Katsuya Kawamoto

Characterization of products obtained from pyrolysis and steam gasification of wood waste, RDF, and RPF

Pyrolysis and steam gasification of woody biomass chip (WBC) obtained from construction and demolition wastes, refuse-derived fuel (RDF), and refuse paper and plastic fuel (RPF) were performed at various temperatures using a lab-scale instrument. The gas, liquid, and solid products were examined to determine their generation amounts, properties, and the carbon balance between raw material and products. The amount of product gas and its hydrogen concentration showed a considerable difference depending on pyrolysis and steam gasification at higher temperature. The reaction of steam and solid product, char, contributed to an increase in gas amount and hydrogen concentration. The amount of liquid products generated greatly depended on temperature rather than pyrolysis or steam gasification. The compositions of liquid product varied relying on raw materials used at 500°C but the polycyclic aromatic hydrocarbons became the major compounds at 900°C irrespective of the raw materials used. Almost fixed carbon (FC) of raw materials remained as solid products under pyrolysis condition whereas FC started to decompose at 700°C under steam gasification condition. For WBC, both char utilization by pyrolysis at low temperature (500°C) and syngas recovery by steam gasification at higher temperature (900°C) might be practical options. From the results of carbon balance of RDF and RPF, it was confirmed that the carbon conversion to liquid products conspicuously increased as the amount of plastic increased in the raw material. To recover feedstock from RPF, pyrolysis for oil recovery at low temperature (500°C) might be one of viable options. Steam gasification at 900°C could be an option but the method of tar reforming (e.g. catalyst utilization) should be considered.

Direct synthesis of highly loaded and well-dispersed NiO/SBA-15 for producer gas conversion

To design a new Ni based catalyst for producer gas (CO2 + H2) conversion with high conversion and selectivity, highly loaded and well-dispersed NiO/SBA-15 was obtained for the first time by the direct synthesis method. The NiO particles were dispersed into the SiO2 structure of SBA-15, unlike when prepared by the post synthesis method. The NiO/SBA-15 exhibited excellent efficiency and selectivity for producer gas conversion, comparable to that obtained by the post synthesis method. The synthesis method affected the CO selectivity. The temperature and H2/CO2 ratio played an important role in CO2 conversion, indicating that a high temperature and high H2/CO2 ratio favored CO2 conversion. The NiO loading did not affect the CO2 conversion. Although there was no difference in the CO selectivity when the NiO loading was increased at high temperature, it was influenced greatly by NiO loading at low temperature as a result of CH4 formation. In NiO/SBA-15 with low NiO loading, it can be considered that the NiO particles were separated into single NiO particles, which only catalyzed the reverse water gas shift (RWGS) reaction, regardless of the temperature, resulting in a CO selectivity of 100%. However, in NiO/SBA-15 with high NiO loading, the NiO particles aggregated to result in one or more NiO particles existing near each other. In this case only the RWGS reaction could occur at high temperature, and both methanation and the RWGS reaction were catalyzed at low temperature, resulting in a CO selectivity of less than 100%.

Grafting Ni particles onto SBA-15, and their enhanced performance for CO2 methanation

By a post synthesis method, nickel (Ni) particles could be grafted onto SBA-15 for the first time through chemical bond (–O–Ni–O–Si–O–) formation between silicon (Si) and Ni via oxygen (O) using Ni ammonia (NH3) complex ions (Ni(NH3)x)2+ with an NH3/Ni mole ratio of 1–5, which existed as Ni phyllosilicate on the SBA-15 surface, while Ni particles could not be grafted onto SBA-15 in the absence of NH4OH (NH3/Ni mole ratio of 0). An NH3/Ni mole ratio of 2–4 was suitable for grafting conditions, which could give a product with the closest Ni amount to that of raw Ni complex ion solution. The product obtained was named as the Ni-grafted SBA-15 sample. XPS, UV-vis and H2-TPR analyses demonstrated that a chemical bond was formed between Ni and silicon (Si) via oxygen (O), and no bulk nickel oxides existed in the Ni-grafted SBA-15 sample. The formation of –O–Ni–O–Si–O– was completed via the reaction between hydrolyzate (Ni(OH)(NH3)x−1)+ from (Ni(NH3)x)2+ and Si–OH (silanol sites) on the SBA-15 surface. The Ni-grafted SBA-15 catalyst suited CO2 methanation, resulting in higher CO2 conversion and methane selectivity than a NiO dispersed SBA-15 catalyst obtained by the conventional post synthesis method. The activation energy for CO2 methanation increased with a decreasing initial Ni amount used. The rate equation for CO2 methanation could be expressed as: r = kCCO20.64CH24.05, where C is the concentration. The Ni-grafted SBA-15 catalyst had high thermal stability for CO2 methanation.

Bench-scale gasification of cedar wood - Part I: Effect of operational conditions on product gas characteristics.

The present study was conducted within the framework of R&D activities on the development of gasification and reforming technologies for energy and chemical recovery from biomass resources. Gasification of the Japanese cedar wood has been investigated under various operating conditions in a bench-scale externally heated updraft gasifier; this was followed by thermal reforming. Parametric tests by varying the residence times, gasification temperatures, equivalence ratios (ERs) and steam-to-carbon (S/C) ratios were performed to determine their effects on the product gas characteristics. Thermodynamic equilibrium calculations were preformed to predict the equilibrium gas composition and compared with the experimental value. We found that the product gas characteristics in terms of the H(2)/CO ratio, CO(2)/CO ratio, and CH(4) and lighter hydrocarbons concentrations are significantly affected by the operating conditions used. Increasing the residence time decreased the CO(2)/CO ratio; however, a nominal effect was noticed on H(2) concentration as a function of the residence time. At sufficient residence time, increasing the temperature led to higher H(2) yields, CO efficiency and higher heating value (HHV) of the product gas. The presence of steam during gasification effectively enhanced the proportion of H(2) in the product gas. However, higher S/C ratio reduced the HHV of the product gas. Increasing the ER from 0 to 0.3 increased the H(2) yields and CO efficiency and decreased the HHV of the product gas. The evolution of CH(4) and lighter hydrocarbons at low gasification temperatures was relatively higher than that at high temperature gasification. The evolution of CH(4) and lighter hydrocarbons at high gasification temperatures hardly varied over the investigated operating conditions.

Woody biomass and RPF gasification using reforming catalyst and calcium oxide

This study focused on steam gasification and reforming of waste biomass using a reforming catalyst. The purpose of the study was to evaluate the durability of a commercial Ni reforming catalyst and the effect of CaO on the reforming behavior, and to clarify detailed factors of catalytic performance, as well as the effect of operating parameters on the characteristics of produced gas composition. Moreover, catalyst regeneration was carried out and the behavior of catalytic activity based on gas composition was investigated. Using a fluidized bed gasifier and a fixed bed reformer, gasification and reforming of waste biomass were carried out. Commercial Ni-based catalyst and calcined limestone (CaO) were applied to the reforming reaction. Temperature of the gasifier and reformer was almost 1023K. Ratio of steam to carbon in the feedstock [molmol(-1)] and equivalence ratio (i.e., ratio of actual to theoretical amount of oxygen) [-] were set at about 2 and 0.3, respectively. The feed rate of the feedstock into the bench-scale gasifier was almost 15kgh(-1). The results of waste biomass gasification confirmed the improvement in H(2) composition by the CO(2) absorption reaction using the reforming catalyst and CaO. In addition, CaO proved to be especially effective in decreasing the tar concentration in the case of woody biomass gasification. Catalytic activity was maintained by means of catalyst regeneration processing by hydrogen reduction after air oxidation when woody biomass was used as feedstock.

Potential formation of PCDD/Fs and related bromine-substituted compounds from heating processes for ashes

Thermal experiments were conducted using real boiler ash and fly ash samples from three types of municipal or industrial solid waste incineration plants to understand the formation reactions of polychlorinated dibenzo-p-dioxin and furans (PCDD/Fs) and related bromine compounds that were chlorinated-brominated dibenzodioxins and furans (PXDD/Fs) and polybrominated dibenzo-p-dioxin and furans (PBDD/Fs). The results obtained were as follows: The formation of PCDD/Fs was clearly shown, and fly ash containing abundant carbon matter had a significant potential for de novo synthesis. The homologous distribution change apparently showed that the formation of PXDD/Fs occurred from the substitution of a bromine atom with a chlorine atom in the PCDD/F molecules. This suggests that PXDD/Fs are usually formed with PCDD/Fs on the ash. PBDD/Fs might be formed from any reaction mechanism different from that of PXDD/Fs. The existence of carbonaceous matters always does not mean the potential formation of PCDD/Fs. However, any addition of catalytic copper may influence the nature of ash to increase the formation potential. The findings suggest that there are many instances that result in the unintended production of trace hazardous pollutants in the incineration process and show that careful and sophisticated control is required to prevent the formation of pollutants.

Transition metal-rich mesoporous silicas and their enhanced catalytic properties

A controllable and simple direct hydrothermal synthesis route was designed for synthesizing well-ordered mesoporous silica incorporating transition metals (M) (Ni, Cu, Zn, Co) with high metal loading. M-incorporated mesoporous silica could be obtained from a starting synthesis mixture with a Si/M mole ratio of 5 using transition metal–ammonia (NH3) complex ions [M(NH3)x]n+ as base. The Si/M mole ratio of 5 is the lowest value yet reported. XPS, UV-vis and H2-TPR analyses demonstrated that a chemical bond was formed between metal and silicon via oxygen and no bulk metal oxides existed in any of the M-MCM-41 samples; in other words, only tetrahedral coordinated metal species were detected. The formation of –O–M–O–Si–O– is completed via the reaction between hydrolyzate [M(OH)(NH3)x−1](n−1)+ from [M(NH3)x]n+ and Si–OH (silanol sites) from a silica source (tetramethoxysilane (TMOS)). All the M-MCM-41 samples possessed remarkable physical properties and thermal stability. Ni-MCM-41, Cu-MCM-41 and CoMCM-41 catalysts exhibited excellent catalytic efficiency for carbon dioxide (CO2) hydrogenation, although Zn-MCM-41 catalyst did not. Ni-MCM-41 catalyst suited methanation, resulting in high CO2 conversion rate and methane selectivity, while Cu-MCM-41 catalyst favored the reverse water gas shift (RWGS) reaction and realized high CO2 conversion rate to carbon monoxide. A kinetic study was also carried out for methanation and RWGS reaction. Using Ni-MCM-41 catalyst for methanation, the rate equation could be expressed as r = kCCO20.68CH23.31, where C represents concentration. Using Cu-MCM-41 catalyst for RWGS reaction, the rate equation could be expressed as r = kCCO20.5CH21.1, where C represents concentration.

Dioxin formation and control in a gasification-melting plant.

We investigated dioxin formation and removal in a commercial thermal waste treatment plant employing a gasification and melting process that has become widespread in the last decade in Japan. The aim was to clarify the possibility of dioxin formation in a process operation at high temperatures and the applicability of catalytic decomposition of dioxins. Also, the possible use of dioxin surrogate compounds for plant monitoring was further evaluated. The main test parameter was the influence of changes in the amount and type of municipal solid waste (MSW) supplied to the thermal waste treatment plant which from day to day operation is a relevant parameter also from commercial perspective. Here especially, the plastic content on dioxin release was assessed. The following conclusions were reached: (1) disturbance of combustion by adding plastic waste above the capability of the system resulted in a considerable increase in dioxin content of the flue gas at the inlet of the bag house and (2) bag filter equipment incorporating a catalytic filter effectively reduced the gaseous dioxin content below the standard of 0.1xa0ng toxic equivalency (TEQ)/m3N, by decomposition and partly adsorption, as was revealed by total dioxin mass balance and an increased levels in the fly ash. Also, the possible use of organohalogen compounds as dioxin surrogate compounds for plant monitoring was further evaluated. The levels of these surrogates did not exceed values corresponding to 0.1xa0ng TEQ/m3N dioxins established from former tests. This further substantiated that surrogate measurement therefore can well reflect dioxin levels.

Dispersion and distribution of bimetallic oxides in SBA-15, and their enhanced activity for reverse water gas shift reaction

We used the direct hydrothermal synthesis method to obtain various well-dispersed bimetallic oxides/SBA-15 for the first time. It is possible that well-dispersed relatively large bimetallic sulfates are formed during the hydrothermal synthesis process and then re-dispersed with difficulty during the heat treatment process resulting in the formation of well-dispersed oxide particles in SBA-15. TEM elemental maps of CuO–NiO/SBA-15 clearly illustrated that CuO and NiO particles were monodispersed in SBA-15. TEM–EDX line analysis revealed that NiO particles were well distributed on the SBA-15 surface, and then covered by CuO particles. TEM elemental maps of CuO–CeO2/SBA-15 clearly showed that CuO and CeO2 particles aggregated slightly in SBA-15. TEM–EDX line analysis showed that CeO2 particles were well distributed on the SBA-15 surface, and then covered by CuO particles. TEM elemental maps of NiO–CeO2/SBA-15 clearly illustrated that NiO and CeO2 particles aggregated slightly in SBA-15. TEM–EDX line analysis revealed that NiO particles were largely mixed with CeO2 on the SBA-15 surface. Therefore, TEM elemental maps can be used to study the dispersion of bimetallic oxides, and TEM–EDX line analysis is very effective for investigating their distribution in SBA-15. Compared with monometallic oxides/SBA-15, the obtained bimetallic oxides/SBA-15 catalysts exhibited excellent efficiency as regards reducing CO2 to CO by the reverse water–gas shift (RWGS) reaction. In particular, the bimetallic oxides/SBA-15 catalysts could result in the high CO2 conversion to CO at low temperature.

Survey of carbonization facilities for municipal solid waste treatment in Japan.

The operations of carbonization facilities for municipal solid waste treatment in Japan were examined. Input waste, system processes, material flows, quality of char and its utilization, fuel and chemical consumption, control of facility emissions, and trouble areas in facility operation were investigated and analyzed. Although carbonization is a technically available thermochemical conversion method for municipal solid waste treatment, problems of energy efficiency and char utilization must be solved for carbonization to be competitive. Possible solutions include (1) optimizing the composition of input waste, treatment scale, organization of unit processes, operational methods, and quality and yield of char on the basis of analysis and feedback of long-term operating data of present operating facilities and (2) securing stable char demands by linking with local industries such as thermal electric power companies, iron manufacturing plants, and cement production plants.