Optimal production of vanillin and 4-hydroxybenzaldehyde from rice straw hydrolysis residue (RSHR) over TiO2/UV and ZnO/UV system

Numerous approaches and technologies have been used in the past few decades to produce value-added chemicals from waste lignin. However, the existing technologies were not efficient and economical to produce the value-added chemicals. Rice straw hydrolysis residue (RSHR) was subjected to alkali treatment followed by photocatalysis with a 125 W UV bulb. Producing vanillin and 4-hydroxybenzaldehyde was confirmed by GCMS. The process parameters, irradiation time (IT), and catalyst dose (CD) were optimized using RSM to obtain the maximum yields of responses. Experiments were designed as per matrix generated according to central composite design (CCD) over TiO₂ and ZnO photocatalyst. The formation of compounds first increased attained their maxima, and thereafter decreased with increasing irradiation time. The higher dose of catalysts gradually increased the formation of compounds in all cases. To get maximum production of compounds, ZnO photocatalyst was found better than TiO₂ photocatalyst. The statistical analysis was also carried out in terms of RMSE, R², AAD, and % error band that showed a good agreement with the experimental results in all cases. However, the RSM model showed excellence for 4-hydroxybenzaldehyde production as compared to vanillin production over both catalysts.