Mathematical modelling of chemical agent removal by reaction with an immiscible cleanser

When a hazardous chemical agent has soaked into a porous medium, such as concrete, it can be difficult to neutralise. One removal method is chemical decontamination, where a cleanser is applied to react with and neutralise the agent, forming less harmful reaction products. There are often several cleansers that could be used to neutralise the same agent, so it is important to identify the cleanser features associated with fast and effective decontamination. As many cleansers are aqueous solutions while many agents are immiscible with water, the decontamination reaction often takes place at the interface between two phases. In this paper, we develop and analyse a mathematical model of a decontamination reaction between a neat agent and an immiscible cleanser solution. We assume that the reaction product is soluble in both the cleanser phase and the agent phase. At the moving boundary between the two phases, we obtain coupling conditions from mass conservation arguments and the oil–water partition coefficient of the product. We analyse our model using both asymptotic and numerical methods, and investigate how different features of a cleanser affect the time taken to remove the agent. Our results reveal the existence of two regimes characterised by different rate-limiting transport processes, and we identify the key parameters that control the removal time in each regime. In particular, we find that the oil–water partition coefficient of the reaction product is significantly more important in determining the removal time than the effective reaction rate

Mathematical modelling of chemical agent removal by reaction with an immiscible cleanser

When a hazardous chemical agent has soaked into a porous medium, such as concrete, it can be difficult to neutralise. One removal method is chemical decontamination, where a cleanser is applied to react with and neutralise the agent, forming less harmful reaction products. There are often several cleansers that could be used to neutralise the same agent, so it is important to identify the cleanser features associated with fast and effective decontamination. As many cleansers are aqueous solutions while many agents are immiscible with water, the decontamination reaction often takes place at the interface between two phases. In this paper, we develop and analyse a mathematical model of a decontamination reaction between a neat agent and an immiscible cleanser solution. We assume that the reaction product is soluble in both the cleanser phase and the agent phase. At the moving boundary between the two phases, we obtain coupling conditions from mass conservation arguments and the oil–water partition coefficient of the product. We analyse our model using both asymptotic and numerical methods, and investigate how different features of a cleanser affect the time taken to remove the agent. Our results reveal the existence of two regimes characterised by different rate-limiting transport processes, and we identify the key parameters that control the removal time in each regime. In particular, we find that the oil–water partition coefficient of the reaction product is significantly more important in determining the removal time than the effective reaction rate

The effect of pore-scale contaminant distribution on the reactive decontamination of porous media

A porous material that has been contaminated with a hazardous chemical agent is typically decontaminated by applying a cleanser solution to the surface and allowing the cleanser to react into the porous material, neutralising the agent. The agent and cleanser are often immiscible fluids and so, if the porous material is initially saturated with agent, a reaction front develops with the decontamination reaction occurring at this interface between the fluids. We investigate the effect of different initial agent configurations within the pore space on the decontamination process. Specifically, we compare the decontamination of a material initially saturated by the agent with the situation when, initially, the agent only coats the walls of the pores (referred to as the ‘agent-on-walls’ case). In previous work (Luckins et al., European Journal of Applied Mathematics, 31(5):782–805, 2020), we derived homogenised models for both of these decontamination scenarios, and in this paper we explore the solutions of these two models. We find that, for an identical initial volume of agent, the decontamination time is generally much faster for the agent-on-walls case compared with the initially saturated case, since the surface area on which the reaction can occur is greater. However for sufficiently deep spills of contaminant, or sufficiently slow reaction rates, decontamination in the agent-on-walls scenario can be slower. We also show that, in the limit of a dilute cleanser with a deep initial agent spill, the agent-on-walls model exhibits behaviour akin to a Stefan problem of the same form as that arising in the initially saturated model. The decontamination time is shown to decrease with both the applied cleanser concentration and the rate of the chemical reaction. However, increasing the cleanser concentration is also shown to result in lower decontamination efficiency, with an increase in the amount of cleanser chemical that is wasted

The influence of porous media microstructure on filtration

We investigate how a filter media microstructure influences filtration performance. We derive a theory that generalizes classical multiscale models for regular structures to account for filter media with more realistic microstructures, comprising random microstructures with polydisperse unidirectional fibres. Our multiscale model accounts for the fluid flow and contaminant transport at the microscale (over which the media structure is fully resolved) and allows us to obtain macroscopic properties such as the effective permeability, diffusivity, and fibre surface area. As the fibres grow due to contaminant adsorption this leads to contact of neighbouring fibres. We propose an agglomeration algorithm that describes the resulting behaviour of the fibres upon contact, allowing us to explore the subsequent time evolution of the filter media in a simple and robust way. We perform a comprehensive investigation of the influence of the filter-media microstructure on filter performance in a spectrum of possible filtration scenarios

Development of a method to study retention of hydrophobic actives from cosmetic emulsions on optimized skin biomimics

All-in-one products are a popular trend in cosmetics, personal and home care. In particularly, personal care products that serve multiple purposes are especially popular due to their multifunctional action which simultaneously provides cleaning, conditioning and protection of the treated area such as, skin or hair, in a fraction of the time in comparison to when using traditional products. In this research programme, a dedicated method was developed towards the evaluation of the conditioning performance of ‘all-in-one’ cleansing products. Hence, all steps of product usage were replicated in a controlled environment and suitable characterization methods were employed. Optimized skin mimics were fabricated to be used as test substrates and model systems of cosmetic formulations were produced, which demonstrated both cleaning and moisturizing capabilities as well as a repetitive and highly-controlled deposition set-up and a cleaning set-up. The conditioning performance of the emulsions was studied and post-wash retention levels of the hydrophobic active on skin bio-mimics were systematically characterised. Techniques including fluorescent microscopy, gravimetric analysis and tribometry were employed to provide further, into-depth quantitative data of the retention. Properties of the formulation including oil droplet-size, viscosity and volume-fraction and cleaning parameters including rinsing-duration and flow-angle were tested for their impact on retention

Investigating Anions and Hydrophobicity of Deep Eutectic Solvents by Experiment and Computational Simulation

Deep eutectic solvents are a new generation of ionic liquid-like solvents formed by combining hydrogen bond acceptor with hydrogen bond donor which result in the depression of the melting point of the solvent. Like ionic liquids, anions play a critical role in tuning the polarity, physicochemical properties, and thermodynamic behavior of deep eutectic solvent (DES). Choline chloride is the most widely used quaternary ammonium salt (QAS) in the literature and has remarkable advantages from reduced cost to low toxicity and volatility. Choline bromide and choline iodide are other QAS that have not been used often for DES synthesis and applications, probably with the opinion that chlorides form stronger hydrogen bonds. Developing new DES from these anions will broaden the scope of green solvents selection for diverse applications. The first objective of this dissertation looked into the synthesis and characterization of DES from choline chloride, choline bromide, and choline iodide with malic acid, malonic acid, and urea. Also, we studied the thermodynamic behavior of the solvents by measuring their vapor pressure, density, and infinite activity coefficient in polar and nonpolar solvents. The results show that choline bromide can sometimes be used to replace choline chloride because both QAS share comparable physicochemical behavior. In most cases, choline iodide forms weaker hydrogen bonding with the donors leading to the formation of a solid at room temperature. Nevertheless, all the solvents have melting temperature below 100℃. In summary, DES can be synthesized from the choline cation bonded with the halides, with the melting point and nature of the solvent dependent on the hydrogen bond donor (HBD). Secondly, despite the rapid rise in publications and applications since their inception in 2001, most of the DES synthesized are generally hydrophilic. The low cost, low toxicity, and bioavailability of DES make the solvent green and sustainable for diverse applications. Conversely, the hydrophilicity of DES practically limits their application to only polar compounds, which is a major drawback of the solvent. For the past three years, hydrophobic deep eutectic solvents (HDES) have emerged as alternative extractive media capable of extracting nonpolar molecules from aqueous environments. In chapter three of this dissertation, the general objective was to design a cost-effective hydrophobic DES from choline chloride and fatty acids. Varying the alkyl chain of the fatty acid broadened our understanding about the role of HBD in DES and also helped in the tunability of the HDES polarity. Due to the infancy of HDES, for the first time, this dissertation expands on the design, synthesis, and physicochemical characterization of HDES developed from choline chloride and fatty acids. To understand the hydrogen-bonding pattern of HDES, a multivariate unsupervised principal component analysis was used to cluster HDES by using known DES as a control. The HDES was able to extract about 70% of piperine, a bioactive compound from Piper nigrum. In the future, it is believed that HDES could replace the majority of toxic organic solvents used for analytical purposes. Lastly, the electronic and molecular properties of the HDES synthesized were studied by using a solvatochromic molecular probes and a hybrid density functional theory at 6-31G (d) basis set. The empirical polarity assay and quantum theoretical calculations showed that decreasing the alkyl chain length of the hydrogen bond donor increases viscosity of the DES. Optimization of the DES molecular geometry indicates a reduced bond angle between the C15-O16-H17 atoms in choline chloride, signifying a change in electronegativity of the central atom (O16) during DES formation. From our results, we predict a possible molecular reorientation between the donor and the acceptor molecules during DES formation. The combined theoretical calculations and experimental approaches are useful to establish clear correlations between electronic parameters and physiochemical parameters like polarity, viscosity, and stability of carboxylic acid-DES and can be extended to other conventional solvents

Ceramic Thin Films with Embedded Magnetic Nanofibers or Nanorods of Controlled Orientations

Ceramic thin films embedded with oriented magnetic nanofibers or nanorods are highly demanded for the applications in remote sensing, electromagnetic shielding, and thermal management at high temperatures. The general strategy for developing ceramic composite thin films with aligned magnetic nanorods or nanofibers has not been developed yet. This dissertation is centered on fundamentally understanding a sol-gel and polymer-based route towards creation of ceramic thin films with aligned magnetic nanostructures. The topics cover fabrication and properties of ceramic and ceramic-based nanofibers, precipitating magnetic nanoparticles within ceramic fibers, aligning and embedding nanofibers or nanorods within ceramic films, and preventing cracking during the sol-gel film dip-coating processing on flat substrates or on substrates with protrusions such as nanorods or nanofibers. The recent status and challenges in developing ceramic based nanocomposite and its potential applications are reviewed in chapter I. The feasible methodologies and general approaches are described. In chapter II and chapter III, we present the development of mullite and mullite-based composite nanofibers as potential fillers in ceramic thin films. The detailed schemes of materials formation and approaches for microstructure control are discussed in detail. The mechanical and magnetic properties of the mullite-based fibers are studied. In chapter IV, the high temperature in situ precipitation of nickel nanoparticles within the mullite fiber host is studied, to fundamentally understand the processing mechanism and its potential for high temperatures applications. In chapter V, we present the fundamental understanding of processing crack-free mullite thin films by sol-gel method. In chapter VI, the scientific approach is described for processing macroscopic ceramic thin films embedded with magnetic nanorods of controlled alignment. In chapter VII, the ceramic thin film formation with embedded nanorods is studied both theoretically and experimentally. The mechanism and criterion of microscopic cracking within the thin film composites is discussed

Evaluation of mixed microalgae species biorefinery of Desmodesmus sp. And Scenedesmus sp. For bioproducts synthesis

Microalgae is known to produce numerous bioactive compounds for instance proteins, fatty acid, polysaccharides, enzymes, sterols, and antioxidants. Due to their valuable biochemical composition, microalgae are regarded as a very intriguing source to produce novel food products and can be utilised to improve the nutritional content of traditional foods. Additionally, microalgae are used as animal feed and additives in the cosmetics, pharmaceutical as well as nutraceutical industries. As compared to other terrestrial plants and other microorganisms, microalgae possess few advantages: (1) rapid growth rate; (2) able to grow in non-arable land and harsh cultivation conditions; (3) low nutritional requirements; (4) high productivity; and (5) reduce emission of carbon dioxide. Despite the large number of microalgae species found in nature, only a few species are identified and commercialized such as Chlorella sp., Spirulina sp. Haematococcus pluvialis, Nannochloropsis sp. and Chlamydomonas reinhardtii, which is one of the major obstacles preventing the full utilisation of microalgae-based technology. This thesis provides information on the overall composition of mixed microalgae species, Desmodesmus sp. and Scenedesmus sp., for instance protein, carbohydrate, lipid, antioxidants, and pigment. This thesis firstly introduces the application of triphasic partitioning (TPP) in the extraction and partitioning of the biomolecules from the microalgae. The latest advancement of technology has evolved from a liquid biphasic flotation (LBF) to TPP. T-butanol and ammonium sulphate are used in TPP to precipitate desired biomolecules from the aqueous solutions with the formation of three layer. TPP is a simple, time- and cost- efficient, as well as scalable process that does not require toxic organic solvents. Lipase is abundantly produced by microbes, bacteria, fungi, yeast, mammals, and plants. Lipase is widely used in the oleochemical, detergent, dairy, leather, cosmetics, paper, cosmetics, and nutraceutical industries. Therefore, this thesis also discusses the possibility of identifying and extracting enzyme lipase from the microalgae using LBF. Several parameters (volume and concentration of solvents, weight of biomass, flotation kinetics and solvent types, etc.) have been investigated to optimize the lipase extraction from LBF. Chlorophyll is the main pigment present in the microalgae. Thus, this work proposes the digital imaging approach to determine the chlorophyll concentration in the microalgae rapidly because the chlorophyll content has a significant impact on microalgae physiological health status as well as identifies the chlorophyll concentration in the production of by-products. Lastly, microalgae oil can be used as the feedstock for biodiesel as well as nutraceutical, pharmaceutical, and health-care products. The challenge in the lipid extraction is the co-extraction of chlorophyll into the oil, which can have serious consequences for downstream processing. Therefore, the removal of the chlorophyll from the microalgae using activated clay or sodium chlorite in the pre-treatment procedure are examined. The research achievements in these works and future opportunities are highlighted in the last chapter of the thesis

Testing, Validation and Dissemination of an Innovative Biotechnology for Air and Water Treatment.

The present study is aimed to follow the start-up in the Italian and European framework of an American biotechnology for environmental decontamination and it focused on field testing stage for air treatment application, in parallel with a bench/pilot scale application on industrial wastewater treatment. The biotechnology applied is based on immobilized cell bioreactors, where air is ventilated and water is recirculated to provide the optimal conditions for the development of a mixed bacteria consortium, growing on contaminants captured from contaminated media (i.e. air or wastewater). The technology proposed has been studied from different perspectives, i.e. emission risk, overall sustainability and remediation performance. Several pilot installations have been accomplished for air treatment application, in different areas of interest. In particular, in the healthcare sector (hemodialysis unit, operatory room, intensive care unit and anatomo-pathological laboratory), where the protection against microbial and chemical agents is perceived as a necessity, both for operators and patients, the biotechnology displayed remarkable results, particularly on VOCs and bacterial count. In order to try and address one of the most challenging issue for air treatment, i.e. odor containment, two major pilot applications have been performed, on waste and wastewater treatment plant, with promising, but still unsteady results. A new opportunity for application was envisaged in radioactivity contaminated indoor environments and a preliminary impact assessment has been outlined, based on results obtained in different fields. For wastewater treatment, a single pilot scale plant was implemented and silk manufacturing effluent was object of the experimental remediation attempted. In a cost-effective perspective, the implementation of this system appears to be suitable for several solutions, i.e. within the framework of a multi-stage treatment process or as independent and easily implementable wastewater technology for cottage-scale manufacturing or small communities