemists' Soc. 55:792.

EI-Shattory, deMan and deMan/57

Baltes, J. 1967. Ziir Kenntnis schwefelhaltiger Fette und ihres Hartungsverhaltens. Fette-Seifen-Anstrichm. 69:512. Coenen, J.W.E. 1976. Hydrogenation of edible oils. J. Am. Oil Chemists' Soc. 53:382. Daun, J. K. and Hougen, F. W. 1976. Identification of sulfur compounds in rapeseed oil. J. Am. Oil Chemists' Soc. 54:351. Embong, M. B. and Jelen, P. 1977. Technical feasability of aqueous extraction of rapeseed oil - A laboratory study. Can. Ins!. Food Sci. Technol. J. 10:239.

58/ EI-Shattory, deMan and deMan

Mertens, W.G. and deMan. J.M. I972a. Automatic melting point determination of fats. J. Am. Oil Chemists' Soc. 49:366. Mertens, W.G. and deMan, J.M. 1972b. The influence of temperature treatment on solid-liquid ratios of fats determined by wide-line N M R. Can. Ins!. Food Sci. Technol. J. 5:77. Teasdale, B.F. 1980. Edible oil products from low-erucic acid rapeseed oil (Canola oil). Presented at Annual Meeting of the Am. Oil Chemists' Soc. New York, NY. Accepted July 18, 1980

J. Inst. Con. Sci. TechnoJ. Aliment. Vo!. 14. No. I. Janvier 1981