Showing papers in "Chemical Engineering & Technology in 2005"
TL;DR: In this paper, the authors proposed that 50% of reactions in the fine chemical/pharmaceutical industry could benefit from a continuous process based mainly on microreactor technology, however, the frequent presence of a solid phase still hinders the widespread application of such a technology as a multi-purpose solution.
Abstract: 50 % of reactions in the fine chemical/pharmaceutical industry could benefit from a continuous process based mainly on microreactor technology. However, the frequent presence of a solid phase still hinders the widespread application of such a technology as a multi-purpose solution. For small scale and pilot productions, speed in process R&D, as well as the avoidance of scale-up issues, are the main drivers. On the other hand, for large scale productions, a gain in yield and safety are the main motivations for the use of micoreactor technology. The gain in yield must be significant in order to cope with the increase in capital expenditure associated with the development of a new technology.
507 citations
TL;DR: In this article, three sorbents were compared in order to determine their potential for oil spill cleanup: polypropylene nonwoven web, rice hull, and bagasse with two different particle sizes.
Abstract: Three sorbents were compared in order to determine their potential for oil spill cleanup. Polypropylene nonwoven web, rice hull, and bagasse with two different particle sizes were evaluated in terms of oil sorption capacities and oil recovery efficiencies. Polypropylene can sorb almost 7 to 9 times its weight from different oils. Bagasse, 18 to 45 mesh size, follows polypropylene as the second sorbent in oil spill cleanup. Bagasse, 14 to 18 mesh size, and rice bull have comparable oil sorption capacities, which are lower than those of the two former sorbents. It was found that oil viscosity plays an important role in oil sorption by sorbents. All adsorbents used in this work could remove the oil from the surface of the water preferentially.
422 citations
TL;DR: In this paper, a brief outline of the state of the art of reactions using microreactors with special emphasis on the enhancement of product selectivity is provided. But the authors do not consider the use of micro-reactors in the control of the molecular weight and molecular weight distribution in carbocationic polymerization.
Abstract: This article provides a brief outline of the state of the art of reactions using microreactors with special emphasis on the enhancement of product selectivity. The efficient micromixing possible with a short diffusion path increases the product selectivity of competitive parallel reactions and competitive consecutive reactions. This concept has been expanded to control of the molecular weight and molecular weight distribution in carbocationic polymerization. The efficient heat transfer, based on high surface to volume ratios, allows precise temperature control and is also effective for the control of highly exothermic reactions, such as free radical polymerization.
196 citations
TL;DR: The paper gives a summary of successful methods for measuring protein mass transfer kinetics in ion exchange matrices along with models needed to interpret experimental results, along with the advantages and disadvantages of the various approaches.
Abstract: The paper gives a summary of successful methods for measuring protein mass transfer kinetics in ion exchange matrices along with models needed to interpret experimental results. Both macroscopic methods (isocratic elution, gradient elution, batch adsorption, frontal analysis) and microscopic methods are considered. In all cases the main focus is the determination of the effective intraparticle diffusivity in order to permit a comparison of different stationary phases and provide a basis for predicting chromatographic process performance. Experimental results for representative systems are evaluated alongside the experimental and modeling aspects. Practical criteria for the selection of experimental conditions and the application of different models are discussed along with the advantages and disadvantages of the various approaches.
139 citations
TL;DR: In this paper, the effect of operating parameters such as initial pH, supporting electrolyte concentration, phenol concentration, and charge input was studied using Box-Behnken second order composite experimental design.
Abstract: Electrochemical oxidation of phenol using a Ti/TiO2-RuO2-IrO2 anode in the presence of chloride as the supporting electrolyte was investigated. The experiments were performed in an undivided batch reactor. Preliminary investigations showed that only a small fraction of phenol was oxidized by direct electrolysis, while complete degradation of phenol was achieved by indirect electrochemical oxidation using chloride as a supporting electrolyte. The effect of operating parameters such as initial pH, supporting electrolyte concentration, phenol concentration, and charge input was studied using Box-Behnken second order composite experimental design. The effect of current density on COD removal was studied separately. TOC removal and AOX formation were studied for selected conditions. It was found that the formation of chlorinated organic compounds was pronounced at the beginning of electrolysis, but it was reduced to lower levels by extended electrolysis.
130 citations
TL;DR: In this paper HTS applications presently applied in bioprocess development are reviewed, their use in chromatographic process parameter evaluation is discussed and concepts for the rational design of HTS experiments are presented.
Abstract: The necessity of being “first on the market” paired with the need to cut production costs highlights the need for strategies and techniques allowing a fast process development while at the same time covering a high number of potential process parameters in order to reach an optimal process sequence. This can only be met by the use of high throughput screening (HTS) techniques. In this paper HTS applications presently applied in bioprocess development are reviewed, their use in chromatographic process parameter evaluation is discussed and concepts for the rational design of HTS experiments are presented. A rational approach for chromatographic parameter screening comprehends an initial screening procedure for ligand selection followed by the incorporation of specific adsorbent features using HTS pipetting systems finalized by a fine tuning step using packed mini-columns. The analytical part of these screening techniques clearly sets the bottleneck of these procedures with a trade off between analytical information and analysis time. Finally, intelligent HTS strategies should in addition include efficient data processing paired with modern tools for design of experiments or model based process design.
123 citations
TL;DR: Although a great majority of reports refer to small laboratory scale isolations for research purposes it appears there is much higher potential for more extensive use of His-tags and IMAC at large scale than currently documented.
Abstract: Attachment of oligo-histidine tag (His-tag) to the protein N- or C-terminus is a good example of early and successful protein engineering to design a unique and generalized purification scheme for virtually any protein. Thus relatively strong and specific binding of His-tagged protein is achieved on an Immobilized Metal-Ion Affinity Chromatography (IMAC) matrix. Most popular hexa-histidine tag and recently also deca-histidine tag are used in combination with three chelating molecules: iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), and carboxymethyl aspartic acid (CM-Asp), covalently attached to the chromatographic matrix. The following combinations with divalent metal ions are preferentially used: (Cu, Zn, Ni, Co)-IDA, Ni-NTA, and Co-CM-Asp. At large scale, regarding cost and product purity, a decisive step is precise and efficient cleavage of His-tag by the cleavage enzyme. Two-step IMAC followed by a polishing step appears to be a minimum but still realistic as an approach to generic technology also for more demanding products. Possible drawbacks in using His-tags and IMAC, such as leaching of metal ions, inefficient cleavage, and batch-to-batch reproducibility must be carefully evaluated before transferred to large scale. Although a great majority of reports refer to small laboratory scale isolations for research purposes it appears there is much higher potential for more extensive use of His-tags and IMAC at large scale than currently documented.
112 citations
TL;DR: In this article, a new type of micromixer for rapid mixing was developed based on mixing by both kinetic energy and molecular diffusion of fluids, which was realized by the collision of micro segments, which were divided into several streams in the radial, at the center of the mixer.
Abstract: A new type of micromixer for rapid mixing was developed based on mixing by both kinetic energy and molecular diffusion of fluids. The rapid mixing was realized by the collision of micro segments, which were divided into several streams in the radial, at the center of the mixer. The excellent performance of the developed micromixer was confirmed by examining the Villermaux/Dushman reaction and the precipitation of polymer particles by phase separation. From these results, it was clarified that the rapid mixing was driven by both the breaking of micro segments under a high shear rate and instant molecular diffusion between micro segments. In addition, the mixer had a high throughput and corresponded to a wide range of flow rate ratios of fluids. Thus, it is expected that the proposed design concept for micro mixing will give us an efficient micro processing route in the future.
109 citations
TL;DR: In this paper, the feasibility of an electrocoagulation (EC) process using air injection to remove these inorganic elements with iron electrodes was evaluated using powder X-ray diffraction, scanning electron microscopy, and transmission Mossbauer spectroscopy.
Abstract: Protection of the global environment and, in particular, providing a sustainable source of clean water is a necessity for human survival. The wide use of heavy metals by modern industries has generated by-products containing heavy metals. Specifically, large quantities of chromium and arsenic containing compounds are being discharged into the environment. This study has been conducted to determine the feasibility of an electrocoagulation (EC) process using air injection to remove these inorganic elements with iron electrodes. Powder X-ray diffraction, scanning electron microscopy, and transmission Mossbauer spectroscopy were used to characterize the solid products formed at iron electrodes during EC. The results of this study suggest that magnetite particles and amorphous iron oxyhydroxides are present in the examined EC products. The field pilot-scale study demonstrated the removal of Cr(VI)/Cr(III) and As(III)/As(V) with an efficiency of more than 99 % from both wastewater and wells.
108 citations
TL;DR: The main arguments for using micro-structured reactors are enhanced conversion and selectivity, increased space-time yields, waste reduction and better safety given the small reactor volumes as mentioned in this paper.
Abstract: This article describes the opportunities microstructured reactors offer for chemical plant engineering. This suitability for chemical production is commonly regarded to be the key to market penetration. Century-long practices with batch-type stirring and, correspondingly, the existence of capital-intensive large-scale plants, hinder an easy and fast implementation of chemical micro process engineering. Seen in the long term, there is potential that new plants can be equipped with microstructured reactors. Only economic balances, however, which draw up profitability, will open the door to the usage of chemical micro process engineering for plant construction. The main arguments for using microstructured reactors are enhanced conversion and selectivity, increased space-time yields, waste reduction and better safety given the small reactor volumes. Credit-card sized reaction systems allow one to perform the screening of multi-step reactions in one run. Even more impressively, similar screening is carried out for single-step reactions faster and more reliably. Moreover, safe processing with microstructured reactors in the explosive regime enlarges the traditional range of processing. The reaction guidance by microstructured reactors can further influence subsequent processing steps, such as product purification, and in this way can lower the energy costs of processes.
104 citations
TL;DR: In this paper, the first to investigate photocatalysis using a cutting-edge and energy-efficient solid-state light source: Ultraviolet (UV) Light Emitting Diodes (LED's).
Abstract: This paper is the first to investigate photocatalysis using a cutting-edge and energy-efficient solid-state light source: Ultraviolet (UV) Light Emitting Diodes (LED's). UV LED's do not involve mercury vapor, can be driven with direct current (DC), and have a long lifetime of 100000 hours. UV LED's with a peak wavelength of 375 nm were tested for perchloroethylene (PCE) photocatalytic oxidation over Degussa P-25 TiO 2 . At a UV light output of only 49 μW/cm 2 , the designed reactor delivers a PCE conversion of up to 43 %. If the UV LED price continues to drop, it is very likely that UV LED's will replace UV lamps as the favored light source in photocatalysis applications.
TL;DR: In this paper, a water-cooled fixed bed Fischer-Tropsch synthesis reactor with Fe-HZSM5 catalyst was modeled in two dimensions (radial and axial) using the intrinsic reaction rates previously developed at RIPI.
Abstract: A water-cooled fixed bed Fischer-Tropsch reactor packed with Fe-HZSM5 catalyst has been modeled in two dimensions (radial and axial) using the intrinsic reaction rates previously developed at RIPI. The reactor is used for production of high-octane gasoline from synthesis gas. The Fischer-Tropsch synthesis reactor was a shell and tube type with high pressure boiling water circulating on the shell side. By the use of a two-dimensional model, the effects of some important operating parameters such as cooling temperature, H 2 /CO ratio in syngas and reactor tube diameter on the performance capability of the reactor were investigated. Based on these results, the optimum operating conditions and the tube specification were determined. The model has been used to estimate the optimum operating conditions for the pilot plant to be operated in RIPI.
TL;DR: In this article, the pore structure and pore volume are optimized to enhance the mass transfer and so the dynamic binding capacity of ion exchanger resins, which is also possible by pore size optimization.
Abstract: At the moment ion exchanger resins display the highest binding capacities for proteins. Polymeric surface modification methods utilize the full pore space and allow to guarantee high capacities for small as well as for large proteins. Capacity maximization is also possible by pore size optimization fitting the pore size to the molecule size without loosing a lot of dynamic binding capacity under current process conditions. Further improvements of resins can be achieved by optimizing the pore structure and pore volume, which could enhance the mass transfer and so the dynamic binding capacity.
TL;DR: Process intensification refers to complex technologies that replace large, expensive, energy-intensive equipment or processes with smaller, less costly, more efficient plants, or plants that combine multiple operations into a single apparatus or into fewer devices as discussed by the authors.
Abstract: The progress of basic research in chemical engineering has led to a better understanding of elementary phenomena, and it is now possible to imagine new operating modes of equipment or design novel equipment based on scientific principles. Process intensification refers to complex technologies that replace large, expensive, energy-intensive equipment or processes with smaller, less costly, more efficient plants, or plants that combine multiple operations into a single apparatus or into fewer devices.
TL;DR: In this article, an extended penetration theory is successfully developed to describe the heat transfer coefficient of the covered wall to the bulk solid in a rotary kiln, i.e., h cw-cb = (Xd p /k g + 0.5/2k b ρ b c pb n/Φ 0 ) -1 (0.096 < x < 0.198).
Abstract: Rotary kilns are used ubiquitously in the chemical and metallurgical industries. The mechanism of heat transfer in a rotary kiln is discussed in this paper, in which the effect of rotation is considered in determining heat transfer coefficients. In particular, an extended penetration theory is successfully developed to describe the heat transfer coefficient of the covered wall to the bulk solid in a rotary kiln, i.e., h cw-cb = (Xd p /k g + 0.5/2k b ρ b c pb n/Φ 0 ) -1 (0.096 < x < 0.198). A one-dimensional axial heat transfer model for an internally heated rotary kiln has been developed. Both predicted temperature profiles and heat transfer fluxes agree well with the experimental data of Barr et al. The simulated results are used to successfully explain for the first time the coupling phenomenon of the bulk bed and covered wall temperatures discussed in previous publications.
TL;DR: In this article, the authors investigated the effect of the formation of Dean vortices on heat transfer in periodic serpentine circular-section channels and found that the alignment of the flow with the vorticity in these structures allows significant mixing of the fluid without creating large pressure-drop penalties.
Abstract: The fully developed laminar flow and heat transfer behavior in periodic serpentine circular-section channels has been studied using computational fluid dynamics (CFD). The serpentine elements are characterised by their wavelength (2 L), channel diameter (d), and radius of curvature of bends (Rc) and results are reported for (3 ∼ 200, the flow becomes unsteady. Constant wall heat flux (H2) and constant wall temperature (T) boundary conditions have been examined for a range of fluid Prandtl number (0.7 < Pr < 100). The formation of Dean vortices produces significant heat transfer enhancement relative to flow in a straight pipe, with the effect being greater at higher values of Pr. Pressure drop is also increased but to a lesser extent. The alignment of the flow with the vorticity in these structures allows significant mixing of the fluid without creating large pressure-drop penalties. Dean vortices are also found to inhibit flow separation. These results suggest an effective method for enhancement of heat transfer in deep laminar flows.
TL;DR: In this paper, the direct regioselective hydrogenation of α,β-unsaturated aldehydes in aqueous multiphase catalysis was investigated in a capillary microreactor with channel diameters ranging from 500 to 1000 μm.
Abstract: The direct regioselective hydrogenation of α,β-unsaturated aldehydes in aqueous multiphase catalysis was investigated in a capillary microreactor with channel diameters ranging from 500 to 1000 μm. By connecting two mixers in line, a regular and stable alternating plug flow behavior could be generated, allowing accurate measurement of the plug geometry and hence the calculation of the specific surface area relevant for mass transport. These parameters are essential for reliable kinetic modeling of multiphase reaction systems containing microkinetic as well as transport terms.
TL;DR: In this article, a numerical solution approach for a widely accepted model developed earlier by Pan [1] for multicomponent gas separation by high-flux asymmetric membranes is presented, which does not require initial estimates of the pressure, flow and concentration profiles inside the fiber as does in Pan's original approach, thus allowing faster execution of the model equations.
Abstract: A new numerical solution approach for a widely accepted model developed earlier by Pan [1] for multicomponent gas separation by high-flux asymmetric membranes is presented. The advantage of the new technique is that it can easily be incorporated into commercial process simulators such as AspenPlus [2] as a user-model for an overall membrane process study and for the design and simulation of hybrid processes (i.e., membrane plus chemical absorption or membrane plus physical absorption). The proposed technique does not require initial estimates of the pressure, flow and concentration profiles inside the fiber as does in Pan's original approach, thus allowing faster execution of the model equations. The numerical solution was formulated as an initial value problem (IVP). Either Adams-Moulton's or Gear's backward differentiation formulas (BDF) method was used for solving the non-linear differential equations, and a modified Powell hybrid algorithm with a finite-difference approximation of the Jacobian was used to solve the non-linear algebraic equations. The model predictions were validated with experimental data reported in the literature for different types of membrane gas separation systems with or without purge streams. The robustness of the new numerical technique was also tested by simulating the stiff type of problems such as air dehydration. This demonstrates the potential of the new solution technique to handle different membrane systems conveniently. As an illustration, a multi-stage membrane plant with recycle and purge streams has been designed and simulated for CO 2 capture from a 500 MW power plant flue gas as a first step to build hybrid processes and also to make an economic comparison among different existing separation technologies available for CO 2 separation from flue gas.
TL;DR: In this paper, the authors investigated the pressure drop characteristics during the simultaneous flow of a kerosene-water mixture through a horizontal pipe of 0.025 m diameter, and measured the pressure gradient for different combinations of phase superficial velocities ranging from 0.03-2 m/s.
Abstract: The present study is aimed at an investigation of the pressure drop characteristics during the simultaneous flow of a kerosene-water mixture through a horizontal pipe of 0.025 m diameter. Measurements of pressure gradient were made for different combinations of phase superficial velocities ranging from 0.03-2 m/s such that the regimes encountered were smooth stratified, wavy stratified, three layer flow, plug flow and oil dispersed in water, and water flow patterns. A model was developed, which considered the energy minimization and pressure equalization of both phases.
TL;DR: In this article, a review article describes how microreactors are being applied to synthetic organic chemistry within the pharmaceutical industry and how micro reactors may improve the efficiency of the drug discovery process.
Abstract: This review article describes how microreactors are being applied to synthetic organic chemistry within the pharmaceutical industry and how microreactors may improve the efficiency of the drug discovery process. This article explores how miniaturization may revolutionize chemical synthesis and demonstrates that products are generated in higher yield and purity compared to the equivalent bulk reactions, in much shorter periods of time.
TL;DR: In this paper, a simple model can be used to relate the process efficiency to the ratio of two characteristic times: the space time of process fluid in the system and the characteristic time of the operation.
Abstract: The present study investigates a number of key features of microstructured reactors and components devoted to process miniaturization and intensification. For processes involving transfer operations and/or chemical reactions, a simple model can be used to relate the process efficiency to the ratio of two characteristic times: the space time of the process fluid in the system and the characteristic time of the operation. A detailed analysis of the relationship between these characteristic times and the characteristic dimensions of the system highlights the principal operations that should most benefit from the potential of microstructured process components. The analysis is used to examine how microstructured reactors may be advantageously employed to improve process efficiency (intensification) or to reduce process size (miniaturization), as a function of the operations involved.
TL;DR: In this article, the authors discuss the possibility of safely carrying out reactions involving explosive mixtures in a micro-reaction environment, which is very similar to the one described in this paper.
Abstract: Heterogeneously catalyzed gas-phase reactions are of great technical and economic importance in the chemical industry. Enormous resources continue to be expended on the development and optimization of catalysts, technical concepts for reactors, and/or operating conditions. Microreaction technology is very well suited to making extremely valuable contributions here in many different ways. On account of the geometric ratios and also the high specific surface areas, heat- and mass-transport limitations can generally be largely excluded or drastically reduced. This allows process conditions that cannot be realized in most conventional apparatus, as is convincingly demonstrated by, for example, the possibility of safely carrying out reactions involving explosive mixtures.
TL;DR: In this paper, a drop deformation and break-up visualization system based on a modified Particle Image Velocimetry (PIV) system is described, which has been used with pressures up to 18 MPa and drops as small as 5 mu m.
Abstract: For the creation of sub-micron emulsions in fluids of low viscosity the high pressure homogenizer (HPH) is usually chosen. One way of obtaining deeper knowledge of exactly what happens in the active region is to visualize it. In this work, a drop deformation and break-up visualization system based on a modified Particle Image Velocimetry (PIV) system is described. The system reproduces the gap in a HPH and has been used with pressures up to 18 MPa and drops as small as 5 mu m. The optics of the system are analyzed taking into account limiting factors such as the lens resolving power, the focal depth, and the duration of the laser pulses. It is shown that it is possible to resolve drops down to a few mu m moving in excess of 100 m/s, and that the main limitations are the resolving power and in the focal depth of the objectives. Examples are shown from capillary drop creation and from the deformation and break-up of drops in a HPH. It can be concluded that in a HPH, the drops are only deformed to a limited extent in the inlet of the gap, and that all drop break-up occurs far downstream of the gap. (Less)
TL;DR: In this paper, a review of the literature regarding gas-liquid direct contact evaporators is presented, addressing classic and potential applications, bubble regimes, gas holdup and bubble size distributions, as well as mathematical models proposed for simulating the unit.
Abstract: Gas-liquid direct-contact evaporators are characterized by the bubbling of a superheated gas through the solution to be concentrated. In other words, they are nonisothermal bubble columns. Despite their simplicity of construction, these units exhibit rather complex hydrodynamics and, similar to what occurs to isothermal bubble columns, the design of such units still poses a problem. The present paper reviews the literature regarding this kind of equipment, addressing both experimental studies and modeling efforts. The covered issues include classic and potential applications, bubbling regimes, gas holdup and bubble size distributions, as well as mathematical models proposed for simulating the unit. Additionally, pertinent literature on isothermal bubble columns is also discussed. Recommendations are made for future research.
TL;DR: In this paper, azo coupling of 2-naphthol and cresol novolaks was performed as an example for organic reactions in a microsegmented flow system with microspectrophotometric on-line characterization.
Abstract: The azo coupling of 2-naphthol and cresol novolaks was performed as an example for organic reactions in a microsegmented flow system with microspectrophotometric on-line characterization. A lithographically prepared glass/glass chip microreactor was used for the generation of segments and the mixing of reaction partners. The formation of segments and their transport behavior is strongly influenced by the addition of surfactants. The reaction rates were high in alkaline media at room temperature, so that the formation of dyes could be observed by a microscope-video system. The single reaction volumes were in the range between about 0.05 and 1 μL. The spectrum of each segment was registered with a measuring frequency of 45-50 Hz. The residence time of segments inside the optical measurement channels varied between 0.1 and 1.5 s and is in the range of 0.3 s for typical segment sizes of about 150 nL. The single reaction segments containing azo dyes as well as polymer-based azo dyes were stored in segment sequences inside capillary Teflon tubes.
TL;DR: In this article, a short-time plasma surface modification of polymer powders is proposed, which combines the advantageous characteristics of the downer principle for the fluid dynamics of gas-solid phases with plasma surface modifications.
Abstract: This paper introduces a plasma reactor for short-time plasma surface modification of polymer powders. This reactor type, the so-called plasma downer reactor (PDR), provides a high reaction rate, which is forced by the high gas velocity and high particle dispersion in the plasma. It combines the advantageous characteristics of the downer principle for the fluid dynamics of gas-solid phases with plasma surface modification. This work demonstrates that a very short plasma exposure time of 0.1 s effectively improves the wettability of HDPE and Co-PA powders. The water contact angles of HDPE and Co-PA powder can be reduced to 72° and 76°, respectively. The surface tensions of both polymer powders could be increased by a factor of 2 up to 43 mN/m. Water/polymer suspensions and pastes can be made without tensides.
TL;DR: In this article, the complex separation of a homogenous azeotropic mixture by pressure swing distillation is analyzed based on a rigorous dynamic model considering the system acetonitrile/water.
Abstract: The complex separation of a homogenous azeotropic mixture by pressure swing distillation is analyzed based on a rigorous dynamic model considering the system acetonitrile/water. The model is validated with our own experimental data. Investigations showed that the process can be operated in a very stable and robust manner even when large disturbances set the feed concentration to the other distillation region.
TL;DR: In this article, activated carbon was prepared by sulfuric acid activation, and both batch and column studies were performed for the sorption of phenol, and the kinetic data were fitted to the models of Lagergren, pseudo-second-order and intraparticle diffusion.
Abstract: Activated carbons prepared from tamarind nutshell, an agricultural waste by-product, have been examined for the removal of phenol from aqueous solutions. The activated carbon was prepared by sulfuric acid activation. Both batch and column studies were performed for the sorption of phenol. The kinetic data were fitted to the models of Lagergren, pseudo-second-order and intraparticle diffusion, and closely followed the pseudo-second-order chemisorption model. The Freundlich and Langmuir isotherm models were well fitted. The solution pH greatly affects the sorption process. The column study results indicate that the sorption of phenol is dependent on the flow rate, the inlet phenol concentration as well as on the particle size of the adsorbent.