Liquid Reaction System Research Articles

Effect of reaction engineering factors on biphasic hydroformylation of 1-dodecene catalyzed by water-soluble rhodium complex

Hydroformylation of 1-dodecene in a biphasic system using water-soluble rhodium catalyst RhCl(CO)(TPPTS) 2 [TPPTS: tri(sodium- m-sulfonatophenyl) phosphine] was investigated. The cationic surfactant cetyltrimethyl ammonium bromide (CTAB) was used to enhance the reaction rate of long chain olefin and the ratio of normal/isomeric aldehyde. Experiments were carried out semi-batchwise in a 500 ml stirred autoclave at 100 °C and 1.1 MPa. An orthogonal experimental design was adopted for analyzing the effects of agitation intensity, 1-dodecene concentration, surfactant concentration and organic/water volume ratio on the macro-kinetics and regioselectivity. Several agitation configurations for improving the mixing, dispersion and interphase mass transfer of this gas–liquid–liquid reaction system were tested and higher hydroformylation rate and regioselectivity were achieved. The relationship between the extent of emulsification of reaction mixture and the performance of hydroformylation reaction was also studied. Empirical macro-kinetic equations for the initial rate and the correlation of normal/isomeric aldehyde ratio are proposed, which represented the experimental data reasonably well.

A Ritter-Type Reaction over H–ZSM-5: Synthesis of N-Isopropylacrylamide from Acrylonitrile and Isopropyl Alcohol

Catalytic synthesis of N-isopropylacrylamide from acrylonitrile and isopropyl alcohol has been studied using a variety of solid acids in a solid–liquid reaction system at 423 K. Among typical solid and liquid acids, H–ZSM-5 exhibited an exceptionally high catalytic activity. The activity (per gram) of H–ZSM-5 increased as the Al-content (100Al/(Si+Al)%) increased and then decreased through a maximum at an Al content of 2.63%. The specific activity per one acid site, which was estimated from the initial rate and the acid amount, increased greatly as the Al content decreased, which resembles those of the hydrophobicity and the acid strength. The superiority of H–ZSM-5 activity over other strong and hydrophobic solid acids suggests the importance of the unique pore structure. While H–ZSM-5 deactivated severely during the reaction, the catalytic activities were mostly recovered by calcination at 773 K in air. IR spectroscopy and adsorption measurements revealed that the deactivation of H–ZSM-5 was mainly caused by the formation of a polymer of acrylonitrile on the catalyst surface blocking the micropores, but not limiting desorption of the product from the micropores.

Ritter-type reactions catalyzed by high-silica MFI zeolites

Catalytic reaction of acrylonitrile (AN) with isopropyl alcohol (IPA) to N-isopropyl acrylamide has been studied using MFI zeolites in a solid–liquid reaction system. Turnover number (TON), which was defined as the number of the product molecule divided by the number of the acid site, increased as the Si/Al atomic ratio of MFI zeolites increased. It was deduced that both the hydrophobicity and acid strength of the zeolites were plausible factors in determining the specific activity. Secondary alcohols such as 2-butanol, 3-pentanol, and cyclohexanol as well as IPA showed reactivities in the reaction with AN, while primary alcohols like 1-butanol and isobutyl alcohol gave little products. Tert-butyl alcohol was readily dehydrated to isobutylene and the yield of N- tert-butyl acrylamide was thus low. The reaction of AN with 1-adamantanol was very slow over the MFI zeolites due to the limitation of adsorption in the restricted pores. While MFI zeolites were deactivated due to the blockage of the micropores by the polyacrylonitrile formed during the reaction, the catalytic activity was mostly recovered by calcination at 773 K in air.

Microreaction engineering — is small better?

Microfabrication techniques are increasingly used in different fields of chemistry to realize structures with capabilities exceeding those of conventional macroscopic systems. In addition to already demonstrated chemical and biological analysis applications, microfabricated chemical systems are expected to have a number of advantages for chemical synthesis, chemical kinetics studies, and process development. Chemical processing advantages from increased heat and mass transfer in small dimensions are demonstrated with model gas, liquid, and multiphase reaction systems. These case studies also serve to illustrate benefits of integrating sensors for flow, temperature, and chemical composition with microfluidic reaction and control components. The role of reaction engineering in the development of microreaction technology is described along with new approaches to scale up based upon replication of microchemical devices.

Applicability of laboratory heterogeneous liquid–liquid phase reaction kinetic data for relief vent design

Abstract For the relief area design of safety devices in the case of runaway conditions as a precondition reaction, kinetic data are required. Generally, they are measured in dedicated (quasi adiabatic) reaction calorimeters. In the course of the design, it is then assumed that the same reaction kinetic data in the laboratory and production scale prevail. This assumption seems to only be useful in the case of homogeneous liquid phase reaction systems. In contrast to this supposition the results of experiments with a heterogeneous (immiscible) liquid–liquid reaction system show that the stirring intensity and the reactor size can considerably influence the reaction progress. A novel formal macro reaction kinetics model for thermal runaway heterogeneous reactions including the mixing intensity as scaling parameter is presented.

Selective hydration of dihydromyrcene to dihydromyrcenol over H-beta zeolite.: Influence of the microstructural properties and process variables

H-beta zeolite has been tested for the hydration of dihydromyrcene (DHM) to produce dihydromyrcenol (DHM-OH). By using a non-protic co-solvent like acetone, in order to work under a single phase system, reasonable conversion with excellent selectivity to DHM-OH is obtained, although some double bond isomerization of the terpene is also taking place. The reaction is not controlled by intrapore diffusion, and samples with different crystal sizes gave similar activities and selectivities. However, defect free beta samples with high hydrophobic character are preferred for the reaction due to their improved adsorption properties for non-polar molecules. Working with those materials more than 50% yield of DHM-OH was obtained with a selectivity close to 100%. The influence of zeolite hydrophobicity was further proved in a two-phase liquid reaction system. In such conditions, best results were achieved with the most hydrophobic catalysts.

Preparation and characterization of immobilized acid phosphatase used for an enzyme reactor: evaluation in flow-injection analysis and pre-column liquid chromatography

Acid phosphatase from various sources (plant and animals) was immobilized by attachment with glutaraldehyde to aminoalkylsilyl glass. An amino function of the enzyme was covalently coupled to the aldehyde derivative in the presence of phosphate as an enzyme inhibitor. The highest retention of enzyme activity was obtained by the immobilization of acid phosphatase from sweet potato. The double bond of Schiff base was reduced with sodium tetrahydroborate. The immobilized sweet potato acid phosphatase was active toward three substrates, p-nitrophenyl phosphate, β-glycerophosphate and riboflavin phosphate. The immobilized acid phosphatase retained almost complete activity over 4 months in a refrigerator. The immobilized acid phosphatase was packed into a stainless-steel column (10 × 4 mm i.d.) and used on-line as an immobilized enzyme reactor (IMER). The stability, reusability and utility of the IMER were verified by a flow-injection system and a liquid chromatographic pre-column reaction system. The IMER was extremely stable and reusable at room temperature, and was fully active even in 50% methanol solution.

Gas–liquid–liquid reaction engineering: the Koch synthesis of pivalic acid from iso- and tert-butanol; Reaction kinetics and the effect of a dispersed second-liquid phase

In gas–liquid–liquid reaction systems with fast parallel and consecutive reactions the effects of mass transfer and mixing on the product yield can be significant. The Koch synthesis of pivalic acid, using sulfuric acid as catalyst, was chosen to study these effects. Reaction kinetics and the effect of the catalyst-phase composition have been investigated by using isobutanol as reactant. For studying the effect of an immiscible liquid phase on the reaction products obtained, the more reactive tert-butanol was used. Pivalic acid can be produced from isobutanol using sulfuric acid as a catalyst solution with 2-methylbutanoic acid as main byproduct, if gas–liquid mass transfer limitations are excluded. The selectivity towards 2-methylbutanoic acid is generally less than 20% and decreases strongly with decreasing acidity. The reaction is first order in isobutanol and dehydration is likely to be rate determining. The presence of pivalic acid and isobutanol strongly reduces the apparent reaction rate constant by decreasing the solution acidity (Ho). For the industrially applied backmixed reactors in the Koch synthesis, this may imply that these operate at much lower values for Ho. On addition of an immiscible heptane phase, the reaction products are extracted to some extent and this adds to maintaining a high catalyst solution acidity. Using tert-butanol, the yield and pivalic acid selectivity was found to depend strongly on CO transport to the reaction zone through gas–liquid mass transfer and mixing. The presence of an immiscible heptane phase increased the product yield and selectivity towards pivalic acid significantly.

A new derivatization reagent 2-(pentafluorophenoxy)ethyl 2-(piperidino)ethanesulfonate for gas chromatography

A new sulfonate reagent 2-(pentafluorophenoxy)ethyl 2-(piperidino)-ethanesulfonate (PFPES), structurally having an electrophore and a tertiary amino function, was synthesized for the analytical derivatization in gas chromatography (GC). The reagent is reactive to n-valeric acid, valproic acid, benzoic acid, 2-mercaptoethanol, phenol, thiophenol, ethosuximide and chlorpropamide in a liquid–solid reaction system, and also reactive to iodide, cyanide, nitrite and thiocyanate anions in a liquid biphasic reaction system, all checked by thin layer chromatography (TLC). After derivatization of the analytes in the toluene phase, the excess PFPES can be easily removed from the toluene layer by a simple aqueous acid treatment. This can minimize the interference of excess PFPES in GC separation and detection. Application of the reagent to the derivatization of n-valeric acid and iodide anion as test analytes for capillary GC–electron capture detector (GC–ECD) was performed. The resulting derivatives are highly responsive to an ECD. The detection limits in per injection of n-valeric acid and iodide anion are about 170 fmol (in 0.6 μl) and 15 fmol (in 0.3 μl), respectively.

Liquid phase esterification of acrylic acid with 1-butanol catalyzed by solid acid catalysts

Esterification of acrylic acid with 1-butanol has been studied in a heterogeneous solid–liquid reaction system using a variety of solid acids including an acidic salt of H 3PW 12O 40, Cs 2.5H 0.5PW 12O 40. The catalytic activity (per proton) of liquid acids such as heteropolyacids, H 2SO 4, and para-toluenesulfonic acid increased as the acid strength of the solution increased, but the difference in the activity among them was not significant. In the solid–liquid reaction system, Cs 2.5H 0.5PW 12O 40 exhibited the highest catalytic activity in the unit of catalyst weight among the solid oxide catalysts, while the activity of Cs 2.5H 0.5PW 12O 40 was less than those of organic resins such as Nafion and Amberlyst 15. Contrary to the liquid acids, the specific activity values (per proton) of solid acids were significantly different. It was demonstrated that the activity of Cs 2.5H 0.5PW 12O 40 was almost retained after the addition of water, while the activities of the organic resins greatly decreased. The water-tolerant property of Cs 2.5H 0.5PW 12O 40 is presumed to be due to the hydrophobic nature of the surface.

Water-tolerant catalysis by Mo–Zr mixed oxides calcined at high temperatures

“Water-tolerant catalysis’' of Mo–Zr mixed oxides was investigated using XRD, NH3 temperature-programmed desorption (TPD), adsorption of water and water-concerning reactions such as hydrolysis of ethyl acetate in excess water and esterification of acetic acid with ethanol in a solid–liquid reaction system. It was found that the activities of MoO3–ZrO2 calcined at 1073 K became higher at Mo contents [Mo/(Mo+Zr)] of around 0.2 atomic ratio. When MoO3–ZrO2 was calcined at 873–1073 K, the catalytic activity was greatly enhanced and became comparable to that of H-ZSM-5 (Si/Al=40). Whereas the acid strength of MoO3–ZrO2 measured by NH3-TPD was unaffected by the calcination temperature, the amount of acid and the surface area decreased monotonically as the calcination temperature increased. On the other hand, the surface hydrophobicity estimated from the amount of water adsorbed on the surface was greatly enhanced with increase in the calcination temperature. Therefore, it was concluded that the high activity of MoO3–ZrO2 calcined at high temperatures is predominantly responsible for the enhanced surface hydrophobicity.

An axial dispersion model for gas–liquid reactors based on the penetration theory

An axial dispersion reactor model for gas–liquid reaction systems is proposed in this paper based on the penetration theory. The mass transfer mechanism accompanied by a chemical irreversible first-order reaction is mathematically treated in a new way in order to use its results to develop the model conveniently. Analytical solutions can be obtained for the equation system involving linear differential equations by using of the eigenvalues of the equation system. In addition, an iteration procedure is given to solve the nonlinear differential equation system numerically. The influences of the important model parameters on the concentration profile, the mass transfer and the reactant conversion are also studied.

Solid–solid–liquid reaction systems. A mechanistic study

The mechanism of the alkylation of phenoxide with benzyl bromide, catalysed by polymer-bound phase-transfer catalysts, has been studied as a model for solid–solid–liquid reaction systems. A ‘typical triphase catalyst’ has been compared with a commercial ion-exchange resin. The reactions proceed by a mechanism which is similar to the extraction mechanism of classical phase-transfer catalysis. Depending on the reaction conditions, the reaction rates are either mass-transfer controlled or chemical-reaction controlled. In some cases the C/O-alkylation ratio is found to depend on the water content of the system. The possible mechanisms for the transport of the phenoxide ion to the catalytic site are discussed.

High-performance liquid chromatographic post-column reaction system for the electrochemical detection of ascorbic acid and dehydroascorbic acid

High-performance liquid chromatographic post-column reaction system for the electrochemical detection of ascorbic acid and dehydroascorbic acid

The kinetics of the reaction between CO 2 and diethanolamine in aqueous ethyleneglycol at 298 K: a viscous gas—liquid reaction system for the determination of interfacial areas in gas—liquid contactors

The reaction between CO 2 and diethanolamine (DEA) in aqueous ethyleneglycol (ETG) at 298 K has been studied over the complete composition range. The application of this reaction as a viscous gas—liquid system for the determination of interfacial areas in gas—liquid contactors by the chemical method is discussed. The reaction kinetics have been determined by mass transfer experiments of CO 2 into solutions of DEA in aqueous ETG. To this end laboratory-scale stirred cell reactors with a flat surface have been used. In accordance with the same reaction in water at 298 K the reaction between CO 2 and DEA in aqueous ETG at 298 K can be described by the zwitterion mechanism of Caplow. Special attention has been paid to the reversibility of the reaction between CO 2 and DEA. Calculation show that the influence of the reversibility on the mass transfer rate can be neglected for partial pressures of CO 2 below 3 kPa. It is demonstrated that the reaction between CO 2 and DEA in aqueous ETG can be used for the determination of interfacial areas in gas—liquid contactors at higher viscosities.

The use of the chemical method for the determination of interfacial areas in gas—liquid contactors

The interfacial area a chem in a gas—liquid contactor as determined by the chemical method deviates from the true geometrical interfacial area a geo, because the overall conversion of the gas phase reactant represents an incorrect average if bubble sizes and residence times are not uniform. The deviations of a chem from a geo become larger the broader the distribution τ b/ d b and the higher the overall conversion Ω A of the reactant in the gas phase. Model calculations, which take into account both the effect of gas phase backmixing as well as the effect of bubble coalescence on the deviation of a chem from a geo, are performed for a mechanically agitated gas—liquid reactor and a bubble column at practical micro- and macromixing conditions. For a gas—liquid model reaction, which is first-order in the gas phase reactant, it is found that: (1) for a mechanically agitated reactor the error in a chem will always be smaller than 10% if Ω A is lower than 0.99, and (2) for a bubble column the error in a chem will be smaller than 20% for most practical applications if Ω A is lower than 0.99. Gas—liquid model reaction systems with absorption of CO 2 in alkanolamine solutions are recommended for the determination of interfacial area in gas—liquid contactors.

Effects of gas depletion on gas—liquid reaction systems

The gas holdup and, consequently, the interfacial area for absorption vary inversely with the rate of interfacial mass transfer in a gas—liquid reactor. This is the principal basis for the bounding influence of the gas phase on the rate of absorption when the gaseous feed contains only the reactant and the reaction does not have any gaseous products. A model of a nonisothermal gas-liquid CSTR is formulated that shows the effect of the gas phase on the steady-state temperatures and the steady-state multiplicity. The bounding influence of the gas phase becomes paramount when the gaseous feed is not in excess and the gas solubility and the reaction rate are large. The exothermic reaction between CO 2 and aqueous NaOH solution is studied experimentally in a CSTR. The results show that for this fast reaction system the depletion of both the gaseous and liquid reactants determines the steady state. For such a system, as predicted by the theory, the reactor performance does not depend on the reaction rate, the enhancement factor, the mass-transfer coefficient and the interfacial area, as long as the reaction remains fast.

On-line extraction of metal ions using liquid-liquid segmentation and a membrane type phase separator for fluorescence detection

A liquid segmented post-column reaction system has been used to extract metal ions from an aqueous eluent into an organic solvent for fluorescence detection. The metals Zr(IV), Ga(III), Sc(III), Y(III), In(III), Al(III), La(III), Zn(II), Cd(II), Ca(II) and Mg(II) have been isocratically separated on a C18 column by virtue of the secondary chemical equilibrium established by an eluent containing n-octanesulfonate, tartaric acid, and hydroxyisobutyric acid. The chelating reagent 8-hydroxyquinoline dissolved in methylisobutyl ketone (MIBK) was used to extract the metals and a membrane type phase separator was effective at separating the phases and directing the organic stream to the detector. The response for this detection approach was linear for metal ion concentrations spanning the range of the detector, and detection limits for most metals were low parts-per-billion (ppb). Band broadening for the extraction system was examined and compared to a direct post-column reaction using oxine dissolved in acetone.

Liquid Chromatographic Determination of Amprolium in Chicken Tissues, Using Post-Column Reaction and Fluorometric Detection

A method is presented for determination of amprolium residues in chicken muscles by a liquid chromatographic post-column reaction system. The drug is extracted from muscles with methanol, and the extract is concentrated to 3-4 mL. This aqueous solution is rinsed with n-hexane and cleaned up by alumina column chromatography. The drug is separated from the interferences on a LiChrosorb RP-8 column, reacted with ferricyanide in alkaline solution, and quantitated by fluorometric detection at 367 nm (excitation) and 470 nm (emission). Recoveries of amprolium added to chicken muscles at levels of 0.1 and 0.2 ppm were 74.9 and 80.9%, respectively. The detection limit was 1 ng for amprolium standard and 0.01 ppm in chicken muscles.

Modelle und Berechnungsverfahren für die plötzliche Druckentlastung von Gas/Dampf‐Flüssigkeits‐Reaktionssystemen

AbstractModels and computational methods for the sudden release of pressure in gas/vapour‐liquid reaction systems. Design of pressure‐release sections in safety installations such as safety discs or safety valves for gas/vapour‐liquid reaction systems is essentially determined by thermodynamic and fluid dynamic processes as well as by the occurrence of parallel chemical reactions in the reaction vessels and in closed blow‐off lines. However, because of the highly complex interrelations and, in part, insufficient detailed knowledge, an exact calculation frequently causes difficulties. In order to present and evaluate the current state of the art, the individual phases of pressure release and the most important influencing factors as well as their significance for the pressure distribution as a function of time are described first. There follows a comparison of several computational methods taken from the literature, but which because they treat of the processes involved in a simple way either only permit very imprecise design of pressure‐release sections or which because of their specific model assumptions only apply to particular chemical reaction systems with special boundary conditions. Finally, the problems associated with the development of a generally applicable, reliable computational method are briefly discussed.