The transformation of unsaturated fatty acids was studied at temperature of 300°C in hydrogen or in argon atmosphere [33, 36]. The results indicate that with increasing unsaturation of the feedstock there is a decrease in deoxygenation activity of Pd/C catalyst. As mentioned before (see Sect. 6.2.2.3), deactivation of the catalyst can occur due to formation of aromatic compounds. In deoxygenation experiments with stearic and oleic acid, the initial deoxygenation rates are the same, but for oleic acid reaction there can be visible deactivation of the catalyst with time [36]. Rate of linoleic acid deoxygenation is much lower compared to stearic and oleic acids which indicate that extensive deactivation occurs from the beginning of the reaction (Fig. 6.6).

The deoxygenation of tall oil fatty acids was performed over 1 wt% Pd/C catalyst the temperature range between 300 and 360°C and with different hydrogen content in the reaction atmosphere [29]. Tall oil fatty acids are mixture of free fatty acids derived from wood biomass. The main components are linoleic and oleic acid, whose amounts are varying depending on the origin of crude tall oil used in the distillation. An increase in deoxygenation was achieved with increase of temperature, but at the same time selectivity decreased due to increase of aromatic compounds production, which could be inhibited by increase of hydrogen content in reaction atmosphere, as mentioned before (see Sect. 6.2.2.3).

The deoxygenation of fatty acid esters over Pd/C catalyst was studied in the semibatch reactor [31, 32]. For the transformation of ethyl ester over Pd/C catalyst, the yield of hydrocarbons was lower compared to that achieved with stearic acid [31]. The main product was stearic acid which is an intermediate in the reaction. A higher conversion can be achieved with increase of hydrogen content in the reaction atmosphere than under inert atmosphere [32]. Ethyl stearate transforma­tion was also successfully demonstrated in the fixed bed reactor over Pd/C catalyst [37].

The triglycerides were deoxygenated over 5 wt% Pd/C catalyst at 360°C and

1.2 MPa pressure of 5% hydrogen in argon [7]. The results indicated that a total conversion of tristearine was achieved with hydrocarbon fraction of 64 wt% of the reaction mixture. The n-heptadecane was the main product in the mixture of C17 hydrocarbons isomers.

The renewable diesel, because of its composition, has worse low temperature properties compared to conventional diesel. One of the ways to improve low temperature properties of long-chain hydrocarbons in renewable diesel is skeleton isomerization. Therefore, Pd/SAPO-31 catalyst was studied in the one-pot deox­ygenation and skeleton isomerization of sunflower oil at the temperature range of 310-360°C and 2 MPa of hydrogen [38]. Deoxygenation over Pd/SAPO-31 cat­alyst shows good selectivity to branched hydrocarbons. The ratio between bran­ched and linear hydrocarbons is the highest at temperature between 320 and 350°C. Isomerization of hydrocarbons can be increased as well by the increase of the residence time in the fixed bed reactor. Despite good isomerization properties, Pd/SAPO-31 catalyst deactivates in time on stream showing extensive decrease in selectivity toward branched hydrocarbons after 14 h with the optimal isomeriza­tion conditions (T = 340°C, WHSV = 0.9/h). It is worth to mention that with increase of temperature and residence time, the selectivity toward long (C17 and C18)-chain hydrocarbons decreases from 91 (T = 310°C, WHSV = 0.9/h) to
28 wt% (T = 360°C, WHSV = 0.9/h), which is caused by extensive cracking at higher temperatures.

The different approach for deoxygenation of triglycerides, fatty acids and their esters was shown in their transformation over a PtSnK/SiO2 catalyst [39]. The idea of the process was to obtain olefins and paraffins, which could be used as a diesel fuel or could serve as substitute for petrochemical feedstocks for specialty chemicals. To avoid side reactions of unsaturated products (aromatization, olig­omerization) and to increase selectivity toward olefins, the reactive distillation process was used. It was observed that PtSnK/SiO2 catalyst has high selectivity toward olefins, which also increased with a decrease of product residence time inside the reactor.