Bimetal catalyst based on Fe and Co supported on Al pillared interlayer clays: Preparation, reactivity and mechanism for SCR-CH4.

Montmorillonite was used as raw clay to prepare the Al-pillared interlayer clay (Al-PILC) as support by impregnation methods. Co and Fe were loaded in series on Al-PILC to prepare the bimetal catalysts (Fe-Co/Al-PILC). The SCR-CH4 was evaluated in a fixed bed reactor and the results indicated that 0.27Fe-Co/Al-PILC exhibited 100% N2 selectivity and above 63% NO conversion in the presence of 10% H2O, and the introduction of Fe significantly improved the Co/Al-PILC catalyst's resistance to H2O and SO2. Characterization showed that Lewis and Brønsted acids co-existed on the catalyst surface, and the Lewis acid was the dominant active acid site and enhanced the activation of methane over the 0.27Fe-Co/Al-PILC. Fe promoted the formation of isolated Co2+ and CoO species, and the isolated Fe3+ particles improved CH4-SCR performance. The reaction route was proposed based on in situ DRIFTS tests and the active intermediates were mainly various nitrates and nitromethane (CH3NO2).

Biomass-based adsorbents for post-combustion CO2 capture: Preparation, performances, modeling, and assessment.

The adsorbents are critical carriers in the process of adsorption-based post-combustion CO2 capture. Biomass-based adsorbents (BAs) are considered to have great potential because of their high efficiency, low cost, and good sustainability. To understand the methods, theories, and technologies of BAs-based CO2 capture, this work analyzes their preparation and activation/modification, influencing factors, mechanisms, thermodynamics/kinetics, regeneration and cycle performances, and the pathway to application. It is found that BAs prepared by pyrolysis, chemical activation, and modification with dual heteroatoms are more conducive to improving adsorption sites. CO2 adsorption capacity positively correlates with elemental C and fixed carbon of feedstocks, but negatively with moisture. The BAs prepared at 550-600 °C have high performance. The specific surface area (SSA) increases as the preparation time increases by 9.4%-93.4%. The adsorption capacity is positively correlated to the SSA (R = 0.880) and microporous volume (R = 0.773). Moreover, it decreases linearly with increasing operating temperature with the slope of -0.6 mmol/(g·°C) but increases exponentially with increasing operating pressure and CO2 concentration with the power of 0.824. The adsorption process includes physical and/or physicochemical adsorption. Freundlich isotherm equation and pseudo-second-order model characterize the adsorption thermodynamics and kinetics more effectively with R2 = 0.985-1.000 and R2 = 0.894-1.000. The quantum chemistry indicates that most BAs modified with non-metallic belong to physisorption. The regeneration of BAs has low energy consumption (<3.44 MJ/kg CO2) and loss rate (<8%). Furthermore, the technical pathway is proposed for application. Finally, the challenges are also presented to facilitate the development of BAs-CO2 capture.

Impact of gas impurities on the Hg0 oxidation on high iron and calcium coal ash for chemical looping combustion.

Coal-based mercury pollution from power plants has received increasing attention. In a previous study, high iron and calcium coal ash (HICCA) was found as a promising oxygen carrier (OC) for chemical looping combustion (CLC). The purpose of this study was to investigate the catalytic effect of HICCA on Hg0 removal as well as the impacts of several gas impurities, such as HCl, SO2, and NO. Experiments on Hg0 removal efficiencies for different atmospheres were performed in the fixed-bed reactor at 850 °C. Based upon the characterization of BET, SEM, XRD, XPS, and EDS of reaction products, the reaction mechanisms of different gases with the HICCA samples were established. The mechanisms were further explained using the thermodynamic equilibrium calculations. The experimental results showed that the Hg0 removal efficiency using HICCA was 11.60%, while the corresponding value in the presence of 50 ppm HCl was 90.46%. Hg0 removal by HICCA involving HCl is mainly attributed to homogeneous reaction between Hg0 and HCl as well as the formation of reactive species (Cl, Cl2, Cl2O, O, S, and SCl2) through the reactions of HCl with Fe2O3 and CaSO4 in HICCA. The formation of C-Cl bond is not the main pathway for the promotional effect of HCl on Hg0 removal. SO2 played a negative role in Hg0 removal by HICCA. The inhibition of SO2 may be attributed to its effect on the reduction of Fe2O3 and its bonding with C-O, COOH, and C(O)-O-C. NO enhanced Hg0 removal by HICCA primarily through the homogeneous reactions of Hg0 with N2O and O. In addition, NO also interacted with HICCA and promoted the heterogeneous oxidation of Hg0 by producing more C-O, C=O, and COOH/C(O)-O-C on HICCA surface. This study proved the effectiveness of HICCA on Hg0 removal in iG-CLC and revealed the mechanisms of the interaction between HCl/SO2/NO and MxOy/CaSO4 as well as carbon-oxygen groups.

Emission and conversion of NO from algal biomass combustion in O2/CO2 atmosphere.

Environmental impacts of NO emissions from biomass combustion have become an important concern. To address NO emission and conversion from algal biomass combustion in O2/CO2 atmosphere, three typical algal biomass, Chlorella (Ch), Enteromorpha (En), and Sargassum (Sa), were used to investigate NO emission characteristics in a one-dimensional tube furnace. The effects of the combustion temperature and O2 concentration (21%, 25%, and 30%) on the NO emission were examined. It was found that the main peaks of NO positively are correlated to the O2 concentration and combustion temperature. The NO emission trends of each algal biomass are slightly affected by the O2 concentration at a given temperature. Roughly, the NO yield and conversion rate for each algal biomass increase with increasing O2 concentration at a given temperature. They first increase with the increasing temperature and then decrease beyond 800 °C with exception for Sa in 30% O2/CO2 atmosphere. However, 21% O2/CO2 atmosphere is at least effective to reduce NO emission from most algal biomass combustion compared to air-based atmosphere (21% O2/N2), by 8.2-62.0%, 4.9-45.6%, and 22.5-59.6% for Ch, En, and Sa, respectively. The possible conversion pathway of fuel-N implies that the NO emission from algal biomass combustion in O2/CO2 atmosphere is the result of the combined effect of the NO formation oxidized from N-precursors and NO reduction by CO (converted from CO2) and other reductive components. These results may provide a positive reference for the control of NOx emissions from direct combustion or co-firing of algal biomass for energy utilization.

[Progress in biofixation of CO2 from combustion flue gas by microalgae].

Global warming caused by the increasing CO2 concentration in atmosphere is a serious problem in the international political, economic, scientific and environmental fields in recent years. Intensive carbon dioxide capture and storage (CCS) technologies have been developed for a feasible system to remove CO2 from industrial exhaust gases especially for combustion flue gas. In these technologies, the biofixation of CO2 by microalgae has the potential to diminish CO2 and produce the biomass. In this review, the current status focusing on biofixation of CO2 from combustion flue gases by microalgae including the selection of microalgal species and effect of flue gas conditions, the development of high efficient photobioreactor and the application of microalgae and its biomass product were reviewed and summarized. Finally, the perspectives of the technology were also discussed.

Modeling mercury speciation in combustion flue gases using support vector machine: prediction and evaluation.

Mercury emission from coal combustion has become a global environmental problem. In order to accurately reveal the complexly nonlinear relationships between mercury emissions characteristics in flue gas and coal properties as well as operating conditions, an alternative model using support vector machine (SVM) based on dynamically optimized search technique with cross-validation, is proposed to simulate the mercury speciation (elemental, oxidized and particulate) and concentration in flue gases from coal combustion, then the configured SVM model is trained and tested by simulation results. According to predicted accuracy of indicating generalization capability, the model performance is compared and evaluated with the conventional multiple nonlinear regression (MNR) models and the artificial neural network (ANN) models. As a result, it is found that, the SVM provides better prediction performances with the mean squared error of 0.0095 and the correlation coefficient of 0.9164 for testing sample. Moreover, based on the SVM model, the correlativity between coal properties as well as operating condition and mercury chemical form is also analyzed in order to deeply understand mercury emissions characteristics. The result demonstrates that SVM can offer an alternative and powerful approach to model mercury speciation in coal combustion flue gases.

Simulation of mercury capture by sorbent injection using a simplified model.

Mercury pollution by fossil fuel combustion or solid waste incineration is becoming the worldwide environmental concern. As an effective control technology, powdered sorbent injection (PSI) has been successfully used for mercury capture from flue gas with advantages of low cost and easy operation. In order to predict the mercury capture efficiency for PSI more conveniently, a simplified model, which is based on the theory of mass transfer, isothermal adsorption and mass balance, is developed in this paper. The comparisons between theoretical results of this model and experimental results by Meserole et al. [F.B. Meserole, R. Chang, T.R. Carrey, J. Machac, C.F.J. Richardson, Modeling mercury removal by sorbent injection, J. Air Waste Manage. Assoc. 49 (1999) 694-704] demonstrate that the simplified model is able to provide good predictive accuracy. Moreover, the effects of key parameters including the mass transfer coefficient, sorbent concentration, sorbent physical property and sorbent adsorption capacity on mercury adsorption efficiency are compared and evaluated. Finally, the sensitive analysis of impact factor indicates that the injected sorbent concentration plays most important role for mercury capture efficiency.