Continuous Plug Flow Reactor Research Articles

Thermal and catalytic degradation of pyrolytic waxy oil in a plug flow reactor

Pyrolytic waxy oil as a reactant was obtained from a commercial rotary kiln pyrolysis plant for municipal plastic waste. The characteristics of raw pyrolytic waxy oil are investigated, and in the upgrading of pyrolytic waxy oil, catalytic degradation using a commercial HZSM-5 catalyst is compared with the thermal degradation characteristics. Experiments were carried out in a continuous plug flow reactor at 450 °C for 1 h. The raw pyrolytic waxy oil showed a high boiling point distribution with an approximate range of 300–550 °C. This is a much higher boiling point distribution compared to that of commercial diesel. Upon thermal degradation at 450 °C, the GC peak pattern and carbon number distribution of the product oils show a trend similar to those of raw pyrolytic waxy oil. This indicates that the conversion of pyrolytic waxy oil to light hydrocarbons by the thermal degradation at a high temperature does not occur at a sufficient level. On the other hand, the catalytic degradation using the HZSM-5 catalyst relative to thermal degradation shows a high conversion rate of pyrolytic waxy oil to light hydrocarbons and moreover a high selectivity of light aromatic products in the liquid product. The upgrading of pyrolytic waxy oil is strongly influenced by the HZSM-5 catalyst used in this study.

Continuous production of poly([R]-3-hydroxybutyrate) by Cupriavidus necator in a multistage bioreactor cascade

Poly(hydroxyalkanoates) (PHAs) constitute biodegradable polyesters and are considered among the most promising candidates to replace common petrochemical plastics in various applications. To date, all commercial processes for PHA production employ microbial discontinuous fed-batch fermentations. These processes feature drawbacks such as varying product quality and the inevitable periods of downtime for preparation and post-treatment of the bioreactor equipment. An unprecedented approach to PHA production was chosen in the presented work using a multistage system consisting of five continuous stirred tank reactors in series (5-SCR), which can be considered as a process engineering substitute of a continuous tubular plug flow reactor. The first stage of the reactor cascade is the site of balanced bacterial growth; thereafter, the fermentation broth is continuously fed from the first into the subsequent reactors, where PHA accumulation takes place under nitrogen-limiting conditions. Cupriavidus necator was used as production strain. The focus of the experimental work was devoted to the development of a PHA production process characterized by high productivity and high intracellular polymer content. The results of the experimental work with the reactor cascade demonstrated its potential in terms of volumetric and specific productivity (1.85 g L⁻¹ h⁻¹ and 0.100 g g⁻¹ h⁻¹, respectively), polymer content (77%, w/w) and polymer properties (M (w) = 665 kg/mol, PDI = 2.6). Thus, implementing the technology for 5-SCR production of PHB results in an economically viable process. The study compares the outcome of the work with literature data from continuous two-stage PHA production and industrial PHA production in fed-batch mode.

Development of a new bioethanol feedstock – Anaerobically digested fiber from confined dairy operations using different digestion configurations

Abstract Two types of digesters, continuous stirring-tank reactor (CSTR) and plug flow reactor (PFR), were integrated into a biorefining concept to generate a new cellulosic ethanol feedstock –anaerobically digested fiber (AD fiber) from dairy cow feces. Cellulose content in AD fibers was significantly increased during the anaerobic digestion. CSTR and PFR AD fibers had cellulose contents of 357 and 322 g kg −1 dried AD fiber. The AD fibers were enzymatically hydrolyzed after being pretreated by dilute sulfuric acid or dilute sodium hydroxide, and the hydrolysates were used to produce ethanol. Alkali pretreatment was concluded as a suitable pretreatment method for AD fibers. Under the optimal conditions the AD fibers processed by CSTR and PFR produced ethanol of 26 g kg −1 and 23 g kg −1 dry feces, respectively. Energy balance analysis further indicated that CSTR was a preferred digestion method to prepare AD fiber for ethanol production.

Getting Ring-Closing Metathesis off the Bench: Reaction-Reactor Matching Transforms Metathesis Efficiency in the Assembly of Large Rings

Reported is the first study of the influence of reactor configuration on the efficiency of a challenging ring-closing metathesis (RCM) reaction. With the intention of increasing the generality of RCM scaleup and reducing its dependence on substrate modification, macrocyclization of an unmodified, low effective-molarity diene was explored using different reactor types, in conjunction with a commercial, homogeneous Grubbs catalyst. Optimized performance is compared for a conventional batch reactor (BR), a continuous plug-flow reactor (PFR), and a continuous stirred-tank reactor (CSTR). In the PFR, maximum conversion is achieved most rapidly, but product yields and selectivity are adversely affected by co-entrapment of ethylene with the catalyst, substrate, and product in the traveling "plug". Use of the CSTR, in which ethylene is efficiently swept out, affords an order-of-magnitude increase in total turnover numbers, and reduces the required catalyst loadings by 25× relative to the BR (to 0.2 mol %), while improving RCM yields and selectivity to quantitative levels. Continuous-flow methodologies that support liberation of the ethylene co-product thus show great promise for industrial uptake of RCM.

Toward a Competitive Process Intensification: A New Generation of Heat Exchanger-Reactors

Process Intensification (PI) in chemical production is a major concern of chemical manufacturers. Among the numerous options to intensify a process, the transposition from a batch reactor to a continuous plug flow reactor is a good alternative when the selectivity and the thermal exchange are an issue. In this context, the RAPIC R&D project aims to develop an innovative low-cost component (in the 10 kg/h range). This project deals with the design from the local to the global scale and with testing, from elementary mock-ups to pilot scale. The present paper gives a detailed description of this research project and presents the main results on specification and definition of the reaction channel and the first simple mock-ups.

Supercritical water oxidation of quinoline in a continuous plug flow reactor—part 2: kinetics

AbstractThe results of a detailed investigation into the kinetics of quinoline oxidation in supercritical water are presented. The novel kinetic data presented were obtained in a continuously operated, plug flow reactor where parameters such as temperature, pressure, residence time and stoichiometric ratio of oxidant to quinoline were investigated and detailed in the companion paper (Pinto LDS, Freitas dos Santos LMF, Al‐Duri B and Santos RCD, Supercritical water oxidation of quinoline in a continuous plug flow reactor—part 1: effect of key operating parameters. J Chem Technol Biotechnol). An induction time was experimentally observed, ranging from 1.5 to 3.5 s, with longer times observed in experiments carried out at lower temperatures. A pseudo‐first‐order rate expression with respect to quinoline concentration (with oxygen excess) was first adopted and the activation energy of 234 kJ mol−1 and a pre‐exponential factor of 2.1 × 1014 s−1 were estimated. Furthermore, an integral power rate model expression was established, attributing a reaction order for quinoline as 1 and for oxygen as 0.36. An activation energy and pre‐exponential factor for this model were determined as 224 kJ mol−1 and 3.68 × 1014 M−0.36 s−1, respectively. A global rate expression was then regressed for the quinoline reaction rate from the complete set of data. The resulting activation energy was 226 ± 19 kJ mol−1 and the pre‐exponential factor was 2.7 × 1013 ± 2 M−0.1 s−1. The reaction orders for quinoline and oxygen were 0.8 ± 0.1 and 0.3 ± 0.1, respectively. It was shown that the least‐squares regression method provided the best‐fit model for experimental results investigated in this study. Copyright © 2006 Society of Chemical Industry

Supercritical water oxidation of quinoline in a continuous plug flow reactor—part 1: effect of key operating parameters

AbstractThis work presents the supercritical water oxidation (SCWO) of quinoline, a nitrogen‐containing organic compound found in pharmaceutical wastewaters, to products that are more readily biodegradable. The effects of the operating variables, namely process temperature, stoichiometric ratio of oxidant to organic, residence time and system pressure were studied in order to optimise quinoline removal efficiency and to investigate the fate of carbon and nitrogen after oxidation. Hydrolysis experiments undertaken in the range 480–650 °C showed no significant degradation of quinoline. The present study confirmed that, as an alternative to incineration, the process is fast and effective in treating quinoline in water, converting it into primarily carbon dioxide (CO2), water (H2O) and nitrogen gas (N2) and to a lesser extent ammonium ions (NH4+). Temperature was shown to be the primary variable in the complete destruction of quinoline and TOC reduction, upon operating at around 250 bars. Essentially, complete quinoline removal was observed above 575 °C and complete TOC removal was obtained at 650 °C, where CO2 was the main reaction product. Copyright © 2006 Society of Chemical Industry

Catalytic cracking of C4 alkenes to propene and ethene: Influences of zeolites pore structures and Si/Al 2 ratios

Catalytic cracking of butene to propene and ethene was carried out in a continuous plug-flow stainless steel reactor over various zeolites with different pore structures and Si/Al 2 ratios. It was found that the porous structure and acidity of zeolites play important roles in the zeolite performance in the butene cracking process. The smaller the pore size of the zeolite catalysts, the higher the initial selectivities towards propene and ethene and the lower the initial selectivities to C 3–C 4 alkanes. This is attributed to a suppression of the hydrogen transfer reaction of the alkenes. Although high initial selectivities to propene and ethene could be gained on medium-pore zeolites of ZSM-22, ZSM-23, ZSM-35 and on small-pore zeolite SAPO-34, the stabilities of all these zeolites were poor. On the other hand, due to its special structure characteristic, the ZSM-5 zeolite exhibited the best stability in the catalytic cracking of butene among the tested zeolites. MCM-22 also presented a better catalytic performance. Besides the pore structure, the acidity, which was influenced by the Si/Al 2 ratio of the zeolite, was another important factor affecting the performance of the zeolites. By increasing the Si/Al 2 ratio of the ZSM-5 zeolite, the selectivities to propene and ethene and the stabilities were remarkably increased owing to a suppression of secondary reactions.

On‐line monitoring of bioreductions via membrane introduction mass spectrometry

Real-time and on-line continuous monitoring of reactants, intermediates, and final products for dicarbonyl compound bioreduction in a continuous plug flow reactor packed with baker's yeast (Saccharomyces cerevisiae) whole cells immobilized on calcium alginate beads was performed by membrane introduction mass spectrometry (MIMS) via selective ion monitoring.

Kinetics of Disproportionation of Inorganic Polysulfides in Undersaturated Aqueous Solutions at Environmentally Relevant Conditions

The rate of the reversible homogeneous disproportionation of polysulfides was studied by following the optical absorbance of polysulfide solutions in a continuous plug flow reactor equipped with an on-line photometric detector. In order to avoid heterogeneous slow reactions involving sulfur colloids or precipitate, the reaction was initiated by an abrupt pH change from an undersaturated solution containing predominantly tetrasulfide species to a pH where pentasulfide is the dominant species. The disproportionation was found to follow first order reversible reaction dynamics. At environmentally relevant conditions the characteristic time of the disproportionation reaction is of the order of 10 s. This characteristic time implies that necessary conditions for speciation of the different polysulfide species by chromatography or another separation and subsequent quantification scheme should be of the order of 1 s.

DOE awards chemical makers funding for biomass conversion

Crosslinked, cryostructured monoliths prepared from Lactobacillus reuteri cells were evaluated as potential immobilized whole-cell biocatalyst for conversion of glycerol, to potentially important chemicals for the biobased industry, i.e. 3-hydroxypropionaldehyde (3HPA), 3-hydroxypropionic acid (3HP) and 1,3-propanediol (1,3PDO). Glutaraldehyde, oxidized dextran and activated polyethyleneimine/modified polyvinyl alcohol (PEI/PVA) were evaluated as crosslinkers; the latter gave highly stable preparations with maintained viability and biocatalytic activity. Scanning electron microscopy of the PEI/PVA monoliths showed high density of crosslinked cells with wide channels allowing liquid flow through. Flux analysis of the propanediol-utilization pathway, incorporating glycerol/diol dehydratase, propionaldehyde dehydrogenase, 1,3PDO oxidoreductase, phosphotransacylase, and propionate kinase, for conversion of glycerol to the three chemicals showed that the maximum specific reaction rates were −562.6, 281.4, 62.4 and 50.5 mg/gCDW h for glycerol consumption, and 3HPA (extracellular), 3HP and 1,3PDO production, respectively. Under optimal conditions using monolith operated as continuous plug flow reactor, 19.7 g/L 3HPA was produced as complex with carbohydrazide at a rate of 9.1 g/Lh and a yield of 77 mol%. Using fed-batch operation, 1,3PDO and 3HP were co-produced in equimolar amounts with a yield of 91 mol%. The monoliths embedded in plastic carriers showed high mechanical stability under different modes in a miniaturized plug flow reactor.

Polymerization of liquid propylene with a 4th generation Ziegler–Natta catalyst—influence of temperature, hydrogen and monomer concentration and prepolymerization method on polymerization kinetics

In a batch-wise operated autoclave reactor, liquid propylene was polymerized using a 4th generation, TiCl 4/MgCl 2/phthalate ester–AlEt 3–R 2Si(OMe) 2, Ziegler–Natta catalyst system. By using a calorimetric principle it was possible to measure full reaction rate versus time curves for obtaining data on polymerization kinetics, under industrially relevant conditions. The influence of polymerization temperature, the hydrogen and monomer concentration, and the prepolymerization method on reaction kinetics were investigated. A new method for prepolymerization, the so-called non-isothermal prepolymerization, is described. In this short prepolymerization procedure featuring an increasing polymerization temperature the thermal runaway on particle scale was avoided. It was shown that this prepolymerization method can relatively easily be applied to an industrial process, with the introduction of a continuous plug flow reactor, giving a narrow residence time distribution, acceptable yield-in-prepolymerization and a method for monitoring catalyst activity. Using different methods for calculating the monomer concentration at the active site of the catalyst, the influence of polymerization temperature was determined. It was shown that at high polymerization temperatures, the reaction rate is barely influenced by polymerization temperature, when no prepolymerization is used. This is ascribed to thermal runaway on particle scale of a fraction of the catalyst particles. When a prepolymerization is used, this effect disappears and thermal runaway is avoided. When systematically reducing the monomer concentration ( C m,bulk ) in the bulk by replacing part of the liquid propylene by hexane, the reaction rate proved to be remarkably independent of the monomer concentration. With reducing C m,bulk , reaction rate decreased very slowly until C m, bulk =150 g/ l . When further decreasing C m,bulk , reaction rate dropped rapidly. The hydrogen concentration was varied over a wide range at 60°C and 70°C. For both temperatures it was shown that reaction rates increased rapidly with increasing hydrogen concentration at low hydrogen concentrations. At higher hydrogen amounts, this effect disappeared and a maximum reaction rate was found.

Butanol production by Clostridium beijerinckii BA101 in an immobilized cell biofilm reactor: increase in sugar utilization.

Acetone butanol ethanol was produced in a continuous immobilized cell (biofilm) plug-flow reactor inoculated with Clostridium beijerinckii BA101. To achieve high reactor productivity, C. beijerinckii BA101 cells were immobilized by adsorption onto clay brick. The continuous plug-flow reactor offers high productivities owing to reduced butanol inhibition and increased cell concentration. Although high productivity was achieved, it was at the expense of low sugar utilization (30.3%). To increase sugar utilization, the reactor effluent was recycled. However, this approach is complicated by butanol toxicity. The effluent was recycled after removal of butanol by pervaporation to reduce butanol toxicity in the reactor. Recycling of butanol-free effluent resulted in a sugar utilization of 100.7% in addition to high productivity of 10.2 g/(L x h) at a dilution rate of 1.5 h(-1). A dilution rate of 2.0 h(-1) resulted in a reactor productivity of 16.2 g/(L x h) and sugar utilization of 101.4%. It is anticipated that this reactor-recovery system would be economical for butanol production when using C. beijerinckii BA101.

Hydrodynamic Optimization of a UV-cascade for the Photochemical Oxidation with H2O2

Photochemical reactions are usually of first order, suggesting the use of a continuous plug flow reactor for minimizing reactor volume and energy requirements. The limited radiation penetration depth applied in photochemical reactions, however, requires intensive radial mixing, which is lacking in a plug flow reactor. This may be resolved by using a cascade reactor, which combines low mixing in the flow direction with intensive mixing in the radial direction.

The tau of continuous feeding on simple foods.

Chemical reactor theory under the premise of maximization of net rate of nutrient absorption has been used to predict throughput time, tau, of digesta in animals. Animals that feed on hexoses, such as many vertebrate fruit and nectar eaters, are of central interest in testing reactor theory because they use no hydrolysis before absorption and, hence, should provide valuable, simplified test cases. Graphical methods based on batch reactors and used to make such predictions in the past can give optimal gut throughput times (tauopt) identical with predictions from continuous plug-flow reactor models derived here: in animals with passive, linear uptake alone, tauopt should decline as hexose concentration of food increases. If saturating active uptake is involved, however, a minimum in tauopt (maximum in ingestion rate) is predicted at intermediate hexose concentration, the exact location of this minimum depending on costs of ingestion as well as on uptake kinetics. That is, tauopt first falls to a minimum with increasing hexose concentration and then increases. Optimal throughput time rises as uptake sites become saturated because there is little gross gain and no net gain from increased ingestion rate when uptake already is nearly saturated. It also rises with increasing costs of ingestion. The continuous-time analytic solutions provided here further make the novel and very general prediction of high sensitivity to decreasing tau below tauopt.

Concomitant use of liquid–liquid batch and continuous plug flow reactors for kinetic model discrimination. Application to the Rh/TPPTS catalysed reduction of the C–C double bond in dimethylitaconate

The biphasic catalytic reduction of the C–C double bond of dimethylitaconate with a water soluble rhodium/triphenylphosphinetrisulphonated sodium salt (TPPTS) complex is investigated. Kinetic studies in a well-mixed batch reactor provide kinetics parameters and an activation energy of 71 kJ mol −1 but cannot discriminate between a first order or a complex kinetic model within the range of substrate concentration where the approximation of linear liquid/liquid partition is respected. Catalytic tests in the centrifugal partition chromatograph (CPC) reactor under steady-state operations in chemical regime and plug flow mode allow discriminating the kinetic models, the complex kinetic rate law being preferred.

A liquid-liquid plug-flow continuous reactor for the investigation of catalytic reactions: The centrifugal partition chromatograph

A centrifugal partition chromatograph (CPC) is used as a liquid-liquid reactor for the catalytic reduction of benzaldehyde to benzylic alcohol. The catalyst is a water-soluble ruthenium complex with triphenylphosphinetrisulfonated, sodium salt (TPPTS) as a ligand. Kinetic study in a well-mixed batch reactor reveals that the reaction is of first order with respect to the substrate. Hydrodynamics and mass transfer in the CPC have been studied. Residence-time distribution analysis evidences the plug-flow pattern of the CPC. Comparison of the characteristic reaction time with the mass transfer time shows that the chemistry is the actual limiting process. Finally, catalytic tests in the CPC reactor confirm the kinetic data obtained in the batch reactor. The CPC is thus found to be a very effective continuous plug-flow liquid-liquid catalytic reactor.

Towards a continuous process in heterogeneous coordinated anionic ring opening polymerization

The current article deals with the initial developments of the use of a continuous plug flow reactor using an original heterogeneous catalyst system for the living coordinated anionic polymerization of certain oxygenated rings. This reactor is designed in order to maintain the essential characteristics of the original batch system. One of the pertinent parameters considered here is the residence time of the reactants inside the reactor. The column has been used to investigate ethylene oxide and e-caprolactone oligomerization. Initial experiments have pointed out how the molecular weights can depend on the flow rate for a fixed bed length. Some theoretical problems relative to the reactive column are discussed in order to investigate more in depth the properties of this original continuous process and to model it to find the optimal working conditions.

Manufacture of photoelectric material containing a zeolite matrix

Catalytic cracking of butene to propene and ethene was carried out in a continuous plug-flow stainless steel reactor over various zeolites with different pore structures and Si/Al2 ratios. It was found that the porous structure and acidity of zeolites play important roles in the zeolite performance in the butene cracking process. The smaller the pore size of the zeolite catalysts, the higher the initial selectivities towards propene and ethene and the lower the initial selectivities to C3–C4 alkanes. This is attributed to a suppression of the hydrogen transfer reaction of the alkenes. Although high initial selectivities to propene and ethene could be gained on medium-pore zeolites of ZSM-22, ZSM-23, ZSM-35 and on small-pore zeolite SAPO-34, the stabilities of all these zeolites were poor. On the other hand, due to its special structure characteristic, the ZSM-5 zeolite exhibited the best stability in the catalytic cracking of butene among the tested zeolites. MCM-22 also presented a better catalytic performance. Besides the pore structure, the acidity, which was influenced by the Si/Al2 ratio of the zeolite, was another important factor affecting the performance of the zeolites. By increasing the Si/Al2 ratio of the ZSM-5 zeolite, the selectivities to propene and ethene and the stabilities were remarkably increased owing to a suppression of secondary reactions.

Generation of gas bubbles in water by using zeolite particles for gas storage

Catalytic cracking of butene to propene and ethene was carried out in a continuous plug-flow stainless steel reactor over various zeolites with different pore structures and Si/Al2 ratios. It was found that the porous structure and acidity of zeolites play important roles in the zeolite performance in the butene cracking process. The smaller the pore size of the zeolite catalysts, the higher the initial selectivities towards propene and ethene and the lower the initial selectivities to C3–C4 alkanes. This is attributed to a suppression of the hydrogen transfer reaction of the alkenes. Although high initial selectivities to propene and ethene could be gained on medium-pore zeolites of ZSM-22, ZSM-23, ZSM-35 and on small-pore zeolite SAPO-34, the stabilities of all these zeolites were poor. On the other hand, due to its special structure characteristic, the ZSM-5 zeolite exhibited the best stability in the catalytic cracking of butene among the tested zeolites. MCM-22 also presented a better catalytic performance. Besides the pore structure, the acidity, which was influenced by the Si/Al2 ratio of the zeolite, was another important factor affecting the performance of the zeolites. By increasing the Si/Al2 ratio of the ZSM-5 zeolite, the selectivities to propene and ethene and the stabilities were remarkably increased owing to a suppression of secondary reactions.