M.Tech. (Chemical Engineering) / There are a number of processes for the production of biodiesel. Homogenous catalysed processes are the most popular in large scale production due to short reaction times and less extreme reaction conditions. Despite this, homogenous catalysts have a number of disadvantages which include: high probability of soap formation in the presence of water and free fatty acids; they cannot be re-used since some of the catalyst is consumed during the reaction and the separation of the remaining catalyst from the product is difficult. In contrast, heterogeneous catalysts offer simplified production and purification processes. However, their reaction rates are low due to mass transfer restrictions. This work looked at the unsupported and supported nano-MgO as solid catalyst for soybean oil transesterification reaction. More research is being undertaken to overcome these low reaction rate problems. Nano-MgO was used since it has been considered as a bridge between homogenous and heterogeneous catalysts. It was supported to enable easy separation from the reaction products.

Thesis. 1978. Sc.D.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / Sc.D.

Syftet med arbetet var att undersöka hur olika reaktionsbetingelser skulle påverka syrgasdelignifieringen av en sur sulfitmassa. De betingelser som undersöktes var utbyte, slut-pH, viskositet och kappatal. Massan som användes kom från Nordic Paper Seffle och alkalit som användes var magnesiumoxid.  Syrgasdelignifiering av massan gjordes  i autoklaver i ett PEG bad där tid, temperatur och alkalisatser varierades. Resultaten visar att alla utbyten låg mellan 90-97% och att även de mest aggressiva betingelserna bara gav en viskositets reduktion på 260 enheter, motsvarande 19% av den totala viskositeten. Slut-pH för syrgasavluten hamnade mellan 6,5-9,4 beroende på alkalimängd och temperatur under delignifieringen. Slut-pH minskade när mängden alkali hölls konstant men temperaturen varierades mellan 110-140°C. Kappatalet för massan kunde effektivt reduceras från ett startvärde på 23,4 till ett slutvärde på under 5 med en temperatur på 140°C, alkalisats på 10 kg/ODT och en tid på två timmar utan större förluster av vare sig viskositet eller utbyte. En ovanligt resultat som upptäcktes under arbetet var att delignifieringen tappade i effektivitet med ökad alkalimängd och detta samband gällde vid alla betingelser. En teori om detta kan vara att jonstyrkan i lösningen gör att fibrerna i massan drar ihop sig och att syrgasen får svårare att reagera med ligninet. / The purpose of the study was to investigate how different reaction conditions would affect oxygendelignification of an acid sulfite pulp. The conditions being explored were yield, final-pH, viscosity and kappa number. The pulp used in the testing was collected from Nordic Paper Seffle and the active alkali during the delignification was magnesium oxide. The oxygendelignification of the pulp was done with autoclaves suspended in a PEG bath, where they were allowed to rotate, and time, temperature and alkali amount  was varied throughout the testing. Results show that the yield for all pulp samples were between 90-97% for all conditions used in this project while viscosity of the pulps were only decreased by about 260 units for the most severe of conditions. This accounts for a viscosity loss of 19%. Final-pH varied between 6,5-9,4 depedning on temperature and alkali amount chosen. Final-pH levels dropped when the alkali was kept constant but temperature was varied from 110-140°C. The pulps kappa number could effetively be lowered from its starting value of 23,4 to a final value of under 5 when an alkali amount of 10 kg/ODT and a temperature of 140°C was used during 2 hours. This lead to no substantial losses of either viscosity or yield. A strange result that the project also highlighted was that the delignification lost in efficiency when more alkali was added in at a set temperature. This phenomenom was found at all conditions investigated throughout the project. A theory about this is that it might be the increased ionic strength from the magnesium cations in the solution making the fibers shrink and by that lessening the reaction area of the fibres for the oxygen, which will then have a harder time reacting with the lignin.

Thesis (Ph. D.)--University of Wisconsin, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (MSc.(Materials Science and Metallurgical Engineering)--University of Pretoria, 2007. / Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (p. 107-114).

Master of Science / Department of Chemistry / Kenneth J. Klabunde / In this study, low molecular weight nanocomposites of L-lactic acid were synthesized with Commercial, Nanoactive®, and Nanoactive Magnesium Oxide Plus®, each of which differs in both surface area and shape. Synthesis of the composites was carried out by refluxing the nanoparticles in a solvent suspension. Both methanol and 1-propanol were used during this work. Heating was necessary in order to achieve adequate dispersion of the particles before adding L-lactic acid. Upon addition of the lactic acid monomer, the reactants were refluxed for a total of 3 hours, followed by evaporation of the excess solvent. The products were characterized via DSC, TGA, FTIR, [superscript]1H and [superscript]13C NMR, UV-Vis, XRD, and TEM. Additionally, titrations were performed with the reactants to ensure the particles were not being consumed by the acid regardless of their size. The results of this study indicate that condensation reactions are the primary polymerization route of lactic acid and polymerization appears to initiate on the surface of the magnesium oxide particles, resulting in physically unique composites of lactic acid and magnesium oxide.

3D printing concrete (3DPC) became one of the most investigated topics in cement and concrete research in the last decade. Research within this topic includes examining the role of admixtures on the fresh-state properties, specifically cement rheology, along with the mechanical performance of the printed materials and structures. 3DPC offers a promising platform for sustainable binders, optimized design, and economic and rapid construction that can help reduce the high CO2 impact of Portland cement. This thesis is aimed towards engineering nano-modified cement binders for 3DPC by characterizing the effects of dispersion on fresh, hardening and hardened properties, examining the potential of combining inorganic nanoparticles with organic admixtures to tailor select rheological properties, and developing printing performance measurements, and applying the findings in promising applications. Nanoclays (NC) are one of the most attractive rheological modifiers for 3DPC as they increase structuration and buildability with minimal increase to viscosity or pumping requirements. This work starts by studying the impact of different dispersion techniques (sonication, magnetic stirring, dry powder mixing) on the rheological properties of NC-modified cement paste. In addition, a novel dry dispersion technique that coats cement grains with nanomaterials was developed and compared to conventional dispersion methods. The results revealed that dry dispersion enhanced NC efficiency in increasing the static yield stress of cement paste, effectively reducing NC content requirements by 33% compared to solution dispersion to achieve the same print height. The observed changes in rheological properties at different NC contents and dispersion techniques implied that the origin of structuration in NC-modified cement pastes is mainly driven by the interactive forces between NC needles (NC-NC) more so than with cement (NC-cement). This incentivized exploring partial treatment of cement with dry dispersion at a relatively high NC content of 10 wt.% to maximize the aforementioned NC-NC interactions. The results confirmed that the mixture of 10 wt.% NC-coated cement with uncoated ones performed similar or better than mixtures where dry dispersion was applied to all cement grains while maintaining the same NC dosage. From the collective findings of this investigation, it was deduced that partial treatment of cement with NC using dry dispersion can maximize NC efficiency in increasing the static yield stress for 3DPC. Moreover, because NC-NC interactions were more influential than NC-cement interactions on the structuration of cement paste, NC are likely to be successful in increasing the static yield stress and buildability of alternative binders for 3DPC. The promising performance of NC-coated cement motivated further exploration of dry dispersion on other nanomaterial types. The impact of dry dispersed versus solution sonicated NC, silica and calcium nanoparticles (SNP and CCNP), and graphene nanoplatelets (GNP), on hydration kinetics and mechanical performance was investigated. Results of isothermal calorimetry and quantitative x-ray diffraction for nano-modified cement pastes showed the critical role of the method of dispersion on the progression of cement hydration, which in turn altered strength development. For example, SNP-coated cement paste exhibited a delay in ettringite formation by a few hours compared to solution sonication, which likely caused the delayed compressive strength development observed in SNP-coated cement mortars. Nevertheless, for mortars modified with NC, SNP, and CCNP, processing via dry dispersion and solution sonication showed comparable 28-day compressive strengths, implying the successful application of dry dispersion for all three nanomaterials. In addition, results showed an increase in electrical conductivity of GNP-coated cement pastes with dry dispersion whereas GNP were not dispersible with sonication without surfactants or functionalization. The collective results show the efficacy of dry dispersion as an alternative dispersion technique to sonication but one that offers ready-to-mix or just-add-water nano-engineered cement products. Therefore, nano-coated cements via dry dispersion could be very beneficial for remote 3DPC applications or commercialization of nano-engineered binders. One of the drawbacks of NC reported in literature and confirmed in this work is the significant increase in stiffness that causes filament breakage and tearing during extrusion. To remedy this, a new hybrid rheological modifier combining NC with methyl cellulose (MC) was introduced to tailor cement paste rheology and meet 3DPC requirements. The hybrid mixture of NC and MC proved to increase NC efficiency by up to 900 Pa/1 wt.% of MC in cement paste without jeopardizing its extrudability, essentially decreasing the NC content requirement, and associated costs, to achieve greater print heights. In addition, the hybrid admixture maintained similar or better mechanical performance compared to unmodified cement mortars whereas addition of NC or MC alone showed reduced 28-day mechanical strengths. To capture the effects of the new admixture on ink or filament properties, three recently proposed printer-based ink tests were applied – elastic buckling of thin walls, slug test and cable sag test. The results confirmed that despite the softening effect of the hybrid admixture on elastic modulus of cement paste compared to NC alone, the critical buckling height, which measures structural stability, was not similarly impacted. In addition, ink cohesion measured by both slug and cable sag tests improved with the hybrid admixture compared to NC or MC alone. The collective results suggest that the hybrid admixture can tailor cement rheology to meet 3DPC requirements by enhancing ink or filament properties while maintaining mechanical performance. The last investigation applied the previous findings to enable 3D printing and facilitate CO₂ mineralization for a new alternative binder. Magnesium oxide (MgO), similar to Portland cement, hardens through hydration but only develops mechanical strength through carbonation. However, atmospheric carbonation is a self-depreciating diffusion process where the carbonation of the exterior retards and limits further internal carbonation. Building upon the new understanding of the origin of structuration of NC in cement pastes and the high performance of the hybrid combination of NC and MC, the new admixture was used to enable 3D printing of MgO binders. The results confirmed that NC enhanced shape stability by increasing static yield stress while MC maintained ink cohesion, thereby effectively making MgO pastes printable. Compression tests of 3D printed and conventionally mold cast MgO paste cylinders showed that 3D printing can significantly increase strength by up to an order of magnitude. Examining the effects of different infill patterns (<100% and 100% infill density) and water-to binder ratios, results indicated that the increase in strength is attributed to 3D printing effects like the lack of protective formwork, which increased water evaporation and consequently increased carbon diffusion and intake. This study was the first to be published on tailoring the rheology of MgO binder and studying the effects of infill patterns on the compressive strength of 3D printed MgO pastes. The summary of results demonstrates that 3D printing can introduce significant benefits for carbon cured material systems, such as reactive MgO based systems, to potentially reach CO2 neutrality or negativity. Chapter 1 is the introduction, which describes how the main goal of this work is to explore the use of nanomaterials for 3DPC. Chapter 2 presents a literature review on 3DPC properties, cement rheology, and nanomaterials. Chapter 3 discusses the effects of NC dispersion, including the novel dry dispersion technique, on the structuration behavior of cement pastes. Chapter 4 dives deeper into the application of dry dispersion on other types of nanoparticles, i.e. SNP, CCNP and GNP. Chapter 5 revisits NC with the addition of MC to tailor cement rheology for 3DPC. Chapter 6 utilizes the results of Chapters 3 and 5 by examining 3D printed MgO paste and carbon intake. Chapter 7 summarizes this work and lists all the chapters’ conclusions. Additional discussions of the printer and extrusion head that were designed and built in Columbia CEEM Carleton Laboratory are also included in the appendix of this work, detailing gantry versus delta printers for 3DPC and the development of a low-cost concrete extrusion head with an open-to-atmosphere hopper that eliminates the need for a pumping system. Lastly, multiple in-situ printing properties and ink performance tests developed by the author, which utilize the printing system to characterize the fresh properties of inks on site, were expanded and detailed

No description available.

The stoichiometric Self-propagating High-temperature Synthesis (SHS) thermite reaction involving magnesium oxide (MgO), titanium dioxide (TiO₂), and boron oxide (B₂O₃) forms titanium diboride (TiB₂) and MgO as final products. Selective acid leaching is used to remove the MgO leaving high purity TiB₂ powder. The SHS method to produce TiB₂ is attractive because of the relatively low temperature required to initiate the reaction, fast reaction time, and product purity. This study investigates the acid leaching of SHS produced MgO/TiB2 and a stoichiometric mixture of commercial MgO and TiB₂ powders. Leaching was conducted at 90° C, 60° C, and 30° C at pH levels of 4.0, 2.5, and 1.0 by introduction of concentrated aliquots of HNO₃. This method maintains a minimum pH target throughout the leaching process, thereby sustaining a dynamic concentration to remove the oxide. The optimal leaching conditions were determined to be at 90° C at a minimum pH target of 2.5 for the SHS produced product. At these conditions, conversion percentages of 83%-84% of MgO were measured with only trace amounts of TiB2 measured in the solution (less than 100 ppm). Conversion percentages for each leaching condition and dissolution mass of solid MgO and TiB₂ at each pH are also reported. Results from powder XRD confirm the removal of MgO and minimal dissolution of TiB₂, and indicate the formation of unidentified compounds. Inductively coupled plasma mass spectrometry (ICP) was used to analyze the ionic composition and extent of leaching. Scanning electron microscopy (SEM) was used to observe the particle morphology of the leached powders. / Master of Science