Liquid-phase alcohol promoted methanol synthesis from CO2 and H2

Methanol is an important and versatile compound with various uses as a fuel and a feedstock chemical. Methanol is also a potential chemical energy carrier. Due to the fluctuating nature of renewable energy sources such as wind or solar, storage of energy is required to balance the varying supply and demand. Excess electrical energy generated at peak periods can be stored by using the energy in the production of chemical compounds. The conventional industrial production of methanol is based on the gas-phase synthesis from synthesis gas generated from fossil sources, primarily natural gas. Methanol can also be produced by hydrogenation of CO2. The production of methanol from CO2 captured from emission sources or even directly from the atmosphere would allow sustainable production based on a nearly limitless carbon source, while helping to reduce the increasing CO2 concentration in the atmosphere. Hydrogen for synthesis can be produced by electrolysis of water utilizing renewable electricity. A new liquid-phase methanol synthesis process has been proposed. In this process, a conventional methanol synthesis catalyst is mixed in suspension with a liquid alcohol solvent. The alcohol acts as a catalytic solvent by enabling a new reaction route, potentially allowing the synthesis of methanol at lower temperatures and pressures compared to conventional processes. For this thesis, the alcohol promoted liquid phase methanol synthesis process was tested at laboratory scale. Batch and semibatch reaction experiments were performed in an autoclave reactor, using a conventional Cu/ZnO catalyst and ethanol and 2-butanol as the alcoholic solvents. Experiments were performed at the pressure range of 30-60 bar and at temperatures of 160-200 °C. The productivity of methanol was found to increase with increasing pressure and temperature. In the studied process conditions a maximum volumetric productivity of 1.9 g of methanol per liter of solvent per hour was obtained, while the maximum catalyst specific productivity was found to be 40.2 g of methanol per kg of catalyst per hour. The productivity values are low compared to both industrial synthesis and to gas-phase synthesis from CO2. However, the reaction temperatures and pressures employed were lower compared to gas-phase processes. While the productivity is not high enough for large-scale industrial operation, the milder reaction conditions and simple operation could prove useful for small-scale operations. Finally, a preliminary design for an alcohol promoted, liquid-phase methanol synthesis process was created using the data obtained from the experiments. The demonstration scale process was scaled to an electrolyzer unit producing 1 Nm3 of hydrogen per hour. This Master’s thesis is closely connected to LUT REFLEX-platform.

Síntese e estudo de polioxotungstatos do tipo Keggin com interesse catalítico

O objectivo principal deste trabalho foi estudar as propriedades e comportamento de polioxotungstatos (POM) do tipo Keggin com interesse em catálise oxidativa. Os estudos efectuados centraram-se no comportamento electroquímico dos aniões em meio não aquoso, na estabilidade das suas estruturas em diferentes meios, na sua capacidade de catalisar a oxidação de diferentes substratos orgânicos e na sua eficácia em oxidar, de forma selectiva, um modelo não fenólico da lenhina. Efectuou-se, igualmente, o estudo estrutural de diversos aniões pela técnica de EXAFS. Neste trabalho, prepararam-se e caracterizaram-se alguns dos sais de tetra-n-butilamónio (TBA) dos polioxotungstatos estudados: compostos de Keggin, TBAx[XW12O40], lacunares, TBAxHy[XW11O39], mono-substituídos, TBAxHy[XW11M(H2O)O39]·nH2O, com X= P e Si e M = CoII, NiII, ZnII, CuIl, RuIII, MnIII e FeIII e os compostos com mistura de átomos adenda TBAx[XW11VO40]·nH2O (X = P e Si). Seleccionou-se este conjunto de polioxotungstatos de forma a efectuar-se um estudo comparativo da influência da natureza do heteroátomo central (P e Si) e dos metais de transição M nas propriedades estudadas. O conjunto de sais de TBA dos silicotungstatos estudados mostraram ser isoestruturais, apresentando a mesma estrutura dos fosfotungstatos análogos. O comportamento electroquímico dos polioxotungstatos foi estudado em soluções de acetonitrilo por voltametria cíclica e electrólise a potencial controlado. Verificou-se a ocorrência de vários processos mono-electrónicos de oxi-redução, reversíveis ou quasi-reversíveis, associados aos átomos de WVI/V e a alguns dos metais de transição. Os metais em estado de oxidação +3 reduziram-se mais facilmente do que os átomos de WVI. O metal CuII apresentou um comportamento diferente dos outros metais de transição. Este metal, na estrutura do POM, reduziu-se a CuI, proporcionando a observação do anião [PW11CuIO39]6- pela primeira vez. A redução posterior do CuI conduziu à formação de Cu0, que se depositou na superfície do eléctrodo. A re-oxidação do cobre a CuII conduziu à reconstituição da estrutura do POM, nas condições estudadas. Constatou-se que a ocorrência de protões na fórmula molecular dos POMs influenciou o seu comportamento electroquímico. Para os compostos que apresentam protões, a redução dos átomos de tungsténio ocorreu a potenciais menos negativos do que para aqueles que não apresentam protões na sua fórmula. Para os primeiros observou-se a transferência global de um maior número de electrões no mesmo intervalo de potencial, originando soluções fortemente azuladas. Quando os catiões tetra-n-butilamónio foram substituídos por catiões de menor dimensão, como Li+ e Na+, ocorreu a formação de pares iónicos com os polianiões [PW12O40]3- e [SiW11VO40]5-, originando um aumento do potencial de redução. Não houve evidência da formação de pares iónicos com os catiões TBA+. Este foi o primeiro estudo sistemático do comportamento electroquímico dos aniões lacunares e mono-substituídos em meio não aquoso. Estudou-se a estrutura dos polioxotungstatos em sais de TBA e em soluções de acetonitrilo. A aplicação da técnica de EXAFS ao estudo deste tipo de compostos em solução foi realizada pela primeira vez. Pela análise estrutural nos sólidos verificou-se que, a natureza do metal de transição M e do átomo central X, na estrutura do POM, influenciam o tamanho dos vários octaedros que o constituem. Não se observaram diferenças significativas nas estruturas dos polianiões em solução. A estabilidade da estrutura dos polioxometalatos na presença de um excesso de H2O2, em soluções de acetonitrilo/H2O foi analisada por espectroscopia de absorção de EXAFS, RMN de 31P, IV e espectrofotometria de absorção no UV-Vis. De uma forma geral, os POMs em que o átomo central da estrutura é o Si apresentaram maior estabilidade do que os POMs correspondentes com átomo de P no centro. Em solução de acetonitrilo, na ausência de H2O2, todos os aniões mostraram ser estáveis durante vários dias. Em solução, na presença de H2O2 em excesso (H2O2/POM = 1300), o anião lacunar [PW11O39]7- não é estável, transformando-se no anião de Venturello, {PO4[W(O)(O2)2]4}3-, após a formação de [PW12O40]3-, como produto intermediário. Em relação aos aniões substituídos [PW11M(H2O)O39]p-, M = MnIII, RuIII, FeIII, CoII e ZnII, verificou-se o seguinte na presença de H2O2: os aniões com MnIII e CoII transformaram-se no anião de Keggin, [PW12O40]3-. Os aniões de RuIII e FeIII mantiveram as suas estruturas e o anião de ZnII decompôs-se em {HPO4[W(O)(O2)2]2}2- e fosfato. Para estes casos de não estabilidade estrutural, o processo de decomposição foi mais rápido na presença de maiores conteúdos de água. Pela análise de EXAFS, na presença de um menor excesso de H2O2 (H2O2/POM = 70) e apenas 8% de parte aquosa, verificou-se que os aniões substituídos por MnIII mantiveram a sua estrutura, embora o ligando H2O, coordenado ao Mn, tivesse sido substituído por um grupo oxo no polianião [SiW11Mn(H2O)O39]5-, e por um grupo peroxo no polianião [PW11Mn(H2O)O39]4-. O anião com RuIII, nestas condições, também mostrou substituir o seu ligando H2O por um grupo peroxo ou hidrogenoperoxo. Os polioxotungstatos mono-substituídos e lacunares mostraram ser catalisadores eficientes para a oxidação de cis-cicloocteno, geraniol e ciclooctano com H2O2. A maior novidade deste trabalho residiu na actividade catalítica apresentada pelos silicotungstatos estudados, contrariando o que é referido na literatura. Outro aspecto inovador foi o elevado valor de conversão obtido para a oxidação de ciclooctano. Este substrato foi oxidado com 74% de conversão, após 2h de reacção e com 80% de selectividade para o hidroperóxido de ciclooctilo, na presença do anião [PW11Fe(H2O)O39]4-. Os restantes produtos de reacção foram o ciclooctanol e a ciclooctanona. Os silicotungstatos apresentaram maior selectividade para o hidroperóxido de ciclooctilo do que os fosfotungstatos. O geraniol foi completamente oxidado após 3h de reacção, com 82% de selectividade para o 2,3-epoxigeraniol, na presença do anião [PW11Mn(H2O)O39]4-. O cis-cicloocteno foi oxidado ao seu epóxido, com 92% de conversão ao fim de 5h de reacção, na presença do anião lacunar [PW11O39]7-. O estudo da capacidade oxidativa do anião [SiW11VO40]5- foi analisada utilizando-se um modelo não fenólico da lenhina, a anisoína. Estudaram-se as condições favoráveis à obtenção de uma reacção selectiva para o anisilo, de forma a poder estudar-se a cinética da reacção. A estequiometria da reacção mostrou ser de 1:2 anisoína/POM. As ordens de reacção foram determinadas pelo método das velocidades iniciais e, a partir destes resultados, conheceu-se que o POM não estava envolvido no passo que limita a velocidade da reacção, sendo esta limitada pela transformação da anisoína. O estudo realizado sobre o efeito isotópico sugeriu que o passo que limitou a velocidade de reacção correspondeu à enolação da anisoína. Desta forma, observou-se pela primeira vez, que o POM oxida um modelo não fenólico da lenhina por via de enolação.

Obtenção de polímeros de LCC para aplicação como antioxidante de biodiesel de soja

Biodiesel is a fuel obtained from vegetable oils, such as soy, castorbean, among others. The monoester of fatty acid of these oils have chains with mono, di and tri double connections. The presence of these insaturations are susceptible to oxidization. Antioxidants are substances able to prevent oxidization from oils, fats, fat foods, as well as esters of Alquila( biodiesel). The objective of this work is to summarize a new antioxidant from the Cashew Nut Shell Liquid (CNSL) using the electrolysis technique. A current of 2 amperes was used in a single cell of only one group and two eletrodos of stainless steel 304 in a solution of methanol, together with the eletrolits: acetic acid, sodium chloride and sodium hydroxide, for two hours of agitation. The electrolysis products are characterized by the techniques of cromatography in a thin layer, spectroscopy of infrared and gravimetric analysis. The material was submitted to tests of oxidative stability made by the techniques of spectropy of impendancy and Rancimat (EN 14112). The analyses of characterization suggest that the polimerization of the electrolytic material ocurred. The application results of these materials as antioxidants of soy biodiesel showed that the order of the oxidative stability was obtained by both techniques used

Surface structured platinum electrodes for the electrochemical reduction of carbon dioxide in imidazolium based ionic liquids

The direct CO2 electrochemical reduction on model platinum single crystal electrodes Pt(hkl) is studied in [C2mim+][NTf2−], a suitable room temperature ionic liquid (RTIL) medium due to its moderate viscosity, high CO2 solubility and conductivity. Single crystal electrodes represent the most convenient type of surface structured electrodes for studying the impact of RTIL ion adsorption on relevant electrocatalytic reactions, such as surface sensitive electrochemical CO2 reduction. We propose here based on cyclic voltammetry and in situ electrolysis measurements, for the first time, the formation of a stable adduct [C2mimH–CO2−] by a radical–radical coupling after the simultaneous reduction of CO2 and [C2mim+]. It means between the CO2 radical anion and the radical formed from the reduction of the cation [C2mim+] before forming the corresponding electrogenerated carbene. This is confirmed by the voltammetric study of a model imidazolium-2-carboxylate compound formed following the carbene pathway. The formation of that stable adduct [C2mimH–CO2−] blocks CO2 reduction after a single electron transfer and inhibits CO2 and imidazolium dimerization reactions. However, the electrochemical reduction of CO2 under those conditions provokes the electrochemical cathodic degradation of the imidazolium based RTIL. This important limitation in CO2 recycling by direct electrochemical reduction is overcome by adding a strong acid, [H+][NTf2−], into solution. Then, protons become preferentially adsorbed on the electrode surface by displacing the imidazolium cations and inhibiting their electrochemical reduction. This fact allows the surface sensitive electro-synthesis of HCOOH from CO2 reduction in [C2mim+][NTf2−], with Pt(110) being the most active electrode studied.

Reduction of 1,2-dicarbonyl compounds and of their N-phenylimine derivatives by sodium cyanide under aprotic conditions

Some aromatic 1,2-dicarbonyl compounds, i.e. 9,10-phenanthrenequinone, acenaphthenequinone and benzil, and their corresponding N-phenyl monoimines, have been reduced, using dry acetonitrile as the solvent, in the presence of sodium cyanide as a reducing agent. Comparative potentiostatic preparative-scale electrolysis is described.

Síntese e caracterização do líquido iônico tetrafluoroborato de 1-metil-3-(2,6-(S)-dimetiloct-2-eno)-imidazol como eletrólito para produção de hidrogênio via eletrólise da água

Ionic liquids (ILs) are organic compounds liquid at room temperature, good electrical conductors, with the potential to form as a means for electrolyte on electrolysis of water, in which the electrodes would not be subjected to such extreme conditions demanding chemistry [1]. This paper describes the synthesis, characterization and study of the feasibility of ionic liquid ionic liquid 1-methyl-3(2,6-(S)-dimethyloct-2-ene)-imidazole tetrafluoroborate (MDI-BF4) as electrolyte to produce hydrogen through electrolysis of water. The MDI-BF4 synthesized was characterized by thermal methods of analysis (Thermogravimetric Analysis - TG and Differential Scanning Calorimetry - DSC), mid-infrared spectroscopy with Fourier transform by method of attenuated total reflectance (FTIR-ATR), nuclear magnetic resonance spectroscopy of hydrogen (NMR 1H) and cyclic voltammetry (CV). Where thermal methods were used to calculate the yield of the synthesis of MDI-BF4 which was 88.84%, characterized infrared spectroscopy functional groups of the compound and the binding B-F 1053 cm-1; the NMR 1H analyzed and compared with literature data defines the structure of MDI-BF4 and the current density achieved by MDI-BF4 in the voltammogram shows that the LI can conduct electrical current indicating that the MDI-BF4 is a good electrolyte, and that their behavior does not change with the increasing concentration of water

ELECTROCATALYTIC PROCESSING OF RENEWABLE BIOMASS-DERIVED COMPOUNDS FOR PRODUCTION OF CHEMICALS, FUELS AND ELECTRICITY

The dual problems of sustaining the fast growth of human society and preserving the environment for future generations urge us to shift our focus from exploiting fossil oils to researching and developing more affordable, reliable and clean energy sources. Human beings had a long history that depended on meeting our energy demands with plant biomass, and the modern biorefinery technologies realize the effective conversion of biomass to production of transportation fuels, bulk and fine chemicals so to alleviate our reliance on fossil fuel resources of declining supply. With the aim of replacing as much non-renewable carbon from fossil oils with renewable carbon from biomass as possible, innovative R&D activities must strive to enhance the current biorefinery process and secure our energy future. Much of my Ph.D. research effort is centered on the study of electrocatalytic conversion of biomass-derived compounds to produce value-added chemicals, biofuels and electrical energy on model electrocatalysts in AEM/PEM-based continuous flow electrolysis cell and fuel cell reactors. High electricity generation performance was obtained when glycerol or crude glycerol was employed as fuels in AEMFCs. The study on selective electrocatalytic oxidation of glycerol shows an electrode potential-regulated product distribution where tartronate and mesoxalate can be selectively produced with electrode potential switch. This finding then led to the development of AEMFCs with selective production of valuable tartronate or mesoxalate with high selectivity and yield and cogeneration of electricity. Reaction mechanisms of electrocatalytic oxidation of ethylene glycol and 1,2-propanediol were further elucidated by means of an on-line sample collection technique and DFT modeling. Besides electro-oxidation of biorenewable alcohols to chemicals and electricity, electrocatalytic reduction of keto acids (e.g. levulinic acid) was also studied for upgrading biomass-based feedstock to biofuels while achieving renewable electricity storage. Meanwhile, ORR that is often coupled in AEMFCs on the cathode was investigated on non-PGM electrocatalyst with comparable activity to commercial Pt/C. The electro-biorefinery process could be coupled with traditional biorefinery operation and will play a significant role in our energy and chemical landscape.

NEW MICROFLUIDIC SYSTEM TO INCREASE ROBUSTNESS OF ELECTRODE PERFORMANCE AND DEVELOP POINT-OF-CARE HEMATOCRIT DEVICE

The present dissertation aimed to develop a new microfluidic system for a point-of-care hematocrit device. Stabilization of microfluidic systems via surfactant additives and integration of semipermeable SnakeSkin® membranes was investigated. Both methods stabilized the microfluidic systems by controlling electrolysis bubbles. Surfactant additives, Triton X-100 and SDS stabilized promoted faster bubble detachment at electrode surfaces by lowering surface tension and decreased gas bubble formation by increasing gas solubility. The SnakeSkin® membranes blocked bubbles from entering the microchannel and thus less disturbance to the electric field by bubbles occurred in the microchannel. Platinum electrode performance was improved by carbonizing electrode surface using red blood cells. Irreversibly adsorbed RBCs lysed on platinum electrode surfaces and formed porous carbon layers while current response measurements. The formed carbon layers increase the platinum electrode surface area and thus electrode performance was improved by 140 %. The microfluidic system was simplified by employing DC field to use as a platform for a point-of-care hematocrit device. Feasibility of the microfluidic system for hematocrit determination was shown via current response measurements of red blood cell suspensions in phosphate buffered saline and plasma media. The linear trendline of current responses over red blood cell concentration was obtained in both phosphate buffered saline and plasma media. This research suggested that a new and simple microfluidic system could be a promising solution to develop an inexpensive and reliable point-of-care hematocrit device.

Study of the Electrochemical, Physical and Morphological Characteristics of Anode Catalysts for Perfluorosulfonic Acid (PFSA) Membrane Water Electrolysers

A number of supported and un-supported Oxygen Evolution Reaction (OER) iridium based electrocatalysts for Polymer Electrolyte Membrane Water Electrolysis (PEMWE) were synthesized using a polyol method. The electrocatalysts and the supports were characterized using a wide range of physical and electrochemical characterization methods. The effect of morphological characteristics of the OER electrocatalyst and the support on the OER activity was studied. The results of this thesis contribute to the existing research to reduce the cost of PEMWE by enhancing the utilization of precious metal for OER electrocatalysis. Iridium electrocatalysts supported on antimony tin oxide (Ir/ATO) were synthesized using the polyol method with two different heating techniques: conventional and microwave-irradiation. It was shown that the physical morphology and electrochemical properties of Ir/ATO synthesized with the two heating methods were comparable. However, the microwave irradiation method was extremely faster than the conventional heating method. Additionally, the effect of heat treatment (calcination temperature) on the morphology and OER activity of Ir/ATO synthesized electrocatalyst with the conventional polyol method. It was found that the iridium electrocatalyst synthesized with the polyol method, consisted of 1-5 nm particles, possessed an amorphous structure, and contained iridium with an average oxidation state of less than +4. Calcining the catalyst at temperatures more than 400 ºC and less than 700ºC: 1) increased the size of the iridium particles to 30 nm, 2) changed the structure of iridium particles from amorphous to crystalline, 3) increased the iridium oxidation state to +4 (IrO2), 4) reduced the electrochemically active surface area by approximately 50%, and 5) reduced the OER activity by approximately 25%; however, it had no significant effect on the physical and chemical morphology of the ATO support. Moreover, potential support metal carbides and oxides including: Tantalum Carbide (TaC), Niobium Oxide (Nb2O5), Niobium Carbide (NbC), Titanium Carbide (TiC), Tungsten Carbide (WC) and Antimony-doped Tin Oxide (ATO, Sb2O5-SnO2), were characterized, and used as support for the iridium OER electrocatalysts. TaC was found to be a promising support, and increasing its surface area by 4% improved the OER performance of the final supported catalyst by approximately 50%.