Continuous Flow Tubular Reactor Research Articles

Finite Element Modeling of Continuous Flow Tubular Electrochemical Reactor for Industrial and Domestic Wastewater Treatment

Continuous flow tubular electrochemical reactor (CTER) was simulated by finite element method (FEM) for industrial and domestic wastewater treatment in this study. CTER was operated at response surface optimized conditions and the reaction kinetics was determined by the method of initial rates. Continuous flow tubular electrochemical reactor was divided into 26668 elements with minimum element quality of 0.07383, and the governing equations were solved in 28800 s for paint industry and textile industry wastewater, and in 14400 s for domestic wastewater with time step of 1 s using COMSOL Multiphysics 4.1. In the convection-diffusion-reaction model, a semi-empirical reaction rate with time-dependent weight ratios was defined for the overall COD removal in order to balance the contribution of reaction kinetics and electrochemical mass transfer due to the complex reaction mechanism of the electrochemical oxidation phenomena. This approximation gives flexible behavior in all reaction regimes with significant structures. Regression coefficients of the model simulation indicated an excellent correlation with the experimental data of electrochemical treatment of industrial and domestic wastewater.

Deposition Properties of Sodium Carbonate in Supercritical Water in a Continuous-Flow Tubular Reactor

Supercritical water oxidation (SCWO) has a promising future for treating high concentration and bio-refractory organic wastewaters. However, the reactor plugging problem induced by salt deposition has hindered its extensive commercial application. In this work, we used a continuous-flow experiment plant to systematically examine the influences of the pressure, temperature, running time, initial concentration and flow rate on the deposition properties of Na2CO3 under supercritical water conditions. Two parameters including the deposition ratio (R) and the deposition rate (V) were defined to evaluate the deposition extent of Na2CO3 in the reactor. The results showed that the pressure and temperature had remarkable influences on the R and V of 1 wt% Na2CO3, and their increase would make R and V reduce. The running time had slight effect on the varieties of R and V. Both R and V would rise with the initial Na2CO3 concentration increasing. However, V had a reverse change tendency compared with R as the flow rate rose. The R and V of 1 wt% Na2CO3 with the flow rate of 0.65 L/h at 550 °C and 25 MPa were higher than 80% and 64 μm/h, respectively. This meant a high reactor plugging risk under the long-time run conditions. Moreover, NaOH was not suitable as the alkali neutralizer of the SCWO process at the low velocity condition in the reactor.

Microstructure and Thermal Profile of Structured Lipids Produced by Continuous Enzymatic Interesterification

AbstractEnzymatic interesterification has been shown to be an alternative for the production of structured lipids resembling human milk fat. The knowledge of the physical properties of fat is an important tool for the implementation of this fat in a food matrix. The enzymatic interesterification reaction modifies the composition of triacylglycerols changing the crystallization properties and polymorphic form of fats. Blends containing different proportions of lard and soybean oil (80:20, 70:30, 40:60, 30:70 and 20:80) were enzymatically interesterified in a continuous flow tubular reactor and analyzed for crystalline structure by polarized light microscopy, the polymorphic form using X‐ray diffraction and thermal properties by differential scanning calorimetry. The structural modifications resulting from continuous enzymatic interesterification changed the crystallization behavior and thermal profile of the samples, reducing enthalpy values. Structural changes were also evident on polarized light microscopy images, disclosing an increase in the crystallization rate among the samples after the continuous enzymatic reaction.

Hydrogen production from glycerol by supercritical water gasification in a continuous flow tubular reactor

In this work, glycerol was used for hydrogen production by supercritical water gasification. Experiments were conducted in a continuous flow tubular reactor at 445∼600 °C, 25 MPa, with a short residence time of 3.9∼9.0 s. The effects of reaction temperature, residence time, glycerol concentration and alkali catalysts on gasification were systematically studied. The results showed that the gasification efficiency increased sharply with increasing temperature above 487 °C. A short residence time of 7.0 s was enough for 10 wt% glycerol gasification at 567 °C. With the increase of glycerol concentration from 10 to 50 wt%, the gasification efficiency decreased from 88% to 71% at 567 °C. The alkali catalysts greatly enhanced water-gas shift reaction and the hydrogen yield in relation to catalysts was in the following order: NaOH > Na2CO3>KOH > K2CO3. The hydrogen yield of 4.93 mol/mol was achieved at 526 °C with 0.1 wt% NaOH. No char or tar was observed in all experiments. The apparent activation energy and apparent pre-exponential factor for glycerol carbon gasification were obtained by assuming pseudo first-order kinetics.

Measurement and analysis of spatial reactor profiles in high temperature catalysis research

Abstract Spatial reactor profile measurements are a novel tool in chemical reaction engineering research. In this technique species concentrations or molar flow rates, phase temperatures and spectroscopic information are measured as function of the axial coordinate in a continuous flow tubular reactor. The obtained spatial gradients can be analyzed in terms of kinetic and mechanistic information about the reaction under study. The advantage of the spatial profile technique is that transient data are obtained at steady state and that it can be applied at temperature and pressure conditions relevant for industrial application. After a detailed description of the method various application examples are discussed such as methane catalytic partial oxidation on rhodium and platinum coated foam catalysts, methane oxidative coupling in the gas phase and oxidative dehydrogenation of ethane to ethylene on a supported molybdenum oxide catalyst. It is demonstrated how information about film transport limitation and reaction pathways can be extracted. The importance of spatial reactor profiles for validation of microkinetic models is highlighted for gas phase methane oxidative coupling at elevated pressure. Finally the idea of spatially resolved Raman spectroscopy using an optical fiber sensor is demonstrated and key parameters such as spatial resolution and position accuracy are determined.

Screening of supported transition metal catalysts for hydrogen production from glucose via catalytic supercritical water gasification

In total 17 heterogeneous catalysts, with combinations of 4 transition metals (Ni, Ru, Cu and Co) and various promoters (e.g., Na, K, Mg, or Ru) supported on different materials (γ-Al 2O 3, ZrO 2, and activated carbon (AC)), were investigated with respect to their catalytic activity and stability for H 2 production from glucose via supercritical water gasification (SCWG). The experiments were carried out at 600 °C and 24 MPa in a bench-scale continuous-flow tubular reactor. Ni (in metallic form) and Ru (in both metallic and oxidized forms) supported on γ-Al 2O 3 exhibited very high activity and H 2 selectivity among all of the catalysts investigated for a time-on-stream of 5–10 h. With Ni20/γ-Al 2O 3 (i.e., γ-Al 2O 3 with 20 wt% Ni), a H 2 yield of 38.4 mol/kg glucose was achieved, approximately 20 times higher than that obtained during the blank test without catalyst (1.8 mol/kg glucose). In contrast, Cu and Co catalysts were much less effective for glucose SCWG reactions. As for the effects of catalyst support materials on activity, the following order of sequence was observed: γ-Al 2O 3 > ZrO 2 > AC. In addition, Mg and Ru were found to be effective promoters for the Ni/γ-Al 2O 3 catalyst, suppressing coke and tar formation.

Continuous Hydrolysis of Cuphea Seed Oil in Subcritical Water

AbstractCuphea seed oil (CSO) is a source of decanoic acid which is useful in the preparation of estolide lubricants among other applications. Decanoic acid and other free fatty acids (FFA) can be hydrolyzed from CSO using a catalyst like KOH, followed by neutralization with HCl and extraction with hexane. This procedure, however, uses caustic materials, hazardous solvents and generates waste salt streams. This study investigated the use of water without catalysts to hydrolyze CSO in a continuous flow tubular reactor. Parameters such as the interaction of pressure and temperature, temperature, water to cuphea oil fatty acid residue (H2O:COFAR) molar ratio, and flow rate were examined. The lowest conversions of CSO to FFA were at the lowest temperature (i.e., 300 °C) and the hydrolysis was ca. 90% at 350 °C and 13.8 MPa and ca. 80% at 365 °C and 13.8 MPa. Hydrolysis increased with pressure and leveled off at 13.8 MPa. Hydrolysis increased with temperature and leveled off at ca. 330 °C. The optimal H2O:COFAR molar ratio was found to be 6:1. Conversion rates were inversely proportional to flow rate with 95% conversion at the lowest flow rate (i.e., 0.25 mL/min) corresponding to the longest residence time (i.e., ca. 45.2 min). These results demonstrate a continuous subcritical water process for hydrolyzing CSO to FFA that is effective, requires no catalysts and does not generate a waste salt stream.

Influence of phenol on glucose degradation during supercritical water gasification

Biomass is the ideal alternative renewable energy that might help decrease CO 2 emissions. Super Critical Water Gasification (SCWG) is a recent treatment method which is still being developed as regards wet biomass. Above its critical point, water has specific properties and is able to convert wet biomass into gas, and especially into hydrogen. In order to propose a general reaction scheme of the SCWG as regards the lignocellulosic biomass conversion, the interactions between lignin and cellulose must be highlighted. Lignocellulosic biomass could be modelled with phenol (substitute for lignin) and glucose (substitute for cellulose). In a continuous flow tubular reactor, the gasification of solutions containing phenol and glucose or either of the two pure compounds is more efficiently performed when in presence of an alkaline catalyst. The comparison of global parameters, such as the Total Organic Carbon content (TOC), the composition of the liquid product phase (glucose, phenol, etc.), the volume and composition of the gas phase (H 2, CO 2, CH 4, etc.), showed that a small quantity of phenol in a glucose solution dramatically decreased the efficiency of the solution's conversion.

Steam Cracking and Steam Reforming of Waste Cooking Oil in a Tubular Stainless Steel Reactor with Wall Effects

Energy production from renewable feedstocks that would simultaneously solve ecological problems related to waste disposals would be very attractive. The present work is aimed at showing that atmospheric pressure thermal cracking of waste cooking oil in the presence of steam would be a potential option, particularly when the operating conditions direct the process either toward steam cracking or toward steam reforming in order to produce specific target bioenergy vectors: hydrogen, synthesis gas, or gaseous fuel. A commercial crude waste cooking oil (VEG) was selected as feed material. Using a bench-scale continuous flow tubular stainless steel reactor, experiments were conducted to study the final product distribution as a function of temperature, residence time of the feed material, extent of dilution, addition of a cracking initiator, and addition of a surface catalytic effect inhibitor. Several operating conditions of the VEG thermal cracking in the presence of steam were identified to meet the above-m...

Supercritical water oxidation of phenol with air. Experimental results and modelling

Hydrothermal oxidation is an efficient and clean way for the treatment of wastewater containing organic matter. Because of its specific properties, supercritical water ensures high conversion of a wide range of organic load in the presence of an oxidant. The purpose of this work is to develop a mathematical model for a continuous flow tubular reactor devoted to hydrothermal oxidation. This reactor has a low ratio diameter length with one air injection. The mathematical model is based on plug flow assumption. The governing equations are: momentum, mass, species and energy balances. According to this model, the profiles of temperature and concentration of chemical species are computed along the reactor. The numerical predictions of the model are compared to experimental profiles obtained in the case of supercritical oxidation of phenol. These comparisons show very good agreement.

Chromium catalyzed tetramerization of ethylene in a continuous tube reactor—Proof of concept and kinetic aspects

Highly selective processes for the tri- and tetramerization of ethylene offer an interesting alternative to conventional ethylene oligomerization processes that are constrained by yielding mathematical distributions of linear α-olefins. This inherent lack of selectivity often makes it difficult for full slate producers to respond to changing market demands in each product segment. This is the first known report on the continuous tri- and tetramerization of ethylene in a continuous plug flow tubular reactor. Standard run times of 10 h and a catalyst comprising Cr(acac) 3, 1,2-dimethylpropyl-bis(diphenylphosphino)amine ligand and the aluminum-based activator MMAO-3A was used. Activities exceeding 3,700,000 g/(g Cr h) and combined selectivities for 1-hexene and 1-octene of more than 90% were achieved. The influence of temperature, catalyst concentration, and ethylene concentration in the reactor on reaction rate (catalyst activity) and selectivity has also been investigated. In addition, supporting kinetic studies were performed in a semi-batch reactor setup with the aim to explain the influence of ethylene concentration on product selectivity found in the continuous runs. It was found that the reaction orders in ethylene for 1-hexene and 1-octene are different, with 1-octene formation being significantly more sensitive to ethylene concentration.

Effect of Weak Acids as a Catalyst on the Transesterification of Soybean Oil in Supercritical Methanol

To obtain a high biodiesel yield, the conditions of transesterification of vegetable oil with supercritical methanol are harsh. The reaction temperature is required between 350 and 400 °C, and the reaction pressure is required above 20 MPa. To reduce the operating temperature and pressure, many researchers adopted various methods, such as the selection of a new reactor, the addition of a co-solvent, or the usage of microwave irradiation. According to the characteristics of transesterification, a small amount of organic or inorgnic acid was added into the reaction system, and the effects of an acidic condition on transesterification was investigated in this paper. The experiment was conducted in a continuous flow tubular reactor; the temperature ranged from 270 to 350 °C; the pressure covered the range from the normal pressure to 15 MPa; the molar ratio of methanol/oil was from 20:1 to 60:1; and the acidity of acidified soybean oil was from 5 to 30 mg of KOH/g. The results showed that the higher yield of b...

Hydrolysis of glycylglycine in subcritical water conditions

The hydrolysis of glycylglycine was studied at the temperature range of 240 to 300°C and reaction time up to 200 s. The Experiments were conducted using a continuous-flow tubular reactor. An interesting reaction phenomenon relating to the production of amino acids from hydrolysis of proteins in subcritical water was observed. Other than hydrolysis of glycylglycine to produce glycine, cyclodehydration also took place producing cycloglycylglycine. The product of glycine from cycloglycylglycine was also verified. Under the temperature range in this study, it was observed that the temperature did not has any effect on the reaction selectivity of hydrolysis and cyclodehydration of glycylglycine.

Generalized predictive control applied to a pH neutralization process

In this work, generalized predictive control (GPC) was applied to a pH neutralization process. The process consists of a continuous flow tubular reactor. The process stream is a water solution of acetic acid and the titrating stream is a water solution of sodium hydroxide. The aim of the control is to keep the pH value at a given set point value when the process is subjected to variations in feed flowrate. The use of polynomial autoregressive integral moving average with external input (ARIMAX) model related with pH and base flowrate was emphasized. The model parameters were determined by using Bierman and Genetic algorithms. The λ weighting was varied in order to achieve optimal GPC performance. The efficiency of the GPC was observed by calculating the integral of the square of the error (ISE) and the integral of the absolute value of the error (IAE) from experimental results.

Simultaneous recovery of chromium and destruction of organics from LCD manufacturing process wastewater by supercritical water oxidation

The effectiveness of supercritical water oxidation (SCWO) process for the simultaneous recovery of chromium and destruction of organics from liquid crystal display (LCD) manufacturing process wastewater was investigated. The experiments were performed in an isothermal continuous-flow tubular reactor and H 2O 2 was used as an oxidant. The reaction temperatures ranged from 400 to 605 °C and the residence times ranged from 15 to 31 s at a fixed pressure of 25 MPa. The effect of temperature, oxidant concentration and residence time on chromium recovery and chemical oxygen demand (COD) conversion was investigated. The results of this study demonstrated that the SCWO process recovered chromium and decreased chemical oxygen demand up to 99.3% and 99.9%, respectively. The analyses showed that chromium are recovered as chromium oxide (α-HCrO 2 and Cr 2O 3). The SCWO process is an effective technique for simultaneously recovering chromium and for the destruction of hazardous organics in the LCD manufacturing process wastewater. Our study showed that there are two consequent reactions, chromium recovery reaction (hydrolysis) followed by the organic decomposition reaction (oxidation). The recovery of chromium can be achieved without major organic decomposition.

Reaction Kinetics of Amino Acid Decomposition in High-Temperature and High-Pressure Water

Decomposition behavior of five selected amino acids in high-temperature and high-pressure water was studied using a continuous-flow tubular reactor. The reaction was carried out in the temperature range of 200−340 °C at a pressure of 20 MPa. Alanine and its derivatives leucine, phenylalanine, serine, and aspartic acid were used as model amino acids. The effect of temperature on reaction products, pathway, and rate was determined as a function of reaction time. Alanine decomposed into lactic acid and pyruvic acid, then finally mineralized to carbon dioxide with an activation energy of 154 [kJ/mol] at 20 MPa. The degradation rate decreased in the following order: aspartic acid, serine, phenylalanine, leucine, and alanine. The general reaction network of amino acids under hydrothermal conditions takes two main paths: deamination to produce ammonia and organic acids, and decarboxylation to produce carbonic acid and amines. Deamination was the predominant reaction in the decomposition of aspartic acid, an ac...

High-quality nickel manganese oxalate powders synthesized in a new segmented flow tubular reactor

High-quality nickel manganese oxalates have been prepared using an innovative approach for the production of homogeneous powders, the continuous Segmented Flow Tubular Reactor (SFTR). This new reactor is mainly composed of a mixer, a segmenter, a tubular section and a decanter. Mixed Ni–Mn oxalates are synthesized in the SFTR. The powders present controlled morphology, narrow particle size distribution, high purity and desired stoichiometry. Their characteristics are compared to those of powders obtained in a batch reactor. These oxalates are precursors for nickel manganites, used as negative temperature coefficient thermistor (NTC) ceramics.

Development of a Continuous Segmented Flow Tubular Reactor and the “Scale‐out” Concept – In Search of Perfect Powders

AbstractThe synthesis of powders with controlled shape and narrow particle size distributions is still a major challenge for many industries. A continuous Segmented Flow Tubular Reactor (SFTR) has been developed to overcome homogeneity and scale‐up problems encountered when using batch reactors. Supersaturation is created by mixing the co‐reactants in a micromixer inducing precipitation; the suspension is then segmented into identical micro‐volumes by a non‐miscible fluid and sent through a tube. These micro‐volumes are more homogeneous when compared to large batch reactors leading to narrower size distributions, better particle morphology, polymorph selectivity and stoichiometry. All these features have been demonstrated on single tube SFTR for different chemical systems. To increase productivity for commercial application the SFTR is being “scaled‐out” by multiplying the number of tubes running in parallel instead of scaling‐up by increasing their size. The versatility of the multi‐tube unit will allow changes in type of precipitate with a minimum of new investment as new chemistry can be researched, developed and optimised in a single tube SFTR and then transferred to the multi‐tube unit for powder production.

Spatiotemporal patterns in a two-dimensional reaction-diffusion-convection system: Effect of transport parameters

We report on spatiotemporal patterns emerging in a system consisting of an autocatalytic reaction in a continuous flow tubular reactor. The autocatalyst undergoes a mutation and the resulting mutant is assumed to compete with the original autocatalyst. The system is modeled by a set of three partial differential equations with eight design parameters. We examine and discuss the effect of transport parameters, reactor inlet boundary condition, and reactor aspect ratio on the dynamics of the system. The results show a variety of regimes going from steady propagation of a reaction front to the development of chemical waves in the form of pulsating, more or less regularly, reaction front.

High Quality Powder Precipitation Using a Continuous Segmented Flow Tubular Reactor and the “Scale-Out” Concept

High Quality Powder Precipitation Using a Continuous Segmented Flow Tubular Reactor and the “Scale-Out” Concept