Ray Allen

Density-Viscosity Product of Small-Volume Ionic Liquid Samples Using Quartz Crystal Impedance Analysis

Quartz crystal impedance analysis has been developed as a technique to assess whether room-temperature ionic liquids are Newtonian fluids and as a small-volume method for determining the values of their viscosity-density product, rho eta. Changes in the impedance spectrum of a 5-MHz fundamental frequency quartz crystal induced by a water-miscible room-temperature ionic liquid, 1-butyl-3-methylimiclazolium trifluoromethylsulfonate ([C4mim][OTf]), were measured. From coupled frequency shift and bandwidth changes as the concentration was varied from 0 to 100% ionic liquid, it was determined that this liquid provided a Newtonian response. A second water-immiscible ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4mim][NTf2], with concentration varied using methanol, was tested and also found to provide a Newtonian response. In both cases, the values of the square root of the viscosity-density product deduced from the small-volume quartz crystal technique were consistent with those measured using a viscometer and density meter. The third harmonic of the crystal was found to provide the closest agreement between the two measurement methods; the pure ionic liquids had the largest difference of approximately 10%. In addition, 18 pure ionic liquids were tested, and for 11 of these, good-quality frequency shift and bandwidth data were obtained; these 12 all had a Newtonian response. The frequency shift of the third harmonic was found to vary linearly with square root of viscosity-density product of the pure ionic liquids up to a value of square root(rho eta) approximately 18 kg m(-2) s(-1/2), but with a slope 10% smaller than that predicted by the Kanazawa and Gordon equation. It is envisaged that the quartz crystal technique could be used in a high-throughput microfluidic system for characterizing ionic liquids.

Carbon dioxide utilisation for production of transport fuels: process and economic analysis

Utilising CO2 as a feedstock for chemicals and fuels could help mitigate climate change and reduce dependence on fossil fuels. For this reason, there is an increasing world-wide interest in carbon capture and utilisation (CCU). As part of a broader project to identify key technical advances required for sustainable CCU, this work considers different process designs, each at a high level of technology readiness and suitable for large-scale conversion of CO2 into liquid hydrocarbon fuels, using biogas from sewage sludge as a source of CO2. The main objective of the paper is to estimate fuel production yields and costs of different CCU process configurations in order to establish whether the production of hydrocarbon fuels from commercially proven technologies is economically viable. Four process concepts are examined, developed and modelled using the process simulation software Aspen Plus® to determine raw materials, energy and utility requirements. Three design cases are based on typical biogas applications: (1) biogas upgrading using a monoethanolamine (MEA) unit to remove CO2, (2) combustion of raw biogas in a combined heat and power (CHP) plant and (3) combustion of upgraded biogas in a CHP plant which represents a combination of the first two options. The fourth case examines a post-combustion CO2 capture and utilisation system where the CO2 removal unit is placed right after the CHP plant to remove the excess air with the aim of improving the energy efficiency of the plant. All four concepts include conversion of CO2 to CO via a reverse water-gas-shift reaction process and subsequent conversion to diesel and gasoline via Fischer–Tropsch synthesis. The studied CCU options are compared in terms of liquid fuel yields, energy requirements, energy efficiencies, capital investment and production costs. The overall plant energy efficiency and production costs range from 12–17% and £15.8–29.6 per litre of liquid fuels, respectively. A sensitivity analysis is also carried out to examine the effect of different economic and technical parameters on the production costs of liquid fuels. The results indicate that the production of liquid hydrocarbon fuels using the existing CCU technology is not economically feasible mainly because of the low CO2 separation and conversion efficiencies as well as the high energy requirements. Therefore, future research in this area should aim at developing novel CCU technologies which should primarily focus on optimising the CO2 conversion rate and minimising the energy consumption of the plant.

Micro-PIV simulation and measurement in complex microchannel geometries

Using low numerical aperture lenses to achieve a large field of view when carrying out micron resolution particle image velocimetry (micro-PIV) experiments may result in the out-of-plane resolution being a significant fraction of the overall channel depth. A method to estimate the effect of out-of-plane resolution on micro-PIV velocity measurements is applied to two microchannel flows: a two-dimensional developed flow in a straight channel and a three-dimensional periodic flow in a ribbed channel. The method combines numerical simulation based on computational fluid dynamics (CFD) with an approximation for the contribution to the correlation function arising from partially defocused particles. The flows are then investigated experimentally with measurements obtained on a number of evenly spaced planes. The dominating factor in the comparison between the micro-PIV results and CFD simulations is not the spatial resolution of the experimental data, but instead the precision with which the geometrical parameters can be determined. A methodology is also presented for using micro-PIV results to measure the depth of microfluidic devices. Parabolic fitting of flow profiles allows the top and bottom surfaces of the channel to be located to within 0.2 µm.

Small volume laboratory on a chip measurements incorporating the quartz crystal microbalance to measure the viscosity-density product of room temperature ionic liquids.

A microfluidic glass chip system incorporating a quartz crystal microbalance (QCM) to measure the square root of the viscosity-density product of room temperature ionic liquids (RTILs) is presented. The QCM covers a central recess on a glass chip, with a seal formed by tightly clamping from above outside the sensing region. The change in resonant frequency of the QCM allows for the determination of the square root viscosity-density product of RTILs to a limit of approximately 10 kg m(-2) s(-0.5). This method has reduced the sample size needed for characterization from 1.5 ml to only 30 mul and allows the measurement to be made in an enclosed system.

Development of a Microfluidic Unit for Sequencing Fluid Samples for Composition Analysis

A microfluidic sample-sequencing unit was developed as a part of a high-throughput catalyst screening facility. It may find applications wherever a fluid is to be selected for analysis from any one of several sources, such as microreactors operating in parallel. The novel feature is that the key components are fluidic valves having no moving parts and operating at very low sample flow Reynolds numbers, typically below 100. The inertial effects utilized in conventional no-moving-part fluidics are nearly absent; instead, the flows are pressure-driven. Switching between input channels is by high-Reynolds-number control flows, the jet pumping effect of which simultaneously cleans the downstream cavities to prevent cross-contamination between the samples. In the configuration discussed here, the integrated circuit containing an array of 16 valves is etched into an 84 mm diameter stainless steel foil. This is clamped into a massive assembly containing 16 mini-reactors operated at up to 400° C and 4 MPa. This paper describes the design basis and experience with prototypes. Results of CFD analysis, with scrutiny of some discrepancies when compared with flow visualization, is included.

High Throughput Testing of Catalysts for The Hydrogenation of Carbon Monoxide to Ethanol

An accelerated method of catalyst testing, based on a genetic algorithm catalyst library searching technique, multi-channel reactor containing a no moving part fluidic switching valve plate and quantitative on-line IR analysis is being developed to identify the optimum catalyst from a defined library of over 16000 catalysts for the hydrogenation of CO to ethanol. The research programme is positioned at the secondary screening stage of catalyst discovery where detailed quantitative information about all the major products of the reaction is required. The catalysts employed are based on rhodium, cobalt, manganese with alkali metal promoters, supported on silica with the metal concentrations being varied within carefully chosen limits. The performance parameter chosen for the genetic algorithm to optimise on was a formula based primarily on activity and selectivity to ethanol.

Determination of the physical properties of room temperature ionic liquids using a love wave device

In this work, we have shown that a 100 MHz Love wave device can be used to determine whether room temperature ionic liquids (RTILs) are Newtonian fluids and have developed a technique that allows the determination of the density-viscosity product, ρη, of a Newtonian RTIL. In addition, a test for a Newtonian response was established by relating the phase change to insertion loss change. Five concentrations of a water-miscible RTIL and seven pure RTILs were measured. The changes in phase and insertion loss were found to vary linearly with the square root of the density-viscosity product for values up to (ρη)(1/2) ~ 10 kg m(-2) s(-1/2). The square root of the density-viscosity product was deduced from the changes in either phase or insertion loss using glycerol as a calibration liquid. In both cases, the deduced values of ρη agree well with those measured using viscosity and density meters. Miniaturization of the device, beyond that achievable with the lower-frequency quartz crystal microbalance approach, to measure smaller volumes is possible. The ability to fabricate Love wave and other surface acoustic wave sensors using planar metallization technologies gives potential for future integration into lab-on-a-chip analytical systems for characterizing ionic liquids.

Continuous-flow Heck synthesis of 4-methoxybiphenyl and methyl 4-methoxycinnamate in supercritical carbon dioxide expanded solvent solutions

Summary The palladium metal catalysed Heck reaction of 4-iodoanisole with styrene or methyl acrylate has been studied in a continuous plug flow reactor (PFR) using supercritical carbon dioxide (scCO2) as the solvent, with THF and methanol as modifiers. The catalyst was 2% palladium on silica and the base was diisopropylethylamine due to its solubility in the reaction solvent. No phosphine co-catalysts were used so the work-up procedure was simplified and the green credentials of the reaction were enhanced. The reactions were studied as a function of temperature, pressure and flow rate and in the case of the reaction with styrene compared against a standard, stirred autoclave reaction. Conversion was determined and, in the case of the reaction with styrene, the isomeric product distribution was monitored by GC. In the case of the reaction with methyl acrylate the reactor was scaled from a 1.0 mm to 3.9 mm internal diameter and the conversion and turnover frequency determined. The results show that the Heck reaction can be effectively performed in scCO2 under continuous flow conditions with a palladium metal, phosphine-free catalyst, but care must be taken when selecting the reaction temperature in order to ensure the appropriate isomer distribution is achieved. Higher reaction temperatures were found to enhance formation of the branched terminal alkene isomer as opposed to the linear trans-isomer.

Density and viscosity measurements of room temperature ionic liquids using patterned Quartz Crystal Microbalances

Ionic liquids are becoming of increasing interest for an extensive range of applications. Small scale characterization processes are being continually researched to find cheap and efficient methods for processing ever smaller sample volumes. This work presents a dual Quartz Crystal Microbalance (QCM) setup with one smooth, and one patterned surface using chemically compatible materials allowing separate viscosity and density measurements of room temperature ionic liquids. Measurements were corroborated with standard measurement techniques and show good agreement, demonstrating the merit of the dual QCM setup in determining the physical properties of these exciting new solvents.

Integrated CO2 Capture and Utilization Using Non-Thermal Plasmolysis

In the presented work, 2 simple processes for carbon dioxide (CO2) capture and utilisation have been combined to form a whole systems approach to carbon capture and utilisation (CCU). The first stage utilises a pressure swing adsorption (PSA) system, which offers many benefits over current amine technologies. It was found that high selectivity can be achieved with rapid adsorption/desorption times whilst employing a cheap, durable sorbent that exhibits no sorbent losses and is easily regenerated by simple pressure drops. The PSA system is capable capturing and upgrading the CO2 concentration of a waste gas stream from 12.5% to a range of higher purities. As many CCU end processes have some tolerance towards impurities in the feed, in the form of nitrogen (N¬2) for example, this is highly advantageous for this PSA system since CO2 purities in excess of 80% can be achieved with only a few steps and minimal energy input. Non-thermal plasma is one such technology that can tolerate, and even benefit from, small N2 impurities in the feed, therefore a 100% pure CO2 stream is not required. The second stage of this process deploys a nanosecond pulsed corona discharge reactor to split the captured CO2 into carbon monoxide (CO), which can then be used as a chemical feedstock for other syntheses. Corona discharge has proven industrial applications for gas cleaning and the benefit of pulsed power reduces the energy consumption of the system. The wire-in-cylinder geometry concentrates the volume of gas treated into the area of high electric field. Previous work has suggested that moderate conversions can be achieved (9%), compared to other non-thermal plasma methods, but with higher energy efficiencies (>60%).