New single-step process for production of biogasoline, green diesel and biojet range fuels from palm kernel oil
Researchers at Universidade Federal de Minas Gerais in Brazil have produced biohydrocarbons in the distillation ranges of gasoline, diesel and aviation kerosene from palm kernel oil and palm olein using beta zeolite (HBeta) under relatively mild process conditions.
Deoxygenation, cracking and isomerization over HBeta were conducted in single step, without noble metals. Deoxygenation reactions occurred at 350 °C under 10 bar H2 atmosphere to furnish as much as 96% conversion to liquid hydrocarbons. A report on their work is published in the journal Fuel.
Sousa et al.
Broadly, drop-in biohydrocarbon fuels—e.g., hydrocarbons in the range of gasoline, aviation kerosene and diesel—can be synthesized by the reduction of fatty materials at high temperatures under hydrogen pressure using special catalysts.
Heterogeneous acid catalysts can be used for isomerization and cracking reactions. Zeolites exhibit great catalytic activity, but in most studies in the literature, they are used as supports for noble metals such as Pt and Pd in bifunctional catalysts with high costs.
Aiming to reduce the costs of biohydrocarbons, which must be competitive with fossil fuels, there is a demand for studies of the deoxygenation of fatty compounds using non-doped zeolites, and the dearth of studies in the literature justifies new research. In the present paper, deoxygenation reactions of palm kernel oil (palmist) and olein oil (palm olein) were investigated. Their respective free fatty acids obtained via previous alkaline hydrolysis, were also tested using the non-doped beta zeolite as catalyst. The hydrolysis was done to evaluate the shape-selectivity of HBeta catalyst and to simulate the use of highly degraded, low-priced fatty materials. Zeolites are known as catalysts in isomerization processes because of their acidic character. Their performance was evaluated for producing linear and cyclic or branched biohydrocarbons in a single step.
Simultaneous deoxygenation, cracking and isomerization are of great industrial interest because this route would contribute to reduce costs, which would make the use of biogasoline, green diesel and aviation biokerosene feasible and meet the new demands of the highway and aeronautical sectors with great environmental benefits.—Sousa et al.
The researchers performed a special heat treat on the zeolite before testing. The team performed simultaneous deoxygenation, cracking and isomerization reactions in a reactor with 10 g of fatty material (palm kernel oil, hydrolyzed palm kernel oil, palm olein and hydrolyzed palm olein) and 1.5 g of the HBeta catalyst. Reaction times ranged from 5 h to 10 h, the temperature was 300–350 °C, the initial H2 pressure was 10 bar and stirring was at 800 rpm.
Among their findings:
Beta zeolite, without the presence of noble metals, but subjected to the special heat treatment, was efficient for catalyzing deoxygenation, cracking and isomerization reactions of palm kernel oil (palmist) and previously hydrolyzed palm olein with hydrocarbon yields of up to 80% and 96%, respectively, at a hydrogen pressure of only 10 bar.
The deoxygenation reaction showed a greater selectivity for intermediate-sized molecules, which is related mainly to the structure of beta zeolite.
Partial isomerization, simultaneous with the deoxygenation and cracking of the fatty materials, resulted in the formation of branched and aromatic products. This, the researchers noted, is a positive cost-reducing factor.
The products had low freezing temperatures (−18 and −30 °C), favoring their use as drop-in aeronautical biofuels or as a special green diesel for countries with cold weather. However, the use of these products as biokerosene requires an additional refining step for separating the fraction that meets the specifications required for this fuel.
These biohydrocarbons in the crude form presented a potential to be used in blends with the fossil kerosene without significant losses in the cold properties. The fact that the beta zeolite was not coated with metals, but still presented excellent performance for deoxygenation and isomerization under mild reaction conditions, besides its high stability, shows the viability for industrial use with economic gains.
The work also demonstrated the adequacy of palm oil, the most widely produced vegetable oil in the world, for the production of biogasoline, aeronautical biofuel and green diesel. Its transformation does not require low acidity fatty materials, unlike biodiesel or food triglycerides. This factor is very relevant because it minimizes the care that must be taken in the production of these fatty materials, and consequently, reduces cost, in addition to stimulating the use of residual oils with high acidity at a lower price to furnish large environmental gains.—Sousa et al.
Fabiana P. Sousa, Larissa Noemí Silva, Daniel B. de Rezende, Luiz Carlos A. de Oliveira, Vânya M.D. Pasa (2018) “Simultaneous deoxygenation, cracking and isomerization of palm kernel oil and palm olein over beta zeolite to produce biogasoline, green diesel and biojet-fuel,” Fuel, Volume 223, Pages 149-156 doi: 10.1016/j.fuel.2018.03.020