Solar assisted catalytic thermochemical processes: pyrolysis and hydropyrolysis of Chlamydomonas reinhardtii microalgae

Abstract Thermochemical processes using solar energy are considered promising approaches. To improve the product properties, alternative techniques have also been investigated, including the use of catalyst and hydrogen atmosphere. These techniques individually have proved to be efficient to overcome some inherent challenges of this process. However, they have never been studied as an integrated process. Thus, in this work the solar assisted catalytic hydropyrolysis process using microalgae Chlamydomonas reinhardtii as biomass source and hydrotalcite-derived mixed oxides as catalyst (in an ex-situ approach) was successfully investigated as an integrated approach. The effects of reaction time and catalyst percentage on the product distribution and the bio-oil content produced from distinct processes: ex-situ catalytic solar pyrolysis (CSP) and ex-situ catalytic solar hydropyrolysis (CSH) were investigated. The hydrogen used in CSH has been produced by solar aqueous alkaline electrolysis. The results showed that CSH produced higher liquid yields than CSP, reaching 48.83% in its best condition. The content of oxygenated compounds in bio-oil produced by hydropyrolysis was, on average, about 12% lower than that obtained by CSP. However, CSP presented individual tests with less nitrogenated (6.01%) and oxygenated (22.49%) compounds. The hydrocarbon production reached 35.58% for CSP and 37.01% for CSH.