1,721,028 research outputs found
Dynamic Electrochemical Promotion of Catalysis
No full textElectrochemical Promotion of Catalysis (EPOC) is a method for enhancing a catalytic reaction by modifying the surface properties of the catalyst through the application of a small amount of current or interfacial potential. It can also be used to enhance the selectivity of heterogenous catalytic reactions. It was first discovered by M. Stoukides and C. Vayenas in early 1980s. This phenomenon can increase the catalytic rate by 10 to 10^5 times compared to the electrochemical rate of supply of ions to the catalyst which is given by Faraday’s law. Therefore, the process is no longer faradaic and hence, it is also known as “Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA)".Today, the EPOC mechanism has been widely researched by different research groups, and many reactions have been investigated, but unfortunately, no commercial application of the technology is available. The main problem with EPOC is the lower activity per unit mass of the catalyst compared to the commercially used catalysts in conventional reactors. This drawback has been hindering the commercialisation of this idea.A new route has been proposed, which is called "Dynamic Electrochemical Promotion of Catalysis (DEPOC). The difference between EPOC and DEPOC comes from the dynamic operation of the system. In DEPOC, the current or the potential over the catalyst is varied periodically at different frequencies, symmetries and amplitudes of the wave-forms. This periodic modification is expected to have a role on selectivity of products and reaction rate.The main application that is considered for this mechanism is the Fischer-Tropsch (FT) reaction. It is a polymerization process which leads to hydrogenation of carbon monoxide forming liquid hydrocarbons. Controlling the selectivity of this reaction is hard, and normally a wide distribution of carbon chain lengths are obtained. With periodic application of voltage on the DEPOC catalyst, it is expected to be able to control the selectivity of the reaction or in other words the product distribution of the reaction. In this thesis, the DEPOC effect will be mainly studied from a theoretical perspective. First, the EPOC phenomenon will be analysed and the theory will be extended to the DEPOC effect. The study will be based on understanding the thermodynamics and the kinetics of these mechanisms. Lastly, a conceptual reactor design approach will be studied for the process.Mechanical Engineerin
Absorption of CO2 from the air using polyamines: Experiments, modelling and design
No full textCO2 concentration in the atmosphere is increasing leading to global warming and thus, climate change. Moreover, current renewable technologies such as wind or solar energy only cover the electricity market. A big part of the global energy market is still based on fossil fuels and difficult to electrify. Hence, there is an urgent need to produce renewable liquid hydrocarbons to replace fossil fuels. Zero Emission Fuels (ZEF) is a start-up that aims to develop a small-scale chemical plant to convert carbon dioxide (CO2) and water (H2O) from the air into methanol (MeOH) using photovoltaic energy. In this work, the absorption of CO2 using bulk polyamines was characterized experimentally, as well as through numerical modelling. In addition to this, guidelines for the design of the absorber, part of the Direct Air Capture (DAC) unit of ZEF’s micro-plant, are given. The focus of the study is placed on the kinetics and loading of CO2. To be able to model the absorption process an experimental approach has been developed regarding the uptake of CO2 and H2O. Firstly, pure H2O absorption experiments were performed in a climate chamber in order to obtain the H2O loadings using polyamines for different H2O content in the air. Secondly, air capture experiments were performed at lab conditions in order to obtain both H2O and CO2 loadings for different process conditions. Thirdly, constants relevant for the modelling part (reaction rate constant and Henry constant) were obtained experimentally. An absorption model, developed in MATLAB, was used to estimate the diffusion coefficient of both H2O and CO2 using the experimental H2O and CO2 loadings. Two main conclusions are obtained from the absorption model of CO2: the absorption of CO2 on polyamines is diffusion-limited and the diffusion coefficient of CO2 is two orders of magnitude lower than the diffusion coefficient of H2O. Based on the fact that the CO2 absorption process is diffusion-limited the mixing patterns should be introduced in the design of the continuous absorber. However, due to the fact that viscosity could influence the flowing behaviour of polyamines, more research is needed.Mechanical Engineerin
Direct Air Capture: Desorption of CO2 and H2O from amines
No full textZero Emission Fuels(ZEF) is a start up, and ZEF is building a micro plant which is ableto produce bio-methanol from solar energy and air. CO2and H2O are absorbed from theair, the H2O is split into H2which is fed together with the CO2in the methanol synthesisreactor. The reaction product is distilled and Grade AA MeOH is the product. Thisresearch the focus is on the continuous Direct Air Capture unit. The component consistsof 2 sub components, the absorber and the desorber. In the absorber the amine is broughtin contact with the air and absorbs CO2and H2O. As pure CO2and H2O molecules areneeded, the amine is desorbed in the desorber.This research specifically focuses on the desorption part of the DAC, amines(PEI andTEPA) are used to capture the CO2and H2O. The CO2is captured in two ways, via thecarbamate and the bicarbonate route. Carbamate is formed with primary and secondaryamines, bicarbonate is formed with the help of H2O and protonated primary, secondaryor tertiary amines. Bicarbonate is formed at loadings higher than 0.4 [mol CO2/ mol Namine], as the absorption capture capacity is low due to the low CO2partial pressure inthe air, this means that bicarbonate is not formed in the range of ZEF. After absorption30 wt% H2O and the CO2loading is expected to be 1.5 [mol CO2/ mol N amine].A VLE experiment is done to find the equilibrium between CO2in the gas phase andCO2in the amine, using the apparatus is was also possible to find the H2-Amine VLE.The experiment done with a 30 wt% failed due to high viscosity after which the solutionwas not homogeneous anymore. Adding more H2O up to 70 wt% solves the problem.However, the VLE is not accurate enough in low loading range(ZEF range. But, usingtwo isotherms, at 80 and 120°C the heat of absorption can be calculated. The results isa heat of absorption of -73.6 and -68.2 [kJ/mol CO2] for TEPA and PEI, respectively.To find the total desorption of CO2and H2O a desorption experimental setup isbuilt, experiments are performed at three pressures(50 100 and 200 mbar) and increasingtemperatures steps(80,90,100,110,120°C) . As the H2O evaporated at low temperature(<80°C). At higher temperatures than 90°C only CO2was present in the gas phase, hencethe partial pressure is equal to the total pressure. The output of CO2increases withdecreasing pressure and increases with temperature. The maximum output is equal to0.9 [mol CO2/ kg amine] using TEPA. The output of TEPA is twice as high as the outputof PEI.Using the experimental data from both tests, an energy model is made find the energypenalty of the desorption component. A base case study, a simple one-stage flash vesselat T = 120°C and p = 100 mbar, a total energy penalty of 18.1 and 33.6 MJ/ kg CO2,TEPA and PEI respectively. By altering the pressure and temperature the energy penaltycan be reduced to 16.6 [MJ/ kg CO2]. As the CO2demand is known, the correspondingneeded power is equal to 159 [W]. A design is suggested to put two flash vessels in parallelto reduce the H2O output of the system. At at temperature of 100 and 110°C with aconstant pressure of 100 mbar, a minimum of 15 [MJ/ kg CO2] is reached, a reductioni of 17% compared to the base case. Using a pinch analysis 93 [W] of the total 159 [W]can be retrieved by heat integration. Furthermore, the integration of a specially designedsolar boiler could provide the remained 66 [W] with hea
Development And Characterization Of A Small Scale Methanol Synthesis Reactor Based On Natural Convection
No full textIncreasing renewable electricity production calls for innovative methods to store electricity as well as a desire for electrification of processes that currently rely on fossil fuels. Zero Emission Fuels is a company that is developing a system to convert carbon dioxide and water from the air into methanol, a liquid hydrocarbon fuel, using photovoltaic energy. The scale of the system is fit for a single solar PV panel. The desired methanol output is 25 grams per hour.In this work, a new design for the methanol synthesis reactor of the system is developed, built and experimentally characterized. Knowledge from work by Basarkar and Gutierrez on a previous prototype is used as the starting point. The focus of the new design is placed on the heat integration network, the natural circulation effects, and tilting of the reactor. The heat exchanger makes use of heat pipes to transfer heat. Natural circulation is increased by increasing the channel dimensions of the system. This led to an increase in mass flow rate of over 3000%, making the mass flow rate the limiting factor for reactor performance. The mass flow rate is roughly 800% higher than assumed in the design phase; the resulting energy flows are too high for the heat exchanger to work effectively. Nevertheless, the heat exchanger heating duty relative to total heating is 230% higher than Basarkar. Tilting the reactor 20 degrees reduced the mass flow rate by 46% to 0.41 g/s, improving almost all aspects of reactor performance. Productivity increased by 58% to 15.7 g/h; 182% higher than Basarkar, though the space time yield is lower (4.1 vs 6.8 mmol/gcat/h). The energy efficiency of the system is close to Basarkar at 36.5% (vs. 37.5%). It is clear from experimental correlations that reducing mass flow rate will increase productivity, energy efficiency and heat exchanger performance.By simulating the requirements for an autothermal reactor it is found that the catalyst bed dimensions should be increased in terms of diameter and length to increase to residence time in the catalyst bed. The results agree with the experimental conclusion that the mass flow rate should be reduced. Furthermore, it is recommended to heat the fluid by convection instead of conduction to ensure a more homogeneous temperature profile in the catalyst bed. Also, the heat exchanger should be expanded by adding more heat pipes and increasing the heat transfer surface area.Mechanical Engineering | Energy and Process Technolog
Direct Air Capture: Characterization and design of a novel absorption process
No full textRising concentration of CO2 in the atmosphere has become a significant concern, paving the way for worldwide research on mitigation techniques like carbon capture and storage (CCS) and carbon capture and utilization (CCU). Zero Emission Fuel (ZEF), an aspiring startup based in the Netherlands, aims to develop a micro plant that produces methanol from just solar energy and air. Their process involves capturing CO2 and H2O directly from the air, splitting H2O to obtain H2 and producing methanol by reacting CO2 with H2. The focus of this research is on the absorption process of ZEF's direct air capture unit. Instead of capturing CO2 and H2O through a widely used batch direct air capture process, ZEF chooses to side with a novel continuous absorption and desorption process involving a flow of bulk polyamines without any conventional support structures. Polyethyleneimine (PEI-MW-600) and Tetraethylenepentamine (TEPA) are used as absorbents to achieve a target of capturing 825 grams of CO2 in 8 hours every day from a single direct air capture unit. Preliminary investigations show that the viscosity of PEI-600 is significantly higher than that of TEPA. An increase in CO2 concentration increases the viscosity of both polyamines significantly. In comparison, increasing H2O concentration leads to a maximum viscosity point in both polyamines and subsequent decrease in viscosity with a further increase in H2O concentration. Although, compared to CO2, H2O has a smaller effect on viscosity. Moreover, premixed samples of PEI-600 and TEPA with H2O show an increase in the CO2 absorption rate when pure CO2 is bubbled through the samples. In order to study and characterize the novel absorption process, an experimental setup facilitating a flow of absorbent is developed, and experiments are conducted following an experimental approach to calculate the mass transfer rates and average concentrations of CO2 and H2O. Fourier-transform infrared spectroscopy is used to estimate these concentrations. Experiments are performed on different initial concentrations of PEI and TEPA. TEPA is found to have a better absorption performance with an average CO2 absorption rate that is two times higher than PEI-600. Contrary to preliminary investigations done by bubbling CO2 into polyamines, absorbents with premixed water flowing down a channel were found to have lower CO2 absorption rates than pure polyamines. A multiple regression viscosity model, heat model, and a model of absorption column is developed using the data collected to estimate average viscosity, the heat of absorption of water, and characteristics of the absorption process. Diffusion of CO2 through the absorbent layers is found to be the primary limiting factor, while mass flow rates of absorbent and air are also found to influence the absorption process. Finally, a design of the absorption column is made to meet ZEF's requirement taking into account various performance characteristics studied during the thesis
DECAB: process development of a phase change absorption process
No full textThis work describes the conceptual design of a novel separation process for CO2 removal from flue gas based on precipitating solvents. The process here described (DECAB) is an enhanced CO2 absorption based on the Le Chatelier's principle, which states that reaction equilibrium can be shifted by removing one of the constituents in the reaction. A conceptual design of this process has been developed based on literature data, thermodynamic principles and a limited number of experiments. As solvent example, the potassium salt of taurine was selected. The strategy followed is based on the compilation and determination of the key properties and parameters that govern the absorption and regeneration of the solvent. Then, the performance of the process is evaluated with the aid of short cut design methods. Results show that the key advantages of this process are environmental friendliness (no emissions to the air) and low energy consumption related to a lower vapor pressure of the solvent and higher net loading than conventional processes. The design developed allows for future economic evaluation and assessment of options that will further lead to benefits over conventional processes. © 2011 Published by Elsevier Ltd
Offshore Methane Pyrolysis: A techno-economic analysis to assess the feasibility of offshore methane pyrolysis for the production of hydrogen
No full textMethane pyrolysis is a technology that has the potential to greatly reduce the CO2 emissions of hydrogen production on a large scale. The process generates solid carbon instead of gaseous, thereby inhibiting emissions and has a relatively low process energy demand.A three-step approach was taken to investigate the feasibility of offshore methane pyrolysis for sustainable hydrogen production. Firstly, a model was developed to evaluate the potential for converting methane into hydrogen under various design scenarios. Secondly, the model was utilized as a tool to create an offshore design for the methane pyrolysis reactor, including necessary auxiliary equipment. Finally, a calculation of the levelized cost of hydrogen (LCOH) was conducted to compare it with conventional methane reforming technologies for hydrogen production.The ultimate results showed a higher LCOH of offshore methane pyrolysis compared to the reforming technologies, however, two main components were identified that have the potential to close this gap. First, the sales of the solid carbon by-product would reduce the LCOH of offshore hydrogen and second the introduction of a CO2 tax would increase the LCOH of reforming technologies where methane pyrolysis is not affected. Thus, it can be inferred that offshore methane pyrolysis can be cost-competitive under the appropriate conditions.Offshore and Dredging Engineerin
Characterization of Transient behaviors and Operability study of a novel small scale Methanol Synthesis Reactor: Working on feed recycle by Natural Convection
No full textThe dwindling of natural resources, mainly fossil fuels, and the alarming increase in the global average temperatures, are the biggest concerns of the engineering and scientific community of 21st century. Studies have found that known reserves of oil and natural gas will last another 50 years. Coal will last another 110 years, which points towards dire consequences. The experience will not be that of a car slowly running out of gas, but rather like driving off a cliff, since we innately depend on these resources. The realization of these concerns has lead to a rise in the investments all over the globe for Sustainability. The right questions are now being asked. How can we fulfill our demands without compromising the demands of our future generations? One of the keen areas of interest is the conversion of power into fuel. Synthesis of hydrocarbons from sequestrated carbon can produce carbon-neutral fuels that can replace some of the conventional fossil fuels. Methanol has been actively wiping the floor with the research community due to its simplicity of production and less toxic nature. While there are quite a lot of ways of producing methanol, very few of them are carbon neutral. Zero Emission Fuels B.V. has embarked on a venture to produce methanol by a totally carbon neutral process. They begin by capturing carbon dioxide and water from air and splitting the water into hydrogen and oxygen using solar power. Carbon dioxide and hydrogen are then combined in a reactor to form methanol, making a truly carbon-neutral process. They aim to make fuel consumption, a completely circular process while keeping it economic. An experimental characterization of ZEF’s methanol reactor under varying pressures and H2/CO2compositions was done. The new reactor design focuses on heating the feed gases before catalyst bed, more heat integration, reliable sensor data, and the ability to mix gases in desired compositions. Methanol yield, quality, energy efficiency, reactor inlet and outlet temperatures, power requirements were experimentally determined in a transient analysis. It was seen that the reactor produces 4.84 mmol/gcat /hr of methanol at 50 Bar and reactor wall temperature of 250◦C with H2 : CO2 = 3:1 mol% feed gas. The catalyst exhibited partial deactivation during night after shutdown. Contrary to expectation, the reactor produced more methanol at lower pressure. The production was reported at 5.96 mmol/gcat /hr at 35 Bar. Although, only 4.36 mmol/gcat /hr at 25 Bar. Moreover, the pressure reduction caused the natural circulation to slow down, and increase the inlet temperature from 208◦C at 50 Bar to 234◦C at 35 Bar, which is the reason for the observed increase in yield. It can be concluded that the reactor yield under these conditions is limited by kinetics and not thermodynamics. The reduced mass flow rate allowed the reactor to consume less power and show higher energy efficiency. It increased from 34.7% at 50 Bar to 43.2% at 35 Bar. The rate of pressure decline in the reactor was correlated with the methanol yield using gas law by accounting for non-ideality with the compressibility factor. The predicted yield was seen to be in good agreement with experimentally determined. The methanol yield of the reactor with variable feed gas composition was obtained for 50 Bar and 250◦C reactor wall temperature and seen to decrease on either side of the ideal composition. It was concluded that the yield becomes both stoichiometrically and kinetically limited. It is recommended that similar experiments be done at increasing temperatures and equilibrium yield be determined experimentally. Additionally, the reactor needs to be operated with varying compositions and higher reactor wall temperatures at constant pressure, to obtain the operating line for maximum production of reactor.Mechanical Engineering | Energy and Process Technolog
Continuous Direct Air Capture, understanding mass transfer in reactive absorption of carbon dioxide: Experimenting and modelling a novel DAC absorption process
No full textIncrease in global energy demand has brought to a massive rise in greenhouse gases emissions. In particular, the continuously increasing atmospheric concentration of carbon dioxide is a major concern among the scientific community. This paved the way for an intense research of CO2 emissions mitigating technologies. Those ones including carbon capture, storage and utilisation are seen as part of the solution for this global problem. In this framework, Zero Emission Fuels (ZEF), a startup company located in Delft (The Netherlands) set the ambitious goal of developing a micro process plant producing methanol from ambient air and sunlight only. Part of the process involves direct capture of carbon dioxide from the atmosphere (direct air capture) with the use of a pure tetraethylenepentamine (TEPA) absorbent. ZEF sets itself aside from the rest of the industry developing an absorber which collects CO2 with no support structure by continuously flowing TEPA inside open channels. Previous research shows how this approach brings limitations connected to slowly diffusing CO2 molecules in the absorbent liquid film in proximity of the gas-liquid interface. In this framework, circulation of TEPA particles from the gas-liquid interface into the bulk of the flowing absorbent is seen as a viable solution to improve the process. This thesis focuses on investigating this hypothesis by inducing mixing on the liquid side. That is done by building two experimental setups investigating both passive and active mixing. Experimental results show that active mixing can be used to improve the rate of CO2 absorption, while passive mixing does not bring significant advantages. Results from the passive mixing experiments are further investigated by modelling the fluid dynamics of the process through a Direct Numerical Simulation of the particular Stokes’ flow in the engineered absorption channel. The process is characterised with the definition of a theoretical framework describing mass transfer in the liquid side. Following an analogy with ice formation on top of a frozen lake, this theory, also known as the ”Ice-Sheet” theory, shines some light on the way this diffusion limitations are happening at a molecular level. In particular, a highly viscous, heavily loaded layer of sorbent on the gas-liquid interface is believed to be the cause for observed CO2 diffusion limitations. This theory is backed-up by defining its mathematical equivalent in the form of a mass transfer model. Comparing the results of the model with experimental results, a very good agreement is observed. That is believed to add credibility to the proposed theory. Moreover, that is also found to be in line with the latest knowledge available in literature about CO2 absorption in TEPA films. Finally, the experimental results and the developed models are used to engineer a new iteration of ZEF’s absorber on a cost reduction basis
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