A theoretical and experimental study on biochar as an adsorbent for removal of acid gases (CO₂ and H₂S)

Biochar, a carbon-rich material that is obtained from forestry wood residues through thermochemical conversion in the absence of oxygen (i.e. pyrolysis), is a potential alternative to commercial adsorbents for acid gas treatment. Acid gases (CO₂ and H₂S) are present in landfill gases, fossil fuel gases, and mining operations. These gases must be treated to improve environmental safety and limit operational issues such as pipeline corrosion. Common processes for removal of acidic gases from landfill, flue, and natural gas streams include amine absorption processes, which are energy and space intensive due to required regeneration, and solid adsorbents (which can be costly to produce and dispose of). In this work, CO₂ adsorption using biochar as a solid adsorbent was investigated. Use of biochar as an adsorbent for acid gas removal is relatively novel. The specific objectives included; characterize the biochar structure (i.e. chemical, physical, and morphological) through a series of analyses; determine the operating conditions for obtaining maximum adsorption capacity; modify the biochar surface to determine impact on adsorption; and develop a molecular model to simulate the adsorption process to determine if it can be used as a tool in experimental design. Chapter one gives an overview of the conceptual framework of acid gas purification and outlines the objectives, the scopes, and the significance of this study along with a summary of the thesis chapters. Chapter two provides a literature review to identify different types of biochar production methods, reaction conditions (e.g. temperature and residence time), and woody biomass as one of possible feedstock materials. The biochar was compared with commercial adsorbents and the results indicated biochar could be used as a feasible alternative to activated carbon as it is environmentally friendly and a low-cost adsorbent. In addition, the impact of production conditions on biochar properties were investigated and it was found that carbon, hydrogen content, and surface area were significantly affected by pyrolytic temperature. The reported isotherms in the literature were compared and the Freundlich isotherm was the best fit with the biochar. The application of molecular modeling to describe adsorption process and different simulation methods were studied. The biochar for this research was produced from three different woody biomasses: softwood (sawdust and bark (Balsam fir)) and hardwood (Ash wood) through fast pyrolysis at 400-500⁰C and then compared in terms of chemical and physical properties in chapter three. Chapter four looks at the impact of three operating conditions, temperature, inlet feed flow rate, and CO₂ concentration, on biochar adsorption capacity and the interaction of these parameters were evaluated using response surface methodology. The operating conditions for maximizing CO₂ uptake were determined and the Freundlich isotherm best represented the equilibrium adsorption and the pseudo first-order was selected as a kinetic model. Thermodynamic analysis indicated the adsorption process was spontaneous and exothermic. Further, we found that biochar derived from “waste” materials had better adsorption capacity relative to commercial zeolite. Chapter five describes chemical modification of the biochar using two novel methods of amine functionalization and the maximum adsorption capacity was measured at the conditions obtained in chapter four. The results indicated functionalization decreased the pore volume, surface area, and subsequently the adsorption capacity of the biochar. In order to enhance capacity, the biochars (unmodified and chemically modified) were thermally activated via air diluted with nitrogen at a moderate 560⁰C. Some nitrogen functionality retained in the biochar structure even after activation. The synthesized N-enriched biochar followed by thermal activation was found to have much higher adsorption capacity as compared with commercially available activated carbon (Norit CA1) and recent carbon based adsorbents in the literature. Chapter six is dedicated to molecular modeling and linking the experimental results with simulations. The effect of various functional groups on adsorption of CO₂/H₂S on biochar surface was investigated. It was found that the presence of functional groups promotes CO₂ adsorption on the surface with exothermic adsorption energy. As expected, the DFT calculations showed amine functional groups enhanced CO₂ adsorption with more exothermic adsorption likely because of stronger bonding compared to other functional groups. The thermodynamic outcomes (Enthalpy and Gibbs free energy) validated that the affinity of the chars for CO₂ is on the same order of magnitude as H₂S. The simulated thermodynamic parameters and IR vibrational frequencies were calculated and both showed reasonable agreement with experimental results (chapter four and five). The results of this study would be helpful for developing future work, on the scale-up of the adsorption system, further modification of the biochar, CO₂ sequestration, regeneration, and atomic-level design of carbon surfaces

Studies on the adsorption/absorption-based CO₂ capture process focusing on implications of process design and adsorbent selection

At COP26 in Glasgow in November 2021, a decisive commitment was made to limit the rise in global temperature to a maximum of 1.5 degrees. Urgent actions are required to achieve the worldwide goal of net-zero carbon emissions by the middle of the century, necessitating a reduction in greenhouse gas emissions. Renewable energy development in the long term and Carbon Capture and Storage (CCS) in the short term are identified as the most effective methods to combat the dramatic increase in CO₂ emissions from industrial processes and fossil-fuel electricity generation. In this thesis, investigations focus on two industrial emission points with carbon capture technology: integrated gasification combined cycle (IGCC) integrated with pre-combustion CO₂ capture and conventional coal-fired power plants integrated with post-combustion CO₂ capture. Primarily, this thesis sought to design and evaluate two process configurations of an IGCC integrated with pre-combustion CO₂ capture unit (Chapter 4). One IGCC process is configured with sour shift, while the other is based on sweet shift. Incorporating water-gas shift reactors (WGSRs) consuming vast amount of shift steam into an IGCC involves significant alternations to the associated steam cycle, in addition to simply changing the location of the H₂S removal step around the shift reactors. Although the sweet shift case requires 4.6 times more shift steam compared to the sour shift case, the energy penalties incurred by carbon capture integration for both configurations were estimated to be almost equal. This similarity is attributed to the water quench requirements of sour shift, leading to a reduction in power generation during the steam cycle. In both cases, the sizes of high and low-temperature water-gas shift reactors were estimated using the reaction rate models reported in literature. Additionally, this thesis aims to evaluate and compare conventional and emerging porous adsorbents in their applications to an adsorption-based CO₂ capture processes from the flue gas produced by the conventional coal-fired power plant (15% CO₂ and 85% N₂) (Chapter 5). The adsorbent candidates involved in this thesis include zeolites, carbons, MOFs, and triazine-based benzimidazole-linked polymers (TBILPs). The choice of adsorbent material significantly affects process performance in the design of efficient CO₂ capture processes. It was demonstrated that adsorbents with high CO₂ recovery did not necessarily correspond to increased productivity. Productivity depends on desorption pressure and CO₂ isotherm shape. Despite MFI demonstrating the highest CO₂ recovery among all zeolite candidates, it exhibited the lowest productivity due to its lowest CO₂ adsorption capacity. Likewise, the adsorption materials with flat CO₂ isotherms such as BPL AC, UiO-66, MIL-101(Cr)-F, MIL-101(Cr)-OH, and TBILPs also showed better CO₂ recovery but less productivity compared to the commercial zeolite 13X. In contrast, Mg-MOF-74 showed the highest productivity, attributed to its steepest CO₂ isotherm during the initial stage of the adsorption. However, a low desorption pressure was required to reach a high CO₂ recovery, leading to extremely high energy consumption. To further investigate adsorbents for adsorption-based CO₂ capture, a two-stage VSA process was simulated by gPROMS upon achieving the desired operational criteria of 90% CO₂ recovery and 90% CO₂ purity (Chapter 6). The first stage was packed with MFI, while the second stage employed activated carbon (AC), namely MFI-AC case. As a comparative analysis, an alternative two-stage VSA process utilised zeolite 13X in the first stage and AC in the second stage (zeolite 13X-AC case). As a result, the total productivities for both MFI-AC and zeolite 13X-AC cases were found to be similar, around 6.3 //ℎ. However, it is essential to note that the MFI-AC process exhibited a higher minimum specific energy consumption, estimated at 17.1 /₂, in comparison to the zeolite 13X-AC process. This thesis contributes to an advanced understanding of the process design in pre-combustion IGCC plant integrated with the adsorption-based CO₂ capture process with a focus on the choice between sour or sweet shift configurations. Besides, this thesis comprehensively evaluates various porous adsorbents for CO₂ separation from the flue gas using a P/VSA process and provide a systemic guideline for selecting adsorbents

Technologies to Capture CO2_2 directly from Ambient Air

Building a carbon-neutral world needs to remove the excess CO$_2$ that has already been dumped into the atmosphere. The sea, soil, vegetation, and rocks on Earth all naturally uptake CO$_2$ from the atmosphere. Human beings can accelerate these processes in specific ways. The review summarizes the present Direct Air Capture (DAC) technology that contribute to Negative Emissions. Research currently being done has suggested future perspectives and directions of various methods for Negative Emission. New generations of technologies have emerged as a result of recent advancements in surface chemistry, material synthesis, and engineering design. These technologies may influence the large-scale deployment of existing CO$_2$ capture technologies in the future

POROUS NANOMATERIALS AS CONTROLLED DRUG DELIVERY SYSTEMS

MIL-53(Fe) was synthesized by conventional electric (CE) heating, and by ultrasound (UTS) and microwave (MW) irradiation to develop rapid and energy efficient synthesis techniques. MW and UTS conditions rapidly produced small and highly crystalline materials in 10 and 7 minutes, respectively. The energy consumption of UTS and MW irradiation were less than CE heating, confirming that these two technologies are quicker, more efficient and greener alternatives to conventional synthesis methods. The use of MIL-53(Fe), MIL-101, and SBA-15 as matrices for the adsorption and in vitro drug delivery of acetaminophen, progesterone, and stavudine was studied. An initial burst release from both MIL-53(Fe) and MIL-101 was followed by a slow diffusion-controlled release, which occurred for up to 6 and 5 days, respectively. Complete release from SBA-15 occured in as quickly as 30 minutes as a result of rapid drug dissolution and diffusion out of the pores

Novel Metal Oxide Nanostructures for Adsorption and Photocatalytic Degradation of Organic Dyes from Aqueous Stream

Recent research focused on the applications of nanomaterials in environmental remediation especially the treatment of natural waters, industrial and domestic waste water and the polluted underground water. Providing clean water and a clean environment for the world growing population is a challenging task. The present thesis represents an extensive view of the use of nanomaterials in environmental remediation such as water purification using single and composite metal oxide nanomaterials by sorption and photocatalysis of toxic organic dyes. In the present study, we have synthesized 1D iron oxide nanomaterials and iron oxide based nanocomposites such as Fe2O3-SnO2, Fe2O3-CuO, Fe2O3/ZnFe2O4/ZnO, and MgFe2O4-Fe2O3 of different morphology using precipitation, hydrothermal and reflux methods. Apart from this we have also synthesized MgO nanomaterials and iron oxide impregnated mesoporous MCM-41 by wet chemical impregnation method. The obtained metal oxide nanomaterials and their nanocomposites were characterized using XRD, SEM, TEM, EDAX, XPS, Raman, FTIR, UV-Vis-DRS and BET surface area analytical techniques and were used as adsorbents and photocatalysts for decontamination of organic dyes from aqueous solutions. We have synthesized ferrous oxalate, hematite and maghemite nanorods by precipitation method. The XRD patterns indicate the formation of different crystalline phases of ferrous oxalate (FeC2O4.2H2O), hematite (α-Fe2O3) and maghemite (γ-Fe2O3). The SEM and TEM images confirm the formation of rod shaped morphology with diameter in the range of 100-200 nm and length up to micrometers. The prepared nanorods were used as adsorbents for removal of carcinogenic Congo red dye from aqueous solution. After the batch adsorption study, the maximum adsorption capacities of the adsorbents were found to be 103, 232 and 78 mg/g for FeC2O4.2H2O, γ-Fe2O3 and α-Fe2O3 nanorods, respectively. We have also prepared Fe2O3-SnO2 composite nanorods by using same precipitation method. XRD study revealed the presence of magnetic γ-Fe2O3 phase along with SnO2 in Fe2O3–SnO2 composite. The Fe2O3–SnO2 composite nanorods were used as adsorbents for removal of Congo red dye from aqueous solution. Among different compositions, Fe2O3–SnO2 (Fe:Sn=8:2) composite nanorod showed highest percentage adsorption with sorption capacity of 182 mg/g. Mesoporous MCM-41 and MCM-41 impregnated with iron oxide nanomaterials (Fe-MCM-41) were prepared by a facile surfactant based wet chemical method. The experimental results indicate the formation of porous nanostructure with high surface area (>800 m2/g) and particle size in the range of 200-400 nm. The mesoporous materials were used as adsorbents for the removal of Methylene blue from aqueous media. The maximum adsorption capacity of Fe-MCM-41 was found to be 194 mg/g and was higher than that of MCM-41. MgO nanomaterials with different morphologies such as: nanorods, hierarchical nanostructures and nanoflakes were synthesized by precipitation, reflux and hydrothermal methods, respectively. The prepared nanomaterials were used as adsorbents to remove as Malachite green and Congo red from aqueous media. The hierarchical MgO nanostructure exhibited excellent adsorption performance for removal of Malachite green and Congo red with maximum sorption capacities of 1205 and 1051 mg/g, respectively. Using same synthesis methods we have used iron salt precursor along magnesium to prepare MgFe2O4 and MgFe2O4-Fe2O3 composite nanostructures. The MgFe2O4-Fe2O3 nanocomposite prepared by precipitation method was regarded as a superb photocatalyst for 99.9 % methylene blue degradation. We have also synthesized Fe2O3-CuO composite nanorod by same precipitation method. From FESEM and TEM analysis it was observed that the spherical CuO nanoparticles are decorated uniformly onto the α-Fe2O3 nanorod surface forming a one-dimensional heteronanostructure. The obtained 1D Fe2O3-CuO nanocomposite exhibited higher photocatalytic activity than individual α-Fe2O3 nanorods and CuO nanoparticles for degradation of Methyl orange from aqueous media under solar light irradiation. Furthermore, we have synthesized α-Fe2O3 nanoparticle and Fe2O3/ZnFe2O4, Fe2O3/ZnFe2O4/ZnO and ZnFe2O4/ZnO mixed oxide nanocomposites by varying different molar ratio of Fe and Zn using hydrothermal method. The nanocomposite with Fe:Zn=70:30 and 60:40 contains ternary Fe2O3/ZnFe2O4/ZnO phase. The nanomaterials have been used for photocatalytic degradation of Malachite green from aqueous media using solar light irradiation. The ternary Fe2O3/ZnFe2O4/ZnO (Fe:Zn=70:30) nanocomposite exhibits highest photocatalytic activity among all the prepared nanomaterials. The enhanced activity could be attributed to the cascade electron transfer from ZnFe2O4 to ZnO to Fe2O3through the interfacial potential gradient in the ternary nanostructur

Silica and Silicon Based Nanostructures

Silica and silicon-based nanostructures are now well-understood materials for which the technologies are mature. The most obvious applications, such as electronic devices, have been widely explored over the last two decades. The aim of this Special Issue is to bring together the state of the art in the field and to enable the emergence of new ideas and concepts for silicon and silica-based nanostructures

Estudio de sistemas líquido iónico/carbón activo y sus aplicación en la retención de contaminantes = Essays on ionic liquid/activated carbon systems and heir application to pollutants removal

Tesis doctoral inédita, leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Departamento de Química Física Aplicada. Fecha de lectura: 20-11-201

Zeolites as Ingredients of Medicinal Products

Development of new medicinal products for particular therapeutic treatment or for better manipulations with better quality and less side effects are possible as a result of advanced inorganic and organic materials application, among which zeolites, due to their properties and versatility, have been gaining attention. This paper is an overview of the development in the use of zeolite materials and their composites and modifications as medicinal products for several purposes such as active agents, carriers, for topical treatments, oral formulations, anticancer, the composition of theragnostic systems, vaccines, parenteral dosage forms, tissue engineering, etc. The objective of this review is to explore the main properties of zeolites and associate them with their drug interaction, mainly addressing the advances and studies related to the use of zeolites for different types of treatments due to their zeolite characteristics such as molecule storage capacity, physical and chemical stability, cation exchange capacity, and possibility of functionalization. The use of computational tools to predict the drug—zeolite interaction is also explored. As conclusion was possible to realize the possibilities and versatility of zeolite applications as being able to act in several aspects of medicinal products

Innovative Materials and Methods for the Removal of Pollutants from the Environment

The progress of society has led to an improvement of the quality of life of a significant number of people. On the other hand, anthropogenic pollution dramatically increased, with serious consequences for the environment and human health. Controlling and remedying environmental pollution is one of the main challenges of our century. Fundamental and applicative research are called to collaborate, involving scientists in the development of realistic and effective systems for the prevention and the removal of pollutants from the environment. Spreading knowledge is among the missions of researchers and this is the aim of this book, offering an updated view on innovative materials and methods for pollutant treatment. It is composed of 18 articles, among them 5 reviews and 13 original articles, dedicated to new adsorbent materials (inorganic, organic, and hybrid materials) for the capture of pollutant species and for their catalytic conversion into non-toxic substances, and to bioremediation approaches to treat contaminated media. Water, air, and soil pollution was investigated, both at the lab and large scale, with special relevance for wastewater treatments for the removal of heavy metals and organic pollutants. We are grateful to “Molecules” for the opportunity to edit the Special Issue on “Innovative Materials and Methods for the Removal of Pollutants from the Environment”. We created, for this book, an original cover image, dedicated to the efforts of chemistry to defend the beauty of environment, represented by flowers, against every prejudice that considers chemistry an enemy of life