*3.3.1. Activity of Ni/SiG and Ni-Mg/PF catalysts in partial hydrogenation of SFO*

The Ni/SiG and Ni-Mg/PF catalysts were tested for comparison, in order to determine their activity in the sunflower oil hydrogenation. The obtained results in the laboratory reactor system (**Figure 3**) are shown in **Table 11** and **Figure 12**.


a Process parameters: 160°C (temperature); 0.20 MPa (H<sup>2</sup> pressure); 1200 rpm (stirring rate).

b Ni loading in catalyst charge for hydrogenation run; Ni concentration: 0.06 wt% with respect to oil.

c Selected value of IV to compare catalyst activity corresponds to the final iodine value (IV<sup>f</sup> ) in the hydrogenation of sunflower oil over the catalyst with the lowest activity (Ni/SiG-B).

<sup>d</sup>Hydrogen consumption for decrease of iodine value from starting (131.5) to selected value.

**Sample code Rate constantsa** *k***1 (min−1)**

<sup>a</sup>Refers to the first order kinetic rate constants.

constants (T = 160°C).

*k***2 (min−1)**

164 New Advances in Hydrogenation Processes - Fundamentals and Applications

*k***3 (min−1)** *k***4 (min−1)**

**Figure 11.** Hydrogenation of SBO: (a) reaction scheme; (b–d) correlation between experimental data and model predictions for SBO hydrogenation over Ni-Mg/D and Ni-Mg-Ag/D catalytic systems under operating conditions used.

Ni-Mg/D 1.0 <sup>×</sup> 10−2 3.0 <sup>×</sup> 10−4 1.0 <sup>×</sup> 10−2 3.5 <sup>×</sup> 10−4 1.5 <sup>×</sup> 10−3 2.5 <sup>×</sup> 10−3 1.5 <sup>×</sup> 10−2 1.5 <sup>×</sup> 10−2 Ni-Mg-Ag0.16/D 0.9 <sup>×</sup> 10−2 5.6 <sup>×</sup> 10−4 6.0 <sup>×</sup> 10−3 6.0 <sup>×</sup> 10−5 6.0 <sup>×</sup> 10−4 2.0 <sup>×</sup> 10−3 9.0 <sup>×</sup> 10−3 1.0 <sup>×</sup> 10−2 Ni-Mg-Ag1.55/D 0.2 <sup>×</sup> 10−2 3.0 <sup>×</sup> 10−4 0.7 <sup>×</sup> 10−3 2.5 <sup>×</sup> 10−5 0.1 <sup>×</sup> 10−4 0.9 <sup>×</sup> 10−3 3.0 <sup>×</sup> 10−3 4.0 <sup>×</sup> 10−3 Ni-Mg-Ag5.88/D 0.1 <sup>×</sup> 10−2 2.0 <sup>×</sup> 10−4 0.4 <sup>×</sup> 10−3 2.0 <sup>×</sup> 10−5 0.1 <sup>×</sup> 10−4 0.1 <sup>×</sup> 10−3 1.5 <sup>×</sup> 10−3 2.0 <sup>×</sup> 10−3

**Table 10.** Hydrogenation of soybean oil over Ni-Mg/D and Ni-Mg-Ag/D catalysts—computed values of the rate

*k***5 (min−1)** *k***6 (min−1)** *k***7 (min−1)** *k***8 (min−1)**

**Table 11.** Sunflower oil hydrogenation over Ni/SiG and Ni-Mg/PF catalysts in laboratory reactor system—catalytic activity test runs results.

A comparative study of SFO hydrogenation over Ni/SiG catalyst samples was performed at the same level of conversion (17.3%) in order to obtain more accurate comparative results. Activity was calculated according to Eq. (1) as hydrogenation overall activity, referred to the hydrogen consumption for a target IV value of 108.7. Analyzing the activity presented in **Table 11**, a significant variation of the values obtained for the different catalysts can be observed. As all catalysts are expected to present the same kind of active sites (metallic nickel), an explanation for this behavior should be sought in different structural and textural properties of the studied catalysts. Considering the structure of the Ni/SiG-A, Ni/SiG-B and Ni/SiG-C samples and dispersion of the nickel metal, no clear correlation of the experimental data was found. It is likely that nonuniform distribution of nickel is the main reason for this behavior of the studied catalysts. To verify this assumption, it is necessary to establish a functional relationship between the concentration of the available nickel surface area in the reaction mixture and the initial global hydrogenation rate [110]. Analyzing the results of NP measurements for the Ni/SiG system (**Table 4**), it appears that the activity of the samples is associated with their mesoporosity. The hydrogenation overall activity Ni/SiG-B < Ni/SiG-C < Ni/SiG-A follows the same order as surface area in the mesopore range (available for the hydrogenation, see **Tables 4** and **11**).

**Figure 12.** Time course (a) and IV decay (b) profiles of reactants and products during the hydrogenation of SFO over the Ni-Mg/PF-1 catalyst.

Regarding the performance of the Ni-Mg catalyst supported on perlite (Ni-Mg/PF-1), the hydrogenation activity was found to be very high. In addition, the Ni-Mg/PF-1 catalyst demonstrated a high activity in SFO deep hydrogenation (decrease in IV of 82.8, **Figure 12**) [31].

In **Figure 12a**, linoleic acid (C18:2*c*) was almost depleted within 30 min of reaction. This may be attributed to complex reactions evolving concomitantly. Such reactions may include hydrogenation of C18:2*c* to C18:1*t*; isomerization of C18:2*c* to C18:2*t* then hydrogenation to C18:1*t* as well as isomerization of C18:12*c* to C18:1*t*. The level of oleic acid initially increased, then leveled off; while the stearic acid rapidly increased. The monoenic *trans* fatty acid content (C18:1*t*) monotonically increased up to 33.8% after 30 min of reaction and continued to decrease slowly reaching a final level of 32.3%. Dienic *trans* fatty acid profiles (C18:12*t*) exhibited a different behavior characterized by an increase up to 4% followed by a decrease due to their conversion to stearic acid and possibly also to *trans* monoenic acid (C18:1*t*). From the standpoint of health and technical functional properties, taking into account unsatisfactory product distribution (34.3% TFAs and 37.6% stearic acid), it is necessary to optimize the properties of this catalyst with the aim of finding a good compromise between the activity and capacity to produce undesirable TFAs and stearic acid.

#### *3.3.2. Kinetic study of SFO hydrogenation over Ni/SiG catalysts*

for this behavior should be sought in different structural and textural properties of the studied catalysts. Considering the structure of the Ni/SiG-A, Ni/SiG-B and Ni/SiG-C samples and dispersion of the nickel metal, no clear correlation of the experimental data was found. It is likely that nonuniform distribution of nickel is the main reason for this behavior of the studied catalysts. To verify this assumption, it is necessary to establish a functional relationship between the concentration of the available nickel surface area in the reaction mixture and the initial global hydrogenation rate [110]. Analyzing the results of NP measurements for the Ni/SiG system (**Table 4**), it appears that the activity of the samples is associated with their mesoporosity. The hydrogenation overall activity Ni/SiG-B < Ni/SiG-C < Ni/SiG-A follows the same order as sur-

166 New Advances in Hydrogenation Processes - Fundamentals and Applications

face area in the mesopore range (available for the hydrogenation, see **Tables 4** and **11**).

Regarding the performance of the Ni-Mg catalyst supported on perlite (Ni-Mg/PF-1), the hydrogenation activity was found to be very high. In addition, the Ni-Mg/PF-1 catalyst demonstrated a high activity in SFO deep hydrogenation (decrease in IV of 82.8, **Figure 12**) [31]. In **Figure 12a**, linoleic acid (C18:2*c*) was almost depleted within 30 min of reaction. This may be attributed to complex reactions evolving concomitantly. Such reactions may include hydrogenation of C18:2*c* to C18:1*t*; isomerization of C18:2*c* to C18:2*t* then hydrogenation to C18:1*t* as well as isomerization of C18:12*c* to C18:1*t*. The level of oleic acid initially increased, then leveled off; while the stearic acid rapidly increased. The monoenic *trans* fatty acid content (C18:1*t*) monotonically increased up to 33.8% after 30 min of reaction and continued to decrease slowly reaching a final level of 32.3%. Dienic *trans* fatty acid profiles (C18:12*t*) exhibited a different behavior characterized by an increase up to 4% followed by a decrease due to their conversion to stearic acid and possibly also to *trans* monoenic acid (C18:1*t*). From the standpoint of health and technical functional properties, taking into account unsatisfactory product distribution (34.3% TFAs and 37.6% stearic acid), it is necessary to optimize the properties of this catalyst with the aim of finding a good compromise between the activity

**Figure 12.** Time course (a) and IV decay (b) profiles of reactants and products during the hydrogenation of SFO over the

and capacity to produce undesirable TFAs and stearic acid.

Ni-Mg/PF-1 catalyst.

A lumped kinetic model was developed to describe the evolution of the products during the SFO hydrogenation over the Ni/SiG system. This model considers the saturation of double bonds along the fatty acid chains and *cis*/*trans* isomerization, which take place simultaneously with the hydrogenation of fatty acids. The assumed reaction pathway is described in **Figure 13a**. The reaction pathway contains 12 reactions that include all possible reactions. The reaction scheme does not exclude reverse isomerization reactions (*trans* to *cis*), nor does it exclude hydrogenation with isomerization (C18:2*t* to C18:1*c*), but their low probability is emphasized with dashed arrows (see **Figure 13a**). Due to the fact that there are 12 reactions we considered all 12 reaction rate constants. For calculation of kinetic parameters, the same method as for the hydrogenation of SBO was used. Lines in **Figure 13b**–**d** depict the predicted data of fatty acid composition for the catalysts with the highest (Ni/SiG-A) and the lowest (Ni/SiG-B) activity. **Table 12** shows the best fitting kinetic constant values for all three catalysts.

**Figure 13.** Hydrogenation of SFO: (a) reaction pathway; (b–d) correlation between experimental data and model predictions for SFO hydrogenation over Ni/SiG catalysts under the experimental conditions used.

The results in **Table 12** indicate that the values of the rate constants show a significant difference, regardless of the catalyst activity and hence the contribution of the individual reactions in the reaction mechanism can be recognized.


**Table 12.** Kinetic constant values for Ni/SiG catalysts at 160°C and 0.2 MPa.

In order to simplify the reaction pathway shown in **Figure 13a**, without compromising the accuracy of predicting the concentration of fatty acid change as criteria of importance for some rate constants, we used a value of 1% of the highest rate constant for the particular catalyst (1% *k*max). Rate constants higher than 1% *k*max were declared as significant and marked bold in **Table 12**. On the contrary, rate constants less than 1% *k*max are associated as insignificant. It was shown that the number of significant rate constants increases as the activity of the catalysts grows higher. Significant constants, higher than 1% *k*max, show that Ni/SiG-A has 8, Ni/SiG-C has 7, while the least active catalyst, Ni/SiG-B, has the lowest value 5. Using the criteria of 1% *k*max, we can rewrite a reaction pathway (**Figure 13a**), which will include only significant rate constants for each individual catalyst and are given in **Figure 14**.

Using the reduced reaction pathways, reaction rates were rewritten, using only significant rate constants and the process of hydrogenation was simulated with only those reaction rates. Values of rate constants then obtained were the same as the ones obtained by the initial reaction mechanism, which indicates that the reduction of the initial reaction pathway changes as a function of catalyst activity.
