Gasification of Iranian walnut shell as a bio-renewable resource for hydrogen-rich gas production using supercritical water technology

Gasification in supercritical water (SCW) media is known as an efficient and promising technology for obtaining hydrogen-rich gas from dry and wet bio-renewable materials. Gasification of walnut shell as the main hard nutshell produced in Kurdistan Province of Iran was investigated using a stainless steel batch micro-reactor. Effects of reaction time in the range of 10–30 min, feed loading in the range of 0.06–0.18 g, and temperature in the range of 400–440 °C were investigated to determine the condition for maximum hydrogen yield. Furthermore, carbon gasification efficiency (CGE) and hydrogen gasification efficiency (HGE) were calculated according to the elemental analysis and the yields of gaseous products. Total gas yield and hydrogen yield were directly correlated with temperature. Steam reforming of walnut shell was favored at higher temperatures. Also, walnut shell loading was inversely correlated with total gas and hydrogen yields while production of methane was favored by higher loading of walnut shell. Furthermore, hydrogen yield increased first, when reaction time increased from 10 to 20 min, and then decreased. Maximum hydrogen yield of 4.63 mmol/g of walnut shell was obtained at 440 °C, walnut shell loading of 0.06 g and reaction time of 20 min.