Two-chamber Reactor Research Articles

Catalytic Hydrothermal Liquefaction of a Microalga in a Two-Chamber Reactor

We carried out catalytic hydrothermal liquefaction of Nannochloropsis sp. at 350 °C in a two-chamber batch reactor that physically separated the 5% Pt/C catalyst from the algae and any solid material by a porous metal frit. This two-chamber arrangement provided a higher biocrude yield, a gaseous product richer in hydrocarbons, a biocrude with a larger “light” (hexane-soluble) portion, and a larger portion of biocrude consisting of small molecules than did an equivalent system where algae and catalyst were in physical contact. At the temperature investigated, a longer reaction time reduced the nitrogen and oxygen content in the biocrude, as has been observed in previous studies. Taken collectively, these results demonstrate that physically separating the heterogeneous catalyst and the biomass improves the catalytic hydrothermal liquefaction of microalgae, likely by more effectively doing the separate tasks of biomass liquefaction and biocrude upgrading in a single vessel.

Pd‐Catalyzed Carbonylative α‐Arylation of Aryl Bromides: Scope and Mechanistic Studies

Reaction conditions for the three-component synthesis of aryl 1,3-diketones are reported applying the palladium-catalyzed carbonylative α-arylation of ketones with aryl bromides. The optimal conditions were found by using a catalytic system derived from [Pd(dba)2] (dba=dibenzylideneacetone) as the palladium source and 1,3-bis(diphenylphosphino)propane (DPPP) as the bidentate ligand. These transformations were run in the two-chamber reactor, COware, applying only 1.5 equivalents of carbon monoxide generated from the CO-releasing compound, 9-methylfluorene-9-carbonyl chloride (COgen). The methodology proved adaptable to a wide variety of aryl and heteroaryl bromides leading to a diverse range of aryl 1,3-diketones. A mechanistic investigation of this transformation relying on 31P and 13C NMR spectroscopy was undertaken to determine the possible catalytic pathway. Our results revealed that the combination of [Pd(dba)2] and DPPP was only reactive towards 4-bromoanisole in the presence of the sodium enolate of propiophenone suggesting that a [Pd(dppp)(enolate)] anion was initially generated before the oxidative-addition step. Subsequent CO insertion into an [Pd(Ar)(dppp)(enolate)] species provided the 1,3-diketone. These results indicate that a catalytic cycle, different from the classical carbonylation mechanism proposed by Heck, is operating. To investigate the effect of the dba ligand, the Pd0 precursor, [Pd(η3-1-PhC3H4)(η5-C5H5)], was examined. In the presence of DPPP, and in contrast to [Pd(dba)2], its oxidative addition with 4-bromoanisole occurred smoothly providing the [PdBr(Ar)(dppp)] complex. After treatment with CO, the acyl complex [Pd(CO)Br(Ar)(dppp)] was generated, however, its treatment with the sodium enolate led exclusively to the acylated enol in high yield. Nevertheless, the carbonylative α-arylation of 4-bromoanisole with either catalytic or stoichiometric [Pd(η3-1-PhC3H4)(η5-C5H5)] over a short reaction time, led to the 1,3-diketone product. Because none of the acylated enol was detected, this implied that a similar mechanistic pathway is operating as that observed for the same transformation with [Pd(dba)2] as the Pd source.

Generation of Stoichiometric Ethylene and Isotopic Derivatives and Application in Transition‐Metal‐Catalyzed Vinylation and Enyne Metathesis

Ethylene is one of the most important building blocks in industry for the production of polymers and commodity chemicals. (13)C- and D-isotope-labeled ethylenes are also valuable reagents with applications ranging from polymer-structure determination, reaction-mechanism elucidation to the preparation of more complex isotopically labeled compounds. However, these isotopic derivatives are expensive, and are flammable gases, which are difficult to handle. We have developed a method for the controlled generation of ethylene and its isotopic variants including, for the first time, fully isotopically labeled ethylene, from simple alkene precursors by using Ru catalysis. Applying a two-chamber reactor allows both the synthesis of ethylene and its immediate consumption in a chemical transformation permitting reactions to be performed with only stoichiometric amounts of this two carbon olefin. This was demonstrated in the Ni-catalyzed Heck reaction with aryl triflates and benzyl chlorides, as well as Ru-mediated enyne metathesis.

Experimental Investigation of Vortex Flow in a Two-Chamber Solar Thermochemical Reactor

Recent advances in the field of large-scale solar thermochemical processing have given rise to substantial research efforts and demonstration projects. Many applications of high-temperature solar-thermal technology employ an enclosed cavity environment, thus requiring a transparent window through which concentrated solar energy can enter. One configuration employed is a two-cavity reactor connected by a narrow aperture, where solar flux entering through the window is focused at the aperture plane before diverging into the lower chamber, where the chemical reaction occurs. For the Zn/ZnO thermochemical cycle where Zn is solar-thermally reduced from ZnO in a high-temperature cavity environment, effective removal of the product gas stream containing zinc vapor is of paramount importance to prevent fouling by condensation on the reactor window. Two argon-jet configurations, tangential and radial, located around the circumference of the upper chamber are used to control the gas flow within the reactor cavity. First, the tangential jets drive a vortex flow, and second, the radial wall jet travels across the window before converging at the reactor center line and turning downward to create a downward jet. The tangential jet-induced flow creates a rotating vortex, contributing to overall flow stability, and the radial jet-induced downward flow counters the updraft created by the vortex while actively cooling and sweeping clear the inner surface of the window. Flow visualization in a full-scale transparent model of the reactor using smoke and laser illumination is employed to characterize the effectiveness of aerodynamic window clearing and to characterize the processes by which a vortex flow develops and breaks down in a two-chamber solar reactor geometry. Based on a large dataset of flow visualization images, a metric is developed to define vortex stability over a wide range of flow conditions and identify an ideal operating range for which a vortex formation path is established that maintains stable flow patterns and removes product gases while minimizing the use of argon gas. The predominant influence of vortex instability and breakdown is identified and examined for the case of a beam-down, two-chamber solar reactor geometry.

Reductive Carbonylation of Aryl Halides Employing a Two-Chamber Reactor: A Protocol for the Synthesis of Aryl Aldehydes Including 13C- and D-Isotope Labeling

A protocol has been developed for conducting the palladium-catalyzed reductive carbonylation of aryl iodides and bromides using 9-methylfluorene-9-carbonyl chloride (COgen) as a source of externally delivered carbon monoxide in a sealed two-chamber system (COware), and potassium formate as the in situ hydride source. The method is tolerant to a wide number of functional groups positioned on the aromatic ring, and it can be exploited for the isotope labeling of the aldehyde group. Hence, reductive carbonylations run with (13)COgen provide a facile access to (13)C-labeled aromatic aldehydes, whereas with DCO2K, the aldehyde is specifically labeled with deuterium. Two examples of double isotopic labeling are also demonstrated. Finally, the method was applied to the specific carbon-13 labeling of the β-amyloid binding compound, florbetaben.

Modernized Low Pressure Carbonylation Methods in Batch and Flow Employing Common Acids as a CO Source

Carbonylation reactions, such as Heck, Sonogashira, and radical carbonylations, were successfully carried out in a "two-chamber reactor" where carbon monoxide was produced ex situ by the Morgan reaction (dehydration of formic acid by sulfuric acid). By a subsequent application in a microflow system using a "tube-in-tube" reactor where gas-permeable Teflon AF2400 was used as the inner tube, it is demonstrated that formic acid/sulfuric acid can be employed concomitantly with an amine base such as triethylamine in the Heck aminocarbonylation of aryl iodide.

Reaction kinetics of hydrothermal carbonization of loblolly pine

Hydrothermal carbonization (HTC) is a pretreatment process to convert diverse feedstocks to homogeneous energy-dense solid fuels. Understanding of reaction kinetics is necessary for reactor design and optimization. In this study, the reaction kinetics and effects of particle size on HTC were investigated. Experiments were conducted in a novel two-chamber reactor maintaining isothermal conditions for 15s to 30 min reaction times. Loblolly pine was treated at 200, 230, and 260°C. During the first few minutes of reaction, the solid-product mass yield decreases rapidly while the calorific value increases rapidly. A simple reaction mechanism is proposed and validated, in which both hemicellulose and cellulose degrade in parallel first-order reactions. Activation energy of hemicellulose and cellulose degradation were determined to be 30 and 73 kJ/mol, respectively. For short HTC times, both reaction and diffusion effects were observed.

Use of a two-chamber reactor to improve enzymatic hydrolysis and fermentation of lignocellulosic materials

A special type of bioreactor was designed and tested in order to improve the bioethanol production from lignocellulosic materials via enzymatic hydrolysis and fermentation. The reactor consists of two chambers kept at different temperatures and separated by a porous medium, through which the solutes can diffuse. The reactor was tested using as substrate wheat straw previously steam exploded and detoxified. The yields of cellulose hydrolysis and glucose fermentation obtained using this reactor were compared to those obtained by simultaneous enzymatic hydrolysis and fermentation (SSF) carried out in only one vessel. The results showed that a significant increase in the ethanol yield (20%) can be achieved by using this bioreactor. An additional advantage of the reactor is the confinement of the solid lignin in one chamber, allowing a simplified separation process between broth and unreacted residue.

Test operation of a 100 kW pilot plant for solar hydrogen production from water on a solar tower

The present work describes the realisation and successful test operation of a 100 kW pilot plant for two-step solar thermo-chemical water splitting on a solar tower at the Plataforma Solar de Almería, which aims at the demonstration of the feasibility of the process on a solar tower platform under real conditions. The process applies multi-valent iron based mixed metal oxides as reactive species which are coated on honeycomb absorbers inside a receiver–reactor. By the introduction of a two-chamber reactor it is possible to run both process concepts in parallel and thus, the hydrogen production process in a quasi-continuous mode. In summer 2008 an exhaustive thermal qualification of the pilot plant took place, using uncoated ceramic honeycombs as absorbers. Some main aspects of these tests were the development and validation of operational and measurement strategy, the gaining of knowledge on the dynamics of the system, in particular during thermal cycling, the determination of the controllability of the whole system, and the validation of practicability of the control concept. The thermal tests enabled to improve, to refine and finally to prove the process strategy and showed the feasibility of the control concept implemented. It could be shown that rapid changeover between the modules is a central benefit for the performance of the process. In November of 2008 the absorber was replaced and honeycombs coated with redox material were inserted. This allowed carrying out tests of hydrogen production by water splitting. Several hydrogen production cycles and metal oxide reduction cycles could be run without problems. Significant concentrations of hydrogen were produced with a conversion of steam of up to 30%.

Direct Biological Conversion of Electrical Current into Methane by Electromethanogenesis

New sustainable methods are needed to produce renewable energy carriers that can be stored and used for transportation, heating, or chemical production. Here we demonstrate that methane can directly be produced using a biocathode containing methanogens in electrochemical systems (abiotic anode) or microbial electrolysis cells (MECs; biotic anode) by a process called electromethanogenesis. At a set potential of less than -0.7 V (vs Ag/AgCl), carbon dioxide was reduced to methane using a two-chamber electrochemical reactor containing an abiotic anode, a biocathode, and no precious metal catalysts. At -1.0 V, the current capture efficiency was 96%. Electrochemical measurements made using linear sweep voltammetry showed that the biocathode substantially increased current densities compared to a plain carbon cathode where only small amounts of hydrogen gas could be produced. Both increased current densities and very small hydrogen production rates by a plain cathode therefore support a mechanism of methane production directly from current and not from hydrogen gas. The biocathode was dominated by a single Archaeon, Methanobacterium palustre. When a current was generated by an exoelectrogenic biofilm on the anode growing on acetate in a single-chamber MEC, methane was produced at an overall energy efficiency of 80% (electrical energy and substrate heat of combustion). These results show that electromethanogenesis can be used to convert electrical current produced from renewable energy sources (such as wind, solar, or biomass) into a biofuel (methane) as well as serving as a method for the capture of carbon dioxide.

Fast pyrolysis - Effect of wood drying on the yield and properties of bio-oil

The composition and properties of the products of fast pyrolysis of hardwood, obtained in a two-chamber (drying and pyrolytic) ablation type reactor in the temperature range 450-600ºС, were investigated. It has been found that, upon the additional drying of wood at 200ºС and subsequent pyrolysis, the quality of bio-oil is improved owing to the decrease in the amount of water and acids. It has been shown that the increase of the drying temperature to 240ºС decreases the yield of the main product. Optimum parameters of the drying conditions and the temperature of the pyrolysis of wood, at which the bio-oil yield exceeds 60% and its calorific value makes up 17-20 МJ/kg, have been determined.

FAST PYROLYSIS – EFFECT OF WOOD DRYING ON THE YIELD AND PROPERTIES OF BIO-OIL

The composition and properties of the products of fast pyrolysis of hardwood, obtained in a two-chamber (drying and pyrolytic) ablation type reactor in the temperature range 450-600oС, were investigated. It has been found that, upon the additional drying of wood at 200oС and subsequent pyrolysis, the quality of bio-oil is improved owing to the decrease in the amount of water and acids. It has been shown that the increase of the drying temperature to 240oС decreases the yield of the main product. Optimum parameters of the drying conditions and the temperature of the pyrolysis of wood, at which the bio-oil yield exceeds 60% and its calorific value makes up 17-20 МJ/kg, have been determined.

Vertically aligned carbon nanotube arrays for giant field emission displays

Direct growth of individual and vertically aligned carbon nanotubes (CNT) onto a metallic tip apex using a two-chamber radio-frequency plasma-enhanced chemical vapor deposition reactor is reported. Individual Ni nanocatalysts were the sites for the nucleation of individual CNTs that were freestanding, clean, and vertically aligned by the presence of a controlled applied field. To understand the role of the electric field during the growth of these individual vertically aligned CNTs, we have separated the plasma production from the applied electric field to the CNTs, by the use of the two-chamber reactor. Our results suggest that the growth direction is mainly related to the ion implantation of carbon species in the metal catalyst located on the top of the CNTs. In this model, the direction of ion implantation fixes the distribution of the concentration gradient of carbon atoms across the nanocatalyst particle, i.e., the direction and the growth velocity of the CNTs. Moreover, it lessens the role of surface decomposition and dissolution of the feed gas. For a polarized substrate the growth direction is then vertical to the surface. The obtained arrays of CNTs, having a low-density spatial distribution to avoid mutual electrostatic field screening, gave uniform and stable overall field emission patterns after a conditioning process. Effective total current densities up to 1A∕cm2 can be extracted.

Investigating the Plasma Surface Modification of Polystyrene at Low Ion Power Densities

A new grid-separated, two-chamber low-pressure plasma reactor [Dhayal, M.; Forder, D.; R. Short, D.; Bradley, J. W. Vacuum 2003, 70, 67] 1 has been developed to study the surface modification of polymeric materials under low ion power density bombardment. Through external biasing of the grids, the ion flux r and energy E of the bombarding plasma ions at the substrate can be controlled independently (within certain experimental limits). Importantly, this can be achieved without changing the VUV component of the plasma. In the present arrangement, ion power densities (qΓE) in the range 0.7-15.5 W m - 2 can be achieved. This allows a low power density regime to be explored, not possible in typical glass barrel RF reactors often used for surface modification of polymeric materials, in which ion power densities are typically 10-160 W m - 2 . The effect of ion energy and flux on the surface modification of polystyrene (PS) was quantified by the ratio of atomic oxygen to carbon in the post-treated samples exposed to air (measured by X-ray photoelectron spectroscopy, XPS). It was found that, over the whole available range in ion fluxes, (1.7-5 x 10 1 8 m - 2 s - 1 ) and energies (1.5-23 eV), the O/C ratios did not change with O/C about 0.1 to 0.12 for plasma exposure times of 90 s. With elimination of the ion species from the processing region of the discharge through grid biasing, the O/C ratios were also found not to change, indication that below a certain threshold of ion power (at least 15.5 W m - 2 ) ions play little role in the surface modification. By replacing the grids with a LiF window (cutoff wavelength λ c 104 nm) having a transparency in the VUV region (<200 nm) at least as good as the geometric transmission area of the two grid system we observe again little change in O/C, indicating that the dominant species in production of free radical sites is the VUV, with any excited neutral species and radicals in the plasma playing a minor role.

Microwave assisted phosgenation – alcoholysis using triphosgene

The microwave assisted reaction engineering of the phosgenation of alcohols with triphosgene as a safe-to-handle phosgene substitute was investigated. The phosgenation of n-butanol was carried out in the homogeneous phase as a one-pot reaction, and in a two-chamber reactor in which freshly produced phosgene gas was bubbled through the educt solution. New catalysts such as phenanthroline, benzyltriethylammonium chloride (BTAC), and the ionic liquid 1-ethyl-2,3-dimethylimidazolium-bis-trifluoromethanesulfoneimide (PW1022) were successfully employed for the decomposition of triphosgene, alone or in combination with activated charcoal, which acted as a microwave absorber. In another experimental series, the reaction of a wide range of alcohols (isopropanol, n-butanol, tert-amyl alcohol, 2-butoxy-ethanol, cyclohexanol, benzyl alcohol, 1-phenyl alcohol, n-octanol) with triphosgene was investigated for two different microwave set-ups.

Surface phosphonylation of low-density polyethylene

Surface phosphonylation of thermoplastic polymers was previously demonstrated in both the liquid and gas phase. For the present study, the phosphonylation process was modified through the use of a two-chamber reactor and a dynamic oxygen flow in an effort to secure greater control of the gas phase reaction. Low-density polyethylene films were phosphonylated at both ambient and elevated temperatures for time periods ranging from 15 to 60 min. Subsequently, all films were analyzed by SEM, EDX, horizontal ATR-FTIR, surface roughness, and dynamic contact angle measurements. Analysis of the data indicates that after 15 min at ambient temperature, films do not phosphonylate to a degree that could be detected by the chosen methods. Phosphonylation was achieved at 30 and 60 min at ambient temperature, and at 60 min at 45°C. The data indicate that optimal conditions for gas phase phosphonylation in the described apparatus are 25°C for times greater than 15 min but less than 60 min. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1870–1875, 2000

Surface phosphonylation of low-density polyethylene

Surface phosphonylation of thermoplastic polymers was previously demonstrated in both the liquid and gas phase. For the present study, the phosphonylation process was modified through the use of a two-chamber reactor and a dynamic oxygen flow in an effort to secure greater control of the gas phase reaction. Low-density polyethylene films were phosphonylated at both ambient and elevated temperatures for time periods ranging from 15 to 60 min. Subsequently, all films were analyzed by SEM, EDX, horizontal ATR-FTIR, surface roughness, and dynamic contact angle measurements. Analysis of the data indicates that after 15 min at ambient temperature, films do not phosphonylate to a degree that could be detected by the chosen methods. Phosphonylation was achieved at 30 and 60 min at ambient temperature, and at 60 min at 45°C. The data indicate that optimal conditions for gas phase phosphonylation in the described apparatus are 25°C for times greater than 15 min but less than 60 min. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1870–1875, 2000

Solid Electrolyte Aided Direct Coupling of Methane

Solid electrolyte cells have been utilized as electrochemical oxygen pumps to supply oxygen to or from electrode-catalyst surfaces. Recently, the use of solid electrolytes to promote catalysis for a number of reactions has been investigated. During these investigations, dramatic increases in the oxygen consumption, far exceeding the amount of oxygen supplied through the O[sup 2]-conducting electrolyte, have been observed accompanying overall increases in reaction rates. In addition, this effect has been recently demonstrated in oxidative reactions using Na[sup +]-conducting as well as proton-conducting solid electrolytes. This phenomenon, named NEMCA (nonfaradaic electrochemical modification of catalytic activity), has been attributed to an effect on chemisorption bonding, and hence the reaction rate constant, by altering the catalyst work function. The conversion of methane to ethane and ethylene is a subject of extensive study by a very large number of research groups in the last 7 years. Attempts to convert methane into useful raw materials by using solid oxide electrolytes have been separately reviewed. Recently, a three-electrode cell using Ag and Ni-Zr electrodes on yttria-stabilized zirconia has been used to study the current-voltate relationship during the oxidation of methane at 600-800[degrees]C. The present communication explores the nonoxidative coupling of methane to C[sub 2] hydrocarbonsmore » over silver electrodes using a solid electrolyte with major conductivity via protons. An added feature of this investigation is the utilization of the electrolyte as a support in a one-chamber reactor rather than a solid oxide membrane partition in a two-chamber reactor. This design, adapted from Otsuka et al., simplifies the overall reactor configuration. Using this type of cell, an attempt is made to connect the nonoxidative coupling of methane with the NEMCA phenomenon. 11 refs., 3 figs., 1 tab.« less

Enzymic polymerisation of an unactivated diol/diacid system

The polyesterification of adipic acid and butane-1,4-diol by a commercial lipase (Lipozyme IM-20) has been studied using a two-chamber reactor and molecular sieve as a dehydrating agent. The lower oligomeric products were identified and a low-dispersity polyester averaging 20 repeat units was produced.