Reaction Intensification Research Articles

Numerical study of heat transfer and thermal homogenization in a helical reactor

A fast and accurate control of the flow temperature by heating or cooling through the wall is essential for many chemical applications, in particular to achieve optimal reaction intensification. A numerical study based on computational fluid dynamics (CFD) has been done to investigate thermal homogenization within a horizontally-coiled helical pipe. The main target is to examine and compare the flow and mixing characteristics when heating different axial parts of the coil. The entrance region and two other locations within the fully-developed flow region have been investigated for that purpose; the first, the third and the fifth turn of a ten-turn coil have been heated individually. In each case, temperature field and thermal homogenization were assessed. The performance was quantified in terms of the required axial length for the temperature profile to become uniform again after heating. The investigations were performed for water as a working fluid, and for a wide range of Reynolds numbers between 2000 and 16,000, covering both the laminar range and transition to turbulence in the helical pipe. The thermal mixing performance in the entrance region was found to be noticeably better than that in the fully-developed region, increasingly so at higher Reynolds numbers. Therefore, it is recommended to systematically use the entrance region of a coil reactor for a fast and efficient step rise of the flow temperature.

Intensifying the O2-dependent heterogeneous biocatalysis: Superoxygenation of solid support from H2O2 by a catalase tailor-made for effective immobilization

Besides merely destroying H2O2, an important use of the catalase reaction, H2O2→1/2 O2+H2O, is to supply O2 to oxygenation reactions. Due to convenient spatiotemporal control over O2 release, oxygenation from H2O2 is useful in particular for enzymatic reactions confined to solid supports. Because commercial catalases are difficult to immobilize, we have developed a one-step procedure of purification and immobilization of Bordetella pertussis catalase, recombinantly produced in Escherichia coli. Fusion of the catalase to a positively charged binding module enabled effective immobilization of the chimeric enzyme on anionic support (Relisorb SP 400), giving a controllable activity loading of between 5000 and 100,000 units/g support. Use of the immobilized catalase in combination with H2O2 feeding provided O2 to the reaction of glucose oxidase in solution for a range of volumetric conversion rates (0.2–1.5mM/min). Using optical sensing to measure the O2 concentration in the liquid but also in the solid phase, we showed that internal superoxygenation of the support was made possible under these conditions, resulting in an inverted (that is, negative) O2 concentration gradient between the bulk and the particle and allowing the internal O2 concentration to exceed by up to 4-fold the limit of atmospheric-pressure air saturation in solution. By tailored immobilization of B. pertussis catalase, therefore, an efficient biocatalytic system for hydrogen peroxide conversion in porous solid support was developed. This could find application for bubble-free oxygenation of O2-dependent enzymes co-immobilized with the catalase whereby enhanced internal availability of O2 would contribute to biocatalytic reaction intensification.

Modes of chocked flame instability defined by the peculiarities of combustion kinetics at rising pressure

The aim of the paper was to analyze the structure and the stability of the chocked flames to understand the origins of different possible combustion modes, including quasi-stable supersonic flames and deflagration-to-detonation transition. By means of numerical analysis, it is shown that the chocked flame structure and its stability are defined by two basic mechanisms: compression of the fresh mixture ahead of the flame front and compression of the reacting mixture inside it. The first mechanism provides burning velocity increase; the second one can either accelerate or decelerate reaction depending on the pressure-dependent reaction behavior in the observed pressure range and depending on the rate of compression. In case of reaction intensification with rising pressure, a detonation forms on the leading edge of the flame front. Otherwise, the flame propagates in a quasi-stable supersonic regime consisting of consequential stages of deceleration and re-acceleration of the flame. On the deceleration stage, the compressed fresh mixture priorly chocked by the supersonic flow near the flame tip flows downstream generating the compression wave ahead. The new contact surface between this packet of compressed mixture and the fresh mixture ahead of the flame front can become the kernel of the exothermal reaction, evolving in a new deflagration wave or even detonation.

Integration of biocatalyst and process engineering for sustainable and efficient n‐butanol production

Recent environmental economic developments generate a need for sustainable and cost‐effective (microbial) processes for the production of high‐volume, low‐priced bulk chemicals. As an example, n‐butanol has, as a second‐generation biofuel, beneficial characteristics compared to ethanol in liquid transportation fuel applications. The industrial revival of the classic n‐butanol (ABE) fermentation requires process and strain engineering solutions for overcoming the main process limitations: product toxicity and low space–time yield. Reaction intensification on the biocatalyst, fermentation, and bioprocess level can be based on economic and ecologic evaluations using quantifiable constraints. This review describes the means of process intensification for biotechnological processes. A quantitative approach is then used for the comparison of the massive literature on n‐butanol fermentation. A comprehensive literature study—including key fermentation performance parameters—is presented and the results are visualized using the window of operation methodology. The comparison allowed the identification of the key constraints, high cell densities, high strain stability, high specific production rate, cheap in situ product removal, high n‐butanol tolerance, to operate in situ product removal efficiently, and cheap carbon source. It can thus be used as a guideline for the bioengineer during the combined biocatalyst, fermentation, and bioprocess development and intensification.

Characterization of liquid flow in the spinning cloth disc reactor: Residence time distribution, visual study and modeling

The spinning cloth disc reactor (SCDR) is an innovative enzymatic reaction intensification technology. The SCDR uses centrifugal forces to allow the spread of thin film across the spinning disc which has a cloth with immobilized enzyme. Research has shown this geometry promotes accelerated reactions due to high mass transfer rates and rapid mixing. In this study, the flow regimes in the SCDR were characterized by means of residence time distribution (RTD) analysis and visual study tracking dye staining.RTD analysis showed that the flow pattern on the spinning disc with/without cloth became closer to plug flow with an increase of spinning speed and flow rate. With the cloth, the equivalent number of tanks-in-series was at least 2 times lower than that without cloth at different spinning speeds and flow rates, indicating the flow is better mixed, in contrast to the typical plug flow found for conventional spinning disc reactor. Two flow regimes were observed in the visual study with the dye spreading within the spinning cloth: radial finger-like flow and concentric flow. At low spinning speeds and high flow rates, the flow was in the form of a few random and uneven radial streams, with the zone between these streams free of dye. At higher spinning speeds and lower flow rates, this uneven radial flow was replaced by an even concentric flow. Using tributyrin hydrolysis as a model reaction, a SCDR reactor mathematical model based on perfectly mixed model was developed to simulate the variation in SCDR conversion with spinning speed and flow rate, and the model fitted well with the experimental data. The overall results indicate the SCDR is neither a conventional spinning disc reactor nor a rotating packed bed, but a separate class of spinning disc-type reactor for process intensification, called ‘spinning mesh disc reactors’ (SMDRs).

The spinning cloth disc reactor for immobilized enzymes: A new process intensification technology for enzymatic reactions

The spinning cloth disc reactor (SCDR) is an innovative enzyme reaction intensification technology. Based on spinning disc technology, the SCDR uses centrifugal forces to allow an even spread of a thin film across a spinning horizontal disc which holds a cloth with immobilized enzyme. This geometry promotes accelerated reactions due to high mass transfer rates and rapid mixing. Here, the SCDR has been benchmarked against a conventional batch stirred tank reactor (BSTR) using tributyrin emulsion hydrolysis as a model reaction and lipase immobilized on woolen cloth as the biocatalyst. Reaction intensification has been shown to occur: the conversion in the SCDR was significantly higher than that in a conventional BSTR under comparable conditions. Spinning speed and flow rate control reaction rate and conversion: conversion increased nearly 7% on average as the flow rate rose from 2 to 5mLs−1 and the highest conversion (72.1%) occurred at 400rpm. A Ping Pong Bi Bi kinetic model fitted reaction progress data well. The immobilized lipase showed excellent stability to repeat reactions in the SCDR: 80% of the original activity was retained after 15 consecutive runs. The robustness of the SCDR to industrially relevant feeds was also demonstrated through successful hydrolysis of different vegetable oils at reaction rates 5 times higher than other reactors in the literature. Overall, the above results indicate that the SCDR is an innovative, superior and robust technology for enhancing enzyme reactions, taking enzyme reactors beyond the current state-of-the-art. This concept can readily be extended to other enzyme-catalyzed reactions, where enhanced mass transfer and enzyme stability is needed.

Photocatalytic reaction intensification using monolithic supports designed by stereolithography

An original photocatalytic reactor for the treatment of polluted air is designed. The titanium dioxide is supported on various supports that consist in photopolymers and are built using the stereolithography technique and placed in a glass tube illuminated from the outside, while the air containing the pollutant to be removed flows through the glass tube and the photocatalyst support. It is shown that the gas–solid mass transfer plays a role only at the very smallest gas velocities investigated. The global depollution kinetics are then determined for the different geometrical forms of the photocatalyst support and the efficiency of the forms compared.

Chemiluminescent Enzyme Immunoassays: A Review of Bioanalytical Applications

This review gives an overview of the most recent and innovative developments in the field of chemiluminescent immunoassays through carefully selected examples. First, assays using microtiter plates for high-throughput or multiplexed assays aiming to achieve more complex assays through the multiplication of parameters per wells will be described. Systems will then be presented that have been recently developed, motivated by integration and miniaturization of existing immunoassays in more complex experimental setups. Finally, enhanced-performance chemiluminescent biochips, based on chemiluminescent reaction intensification, will be introduced.

Acute circulatory effects of military low-altitude flight noise

Volunteers aged 70 to 89 years living in a senior citizen's home in Haifa were exposed to flight noise via earphones while watching video films. Their blood pressure and heart rates were measured simultaneously. A high-quality recording and reproduction technique was employed. They were exposed to the noise of two to three overflights with Lmax = 99-114 dB(A) and slow sound pressure level increase (aircraft take off) or with Lmax = 95-112 dB(A) and a fast sound pressure level increase (low-altitude flight at high subsonic speed) at intervals of 10 to 15 min. The systolic and diastolic blood pressure was raised at Lmax = 112 dB(A) and high speed level increase at the average of 23 and 13 mmHg, respectively with individual maximal values of about 40 mm Hg (systolic). In order to prevent risks to the subjects' health, the noise exposure was not raised to levels above 112 dB(A) and fast level increase, although Lmax = 125 dB(A) has been measured in 75 m-low-altitude flight areas. The blood pressure response to a repeated single exposure increased in proportion to the preceding noise exposure. At high intensities and fast level increase an up to fourfold reaction intensification was detected in the majority of subjects. This change in reactivity is regarded as the result of sensitization toward the special type of noise and the implications of these observations for the long-term effects of chronic exposure to low-altitude flight noise are considered. On the basis of these results, proposals are made for limiting values for Lmax and for the speed of sound pressure level increase, the implementation of which would lead to a marked reduction in health risks from low-altitude flight noise.