Bread residues conversion into lactic acid by alkaline hydrothermal treatments

•Bread residues were converted hydrothermally into lactic acid.•Effect of different catalyst, temperature and time of reaction were studied.•Optimum conditions to obtain a high production of lactic acid were determined.•Other products as formic acid, acetic acid, xylitol or acrylic acid were produced.

Bread residues can be converted into a suitable feedstock for chemicals production due to their high starch content. The present study was focused on the production of lactic acid from bread residues using alkaline catalysts. NaOH, KOH, Ca(OH)2, LiOH and K2CO3 were used at 300 °C, 30 min and 0.5 M catalyst concentration. The preliminary experiment showed that KOH, NaOH and Ca(OH)2 are the best catalyst. Using these catalysts further experiments were carried out varying the catalyst concentration at the same operation conditions. The maximum yields of lactic acid from bread residues (% respect to the total initial raw material) were obtained at 300 °C, 30 min by using 0.4 M of KOH (38.11 ± 0.2%), 0.6 M of NaOH (34.46 ± 0.21%) and 3.5 M Ca(OH)2 (72.90 ± 4.45%).