Separation of the acid‐sugar mixtures by using acid retardation and further concentration of the eluents by using continuous‐effect membrane distillation

BACKGROUND A major cost in acid‐catalysed hydrolysis of biomass to fermentable sugars is the consumption of acid itself. In this study, a combined process was developed in which the acid and sugar in the hydrolysate were separated using an acid retardation process and then the dilute aqueous product streams were concentrated using a continuous‐effect membrane distillation ( CEMD ) process, thus acid could be reused as catalyst. RESULTS The recovery rate of sugar was as high as 94.3–99.2% while the recovery rate of sulfuric acid was 92.4–98.9%. The eluents were further concentrated using the CEMD process. When a solution of 2 wt% sulfuric acid was concentrated to c . 40 wt%, the maximum value of permeation flux ( J w ) and gained output ratio ( GOR ) was 6.20 L m −2  h −1 and 15.50, respectively. Meanwhile, the dilute aqueous sugar solution obtained from corn stover was concentrated 20‐fold to a final concentration of c . 497.6 g L −1 using the CEMD process with a final GOR of 5.5. CONCLUSION The combination of acid retardation and CEMD is suitable for the production of sugar, further purification and concentration of eluents; the sugar solution can be used for fermentation and acid solution can be reused as catalyst. © 2015 Society of Chemical Industry