Special Issue "Catalysts for Biomass Conversion"

Abstract: Ethanol and pentose were produced from lignocellulosic napiergrass by the simultaneous saccharification and fermentation process (SSF) using hydrolytic enzyme and S. Cerevisiae. After the ethanol was removed, the pentose solution was subjected to photocatalytic hydrogen evolution with Pt-loaded TiO₂ under UV-irradiation. This process converted 100 g of napiergrass into 12.3 g of ethanol and 1.76 g of hydrogen whose total combustion energy of (∆H) was 615 kJ. This was close to the ∆H (639 kJ) of the pentose (13.6 g) and hexose (27.4 g) obtained by the cellulose-saccharification of 100 g of napiergrass.

Abstract: Waste cooking oil with a high-acid-value (28.7 mg-KOH/g-oil) was converted to bio-hydrogenated diesel by a hydrotreatment process over supported Ru catalysts. The standard reaction temperature, H₂ pressure, liquid hourly space velocity (LHSV), and H₂/oil ratio were 350 °C, 2 MPa, 15.2 h^–1, and 400 mL/mL, respectively. Both the free fatty acids and the triglycerides in the waste cooking oil were deoxygenated at the same time to form hydrocarbons in the hydrotreatment process. The predominant liquid hydrocarbon products (98.9 wt%) were n-C₁₈H₃₈, n-C₁₇H₃₆, n-C₁₆H₃₄, and n-C₁₅H₃₂ when a Ru/SiO₂ catalyst was used. These long chain normal hydrocarbons had high melting points and gave the liquid hydrocarbon product over Ru/SiO₂ a high pour point of 20 °C. Ru/H-Y was not suitable for producing diesel from waste cooking oil because it formed a large amount of C₅–C₁₀ gasoline-ranged paraffins on the strong acid sites of HY. When Al-polyoxocation-pillared montmorillonite (Al₁₃-Mont) was used as a support for the Ru catalyst, the pour point of the liquid hydrocarbon product decreased to −15 °C with the conversion of a significant amount of C₁₅–C₁₈ n-paraffins to iso-paraffins and light paraffins on the weak acid sites of Al₁₃-Mont. The liquid product over Ru/Al₁₃-Mont can be expected to give a green diesel for current diesel engines because its chemical composition and physical properties are similar to those of commercial petro-diesel. A relatively large amount of H₂ was consumed in the hydrogenation of unsaturated C=C bonds and the deoxygenation of C=O bonds in the hydrotreatment process. A sulfided Ni-Mo/Al₁₃-Mont catalyst also produced bio-hydrogenated diesel by the hydrotreatment process but it showed slow deactivation during the reaction due to loss of sulfur. In contrast, Ru/Al₁₃-Mont did not show catalyst deactivation in the hydrotreatment of waste cooking oil after 72 h on-stream because the waste cooking oil was not found to contain sulfur-containing compounds.

Abstract: More than 10 million tons of biodiesel fuel (BDF) have been produced in the world from the transesterification of vegetable oil with methanol by using acid catalysts (sulfuric acid, H₂SO₄), alkaline catalysts (sodium hydroxide, NaOH or potassium hydroxide, KOH), solid catalysts and enzymes. Unfortunately, the price of BDF is still more expensive than that of petro diesel fuel due to the lack of a suitable raw material oil. Here, we review the best selection of BDF production systems including raw materials, catalysts and production technologies. In addition, glycerol formed as a by-product needs to be converted to useful chemicals to reduce the amount of glycerol waste. With this in mind, we have also reviewed some recent studies on the utilization of glycerol.

Abstract: Combustion of solid biomass fuels for heat generation is an important renewable energy resource. The major part among biomass combustion applications is being played by small-scale systems like wood log stoves and small wood pellet burners, which account for 75% of the overall biomass heat production. Despite an environmentally friendly use of renewable energies, incomplete combustion in small-scale systems can lead to the emission of environmental pollutants as well as substances which are hazardous to health. Besides particles of ash and soot, a wide variety of gaseous substances can also be emitted. Among those, polycyclic aromatic hydrocarbons (PAH) and several organic volatile and semi-volatile compounds (VOC) are present. Heterogeneous catalysis is applied for the reduction of various gaseous compounds as well as soot. Some research has been done to examine the application of catalytic converters in small-scale biomass combustion systems. In addition to catalyst selection with respect to complete oxidation of different organic compounds, parameters such as long-term stability and durability under flue gas conditions are considered for use in biomass combustion furnaces. Possible catalytic procedures have been identified for investigation by literature and market research. Experimental studies with two selected oxidation catalysts based on noble metals have been carried out on a wood log stove with a retrofit system. The measurements have been performed under defined conditions based on practical mode of operation. The measurements have shown that the catalytic flue gas treatment is a promising method to reduce carbon monoxide and volatile organic compounds. Even a reduction of particulate matter was observed, although no filtering effect could be detected. Therefore, the oxidation of soot or soot precursors can be assumed. The selected catalysts differed in their activity, depending on the compound to be oxidized. Examinations showed that the knitted wire catalyst showed better activity for the reduction of carbon monoxide, whereas the honeycomb induced a higher reduction of aromatic compounds. The properties of the two catalysts can be combined by integrating both together. The one drawback of the catalyst so far is the deactivation for the conversion of methane.

Abstract: The economic utilization of abundant lignocellulosic biomass as a feedstock for the production of fuel and chemicals would represent a profound shift in industrial carbon utilization, allowing sustainable resources to substitute for, and compete with, petroleum based products. In order to exploit biomass as a source material for production of renewable compounds, it must first be broken down into constituent compounds, such as sugars, that can be more easily converted in chemical and biological processes. Lignocellulose is, unfortunately, a heterogeneous and recalcitrant material which is highly resistant to depolymerization. Many microorganisms have evolved repertoires of enzyme activities which act in tandem to decompose the various components of lignocellulosic biomass. In this review, we discuss recent advances in the understanding of these enzymes, with particular regard to those activities deemed likely to be applicable in commercialized biomass utilization processes.

Abstract: Magnesium nickel silicate (MNS) has been investigated as a catalyst to convert tars and light hydrocarbons to syngas (CO and H₂) by steam reforming and CO₂ reforming in the presence of H₂S for biomass gasification process at NexTech Materials. It was observed that complete CH₄ conversion could be achieved on MNS catalyst granules at 800–900 °C and a space velocity of 24,000 mL/g/h in a simulated biomass gasification stream. Addition of 10–20 ppm H₂S to the feed had no apparent impact on CH₄ conversion. The MNS-washcoated monolith also showed high activities in converting methane, light hydrocarbons and tar to syngas. A 1200 h test without deactivation was achieved on the MNS washcoated monolith in the presence of H₂S and/or NH₃, two common impurities in gasified biomass. The results indicate that the MNS material is a promising catalyst for removal of tar and light hydrocarbons from biomass gasified gases, enabling efficient use of biomass to produce power, liquid fuels and valuable chemicals.

Abstract: This study proposes a gas-cleaning process for the simultaneous removal of sulfur compounds, tar, and particles from biomass-gasified gas using Fe-supported activated carbon and a water-gas shift reaction. On a laboratory scale, the simultaneous removal of H₂S and COS was performed under a mixture of gases (H₂/CO/CO₂/CH₄/C₂H₄/N₂/H₂S/COS/steam). The reactions such as COS + H₂ → H₂S + CO and COS + H₂O → H₂S + CO₂ and the water-gas shift reaction were promoted on the Fe-supported activated carbon. The adsorption capacity with steam was higher than that without steam. On a bench scale, the removal of impurities from a gas derived from biomass gasification was investigated using two activated filters packed with Fe-supported activated carbon. H₂S and COS, three- and four-ring polycyclic aromatic hydrocarbons (PAHs), and particles were removed and a water-gas shift reaction was promoted through the first filter at 320–350 °C. The concentrations of H₂S and COS decreased to less than 0.1 ppmv. Particles and the one- and two-ring PAHs, except for benzene, were then removed through the second filter at 60–170 °C. The concentration of tar and particles decreased from 2428 to 102 mg Nm⁻³ and from 2244 to 181 mg Nm⁻³, respectively.

Abstract: Fischer–Tropsch synthesis is a set of catalytic processes that can be used to produce fuels and chemicals from synthesis gas (mixture of CO and H₂), which can be derived from natural gas, coal, or biomass. Biomass to Liquid via Fischer–Tropsch (BTL-FT) synthesis is gaining increasing interests from academia and industry because of its ability to produce carbon neutral and environmentally friendly clean fuels; such kinds of fuels can help to meet the globally increasing energy demand and to meet the stricter environmental regulations in the future. In the BTL-FT process, biomass, such as woodchips and straw stalk, is firstly converted into biomass-derived syngas (bio-syngas) by gasification. Then, a cleaning process is applied to remove impurities from the bio-syngas to produce clean bio-syngas which meets the Fischer–Tropsch synthesis requirements. Cleaned bio-syngas is then conducted into a Fischer–Tropsch catalytic reactor to produce green gasoline, diesel and other clean biofuels. This review will analyze the three main steps of BTL-FT process, and discuss the issues related to biomass gasification, bio-syngas cleaning methods and conversion of bio-syngas into liquid hydrocarbons via Fischer–Tropsch synthesis. Some features in regard to increasing carbon utilization, enhancing catalyst activity, maximizing selectivity and avoiding catalyst deactivation in bio-syngas conversion process are also discussed.