Comparison of slow and vacuum pyrolysis of sugar cane bagasse

Experimental results for slow and vacuum pyrolysis of sugar cane bagasse, in the same reactor allowing the comparison of these two processes, are reported. The experimental results showed that vacuum pyrolysis leads to a higher BET specific surface area whereas slow pyrolysis seemed to favour the HHV of charcoal. Detailed yields of products are presented and the influence of temperature and heating rate were studied using a design of experiments and an ANOVA analysis. From the results the optimum experimental conditions to maximise the yields of char and bio-oil products, as well as their heating value and specific surface area characteristics, were established.The optimal yields of bio-oil for vacuum pyrolysis were obtained at 400–500 °C and a heating rate of 15–24 °C min−1, and for char the corresponding values are 340–350 °C and 18–24 °C min−1. Slow pyrolysis produced the highest char yield. The optimal ranges of temperature and heating rate differ from that of vacuum pyrolysis mainly due to the short residence time of the vapours in the case of vacuum pyrolysis.Optimum conditions for bio-oil and char yields did not correspond with conditions to optimize the BET surface and HHV for chars, and to minimize the water content of the products.