|One-pot process for conversion of cellulose to hexane, a gasoline component. Credit: ACS, Liu et al. Click to enlarge.|
Researchers at Tohoku University in Japan have developed a one-pot process to convert cellulose to n-hexane in the presence of hydrogen gas. According to the US Environmental Protection Agency (EPA), unleaded gasoline contains about 11.6% n-hexane.
In a paper in the journal ACS Sustainable Chemistry & Engineering, the Tohuku team reports achieving a yield of n-hexane of 83% from ball-milled cellulose and 78% from microcrystalline cellulose. Even using a high weight ratio of cellulose to water (1:1), a 71% yield of n-hexane could be obtained from ball-milled cellulose.
The biphasic transformation consists of the hydrolysis of cellulose to glucose, hydrogenation of glucose to sorbitol, and successive hydrogenolysis of sorbitol to n-hexane. It involves two catalysts: iridium and rhenium oxide on silica support (Ir-ReOx/SiO2 (Re/Ir = 2) catalyst combined with HZSM-5 as co-catalyst.
Recently, our group conducted conversion of sorbitol, glucose, and cellobiose into n-hexane over the Ir-ReOx/SiO2 catalyst combined with HZSM-5. Over 90% yield of n-hexane could be obtained at ≤443 K. However, production of n-hexane from cellulose via these compounds needs the extra step of hydrolysis of cellulose. Direct conversion of cellulose into n-hexane with a heterogeneous catalyst in high yield at mild reaction conditions would be more meaningful. To the best of our knowledge, this conversion process has not yet been reported.
In this work, the binary Ir-ReOx/SiO2 and HZSM-5 catalyst system was applied to one-pot conversion of cellulose into n-hexane. High (∼80%) yield of n-hexane was obtained from ball-milled cellulose or even microcrystalline cellulose.—Liu et al.
They found that the preferable reaction temperature is 463 K (190 ˚C) and 483 K (210 ˚C) for ball-milled and microcrystalline cellulose, respectively. They also found that recycling the Ir-ReOx/SiO2 catalyst + HZSM-5 is feasible under the reaction conditions.
Sibao Liu, Masazumi Tamura, Yoshinao Nakagawa, and Keiichi Tomishige (2014) “One-Pot Conversion of Cellulose into n-Hexane over the Ir-ReOx/SiO2 Catalyst Combined with HZSM-5,” ACS Sustainable Chemistry & Engineering doi: 10.1021/sc5001463