Continuous Loop Reactor Research Articles

A parameter study of ultrasound assisted enzymatic esterification

This work is focused on the study of the esterification parameters for the ultrasound assisted synthesis of isoamyl acetate catalyzed by lipase Lipozyme 435 in a continuous loop reactor. Investigating the influence of different parameters shows that a higher concentration of ester (462 mg/g mixture) can be obtained at a temperature of 50 °C, flow rate 0.16 mL/min. The best ultrasonication conditions are: sonication applied continuously for a short time (20 min), ultrasound power 32 mW and amplitude 20%. The enzyme can be successfully reused tree times without loss of enzyme activity. Reaction kinetics for isoamyl acetate ultrasound assisted production showed that satisfactory reaction concentration (close to the equilibrium concentrations) could be reached in short reaction times (2 h). Ultrasound assisted enzymatic esterification is consequently a cleaner and a faster process.

Kinetics of Epoxidation of Cyclooctene with Ionic Liquids Containing Tungstate as Micellar Catalyst

AbstractThe kinetics of cyclooctene epoxidation with H2O2 by micellar catalysis was studied. As catalyst, an ionic liquid (IL) containing the catalytically active tungstate anion was used. The tungstate IL forms micelles in the aqueous H2O2 phase. It is simply formed by dissolving sodium tungstate and 1‐octyl‐3‐methylimidazolium tetrafluoroborate [OMIM][BF4] in aqueous H2O2. For the epoxidation of cyclooctene by micellar catalysis, a power law kinetic model was determined that takes the critical micelle concentration into account. The kinetics of the [OMIM][BF4]/Na2WO4 catalyst is similar to pure [OMIM]2[WO4], which indicates that the active species is formed in situ. Addition of phenylphosphonic acid improves the activity of the tungstate IL. The most effective catalyst was tested in a semi‐continuous and continuous loop reactor.

Development of a Continuous Flow Process for a Matteson Reaction: From Lab Scale to Full-Scale Production of a Pharmaceutical Intermediate

Within this paper, we present the design, development, and scale-up of a process for a continuous Matteson reaction to produce a key intermediate toward the β-lactamase inhibitor vaborbactam. This includes the successful implementation of the continuous concept at a multiton production scale for the API at Patheon, part of Thermo Fisher Scientific. The first-generation continuous flow production with its discontinuous downstream processing was further developed to a fully continuous production through installation of a continuous loop reactor. This enabled increased productivity and energy efficiency, eliminated volume and time bottlenecks, and reduced waste.

Comments on the use of loop reactors in sonochemical processes

For sonochemical processing on an industrial scale the traditional choice is either a batch or flow system. The former is straightforward in concept but it requires large scale powerful ultrasonic transducers capable of delivering high intensity ultrasound to large volumes of liquid. Unfortunately at the moment the cost and problems involved in building very large sonication devices for batch processes cannot justify the replacement of existing industrial processes. For this reason most sonochemists prefer some form of flow system where small quantities of reagents can be treated as they are pumped from a large vat of reagents through a smaller sonochemical reactor where high intensity ultrasound can be applied. In this short paper we draw attention to a problem which seems common in a number of papers dealing with such flow systems – a confusion between the terms continuous reactor and loop reactor. Further we emphasise the importance of calculating the actual amount of ultrasonic processing experienced by the reaction mixture within the sonication zone of a loop reactor during its operation. The parameters required for such a calculation are: ultrasonic processor volume (Rv in L), pump flow rate (Fr in L/min), stock solution volume in the reservoir (Sv in L) and the overall system operating time (So in min).

Pd-catalyzed telomerization of butadiene and methanol with direct catalyst recycling using a liquid-ionic liquid biphasic, continuous process

The telomerization of 1,3-butadiene with methanol in the presence of a phosphine modified palladium catalyst was investigated in liquid-ionic liquid biphasic systems. Suitable ionic liquids were pre-selected from computational a priori COSMO-RS screening and tested in a batch autoclave. The Pd leaching could be suppressed significantly when the ligand TPPTS was used instead of the monosulfonated ligand TPPMS. The two most promising ionic liquids [EMMIM][NTf2] and [BMMIM][NTf2] were used to immobilize the Pd-TPPTS catalyst in a continuous loop reactor with integrated separation. While the monosulfonated TPPMS ligand failed to efficiently immobilize the catalyst in the ionic liquid, the TPPTS ligand resulted in very good catalyst immobilization and a constant conversion was maintained for more than 200h time-on-stream.

Synthesis of Jatropha curcas oil-based biodiesel in a pulsed loop reactor

Jatropha curcas oil (JCO) has a high content of free fatty acids and has been used extensively as a feedstock in biodiesel production. In the present study, the transesterification reaction of JCO to Jatropha curcas methyl ester (biodiesel) was performed in a continuous pulsed loop reactor under atmospheric conditions. The JCO was pre-treated prior to the reaction to reduce the free fatty acid content to below 1% (w/w). The operating parameters of the loop reactor were optimised based on the conversion of the JCO to Jatropha curcas biodiesel and included reaction temperature, molar ratio of oil to MeOH, reaction time and oscillation frequency. The findings show that the highest reaction conversion of 99.7% (w/w) was achieved using KOH catalyst and 98.8% conversion was obtained using NaOCH3 catalyst. The optimal operating conditions were a molar ratio of 6:1, an oscillation frequency of 6Hz, temperature of 60°C, feedstock FFA content of 0.5% (w/w) and only 10min of reaction time. As a commercial commodity, the physical properties of biodiesel were analysed, and they compared well with the characteristics of fossil-based diesel fuel.

Liquid‐Liquid Biphasic, Platinum‐Catalyzed Hydrosilylation of Allyl Chloride with Trichlorosilane using an Ionic Liquid Catalyst Phase in a Continuous Loop Reactor

AbstractThe platinum‐catalyzed hydrosilylation of allyl chloride with trichlorosilane was investigated in an ionic liquid‐organic biphasic reaction mode. After an ionic liquid screening and repetitive batch mode experiments, the process was realized in a continuous mode using a loop reactor concept with integrated continuous separation and recycling of the ionic liquid catalyst phase. The continuous reactor could be operated for 48 h at constant activity and selectivity without addition of platinum indicating that platinum leaching into the product phase was far below 1 ppm. Enhanced selectivity for the product trichloro(3‐chloropropyl)silane (compared to the state‐of‐the art) and the possibility to use simple platinum tetrachloride (PtCl4) as platinum source are further attractive features of this new ionic liquid‐based process concept.

Kinetic and microstructural study of the continuous emulsion polymerization of an all-acrylics formulation in the loop reactor

The suitability of a continuous loop reactor to produce all-acrylic low Tg latexes was investigated. The effect of the preemulsification level, temperature, average residence time, initiator concentration and surfactant concentration on both kinetics and polymer microstructure (gel content and molecular weight) was studied. It was shown that different polymer architectures could be obtained varying these operation variables, opening the possibility of fine tuning the polymer characteristics.

(Mini)emulsion Polymerization: Effect of the Segregation Degree on Polymer Architecture

A continuous loop reactor was used for the production of 2-ethylhexyl acrylate (2-EHA), methyl methacrylate (MMA) and acrylic acid (AA) pressure sensitive adhesive by both emulsion and miniemulsion polymerization. Similar high monomer conversions were achieved in both processes, but striking differences in polymer architecture were found. A mathematical model was used to analyze these differences concluding that because the costabilizer suppressed monomer diffusion from miniemulsion droplets, the average polymer concentration in the polymerization loci was lower in the miniemulsion process. This resulted in less chain transfer to polymer, and hence in lower sol molecular weight and gel content.

Modeling Particle Size Distribution (PSD) in Emulsion Copolymerization Reactions in a Continuous Loop Reactor

A detailed dynamic mathematical model that describes the evolution of particle size distributions (PSD) during emulsion copolymerization reactions in a continous loop reactor is developed and compared with experimental data. The model is based on the assumption that two distinct particle populations exist: precusor particles and stable latex particles. Precursor particles are colloidally unstable and therefore may undergo coagulation with other precursors and be absorbed by stable latex particles. It is shown that the kinetic model is able to reproduce the rather complex dynamic behavior of the vinyl acetate/Veova 10 emulsion copolymerization in a continuous loop reactor.

Selective dimerisation of 1-butene in biphasic mode using buffered chloroaluminate ionic liquid solvents — design and application of a continuous loop reactor

The dimerisation of 1-butene using (cod)Ni(hfacac) 1 as catalyst has been investigated in different chloroaluminate ionic liquids. Systems prepared by buffering an acidic ionic liquid with weak organic bases proved to be very suitable solvents for the reaction. The reaction takes place in biphasic reaction mode with facile catalyst separation and catalyst recycling. The high intrinsic dimer linearity of catalyst 1 is maintained, but with significant enhancement of catalyst activity and of the selectivity to the dimer product over that observed in toluene solvent. For further investigation, a continuous reactor was designed. Our results in continuous mode show the general technical applicability of the selective Ni-catalysed dimerisation in chloroaluminate ionic liquids using a loop reactor concept.

USING MULTIPLICITY TO IMPROVE REACTOR PERFORMANCE AND PRODUCT QUALITY IN EMULSION POLYMERIZATION IN CONTINUOUS LOOP REACTORS

The emulsion copolymerization of vinyl acetate and Veova 10 in a continuous loop reactor was investigated finding that the system presents steady state multiplicity. It is shown how to take advantage of the reactor dynamics to conduct the process in such a way that a pseudo steady state is reached in which high polymerization rates at low temperatures and/or low initiator concentrations are obtained. These conditions allow to achieve high production rate of a high molecular weight polymer which yields high wet scrub resistance. If these conditions were implemented from the beginning of the process, low conversions, and in some cases coagulation, would be obtained.

Stability Issues in a Continuous Loop Reactor for Free-Radical Polymerization

Continuous loop reactors are potential candidates for replacing stirred tanks in the free-radical polymer industry. Loop reactors present attractive advantages such as improved mixing and heat transfer capabilities and their macroscopic behavior is very close to the continuous stirred tanks. In this contribution, operability and stability issues associated to this equipment are studied. Simulation results are presented for the free-radical solution polymerization of vinyl acetate. It is shown that safe and stable reactor operation is strongly dependent on the proper choice of the process parameters.

Emulsion Polymerization in a Loop Reactor: Effect of the Operation Conditions

The effect of several operation conditions (temperature, residence time, recycle ratio, initiator concentration and emulsifier concentration) on the performance of a continuous loop reactor during the redox initiated emulsion copolymerization of vinyl acetate and Veova 10 was investigated. The study was carried out under industrial-like conditions, namely, high solids content latexes (55wt%) and high conversions (~90%). Both polymerization mechanisms and practical issues such as production rate and product quality are discussed.

Formation of emulsions in a screw loop reactor

AbstractThe following article concerns emulsification reaction in a continuous screw loop reactor. The influence of hydrodynamics on the emulsification process as well as the influence of some specific substances were examined. We produced oil/water model emulsions under different test conditions and we determined the correlations between the mixing behavior of the reactor and the characteristic features of the obtained emulsion. Special consideration was given to the droplet size and its distribution. Variable operating conditions of the reactor are the residence time and the rotational speed of the screw, both of which have a decisive influence on the recycle factor and the number of passages through the rotor/stator system. In addition we determined the dependence of the obtained droplet size distribution on the viscosity of the continuous and dispersed phase, on the interfacial surface tension and on the phase proportions. The influence of the specific type of emulsifying agent and its concentration has been examined as well. The positive effect of the mixing and of the recirculation on the emulsification in the screw loop reactor was particularly evident with low emulsifier concentrations and with emulsifiers with slow adsorption kinetics. The established theories for emulsion formation (Kolmogoroff, Taylor) were used for a quantitative description of the experimental results. The screw loop reactor was compared to an agitated tank reactor and a toothed‐ring dispersing machine (Ultra Turrax) based on the comminution energy which is produced per unit volume of emulsion. The agitated tank reactor produced only coarsely dispersed emulsions through the entire rotational speed range, wheras the screw loop reactor and the Ultra Turrax, particularly at high rotational speeds and, therefore, high power densities, showed a similar emulsification and produced much finer dispersed emulsions.

Emulsion copolymerization of vinyl esters in continuous reactors: Comparison between loop and continuous stirred tank reactors

AbstractThe high solids emulsion copolymerization of vinyl acetate and veova 10 was studied in a continuous loop reactor and in a continuous stirred tank reactor (CSTR) in an attempt to elucidate the similarities and differences between these reactors. Reactions were carried out under comparable conditions, namely, similar macromixing and the same feed composition and space time. The behavior of both reactors was almost the same when the heat generation rate was low; otherwise, thermal runaway occurred in the CSTR whereas the loop reactor temperature was easily controlled. © 1995 John Wiley & Sons, Inc.

Modelling nucleation and particle growth in emulsion copolymerization in continuous loop reactors

AbstractA mathematical model for emulsion copolymerization in continuous loop reactors is presented. The flow pattern of the loop reactor can be represented by a loop formed by two tubular reactors with axial dispersion. The mathematical model combines this flow model with the physico‐chemical characteristics of the emulsion copolymerization. The outputs of the model are monomer conversion, copolymer composition, particle size distribution and latex viscosity. The model was checked during the redox initiated emulsion copolymerization of vinyl acetate and veova 10 carried out in a completely automated continuous loop reactor.

Start-up procedures in the emulsion copolymerization of vinyl esters in a continuous loop reactor

Different start-up strategies for the 55 wt% solids content redox-initiated emulsion copolymerization of vinyl acetate and Veova 10 in a continuous loop reactor were studied to determine the optimal start-up procedure in terms of smoothness of the operation and minimum out-of-specification product. These strategies included different initial charges and temperature profiles. The evolutions of the monomer conversion, particle size, number of polymer particles and molecular weight distribution during the start-up were analysed and the effect of the start-up procedure on the steady-state values of these variables determined.

Effect of initial biomass concentration on the growth of immobilized Nitrosomonas europaea

Nitrosomonas europaea was immobilized in carrageenan-gel beads with a low and a high biomass concentration (100-fold difference). Under growth conditions in a continuous air-lift loop reactor, a low initial concentration yielded a few large micro-colonies per bead, whereas a high initial biomass concentration resulted in many small micro-colonies per bead. The macroscopic consumption rate of the latter was three times higher under the circumstances applied. This is also predicted by our colony-expansion model when diffusion limitation over the micro-colonies is incorporated. This model also predicts that diffusion limitation over the ultimate colonies is negligible when the initial biomass concentration exceeds 0.5 kg·m−3 of carrageenan gel.

Characterization of a denitrifying bacterium immobilized in ?-carrageenan

Cells of a pure strain of a denitrifying bacterium have been immobilized in κ-carrageenan. The influence of pH and temperature on the immobilized cells was determined, as well as the operational stability in a continuous gas-lift loop reactor. Several steady states at different nitrate loadings were reached with respect to activity and dry cell weight. The results show that the immobilized cells form a stable system which rapidly reacts to changes in substrate (nitrate) supply. The maximum conversion rate of the immobilized cells is higher than the rate usually observed with immobilized denitrifying cells but lower than in fluidized-bed systems with attached biomass. It is shown that with increasing immobilized concentration the K m value apparently increases to such an extent that for growing cells no zero-order kinetics may be assumed.