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Understanding the fate of nitrogen in food waste hydrothermal liquefaction.

Food waste is an abundant and inexpensive resource for the production of renewable fuels. Biocrude yields obtained from hydrothermal liquefaction (HTL) of food waste can be boosted using hydroxyapatite (HAP) as an inexpensive and abundant catalyst. Combining HAP with an inexpensive homogeneous base increased biocrude yield from 14 ± 1 to 37 ± 3%, resulting in the recovery of 49 ± 2% of the energy contained in the food waste feed. Detailed product analysis revealed the importance of fatty-acid oligomerization during biocrude formation, highlighting the role of acid-base catalysts in promoting condensation reactions. Economic and environmental analysis found that the new technology has the potential to reduce US greenhouse gas emissions by 2.6% while producing renewable diesel with a minimum fuel selling price of $1.06/GGE. HAP can play a role in transforming food waste from a liability to a renewable fuel.

Transient reaction modulation has found its place in many branches of chemical reaction engineering over the past hundred years. Historically, catalytic reactions have been dominated by the impulse to reduce spatial and temporal perturbations in favor of steady, static systems due to their ease of operation and scalability. Transient reactor operation, however, has seen remarkable growth in the past few decades, where new operating regimes are being revealed to enhance catalytic reaction rates beyond the statically achievable limits classically described by thermodynamics and the Sabatier principle. These theoretical and experimental studies suggest that there exists a resonant frequency which coincides with its catalytic turnover that can be exploited and amplified for a given reaction to overcome classical barriers. This review discusses the evolution of thought from thermostatic (equilibrium), to thermodynamic (dynamic equilibrium), and finally dynamic (non-equilibrium) catalysis. Natural and forced dynamic oscillations are explored with periodic reactor operation of catalytic systems that modulate energetics and local concentrations through a multitude of approaches, and the challenges to unlock this new class of catalytic reaction engineering is discussed.

An automated flow platform based on a tube-in-tube contactor and micro-packed bed reactor is developed to measure the kinetics of gas–liquid–solid hydrogenation reactions. The liquid flowing in the inner tube of the tube-in-tube contactor is rapidly saturated to ensure a constant H2 concentration before entering the micro-packed bed, which transforms the gas–liquid–solid system into a liquid–solid system. A ramping strategy is adopted in which the continuously varied residence time and the corresponding conversion data are obtained in a single experiment. Two reactions including hydrogenation of α-methylstyrene and nitrobenzene are chosen to demonstrate the accuracy and efficiency of this automated platform. Varying the flow rate ramping shows that accurate kinetic determination requires a specific range of flow rate ramps. A kinetic curve of conversion versus residence time (more than ten thousand data points) can be obtained in a single experiment within 50 min. The kinetic parameters obtained with this strategy agree well with literature values. The automated flow platform with flow rate ramping enables accurate determination of gas–liquid–solid reaction kinetics with higher efficiency and lower reagent cost compared with other methods.

Channeling of gas can reduce mass transfer performance in multiphase micropacked-bed reactors. Viscous and capillary forces cause this undesired and often unpredictable phenomenon in systems with catalyst particle sizes of hundreds of micrometers. In this work, we acoustically modify flow in a micropacked-bed reactor to reduce gas channeling by applying high-power sonication at low ultrasonic frequencies (∼40 kHz). Experimental residence time distributions reveal two orders of magnitude reduction in dispersion with ultrasound, allowing for nearly plug-flow behavior at high flow rates in the bed. Sonication appears to partially fluidize the packed-bed under pressurized cocurrent two-phase flow, effectively improving dispersion characteristics. This research was partially funded by the EU project MAPSYN: Microwave, Acoustic and Plasma SYNtheses, under Grant CPIP 309376 of the European Union Seventh Framework Program.

Gas-liquid mass transfer in micro-packed bed reactors is characterized with an automated platform integrated with in-line Fourier transform infrared spectroscopy. This setup enables screening of a multidimensional parameter space underlying absorption and with chemical reaction. Volumetric gas-liquid mass transfer coefficients (kLa) are determined for the model reaction of CO2 absorption in a methyl diethanolamine/water solution. Parametric studies are conducted varying gas and liquid superficial velocities, packed bed dimensions and packing particle sizes. The results show that kLa values are in the range of 0.24∼0.64 s−1, which is about one-to-two orders of magnitude larger than those of conventional trickle beds. An empirical correlation predicts kLa in micro-packed bed reactors in good agreement with experimental data. This article is protected by copyright. All rights reserved.

Hydrodynamics of gas–liquid two-phase flow in micropacked beds are studied with a new experimental setup. The pressure drop, residence time distribution, and liquid holdup are measured with gas and liquid flow rates varying from 4 to 14 sccm and 0.1 to 1 mL/min, respectively. Key parameters are identified to control the experimentally observed hydrodynamics, including transient start-up procedure, gas and liquid superficial velocities, particle and packed bed diameters, and physical properties of the liquids. Contrary to conventional large packed beds, our results demonstrate that in these microsystems, capillary forces have a large effect on pressure drop and liquid holdup, while gravity can be neglected. A mathematical model describes the hydrodynamics in the micropacked beds by considering the contribution of capillary forces, and its predictions are in good agreement with experimental data. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4694–4704, 2017

At high thermal flux and temperatures of approximately 500 °C, lignocellulosic biomass transforms to a reactive liquid intermediate before evaporating to condensable bio-oil for downstream upgrading to renewable fuels and chemicals. However, the existence of a fraction of nonvolatile compounds in condensed bio-oil diminishes the product quality and, in the case of inorganic materials, catalyzes undesirable aging reactions within bio-oil. In this study, ablative pyrolysis of crystalline cellulose was evaluated, with and without doped calcium, for the generation of inorganic-transporting aerosols by reactive boiling ejection from liquid intermediate cellulose. Aerosols were characterized by laser diffraction light scattering, inductively coupled plasma spectroscopy, and high-speed photography. Pyrolysis product fractionation revealed that approximately 3 % of the initial feed (both organic and inorganic) was transported to the gas phase as aerosols. Large bubble-to-aerosol size ratios and visualization of significant late-time ejections in the pyrolyzing cellulose suggest the formation of film bubbles in addition to the previously discovered jet formation mechanism.

Precise knowledge of gas diffusivity in liquids is critical for describing complex multiphase reaction systems. Here we present a high-throughput flow concept to measure gas diffusivity in liquids. This strategy takes advantage of the tube-in-tube reactor design whereby semipermeable Teflon AF-2400 tubes facilitate fast mass transfer between gas and liquid without directly contacting the two fluids. Coupled pseudosteady-state flux balances over the gas and liquid describe the gas dissolution rate and corresponding diffusivity with the aid of a single gas flow meter and a continuously ramped liquid flow rate. This in situ method demonstrates excellent accuracy in diffusion coefficient measurements, with less than 5% deviation from established techniques.

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Utilization of new hierarchical zeolites comprised of small crystallites (

Recent advancements in micro-flow technologies and a drive toward more efficient, greener and safer processes have led to a renaissance in flow-chemistry for pharmaceutical production. In this work, we demonstrate the use of a stabilized Pd nanoparticle-organic-silica catalyst to selectively catalyze the hydrogenation of N-4-nitrophenyl nicotinamide, a functionalized active pharmaceutical ingredient (API) surrogate. Extensive catalyst and reactor characterization is provided to establish an in-depth understanding of the unique multiphase dynamics within the micro-packed bed reactor, including the identification of a large liquid holdup (74-84%), rapid multiphase mass transfer (kma > 1 s-1), and liquid residence time distributions. A kinetic analysis has revealed that the surface catalyzed hydrogenation progresses through a condensation mechanism whereby an azo dimer intermediate is formed and rapidly consumed. Finally, a parametric study was performed at various pressures, temperatures, residence times and flow regimes to achieve quantitative chemoselective conversion of the nitroarene to the corresponding primary amine.

Data on the solubilities of gases in liquids are foundational for assessing a variety of multiphase separations and gas-liquid reactions. Taking advantage of the tube-in-tube reactor design built with semipermeable Teflon AF-2400 tubes, liquids can be rapidly saturated without direct contacting of gas and liquid. The gas solubility can be determined by performing steady-state flux balances of both the gas and liquid flowing into the reactor system. Using this type of reactor, a fully automated strategy has been developed for the rapid in situ measurement of gas solubilities in liquids. The developed strategy enables precise gas solubility measurements within 2-5 min compared with 4-5 h using conventional methods. This technique can be extended to the discrete multipoint steady-state and continuous ramped-multipoint data acquisition methods. The accuracy of this method has been validated against several gas-liquid systems, showing less than 2% deviation from known values. Finally, this strategy has been extended to measure the temperature dependence of gas solubilities in situ and to estimate the local enthalpy of dissolution across a defined temperature range.

The past two decades have witnessed a rapid development of microreactors. A substantial number of reactions have been tested in microchemical systems, revealing the advantages of controlled residence time, enhanced transport efficiency, high product yield, and inherent safety. This review defines the microchemical system and describes its components and applications as well as the basic structures of micromixers. We focus on mixing, flow dynamics, and mass and heat transfer in microreactors along with three strategies for scaling up microreactors: parallel numbering-up, consecutive numbering-up, and scale-out. We also propose a possible methodology to design microchemical systems. Finally, we provide a summary and future prospects.

The condition of heat transfer to lignocellulosic biomass particles during thermal processing at high temperature (>400 °C) dramatically alters the yield and quality of renewable energy and fuels. In this work, crystalline cellulose particles were discovered to lift off heated surfaces by high speed photography similar to the Leidenfrost effect in hot, volatile liquids. Order of magnitude variation in heat transfer rates and cellulose particle lifetimes was observed as intermediate liquid cellulose droplets transitioned from low temperature wetting (500–600 °C) to fully de-wetted, skittering droplets on polished surfaces (>700 °C). Introduction of macroporosity to the heated surface was shown to completely inhibit the cellulose Leidenfrost effect, providing a tunable design parameter to control particle heat transfer rates in industrial biomass reactors.