Hydrogen-rich syngas production from steam reforming of palm oil mill effluent (POME) over LaNiO3 & LaCoO3 catalysts / Cheng Yoke Wang

Faculty of Chemical and Natural Resources Engineering

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang – 2019

Includes bibliographical references

The flourishing development of local oil palm industry inflicts concomitant generation of enormous, highly polluted palm oil mill effluent (POME). The prevalent open ponding treatment was land-intensive, sluggish, and incompetent to degrade POME to below discharge threshold yet being accused for greenhouse gases (CO2 and CH4) emission. This study investigated the potentiality of novel catalytic POME steam reforming over LaNiO3 and LaCoO3 to valorise pollutant-laden POME into valuable H2-rich syngas. The POME feedstock was a brownish (A = ~1.93), acidic (pH of 5), and highly polluted (COD = ~70000 mg/L, BOD5 = ~11000 mg/L, and TSS = ~7700 mg/L) wastewater. POME was composed of 99.73 mol% water and 0.27 mol% organics (mainly carboxylic acids, phenol, and alcohols). Through minimisation of total Gibbs free energy, thermodynamic simulation from 573 – 1173 K confirmed syngas production from POME steam reforming and predicted the likelihood of side reactions. Subsequently, LaNiO3 and LaCoO3 were synthesised using modified citrate sol-gel route. Combination of CO2-TPD and NH3-TPD asserted the net-acidity of LaNiO3 and the net-basicity of LaCoO3. Before POME steam reforming, the catalysts were reduced by H2 to form well dispersed active metal (Ni or Co) on La2O3 support. Specifically, the active metal catalysed the reaction while the La2O3 support suppressed the coking deactivation. For both catalytic POME steam reforming, the optimum syngas yield and degradation efficiencies were determined by tuning temperature (𝑇), POME flow rate (𝑉̇𝑃𝑂𝑀𝐸), catalyst weight (𝑊𝑐𝑎𝑡), and particle size (𝑑𝑐𝑎𝑡). The syngas yield and degradation efficiencies increased with greater 𝑇 up to 873 K, higher 𝑉̇𝑃𝑂𝑀𝐸 up to 0.09 mL/min, greater 𝑊𝑐𝑎𝑡 up to 0.3 g, and smaller 𝑑𝑐𝑎𝑡 down to 74 µm. When T≥973 K, the catalysts experienced significant coking and sintering deactivation. If 𝑉̇𝑃𝑂𝑀𝐸>0.09 mL/min, coking deactivation of catalysts was conspicuous. For 𝑊𝑐𝑎𝑡 >0.3 g, the catalysts certainly agglomerated into a plate-like structure with reduced catalytic surface. When 𝑑𝑐𝑎𝑡<74 µm, pore occlusion of catalysts responsible for appreciably declined catalytic activity. Thus, the optimum conditions of both catalytic POME steam reforming were T = 873 K, 𝑉̇𝑃𝑂𝑀𝐸 = 0.09 mL/min, 𝑊𝑐𝑎𝑡 = 0.3 g, and 𝑑𝑐𝑎𝑡 = 74 – 105 µm. However, the net-acidic LaNiO3 granted higher amount of H2-rich syngas (𝐹𝑆𝑦𝑛𝑔𝑎𝑠 = 132.47 µmol/min, 𝑦𝑆𝑦𝑛𝑔𝑎𝑠 = 72.60%, and HHV = 220.31 kJ/mol) than the netbasic LaCoO3 (𝐹𝑆𝑦𝑛𝑔𝑎𝑠 = 86.60 µmol/min, 𝑦𝑆𝑦𝑛𝑔𝑎𝑠 = 70.71%, and HHV = 231.14 kJ/mol). In addition, the optimal catalytic treatment over LaNiO3 generated a less polluted liquid condensate (COD = 326 mg/L and BOD5 = 27 mg/L) than LaCoO3 (COD = 435 mg/L and BOD5 = 62 mg/L). The net-acidity favoured the cracking of POME’s organics before steam reforming while net-basicity promoted the carbon-consuming reverse Boudouard reaction by facilitating CO2 adsorption. Conclusively, the novel catalytic POME steam reforming over LaNiO3 or LaCoO3 is alluring as it harnesses syngas while degrading the POME wastewater.