Effect of the Presence of HCl on Simultaneous CO2 Capture and Contaminants Removal from Simulated Biomass Gasification Producer Gas by CaO-Fe2O3 Sorbent in Calcium Looping Cycles

This study investigated the effect of HCl in biomass gasification producer gas on the CO2 capture efficiency and contaminants removal efficiency by CaO-Fe2O3 based sorbent material in the calcium looping process. Experiments were conducted in a fixed bed reactor to capture CO2 from the producer gas with the combined contaminants of HCl at 200 ppmv, H2S at 230 ppmv, and NH3 at 2300 ppmv. The results show that with presence of HCl in the feeding gas, sorbent reactivity for CO2 capture and contaminants removal was enhanced. The maximum CO2 capture was achieved at carbonation temperatures of 680 °C, with efficiencies of 93%, 92%, and 87%, respectively, for three carbonation-calcination cycles. At this carbonation temperature, the average contaminant removal efficiencies were 92.7% for HCl, 99% for NH3, and 94.7% for H2S. The outlet contaminant concentrations during the calcination process were also examined which is useful for CO2 reuse. The pore structure change of the used sorbent material suggests that the HCl in the feeding gas contributes to high CO2 capture efficiency and contaminants removal simultaneously.

A Study of the Sorption Characteristics of Nanostructured Calcium Silicate

<p>Nanostructured calcium silicate (NCS) is an X-ray amorphous silicate material consisting of randomly arranged platelets several tens of nanometres in size, forming agglomerates a few micrometres in size. This affords the material a high, readily accessible surface area of up to 600 m2 g -1 with chemically active surface-bound calcium and silanol groups being integral parts of the silicate structure. As such, it makes an ideal material for the sorption of many potential pollutant materials. However, NCS is highly thixotropic. This reduces its applicability for use as a sorbent material on a large scale, the thixotropic nature of NCS precluding its efficient separation from suspension. NCS, in contact with water, will ion-exchange surface-bound calcium with hydrogen ions, releasing calcium into solution, and leading to an increase in the pH value of the solution. The process may be exploited by using the material as a sorbent for cationic metal species forming insoluble hydroxides. This thesis demonstrates the use of NCS as a sorbent material for Cu2+, with the material exhibiting a sorption capacity for this ion of up to 10 mmol g -1. When the sorption capacity of the material is reached, all the calcium initially present in the NCS material (31-38 wt % CaO) is leached into solution. The copper is initially sorbed as an X-ray amorphous phase (most likely Cu(OH)2) but in the presence of excess copper, the more thermodynamically stable crystalline phase Cu2X(OH)3, X being chloride or nitrate, is formed. It was shown that the presence of calcium is necessary for this sorption to occur. When calcium was leached from the material prior to sorption studies, the sorption capacity of the material was significantly decreased. To aid the separation process of NCS from solution, bulk magnetite powder (Fe3O4), or superparamagnetic magnetite or maghemite (g-Fe2O3) were incorporated into the NCS structure during its synthesis. The addition of these additives to the NCS material reduced characteristics such as specific surface area or sorption capacity insofar as extra mass had been added to the system. The structure of the NCS was not degraded. The NCS material containing bulk magnetite powder was shown to be applicable to the sorption of phosphate in a continuous fluidised bed system, utilising the magnetic properties of the material to aid separation. Phosphate was chosen, as the sorption characteristics of NCS with respect to this ion were previously known. Attempts to use magnetic techniques to separate the superparamagnetic composites subsequent to copper sorption were unsuccessful. Although the composite materials exhibited similar sorption capacity for copper to the unmodified one, the acidic conditions of the copper solution degraded the composite, precluding the use of magnetic separation. Finally, composite materials of NCS and a conducting polymer, polyaniline, were prepared which provided potential redox-activity to a high surface area substrate. The sorption characteristics of this material were demonstrated with its use as a sorbent for the perrhenate ion. This rhenium ion was chosen due to its chemical similarity to pertechnetate, a component of many radioactive wastewaters. It was demonstrated that the sorption process proceeded via an electrochemical mechanism in which the polyaniline caused the perrhenate ion to be reduced to a rhenium oxide species.</p>

A Study of the Sorption Characteristics of Nanostructured Calcium Silicate

<p>Nanostructured calcium silicate (NCS) is an X-ray amorphous silicate material consisting of randomly arranged platelets several tens of nanometres in size, forming agglomerates a few micrometres in size. This affords the material a high, readily accessible surface area of up to 600 m2 g -1 with chemically active surface-bound calcium and silanol groups being integral parts of the silicate structure. As such, it makes an ideal material for the sorption of many potential pollutant materials. However, NCS is highly thixotropic. This reduces its applicability for use as a sorbent material on a large scale, the thixotropic nature of NCS precluding its efficient separation from suspension. NCS, in contact with water, will ion-exchange surface-bound calcium with hydrogen ions, releasing calcium into solution, and leading to an increase in the pH value of the solution. The process may be exploited by using the material as a sorbent for cationic metal species forming insoluble hydroxides. This thesis demonstrates the use of NCS as a sorbent material for Cu2+, with the material exhibiting a sorption capacity for this ion of up to 10 mmol g -1. When the sorption capacity of the material is reached, all the calcium initially present in the NCS material (31-38 wt % CaO) is leached into solution. The copper is initially sorbed as an X-ray amorphous phase (most likely Cu(OH)2) but in the presence of excess copper, the more thermodynamically stable crystalline phase Cu2X(OH)3, X being chloride or nitrate, is formed. It was shown that the presence of calcium is necessary for this sorption to occur. When calcium was leached from the material prior to sorption studies, the sorption capacity of the material was significantly decreased. To aid the separation process of NCS from solution, bulk magnetite powder (Fe3O4), or superparamagnetic magnetite or maghemite (g-Fe2O3) were incorporated into the NCS structure during its synthesis. The addition of these additives to the NCS material reduced characteristics such as specific surface area or sorption capacity insofar as extra mass had been added to the system. The structure of the NCS was not degraded. The NCS material containing bulk magnetite powder was shown to be applicable to the sorption of phosphate in a continuous fluidised bed system, utilising the magnetic properties of the material to aid separation. Phosphate was chosen, as the sorption characteristics of NCS with respect to this ion were previously known. Attempts to use magnetic techniques to separate the superparamagnetic composites subsequent to copper sorption were unsuccessful. Although the composite materials exhibited similar sorption capacity for copper to the unmodified one, the acidic conditions of the copper solution degraded the composite, precluding the use of magnetic separation. Finally, composite materials of NCS and a conducting polymer, polyaniline, were prepared which provided potential redox-activity to a high surface area substrate. The sorption characteristics of this material were demonstrated with its use as a sorbent for the perrhenate ion. This rhenium ion was chosen due to its chemical similarity to pertechnetate, a component of many radioactive wastewaters. It was demonstrated that the sorption process proceeded via an electrochemical mechanism in which the polyaniline caused the perrhenate ion to be reduced to a rhenium oxide species.</p>

Different low-cost materials to prevent the alteration induced by formic acid on unstable glasses

The most frequent cause of glass degradation is environmental moisture, which is adsorbed on its surface forming a hydration layer that induces the rupture of the glass network. This pathology is accelerated by the accumulation of volatile organic compounds (VOCs), like formic acid. Although there is extensive knowledge about their impact, concentrations inside display cases are difficult to reduce efficiently. This study presents the assessment of different materials to reduce the concentration of formic acid to mitigate the degradation produced in unstable glasses. With this objective, copper threads, steel wool, silica gel, and activated carbon were chosen as low-cost materials with good adsorption or reactivity to the VOCs, exposing them in desiccators to an environment of 100% RH and 10 ppm of formic acid. Given that silica gel obtained the best results, its optimization as a sorbent material was evaluated by maintaining, regenerating, or renewing it when exposed next to the same glass. The tests carried out concluded that the hygroscopic capacity of the glasses exposed with silica gel decreased and, therefore, a lower degradation is observed on its surface. In addition, regenerating and renewing weekly the silica gel improved the results.

Adsorption of Yttrium Ions on 3-Amino-5-Hydroxypyrazole Impregnated Bleaching Clay, a Novel Sorbent Material

In this work, spent bleaching clay (SBC) was treated with ethyl acetate and impregnation with 3-amino-5-hydroxypyrazole (AHIBC) that utilized as economical sorbent material. The uptake of yttrium ions from aqueous solution using AHIBC was studied under batch process as a function of pH of the solution, contact time, adsorbent dosage, Yttrium ions concentration, and ambient temperature. The adsorption equilibrium was achieved at the value of pH = 6.0 and agitation time of 60 min at room temperature. The utmost adsorption capacity of Y(III) ions on AHIBC was 171.32 mg·g−1. Kinetic, isotherm, and thermodynamic models were applied to the experimental data obtained. Adsorption follows a pseudo–second–order kinetic model, while the adsorption isotherm fits the Langmuir model. A negative value of Gibbs free energy ΔG° revealed that the adsorption of the Y ions on the AHIBC adsorbent was spontaneously in nature. In addition, the electrostatic interaction process between the metal ions and AHIBC was favorable. The negative value of ΔH° states that Y ions adsorption was an exothermic process. Desorption efficiency reduced from 97% to 80% after eight consecutive rounds.

Oil Sorption Performance of Sorbent Materials Examined Under Static and Dynamic Conditions

Oil spill cleanup and subsequent restoration of the environment is majorly a function of spill cleanup methods applied. Some of these methods, though efficient, are, however, very expensive and require more personnel for their application and relative deployment in the field. The study was aimed at examining the efficiency of a locally and readily available, eco-friendly and low cost agricultural waste (coconut husk coir) as sorbent materials for spilled engine oil cleanup under static and dynamic marine water conditions. The sorbent material was prepared and used in three forms: raw coconut husk coir (CHC), modified coconut husk coir (MCHC), and reused coconut husk coir (RCHC). Under static and dynamic marine water conditions, oil sorption batch equilibrium experiments were used to study the engine oil sorption capacity and efficiency of the sorbent. Effects of sorbent dosage and sorption times on the oil sorption and efficiency of CHC, MCHC, and RCHC were studied and determined. At a constant sorption time of 60 minutes and varying sorbent dosages of 2-8 /320 ml of engine oil-marine water concentration, MCHC exhibited the highest oil sorption efficiency of 61.18% and 44.33% for dynamic and static conditions, CHC had 55.61% and 38.50% for dynamic and static conditions, whereas RCHC had 41.66% and 26.04% for dynamic and static conditions, respectively. It is statistically deduced from the results that sorption times and sorbent dosages have significant effects on the sorption efficiency of experimental coir for spilled engine oil removal. Though there is a need for proper blending or modifications of the sorbent material to enhance its affinity to oil and hydrophobicity, there are enough potentials in the materials for mild marine water current spilled engine oil cleanup.

Removal of Cresols From Water By Packed Beds of Cyclodextrin-Based Hydrogels

A cyclodextrin-based polymer was prepared by crosslinking β-cyclodextrin with epichlorohydrin to be assessed as a sorbent material for cresols in packed-bed columns. Both Langmuir and Freundlich isotherms were appropriate to describe the sorption equilibrium in the conditions tested, and the thermodynamic parameters obtained for this process confirmed its exothermic nature with similar enthalpies (between −6.8 and −8.3 kJ/mol) for the three isomers. The removal of cresols from water was carried out in nine cycles of sorption-desorption in fixed-column experiments with the cyclodextrin hydrogel, achieving sorption capacities of 6.2, 11.6, and 15.1 mg/g for o-, m-, p-cresol, respectively. The experimental data for the breakthrough and the elution curves have been successfully modeled by two effective two-parameter equations, a dose-response model for the sorption step and a pulse-peak model for the regeneration step. The cyclodextrin polymer matrix has been proven to be an effective a good sorbent material for removing cresols from water, exhibiting remarkable reusability performance and structural stability throughout the successive elution steps carried out with methanol.

Removal of Dye Acid Red 1 from Aqueous Solutions Using Chitosan-iso-Vanillin Sorbent Material

Sorption of Acid Red 1 (AR1) from aqueous solutions utilizing low-cost sorbent material; (chitosan-iso-vanillin) is studied under batch conditions. The remaining concentrations of the azo dye are measured at λmax = 546 nm by UV spectrophotometric method. Langmuir data reveal that the maximum removal capacity was 555.556 mg/g at pH 3. Freundlich isotherm represents the best fitting model on the removal of AR1 using chemically modified chitosan verifying the sorption takes place on heterogeneous surfaces with multilayer adsorption. Kinetic studies of the sorption process revealed that intraparticle diffusion is not only the rate-determining step but also a chemical reaction takes place as well. The results indicate that high sorption rapidness with almost 90% achieved within 90 min. Thermodynamic investigations suggest that the process favours an exothermic nature. The polymer utilized in the present study is being considered as a feasible sorbent material for the removal of AR1 from waste effluent.