Supercritical water gasification of empty fruit bunches from oil palm for hydrogen production

Empty fruit bunches (EFBs) from the palm plantation sector are abundant agricultural waste products in Malaysia. Supercritical water gasification (SCWG) is a prominent way to convert high-moisture-content biomass such as EFBs into valuable end products. This investigation is focused on EFB conversion into hydrogen-rich products using SCWG (temperature = 380 °C and pressure ≈ 240 bar). Lignocellulosic model compounds (xylan, cellulose, and lignin) were used to study the degradation patterns and gas compositions under similar reaction conditions. The effect of the EFB/water ratio and the SCWG reaction time on the composition of the product gas was examined. Carbon gasification does not improve with increasing EFB/water ratio as well as with increasing reaction time caused by the thermally stable tar formation during reaction. The hydrogen concentration was found to be increased with reaction time along with raising the EFB/water ratio to 0.3 g (3.75 wt%). In addition, the possibility of using palm oil mill effluent as a reaction medium in comparison to deionized water was analyzed

Thermogravimetric study of Chlorella vulgaris for syngas production

The present study investigates the thermal degradation behavior of Chlorella vulgaris using a thermogravimetric analyzer (TGA) to explore application as feedstock for syngas production. The biomass was heated continuously from room temperature to 1000 °C at different heating rates (5, 10 and 20 °C min− 1) under N2/air conditions at a constant flow rate of 25 mL min− 1. Experimental results showed that the combustion process of C. vulgaris can be divided into three major phases; (1) moisture removal, (2) devolatilization of carbohydrates, protein and lipids and (3) degradation of carbonaceous material. A degradation rate of 80% was obtained at the second phase of the combustion process in the presence of air whilst a degradation rate of 60% was obtained under N2 atmosphere at the same phase. The biomass was further gasified for syngas production using a Temperature Programmed Gasifier (TPG). The effect of three different process variables, temperature, microalgal loading, and heating rate was investigated. The maximum H2 production was found at 800 °C temperature with a biomass loading of 0.5 g. No significant effect of heating rate was observed on H2 production. The activation energy values, based on the Kissinger method, were evaluated to be 45.38 ± 0.5 kJ mol− 1 (1st stage), 61.20 ± 0.5 kJ mol− 1 (2nd stage) and 97.22 ± 0.5 kJ mol− 1 (3rd stage). The results demonstrate a significant potential for the utilization of the microalgae biomass as feedstock for large-scale production of syngas via gasification

Catalytic ketonization of palmitic acid over a series of transition metal oxides supported on zirconia oxide-based catalysts

Modification of a ZrO2 based catalyst with selected transition metals dopants has shown promising improvement in the catalytic activity of palmitic acid ketonization. Small amounts of metal oxide deposition on the surface of the ZrO2 catalyst enhances the yield of palmitone (16-hentriacontanone) as the major product with pentadecane as the largest side product. This investigation explores the effects of addition of carefully chosen metal oxides (Fe2O3, NiO, MnO2, CeO2, CuO, CoO, Cr2O3, La2O3 and ZnO) as dopants on bulk ZrO2. The catalysts are prepared via a deposition–precipitation method followed by calcination at 550 °C and characterized by XRD, BET-surface area, TPD-CO2, TPD-NH3, FESEM, TEM and XPS. The screening of synthesized catalysts was carried out with 5% catalyst loading onto 15 g of pristine palmitic acid and the reaction carried out at 340 °C for 3 h. Preliminary studies show catalytic activity improvement with addition of dopants in the order of La2O3/ZrO2 < CoO/ZrO2 < MnO2/ZrO2 with the highest palmitic acid conversion of 92% and palmitone yield of 27.7% achieved using 5% MnO2/ZrO2 catalyst. Besides, NiO/ZrO2 exhibits high selectivity exclusively for pentadecane compared to other catalysts with maximum yield of 24.9% and conversion of 64.9% is observed. Therefore, the changes in physicochemical properties of the dopant added ZrO2 catalysts and their influence in palmitic acid ketonization reaction is discussed in detail

Structural and catalytic studies of Mg1-xNixO nanomaterials for gasification of biomass in supercritical water for H2-rich syngas production

Nowadays, catalytic supercritical water gasification (SCWG) is undoubtedly used for production of H2-rich syngas from biomass. The present study reported the synthesis and characterisation of Mg1-xNixO (x ¼ 0.05, 0.10, 0.15, 0.20) nanomaterials that were obtained via self-propagating combustion (SPC) method, and catalysed the SCWG for the first time. It had found that increased the nickel (Ni) content in the catalyst reduced the crystallite size, thus, increased the specific surface area, which influenced the catalytic activity. The specific surface area followed the order of Mg0.95Ni0.05O (36.2 m2 g1 ) < Mg0.90Ni0.10O (58.9 m2 g1 ) < Mg0.85Ni0.15O (63.6 m2 g1 ) < Mg0.80Ni0.20O (67.9 m2 g1 ). From the Rietveld refinement, the Ni that was successfully partial substituted in the cubic crystal structure of MgO resulting in a cell contraction which ascribed the reduction of crystallite size. Increased the amount of Ni also narrowed the pore size distribution ranging between 4.17 nm and 6.23 nm, as well as increased the basicity active site up to 5741.0 mmol g1 at medium basic strength. All the synthesised nanocatalysts were catalysed the SCWG of OPF (oil palm frond) biomass. Among them, the mesoporous Mg0.80Ni0.20O nanocatalyst exhibited the highest total gas volume of 193.5 mL g1 with 361.7% increment of H2 yield than that of the non-catalytic reaction

Screening of modified CaO-based catalysts with a series of dopants for the supercritical water gasification of empty palm fruit bunches to produce hydrogen

Catalytic supercritical water gasification (SCWG) of empty palm fruit bunches (EFB) was carried out using bulk and modified CaO-based catalysts with several selected dopants. The catalysts were prepared via a wet impregnation method and characterized using X-ray diffraction (XRD), N2 adsorption (BET), temperature programmed reduction (TPR-H2) and temperature programmed desorption (TPD-CO2). The catalytic reactions were performed using 0.3 g of EFB with 5 wt% of the catalysts in 8 mL of deionized water at 380 °C. The results show that addition of the catalysts into the EFB SCWG reaction improves the overall gas yield and hydrogen selectivity. Furthermore, the catalysts after reduction were found to be more active than the unreduced catalysts in which the presence of metallic Ni enhances the gasification reaction. The addition of bulk CaO into the reaction improves the hydrogen yield (50.6 mmol mL−1) when compared to the reactions conducted in the absence of a catalyst (41.3 mmol mL−1) while the addition of 5 wt% of Ni-doped CaO shows a further improvement (57 mmol mL−1). However, the addition of secondary dopants into Ni–CaO shows significant elevation in the hydrogen concentration. Among the catalysts studied, Zn-doped Ni–CaO gave the highest hydrogen yield (105.7 mmol mL−1) due to its increased promotional effects on the water gas shift reaction. The effect of the dopants on the CaO catalyst in the EFB SCWG reaction is discussed in detail

Oil palm (Elaeis guineensis) biomass in Malaysia: The present and future prospects

Oil palm industry is the largest contributor of biomass in Malaysia. Oil palm biomass are constantly generated in large quantities annually with a small fraction being converted into value added product while a large percentage are left underutilized. Several researchers have reported the various technologies available for the conversion of oil palm biomass into useful bio-products, including bio-fuel, biogas, bio-fertilizers, bio-composite and briquettes. In general, these technologies are either underutilized or inadequate for full conversion of these abundantly available biomass, hence, there is an urgent need for upgrading of such technologies. This review article highlights the availability of oil palm biomass in Malaysia, the chemical compositions, as well as a brief description of current technologies for converting oil palm biomass into value added products. The review also outlines a summary of the various products obtained from oil palm biomass. Steps to achieve maximum utilization of biomass from oil palm industry are also proposed