Investigation of competitive tar reforming using activated char as catalyst

Syngas tar removal is one of the biggest challenges for the gasification of biomass as a clean energy source. Efforts to understand the reforming mechanism of tar compounds have been continuous during the last decades. Kinetic studies often employ a single tar species, neglecting possible interactions between different tar compounds. On the other hand, char, a by-product from biomass gasification, presents opportunities to catalyze tar reforming. In this work, reforming experiments were conducted in a fixed-bed reactor using syngas with a known mixture of benzene (C6H6), toluene (C7H8) and naphthalene (C10H8). Hardwood char and an in-situ CO2-activated hardwood char were used as catalysts. The activated hardwood char exhibited the best reforming capabilities by converting 44% and 90% of the tars at 750 and 850°C, respectively, compared to 24% and 87% tar conversion obtained with the regular hardwood char at 750 and 850°C, respectively. From the experiments, a reduced mechanism model was proposed. This mechanism was used in computational simulations for analysis of the reaction kinetics, including possible catalyst selectivity. It was found that under a range of conditions, the benzene degradation is slower than its formation rate from toluene and naphthalene decomposition. This leads to increases in the benzene fraction at temperatures around 700°C. If the naphthalene and toluene concentrations are sufficient, benzene will accumulate even at high temperatures (around 800°C) regardless of residence times. It can be concluded that when benzene, toluene and naphthalene are present together, char favors the heterogeneous reforming of toluene and naphthalene, with benzene following an homogeneous reforming pathway

Effective antimicrobial activity of ZnO and Yb-doped ZnO nanoparticles against Staphylococcus aureus and Escherichia coli

Nanostructured Zn1-xYbxO (0.0 ≤ x ≤ 0.1) powders were prepared by the solution method using polyvinyl alcohol (PVA) and sucrose. The effect of the ytterbium doping content on the structural, morphological, optical and antimicrobial properties was analyzed. X-ray diffraction (XRD) analysis revealed that the hexagonal wurtzite structure was retained, and no secondary phases due to doping were observed. The crystallite size was under 20nm for all the Zn1-xYbxO (0.0 ≤ x ≤ 0.1) powders. The optical band gap was calculated, and the results revealed that this value increased with the ytterbium content, and the Eg values varied from 3.06 to 3.10 eV. The surface chemistry of the powders was analyzed using X-ray photoelectron spectroscopy (XPS), and the results confirmed the oxidation state of ytterbium as 3+ for all the samples. Zn1-xYbxO (0.0 ≤ x ≤ 0.1) nanoparticles were tested as antimicrobial agents against Staphylococcus aureus and Escherichia coli, resulting in a potential antimicrobial effect at most of the tested concentrations. These results were used in an artificial neural network (ANN). The results showed that it is possible to generate a model capable of forecasting the absorbance with good precision (error of 1–2%)

Seroepidemiology of Toxoplasma gondii infection in psychiatric inpatients in a northern Mexican city

BACKGROUND: Patients with psychiatric disorders were found to show a high seroprevalence of Toxoplasma gondii infection. There is scarce information about the epidemiology of T. gondii infection in psychiatric patients in Mexico. Therefore, we sought to determine the prevalence of T. gondii infection and associated socio-demographic, clinical and behavioural characteristics in a population of psychiatric patients in Durango City, Mexico. Seroprevalence in patients was compared with that obtained in a control population. METHODS: One hundred and thirty seven inpatients of a public psychiatric hospital and 180 controls were examined for the presence of IgG and IgM antibodies against T. gondii by enzyme-linked immunoassay (Diagnostic Automation Inc., Calabasas, CA, USA). The control population consisted of blood donors of a public blood bank and elderly persons attending a senior center in the same city. Age in controls (42 years +/- 20.2) was comparable with that of the psychiatric patients (43.7 years +/-13.8) (p = 0.42). Socio-demographic, clinical and behavioral characteristics from the patients were also obtained. RESULTS: Anti-T. gondii IgG antibodies indicating latent infection with T. gondii was found in 25 (18.2%) of 137 psychiatric inpatients and 16 (8.9%) of 180 controls (p = 0.02). Ten (26.3%) of 38 schizophrenic patients had latent infection and this prevalence was also significantly higher than that observed in controls (p = 0.005). Prevalence of anti-T. gondii IgM antibodies was comparable among patients and controls (4.4% vs 2.2%, respectively, p = 0.22). Multivariate analysis showed that T. gondii infection in inpatients was positively associated with sexual promiscuity (adjusted OR = 15.8; 95% CI: 3.8–64.8), unwashed raw fruit consumption (adjusted OR = 5.19; 95% CI: 2.3–11.3), and a history of surgery (adjusted OR = 6.5; 95% CI: 2.6–16), and negatively associated with lamb meat consumption (adjusted OR = 0.26; 95% CI: 0.10–0.63). CONCLUSION: In the present study, psychiatric inpatients in Durango, Mexico, in general and schizophrenia inpatients in particular had a significantly higher prevalence of T. gondii infection than the control group. Results suggest that unwashed raw fruit consumption might be the most important route of T. gondii transmission in our psychiatric inpatients while lamb meat consumption the less important. Additional studies will have to elucidate the causative relation between infection with T. gondii and psychiatric disorders

Computers as a Tool to Empower Students and Enhance Their Learning Experience: A Social Sciences Case Study

Computers in mathematics education help foster abstract concepts and solve problems that are unsolvable by hand. Moreover, students whose major does not have a mathematical background often struggle with the topic and may require learning aid. Although extensive research has been conducted on the effect of computers and different software in learning, students’ perception on computers to solve mathematical problems has scarcely been studied. In this work, a group of undergraduate social sciences students were given computers to learn mathematics and solve contextual real-life problems, with the aim of facilitating learning and providing empowerment. After the courses, the students were asked their perception of computers and mathematics to obtain descriptive results on their perception. Responses indicated that with computers, students felt learning and solving mathematics problems was easier (85% of the answers), they felt more confident about their skills (69%), and could think of new ways to solve problems (54%). Moreover, a text analysis was conducted using software to assess open-ended questions, and the results indicated that most answers were positive in nature. Additionally, the students were given the chance to rate the mathematics course using computers, and the course received a rating of 9.5/10, indicating the methodology was liked

An Energy and Exergy Analysis of Biomass Gasification Integrated with a Char-Catalytic Tar Reforming System

Adequate tar removal is a recurrent challenge for biomass gasification. Materials such as char and activated char are promising catalysts for tar reforming because of their activity, inexpensiveness, and constant production during gasification. Although the behavior of char and activated char as catalysts has been previously studied, an evaluation of the thermodynamic efficiencies of the tar reforming process using char as a catalyst still lacking. This work analyzes the performance of a two-stage system, where gasification is followed by tar reforming using char catalysts. For the study, a model based in a combination of equilibrium thermodynamics and chemical kinetics was developed. The first stage, where gasification occurs, was simulated with a thermodynamic equilibrium model. Gasification equilibrium models available in the literature only predict the fractions of H 2, CO, CO 2, and CH 4; the model developed for this work also predicts the formation of a three-model tar with different characteristics (benzene, toluene, and naphthalene), providing information on the stability of formed tar. The second stage, simulated using kinetics from the literature, consists of reforming the tar with catalysts made of residual char. The effects of the reactor temperature, equivalence ratio, and residence time were assessed via the gas quality, based on the gas lower heating value and tar concentration, and process efficiency, based on the energy and exergy efficiencies. Results showed that using char or activated char catalysts increases the heating value of the gas while reducing its tar concentration. Moreover, the process benefits thermodynamically (i.e., less exergy is destroyed) from low gasification temperatures and high reforming temperatures. Simulations indicate that a tarless gas with a lower heating value of more than 8 MJ/Nm 3 can be produced from gasification at 1023 K with an equivalence ratio of 0.15 and subsequent reforming at 1123 K with a residence time in the catalyst bed of 1 s

The use of gasification solid products as catalysts for tar reforming

The presence of tars in syngas is a major technological constraint for upscaling biomass gasification to produce heat, power, and other value-added chemicals such as biofuels. At the same time, the solid remains from biomass gasification i.e. char and ashes, have capabilities to catalyse the reforming of gasification tars. This work presents a comprehensive analysis of the relevance of gasification chars and ashes as catalysts for tar reforming. A description of the solid products from biomass gasification, their formation, chemical characteristics and potential applications is given. Additionally, a review of the state of the art of the uses of regular char, activated carbon and ashes as a catalyst for tar reforming is presented. Further, kinetics reported in literature, and the homogeneous and heterogeneous mechanisms for tar reforming over char are discussed and explained. From reviewing literature it was found that activated chars exhibit the best reforming capabilities, followed by regular char and ashes. Knowing the role of the interactions between the char and the tars is a key factor for optimization of char catalysts. Ultimately, this work provides guidance for understanding the uses of biomass solids as catalysts for tar reforming, and aid in future research to increase the economic feasibility of biomass gasification

Performance of biochar as a catalyst for tar steam reforming : effect of the porous structure

The application of gasification to thermally treat biomass as carbon neutral resources has been constrained by the technical challenges associated with tar formations, which cause operational problems in downstream equipment for syngas processing. Catalysts, such as transition metals, calcined rocks and char, can be used to catalyse tar reforming. Biochars, which are naturally produced during biomass gasification, are particularly attractive as an alternative catalyst due to their catalytic functions, low cost and long endurance. Despite these promising characteristics, adequate knowledge on the relationship between the porous structure of biochar and its deactivation by coking during the steam reforming of tars is not available. In this work, the influence of the porous structure of biochar on its performance across time for reforming tar was investigated in a fixed-bed reactor, over a temperature range from 650 to 850 °C. Regular biochar and physically activated biochar from the same precursor biomass were employed as bed material. The tar samples were the composed mixture of benzene, toluene and naphthalene. Both fresh and spent catalysts were analysed with Brunauer-Emmet-Teller, t-plot, Fourier Transform Infrared and Scanning Electron Microscopy/Energy Dispersive Spectroscopy. Results showed that, while at moderate temperatures of 650 and 750 °C, the activated biochar offered a higher tar conversion but more severe deactivation than that of the regular biochar. At the high temperature of 850 °C, the difference in the catalytic performance between the two chars was negligible, and over 90% of the initial tar species were removed throughout the 3-hour long experiments. At 850 °C, the coke deposited in the meso- and macro-pores of both chars was gasified, leading to a stable catalytic performance of both chars. The results indicated that meso- and macro-porous biochars are resilient and active enough to become a viable option for tar steam reforming