The Boudouard reaction, which is the reaction of carbon and carbon dioxide to produce carbon monoxide, represents a simple and straightforward method for the remediation of carbon dioxide in the ...environment through reduction: CO2(g) + C(s) ⇌ 2CO. However, due to the large positive enthalpy, typically reported to be 172 kJ/mol under standard conditions at 298 K, the equilibrium does not favor CO production until temperatures >700 °C, when the entropic term, −TΔS, begins to dominate and the free energy becomes negative. We have found that, under microwave irradiation to selectively heat the carbon, dramatically different thermodynamics for the reaction are observed. During kinetic studies of the reaction under conditions of flowing CO2, the apparent activation energy dropped from 118.4 kJ/mol under conventional convective heating to 38.5 kJ/mol under microwave irradiation. From measurement of the equilibrium constants as a function of temperature, the enthalpy of the reaction dropped from 183.3 kJ/mol at ∼1100 K to 33.4 kJ/mol at the same temperature under microwave irradiation. This changes the position of the equilibrium so that the temperature at which CO becomes the major product drops from 643 °C in the conventional thermal reaction to 213 °C in the microwave. The observed reduction in the apparent enthalpy of the microwave driven reaction, compared to what is determined for the thermal reaction from standard heats of formation, can be thought of as arising from additional energy being put into the carbon by the microwaves, effectively increasing its apparent standard enthalpy. Mechanistically, it is hypothesized that the enhanced reactivity arises from the interaction of CO2 with the steady-state concentration of electron–hole pairs that are present at the surface of the carbon due to the space-charge mechanism, by which microwaves are known to heat carbon. Such a mechanism is unique to microwave-induced heating and, given the effect it has on the thermodynamics of the Boudouard reaction, suggests that its use may yield energy savings in driving the general class of gas–carbon reactions.
The steam–carbon reaction, which is the essential reaction of the gasification processes of carbon-based feed stocks (e.g., coal and biomass), produces synthesis gas (H2 + CO), a synthetically ...flexible, environmentally benign energy source. The reaction is very endothermic, which mandates high temperatures and a large expenditure of energy to drive the reaction. We have found that using microwave irradiation to selectively heat the carbon leads to dramatically different observed thermodynamics for the reaction. From measurement of the equilibrium constants as a function of temperature, the enthalpy of the reaction under microwave radiation was found to become significantly more exothermic, dropping from 144.2 kJ/mol at the median reaction temperature of 880 K to 15.2 kJ/mol under microwave irradiation. The reaction conditions under which the steam–carbon reaction was run, and under which the equilibrium measurements were determined, consisted of three other reactions that came to equilibrium. These reactions were the Boudouard reaction, which is the reaction of CO2 with carbon to form CO; the water–gas shift reaction, where CO and water react to form H2 and CO2; and the carbon–hydrogen reaction, which generates methane from the reaction of H2 with carbon. We determined the equilibrium constants and thermodynamic parameters for all of these reactions. The Boudouard reaction, which is also strongly endothermic, was found to be more exothermic under microwave radiation (180.2 kJ/mol (thermal) and 27.0 kJ/mol (MW)). The water–gas shift reaction became more endothermic (−36.0 kJ/mol (thermal) and −11.4 kJ/mol (MW)). The carbon–hydrogen reaction also underwent an endothermic shift, from −79.7 to −9.1 kJ/mol. From the associated equilibrium expressions and the equilibrium constants for the steam–carbon reaction system, the mole fractions of the system components under thermal and microwave conditions were estimated. The effect of the microwave radiation was to change the position of the equilibrium so that the temperature at which H2 was at a maximum dropped from 643 °C in the conventional thermal reaction to 213 °C in the microwave. Notwithstanding the predicted temperature shift, there was an observable threshold below which microwaves could not produce products. In our system, the minimum energy at which H2 appeared was 373 °C (30 W), while the temperature at which equilibrium could be established in a reasonable period of time (100 min) was 491 °C (100 W).
Thermally promoted Friedel–Crafts benzylation of arene solvents has been examined under both conventional convective heating with an oil bath and heating using microwave (MW) energy. Bulk solution ...temperaturesas measured by internal and external temperature probes and as defined by solvent refluxwere comparable in both sets of experiments. MW-specific rate enhancements were documented under certain conditions and not others. The observed rate enhancements at a given temperature are proposed to arise from selective MW heating of polar solutes, perturbing thermal equilibrium between the solute and bulk solution. Central to MW-specific thermal phenomena is the difference between heat and temperature. Temperature is a measure of the ensemble average kinetic molecular energy of all solution components, but temperature does not provide information about solute-specific energy differences that may arise as a consequence of selective MW heating. Enhanced chemical reactivity of the MW-absorbing solute can be described as a MW-specific “extra-temperature thermal effect”, because the measurable solution temperature only captures a portion of the solute kinetic molecular energy. Experimental factors that favor MW-specific rate enhancements are discussed with an eye toward future development of MW-actuated organic reactions, in which the observed thermal reactivity exceeds what is predicted from temperature-based Arrhenius calculations.
Temporary superheating and sustained nucleation-limited "superboiling" of unstirred liquids above the normal atmospheric boiling point have been documented during microwave heating. These phenomena ...are reliably observed under prescribed conditions, although the duration (of superheating) and magnitude (of superheating and superboiling) vary according to system parameters such as volume of the liquid and the size and shape of the vessel. Both phenomena are mitigated by rapid stirring with an appropriate stir bar and/or with the addition of boiling chips, which provide nucleation sites to support the phase-change from liquid to gas. With proper experimental design and especially proper stirring, the measured temperature of typical organic reaction mixtures heated at reflux will be close to the normal boiling point temperature of the solvent, whether heated using microwave radiation or conventional convective heat transfer. These observations are important to take into consideration when comparing reaction rates under conventional and microwave heating.
A series of heterogeneous catalyst materials possessing good microwave absorption properties were investigated for their activity as oxidation catalysts under microwave irradiation. These catalysts, ...a series of nanoscale magnetic spinel oxides of the composition MCr2O4 (M = Cu, Co, Fe), were irradiated in aqueous methanol solution (1:1 MeOH:H2O v:v). This resulted in rapid conversion of methanol to formaldehyde, directly generating aqueous formalin solutions. The catalytic reaction occurred under relatively mild conditions (1 atm O2, 60 °C), with irradiation times of 80 min converting 24.5%, 17.7%, and 13.2% of the available methanol to formaldehyde by the Cu, Fe, and Co chromite spinel catalysts, respectively. Importantly, reactions run under identical conditions of concentration, time, and temperature using traditional convective heating yielded dramatically lower amounts of conversions; specifically, 1.0% and 0.21% conversions were observed with Cu and Co spinels, and no observable thermal products were obtained from the Fe spinels. This work provides a clear demonstration that microwave-driven catalysis can yield enhanced reactivity and can afford new catalytic pathways.
AudienceThis simulation is appropriate for senior and junior emergency medicine residents. IntroductionShortness of breath is a very common presentation in the emergency department and can range from ...mild to severe as well as a chronic or acute onset. In sympathetic crashing acute pulmonary edema (SCAPE), patients typically present with acute onset of dyspnea occurring within minutes to hours and have significantly elevated blood pressure.1 The condition of SCAPE falls into the spectrum of acute heart failure syndromes such as fluid overload pulmonary edema and congestive heart failure exacerbation.1. Educational ObjectivesAt the completion of the simulation and debriefing, the learner will be able to: 1) recognize the physical exam findings and presentation of SCAPE, 2) utilize imaging and laboratory results to further aid in the diagnosis of SCAPE, 3) initiate treatments necessary for the stabilization of SCAPE, 4) demonstrate the ability to assist with the stabilization and disposition of a patient via tele-medicine as determined by the critical action checklist and assessment tool below, 5) interpret the electrocardiogram (EKG) as atrial fibrillation with rapid ventricular response (AFRVR), and 6) recognize that SCAPE is the underlying cause of AFRVR and continue to treat the former. Educational MethodsThis simulation was performed using a high-fidelity mannequin. In order to simulate the telemedicine aspect, the learner evaluated the patient using a video conferencing interface while the two confederates were present with the high-fidelity mannequin. A debriefing session was held immediately after the simulation. Research MethodsThe educational content was evaluated by debriefing and verbal feedback provided immediately after the case. Additionally, a survey was emailed to participants and observers of the case to provide qualitative feedback. ResultsPost-simulation feedback was overall positive with participants and observers. Participants and observers felt this was a safe and realistic simulation of SCAPE and provided them with the opportunity to practice rapid recognition and treatment of this condition. DiscussionSympathetic crashing acute pulmonary edema falls into the spectrum of acute heart failure disorders, and rapid recognition and stabilization is vital for the patient's survival. This simulation case provided learners of all levels the chance to assess and treat a life-threatening condition with limited information in a safe and effective learning environment. The telemedicine component was used while conducting weekly didactics via zoom during the COVID-19 pandemic. Simulation is a large component of our didactic curriculum and implementing the telemedicine component into this case was worth the effort. It is important to familiarize our residents with telemedicine since we expect that it will become a larger part of the practice of emergency medicine in the future, allowing board-certified emergency medicine physicians to assist in providing care in rural emergency departments and smaller hospitals that may be staffed with less experienced providers. TopicsMedical simulation, tele-medicine, pulmonary edema, respiratory distress, cardiac emergencies, resuscitation.
This simulation is appropriate for senior and junior emergency medicine residents.
Shortness of breath is a very common presentation in the emergency department and can range from mild to severe as ...well as a chronic or acute onset. In sympathetic crashing acute pulmonary edema (SCAPE), patients typically present with acute onset of dyspnea occurring within minutes to hours and have significantly elevated blood pressure.1 The condition of SCAPE falls into the spectrum of acute heart failure syndromes such as fluid overload pulmonary edema and congestive heart failure exacerbation.1.
At the completion of the simulation and debriefing, the learner will be able to: 1) recognize the physical exam findings and presentation of SCAPE, 2) utilize imaging and laboratory results to further aid in the diagnosis of SCAPE, 3) initiate treatments necessary for the stabilization of SCAPE, 4) demonstrate the ability to assist with the stabilization and disposition of a patient via tele-medicine as determined by the critical action checklist and assessment tool below, 5) interpret the electrocardiogram (EKG) as atrial fibrillation with rapid ventricular response (AFRVR), and 6) recognize that SCAPE is the underlying cause of AFRVR and continue to treat the former.
This simulation was performed using a high-fidelity mannequin. In order to simulate the telemedicine aspect, the learner evaluated the patient using a video conferencing interface while the two confederates were present with the high-fidelity mannequin. A debriefing session was held immediately after the simulation.
The educational content was evaluated by debriefing and verbal feedback provided immediately after the case. Additionally, a survey was emailed to participants and observers of the case to provide qualitative feedback.
Post-simulation feedback was overall positive with participants and observers. Participants and observers felt this was a safe and realistic simulation of SCAPE and provided them with the opportunity to practice rapid recognition and treatment of this condition.
Sympathetic crashing acute pulmonary edema falls into the spectrum of acute heart failure disorders, and rapid recognition and stabilization is vital for the patient's survival. This simulation case provided learners of all levels the chance to assess and treat a life-threatening condition with limited information in a safe and effective learning environment. The telemedicine component was used while conducting weekly didactics via zoom during the COVID-19 pandemic. Simulation is a large component of our didactic curriculum and implementing the telemedicine component into this case was worth the effort. It is important to familiarize our residents with telemedicine since we expect that it will become a larger part of the practice of emergency medicine in the future, allowing board-certified emergency medicine physicians to assist in providing care in rural emergency departments and smaller hospitals that may be staffed with less experienced providers.
Medical simulation, tele-medicine, pulmonary edema, respiratory distress, cardiac emergencies, resuscitation.
The gasification of carbonaceous material is a long standing industrial process which produces valuable feed stocks of H2 and CO gas (Syngas) that can be reacted further resulting in extended ...hydrocarbons for use in numerous areas of industry. The process of gasification is energy intensive, requiring temperatures >700 °C, which at the industrial scale requires large amounts of excess energy in order to achieve optimal reaction temperatures for ideal compositions and product yields. Conventional convective heating methods of current industrial processes thereby limits the overall efficiency of the gasification process even before the desired product is achieved. Microwave radiation of dipolar or conducting materials is known to produce heat in a significantly different way than conventional heating. Microwaves can specifically heat materials which in turn heats microwave active material to a higher temperature than by conventional methods because less heat is lost to surroundings with limited loss of excess energy to the complete system. It is understood that microwave radiation also leads to enhanced rates of reaction, due to its ability to selectively heat materials and the mechanism by which it heats. An industrially relevant process such as carbon gasification is therefore an ideal candidate for investigation. The disproportionation of CO2 over carbon (Boudouard reaction) as a fundamental reaction in carbon gasification provided a clean and clear starting point in which to study the effects of microwave heating. It was found that the use of microwave radiation to selectively heat the carbon resulted in a profound change in the fundamental thermodynamics of the reaction. From kinetic studies of the reaction under conditions of flowing CO2, it was found that the apparent activation energy decreased from conventional convective heating to the modified system under microwave irradiation. From measurement of the equilibrium constants as a function of temperature, the enthalpy of the reaction also dropped under microwave irradiation. The change in enthalpy affected the position of the equilibrium so that the temperature at which CO becomes the major product dropped significantly from the conventional thermal reaction to the microwave. The changes in the fundamental thermodynamics of the reaction are attributed to the enhanced reactivity of the CO2 with the steady-state concentration of electron–hole pairs that are present at the surface of the carbon as a result of the space-charge mechanism, which is understood to be heating the carbon. Such a mechanism is unique to microwave-induced heating, and, given the effect it has on the thermodynamics of the Boudouard reaction, suggests that its use may yield large energy savings in driving the general class of gas–carbon reactions. To further elucidate the significant increase in efficiency, the carbon-steam process was also examined under microwave irradiation. From equilibrium measurements of the carbon-steam, as well as the various equilibria of comprising secondary reactions, it was observed that the same type of thermodynamic enhancement occurred for this more complicated system.
Current robotic control methods take advantage of high computing power to compute trajectories and perform optimal movements for a given task, yet these robots still fall far short of their animal ...counterparts when interacting with the environment. Animals dynamically adapt to varying terrain and small perturbations almost effortlessly. In order to improve our robotic systems and build better control methods, it makes sense to look more closely at how animals solve this interaction. In this work, I developed a control model of mammalian walking with models grounded in neuroscience and computational neuroscience. First, I developed a neuromechanical model of a rat with 14 degrees of freedom and 28 muscles, and I explored how hypothesized neural architectures can be used to coordinate four limbs in a walking gait for a rat. Additionally, through simulated ablation experiments, I developed hypotheses on how inter-leg pathways work together to maintain limb timing. After this, I developed a procedure to train the neural system to produce dynamic walking in both a rat simulation and a robot named Puppy. This method works by first using a model of the system (rat or robot) to determine required motor neuron activations to produce stable walking. For the robot, this required building a force-length-pressure model of the McKibben actuators to enable accurate force control. Parameters in the neural system are then set such that it produces similar activations to the desired pattern. I applied the same training procedure to both the simulated rat and the robot and show that it is capable of producing continuous, self-supported stepping in both systems.
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