Towards Quantitative Conversion of Microalgae Oil to Diesel‐Range Alkanes with Bifunctional Catalysts

Abstract

Efficient conversion of biomass such as polysaccharides, [1] lignin, [2] and triglycerides [3] to biofuels has attracted considerable attention. Microalgae are being considered in that context as a promising renewable energy resource, having high triglyceride contents (up to 60 wt %) [4] and rapid growth rates that are 10-200 times faster than terrestrial oil crops such as soybean and rapeseed without directly competing with edible food/oil production. [5] Currently, three approaches are used for microalgae oil refining. The first technique involves transesterification of triglycerides and alcohol into fatty acid alkyl esters (FAAEs) and glycerol, which is applied in the first-generation biodiesel production. Such esters, however, have a relatively high oxygen content and poor flow property at low temperatures, limiting their application as high-grade fuels.[6] The second technique employs the conventional hydrotreating catalysts, for example, sulfided NiMo and CoMo, for upgrading. [7] However, these sulfide catalysts contaminate products through sulfur leaching, and deactivate because of its removal from the surface by a reverse Mars-van Krevelen mechanism.[8] The third technique relies on supported noble and base metal catalysts for decarboxylation and decarbonylation of carboxylic acids to alkanes at 300-330 8C, [9] but these catalysts showed low activities and selectivities for C 15 -C 18 alkanes when triglycerides were converted, and the performance was only somewhat improved by a Pt-Re/ZSM-5 catalyst.[10] Contributions addressing microalgae oil upgrading using sulfur-free catalysts have not been reported. Herein, we report for the first time a novel and scalable catalyst, that is, Ni supported on and in zeolite HBeta, to quantitatively convert crude microalgae oil under mild conditions (260 8C, 40 bar H 2 ) to diesel-range alkanes as high-grade secondgeneration transportation biofuels.Microalgae oil mainly consists of neutral lipids such as mono-, di-, and triglyceride. The microalgae oil (provided by Verfahrenstechnik Schwedt GmbH) used for this work consists of unsaturated C 18 fatty acids (88.4 wt %), saturated C 18 fatty acids (4.4 wt %), as well as some other C 14 , C 16 , C 20 , C 22 , and C 24 fatty acids (7.1 wt % in total; see Table S1 in the Supporting Information).Without any purification, the crude microalgae oil was directly hydrotreated in batch mode with 10 wt % Ni/HBeta (Si/Al = 180) at 260 8C and 40 bar H 2 (see Figure 1). After 8 h reaction time, we obtained 78 wt % yield of liquid alkanes (containing 60 wt % yield of C 18 octadecane), which was very close to the theoretical maximum liquid hydrocarbon yield of 84 wt %. Propane (3.6 wt %) and methane (0.6 wt %) were the main products in the vapor phase. The metal leaching after reaction was detected below the atomic absorption spectroscopy (AAS) detection limit (1 ppm). Figure 1 shows that saturated fatty acids were the primary products for microalgae oil conversion, that is, the yield of stearic acid exceeded 70 wt % within 1 h. Then, the...

Supported iron nanoparticles for the hydrodeoxygenation of microalgal oil to green diesel

“…[16] In an effort to establish a more economical sulfur-free catalyst to upgrade renewable oils, Lercher has demonstrated the hydrodeoxygenation of microalgae oil to alkanes by cascade reactions on bifunctional catalysts based on Ni and an acidic zeolite. [14,17] Following work by the same group illustrated the selectivity towards decarbonylation route by supporting Ni catalyst on ZrO2 which directed the conversion through two parallel pathways. [18] The success of Ni in the conversion of renewable feedstocks into green diesel, [14,19] stimulates the exploration of other inexpensive transition metals as catalysts for the process.…”

Multitasking mesoporous nanomaterials for biorefinery applications

“…106 Same researchers have also shown the selectivity towards decarbonylation of FFAs using Ni catalyst supported on ZrO 2 .…”

Catalytic Hydrotreatment of Fatty Acid Methyl Esters to Diesel‐like Alkanes Over Hβ Zeolite‐supported Nickel Catalysts

“…This reaction scheme is similar to that of the supported Ni catalysts referred to previously. [29,30,32,33] Interrelation and balance between metallic and acidic sites on Ni/Hb zeolite To evaluate the influence and interrelation of metallic and acidic sites on Ni/Hb zeolite, the catalytic nature of the catalysts (including different Ni mass loading and Si/Al ratios) in the hydrotreatment of FAMEs was investigated and the results summarized in Table 4.…”

“…This was consistent with previous reports. [32,42] As the acidic nature of the Hb zeolite support was important for the catalyst performance in the isomerization, the effect of Si/Al ratios with the same Ni mass loading on catalyst activity was also investigated (see Table 4). On using Hb zeolite-supported 10 wt % Ni catalysts with higher Si/Al ratios of 50 and 150 and lower acid site concentrations of 1.14 and 0.96 mmol g…”

“…However, the conversion was maximized to generate C 18 products. [32] In addition, the alkane products formed showed excellent low-temperature properties such as cloud point and cold filter plugging point if they contained a significant concentration of isomeric alkanes. High isomerization selectivity and excellent stability were obtained in the HDO of palm oil by nanosized SAPO-11 supported Ni catalysts.…”