Production of hydrogen in a Pd-membrane reactor via catalytic reforming of olive mill wastewater

Abstract Olive mill wastewater (OMW) contributes to environmental issues in Mediterranean regions because of its poor biodegradability and high phytotoxicity. Among the different processes proposed for the treatment of OMW, thermochemical treatments are advantageous as they can recover hydrogen-rich gas mixtures; thus, they can convert a waste into an energetic source. In this work, a noble metals based catalyst supported on rare earth mixed oxides was studied for its ability to reform OMW in a Pd–Ag tubular membrane reactor. The experimental results were compared with those obtained in a previous study using a Pt/Al 2 O 3 catalyst. After filtration and concentration via distillation, OMW was treated in a Pd–Ag tube of thickness 0.143 mm, diameter 10 mm, and length 146 mm. The membrane tube was filled with 4.8 g of catalyst. The reaction tests were performed at 450 °C in the pressure range 100–500 kPa and demonstrated the capability of the membrane reactor to produce up to 3.25 kg of hydrogen per ton of OMW. Higher values of hydrogen recovery and hydrogen yield were measured at 500 kPa when the hydrogen permeated in the shell side was up to 80% of all the hydrogen produced and about 35 wt% of the total organic carbon (TOC) fed. Investigation of carbon formation showed that only 1.2% of the fed carbon was responsible for coke formation by demonstrating that the new catalyst, although tested at low temperature, was effective to limit this phenomenon. When compared to the commercial Pt-based catalyst, the new catalyst exhibited higher selectivity toward the reforming reaction, allowing it to significantly reduce the formation of methane and coke; thus, it exhibited higher hydrogen yield and greater durability.