Showing papers in "Chemical Engineering & Technology in 2012"

Highlights of Photochemical Reactions in Microflow Reactors

Abstract: This review highlights selected examples of photochemical transformations in microflow reactors. The main advantages of microflow reactors over conventional batch systems are superior light penetrations, controlled reaction times, precise temperature control and removal of photoproducts from the irradiated area. These features typically result in higher conversions or yields, improved selectivity,enhanced energy efficiencies and reductions of solvent volumes and consequently waste. Different types of homogeneous and heterogeneous reactions are presented, showing the superiority of microflow photochemistry over batch processes.

Hydrodynamics and Mass Transfer in Gas-Liquid Flows in Microreactors

Abstract: Over the last ten to fifteen years, microreaction echnology has become of increased interest to both academics and industrialists for intensification of multiphase processes. Amongst the vast application possibilities, fast, highly exothermic and/or mass transfer-limited gas-liquid reactions benefit from process miniaturization. Recent studies of hydrodynamics and mass transfer in gas-liquid microreactors with closed and open microchannels, e.g., falling-film microreactors, are reviewed and compared. Special attention is paid to Taylor or slug flow in closed channels, as this regime seems to be most adapted for practical engineering applications.

Potential Analysis of Smart Flow Processing and Micro Process Technology for Fastening Process Development: Use of Chemistry and Process Design as Intensification Fields

Abstract: Flow processes with microstructured reactors allow paradigm changes in process development and thus can enable a faster development time to the final production plant. They do this by exploiting similarity effects along the development chain (modularity) and intensification. The final result can be a (significantly) reduced number of apparatus in the plant, a (significantly) reduced apparatus size, and a higher predictability in the scale-out of the apparatus. So far, this was mainly achieved via transport intensification given in microstructured reactors – improved mixing and heat transfer which increase productivity and possibly improve selectivity. A more new idea is chemical intensification through deliberate use of harsh chemistries at unusual (high) pressure, temperature, concentration, and reaction environment which again increases productivity. A very new idea is the process design intensification – the reaction-maximized flow processes need less separation expenditure and the small unit size together with the high degree in functionality gives large potential for system integration. Both means change and simplify the process scheme totally which can lead to a reduced number of apparatus and has impact on predictability. The modular nature of the small flow units allow an easy implementation to modern modular plant environments (Future Factories) which enables to perform all the testing cycles (lab, pilot, production) in one plant environment; an example are here container plants. All these measures have large potential for (much) decreased overall development time.

Chemical Looping Dry Reforming as Novel, Intensified Process for CO2 Activation

Abstract: Chemical looping dry reforming (CLDR) is a novel, intensified route for CO2 activation. Two nanostructured carriers (Fe-BHA and Fe@SiO2) are synthesized, characterized, and evaluated with regard to activity and stability in thermogravimetric and fixed-bed CLDR reactor studies over a temperature range of ~500–800 °C. Fe-barium hexaaluminate (Fe-BHA) shows fast redox kinetics and stable operation over multiple CLDR cycles, while Fe@SiO2 exhibits poor activity for CO generation due to a partial loss of the core-shell structure and formation of silicates. While the latter could be removed via a two-step oxidation scheme, carrier utilization remained well below that of Fe-BHA (~ 51 % versus ~ 15 %). However, the two-step oxidation configuration turns the net endothermic CLDR process into a net exothermic process, opening up a highly efficient autothermal process alternative.

Implementation of the Finite Element Method for Simulation of Mass Transfer in Membrane Contactors

Abstract: Mathematical modeling and numerical simulation of gas separation by means of polymeric membrane contactors is presented. The finite element method is implemented for numerical simulation. COMSOL Multiphysics is used for simulation. Continuity equations are solved via computational fluid dynamics techniques based on the finite element method. A laminar velocity profile is applied for the solvent. Velocity distribution of the gas flow in the contactor is obtained by Happel's model. The predictions of percent CO2 removal obtained by the modeling were compared with the experimental values from literature for CO2 removal from CO2/N2 gas mixtures with amines. The modeling predictions were in good agreement with experimental data for different values of liquid flow rates.

Screening of Aqueous Amine‐Based Solvents for Postcombustion CO2 Capture by Chemical Absorption

Abstract: In relation with CO2 capture by chemical absorption into aqueous amine-based solvents, absorption and regeneration parameters by separate absorption and regeneration tests are determined. An absorption parameter for different types of amine-based solvents is evaluated by performing absorption tests at 298 K and atmospheric pressure with a gas-liquid contactor and deducing apparent kinetic constants. The regeneration parameter is obtained from a CO2 concentration temporal profile measured in a regeneration cell at the boiling temperature of each solvent. By combining both parameters it is possible to compare the absorption-regeneration performances of all the solvents studied. Good absorption-regeneration performances of cyclical amines, especially of piperidine (PIP) and piperazine (PZ), are highlighted. The interesting potential of 2-amino-2-methyl-1-propanol (AMP) and methyldiethanolamine (MDEA) activated with PZ and PIP is also considered.

Simulated Moving Bed Chromatography: From Concept to Proof‐of‐Concept

Abstract: This work presents a comprehensive insight about simulated moving bed (SMB) technology, from concept to unit operation and process demonstration. A particular relevance is given to SMB nonconventional modes of operation, modeling, and design of SMB-based separations as well as to the construction and operation of SMB units. A conventional separation of a racemic mixture of (S,R)-α-tetralol by means of the FlexSMB-LSRE® unit is addressed to better exemplify a state-of-the-art SMB lab-scale process development and demonstration.

Mixed‐Matrix Membrane for Gas Separation: Polydimethylsiloxane Filled with Zeolite

Abstract: Mixed-matrix membranes (MMMs) comprised of polydimethylsiloxane (PDMS) as continuous and zeolite (ZSM-5) as dispersed phase have been prepared to investigate CO2 separation from gas mixtures, focusing on the high solubility of CO2 in ZSM-5/PDMS MMMs for separating CO2-N2 mixtures. ZSM-5 incorporation in PDMS significantly increases the permeability of single gases and a similar effect is observed for gas mixtures. Membrane performance is evaluated using the Maxwell model; an interphase gap between the filler and the polymeric phase is identified. A modified Maxwell model is applied to account for this additional transport through the membrane.

Functions of Hydrotropes in Solutions

Abstract: Hydrotropes affect a several-fold increase of the solubility of sparingly soluble solutes under normal conditions. Their water-solubility can significantly enhance the solubility of organic solutes such as esters, alcohols, aldehydes, ketones, hydrocarbons, and fats. While the study of hydrotropes is pioneered by a biochemist, greater appreciation of their role and applicability has happened rather in chemistry and chemical engineering than in biology. Hydrotropes are widely used in drug solubilization, as extraction agents for fragrances, as agents to increase the rate of heterogeneous reactions, and for separation of close-boiling liquid mixtures through extractive distillation and liquid-liquid extraction. Applications of hydrotropy and its mechanism are discussed and the scope for future work is presented in this review.

Selective Extraction of Lutein from Alcohol Treated Chlorella vulgaris by Supercritical CO2

Abstract: A pretreatment process using alcohol for the removal of chlorophyll a, b and β-carotene from Chlorella vulgaris was developed to improve the yield and selectivity of lutein in the extract obtained by supercritical carbon dioxide extraction. Supercritical carbon dioxide extraction was carried out after pretreatment in the pressure range of 20 to 40 MPa and the temperature range of 40 to 80 °C. Ethanol and methanol were selected as elution solvents, of which ethanol was found most suitable for the elution, or pretreatment, process. The amounts of lutein and other compounds were analyzed by HPLC with the mixture of methanol and THF as the mobile phase. The amount of lutein in the extract increased with pressure, but decreased with extraction temperature. The highest recovery percentage and the selectivity of lutein were around 52.9 ± 0.02 % and 43.1 ± 0.02 %, respectively, obtained from supercritical carbon dioxide extraction with pretreatment and ethanol entrainer at 40 MPa and 40 °C.

Kinetics of CO2 Absorption by a Blended Aqueous Amine Solution

Abstract: The reaction rates of CO2 in an aqueous blend of amine solutions of N-(2-hydroxethyl)piperazine (N-HEPZ) and 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD) at 298 K were investigated in a concentration range of 0.0025–0.03 kmol m–3N-HEPZ with a blend of 1 kmol m–3 AHPD. The reaction was modeled using a termolecular reaction mechanism with a rate of 12 971 m3kmol–1s–1. The results indicate that the blended aqueous solution of N-HEPZ and AHPD is a potential candidate as an alternative solvent for CO2 absorption, where the sterically hindered AHPD increases the CO2 capacity and the reaction rate is enhanced by the promoter, N-HEPZ.

Carbon Dioxide Capture from Power Generation – Status of Cost and Performance

Abstract: Energy scenarios suggest that CO2 capture and storage (CCS) from power plants might contribute significantly to global greenhouse gas emission reduction. Since CCS from power generation is an emerging technology that has not been demonstrated on a commercial scale, related cost and performance information is still uncertain. This paper presents a detailed analysis of the impact of adding CO2 capture and compression process equipment to fossil-fuelled power plants. For coal-fired power generation, no single capture technology outperforms available alternative capture processes in terms of cost and performance.

Activated Carbon Preparation from Lignin by H3PO4 Activation and Its Application to Gas Separation

Abstract: Activated carbons were produced from corn straw lignin using H3PO4 as activating agent. The optimal activation temperature for producing the largest BET specific surface area and pore volume of carbon was 500?degrees C. The maximum BET specific surface area and pore volume of the resulting carbon were 820?m2g1 and 0.8?cm3g1, respectively. The adsorption isotherm model based on the Toth equation together with the Peng-Robinson equation of state for the determination of gas phase fugacity provide a satisfactory representation of high pressure CO2, CH4 and N2 adsorption. The kinetic adsorption results show that the breakthrough difference between CO2 and CH4 is not obvious, indicating that its kinetic separation performance is limited.

Application of Laser‐Backscattering Instruments for In Situ Monitoring of Crystallization Processes – A Review

Abstract: Laser-backscattering instruments, such as the focused beam reflectance measurement or threefold dynamical optical reflectance measurement, are promising tools to aid crystallization process development, allowing an in situ, real-time, and nondestructive measurement of particle size distributions. Besides the instrument principles, in detail geometrical and optical models are discussed which deconvolute the recorded chord length distribution. Emphasis is thereby laid on the influence of the suspension density on instrument recordings. The application of laser-backscattering devices for determination of kinetic constants is discussed and future directions and perspectives are given.

Microwave Synthesis of the CPM‐5 Metal Organic Framework

Abstract: The metal organic framework CPM-5 (crystalline porous materials) was successfully synthesized and characterized for the first time using microwave irradiation as a rapid and facile synthesis method in about 10 min compared to several days crystallization time required for the conventional solvothermal approaches. Furthermore, CPM-5 produced by microwave-assisted synthesis exhibited a very high surface area of 2187 m2g–1 compared to, e.g., 580 m2g–1 of the conventionally synthesized samples. Moreover, the as-synthesized CPM-5 showed high carbon dioxide uptake.

Micromixing Characteristics in a Small‐Scale Spinning Disk Reactor

Abstract: Thin films formed under the high acceleration fields in the spinning disc reactor (SDR) are characterised by high shear rates and intense surface ripples which are known to play an important role in improving the selectivity, yield, and final product quality in many mixing-dependent processes. In the present investigation, we characterise the micromixing efficiency of a small scale SDR of 10 cm disc diameter for a range of hydrodynamic conditions by means of the iodide-iodate test reaction. We demonstrate herein that, under optimised conditions, the SDR gives better micromixing performance than the mechanically stirred vessel when processing water-like fluids whilst being at least as effective as other intensified mixers/reactors reported in the literature. These results highlight the potential of the SDR as an alternative intensified mixer/reactor for processes where a high degree of mixing is critically important.

Nonlinear Model Predictive Control of a CO2 Post-Combustion Absorption Unit

Abstract: A dynamic model of a chemical CO2 absorption process with aqueous monoethanolamine (MEA) is presented, validated against experimental data. Based on the validated model, a reduced-order model is developed, suitable for an online optimization control strategy. The objective of the optimization is to enable fast adap- tations to changes in operating conditions of the power plant, while minimizing the energy consumption in the operation of the CO2 separation plant. The results indicate that model-based online optimization is a feasible technology for control of CO2 separation systems.

Microfluidic Solvent Extraction of Metal Ions and Complexes from Leach Solutions Containing Nanoparticles

Abstract: Solvent extraction is often hindered by the presence of particles and surfactants that increase the stability of emulsion phases, i.e., crud, thus preventing full recovery of the organic phase and the valuable metal species. It is shown that bypassing the formation of a particle-stabilized crud using a stream-based microfluidic extraction approach has great potential for handling these more challenging and industry-relevant systems provided sufficient throughputs can be realized. Metal ions and complexes are extracted from copper oxide and chromite leach solutions at high efficiencies and extraction rates within the confinement of a microchannel and in the presence of silica nanoparticles. These findings and their implications for process intensification are discussed.

Sorption-Enhanced Steam Reforming of Ethanol: Thermodynamic Comparison of CO2 Sorbents

Abstract: A thermodynamic analysis is performed with a Gibbs free energy minimization method to compare the conventional steam reforming of ethanol (SRE) process and sorption-enhanced SRE (SE-SRE) with three different sorbents, namely, CaO, Li2ZrO3, and hydrotalcite-like compounds (HTlc). As a result, the use of a CO2 adsorbent can enhance the hydrogen yield and provide a lower CO content in the product gas at the same time. The best performance of SE-SRE is found to be at 500 °C with an HTlc sorbent. Nearly 6 moles hydrogen per mole ethanol can be produced, when the CO content in the vent stream is less than 10 ppm, so that the hydrogen produced via SE-SRE with HTlc sorbents can be directly used for fuel cells. Higher pressures do not favor the overall SE-SRE process due to lower yielding of hydrogen, although CO2 adsorption is enhanced.

Ultrasonic Desorption of CO2 – A New Technology to Save Energy and Prevent Solvent Degradation

Abstract: A central concern of future research activities in the field of carbon capture and storage is the reduction of energy demand for solvent regeneration. This also includes, besides the development of more efficient CO2 absorbents, the exploration of alternative desorption methods. The stripping process is generally regarded as the state-of-the-art in amine scrubbing, although significant amounts of heat are required for steam generation in the stripper. Against this background, a new desorption technique on the basis of pressureless amine scrubbing is under development, in which an ultrasonic field is used to accelerate the CO2 desorption. With the new ultrasound method, applied for a patent, desorption of CO2 can be performed at temperatures below 80 °C. This special feature of the ultrasonic-assisted CO2 degassing can be applied advantageously together with weakly binding CO2 absorbents which are in use in connection with a high CO2 partial pressure in the raw gas.

pH and Particle Structure Effects on Silica Removal by Coagulation

Abstract: Coagulation is presented as an efficient alternative to reduce the silica content in effluents from recovered-paper mills that are intended to be recycled by a final reverse-osmosis (RO) step. Coagulation pretreatment by several polyaluminum chlorides (PACls) or FeCl3 was optimized prior to the RO process. PACls with low alumina content and high basicity achieved almost a 100 % removal of silica at pH 10.5. A good reduction of the silica content was attained without regulating the pH by adding one of these PACls. Silica removal was related to the structure of the produced clots in which cylindrical particles produced higher silica removal. All coagulants removed more than 50 % of the chemical oxygen demand (COD).

Numerical Study of Split T‐Micromixers

Abstract: Three-dimensional numerical simulations were performed to study the liquid flow inside split T-type micromixers, investigating the effects of various operating and design parameters on the mixing process. While for small Reynolds numbers, the mixing efficiency of a split T-micromixer is larger than that of a simple T-micromixer, it was found that, when Re = 100, mixing is further enhanced by the formation of vortex pairs. This is not only a function of the flow rate, but it depends also on the geometry of the device and on the ratio between the flow rates in the inlet sub-channels. In general, at a given flow rate, vertical splits induce a much better mixing than horizontal splits, while the reverse may occur for strongly unequal inlet flow rates.

Effects of Brønsted and Lewis Acidities on Catalytic Activity of Heteropolyacids in Transesterification and Esterification Reactions

Abstract: Some salts of H3PW12O40-Mx/nH3–xPW12O40 (abbreviated as Mx/nH3–xPW) were prepared and used as acid catalysts for transesterification and esterification reactions. These catalysts have double acidity properties, i.e., Lewis acidity and Bronsted acidity, that are suitable for the conversion of waste cooking oil into biodiesel. The highest efficiency was 59.2 % and 94.7 % corresponding to transesterification and esterification reactions by Ti0.6H0.6PW with moderate Lewis acidity. The relationship between the acidic properties and the catalytic activity is discussed in detail.

Adsorption Characteristics of Atrazine on Granulated Activated Carbon and Carbon Nanotubes

Abstract: Adsorption of atrazine (ATZ) from aqueous solutions by granular activated carbon (GAC) and carbon nanotubes (CNT) was studied in a batch-mode adsorption system at different initial concentrations of ATZ (1.0–30.0 mg L–1) and at three temperatures of 288, 296 and 304 K. The adsorption isotherms of Langmuir, Freundlich, Polanyi–Manes, and Brunauer–Emmett–Teller (modified) were used to model the process. The adsorption kinetics followed a pseudo-second-order kinetic model. The thermodynamic parameters ΔH0, ΔS0, and ΔG0 of the adsorption were estimated. The thermodynamic parameters indicate that the adsorption process is spontaneous and exothermic.

Sequential Centrifugal Partition Chromatography: A New Continuous Chromatographic Technology

Abstract: In solid-support-free liquid-liquid chromatography, both phases can be used as a mobile phase and, moreover, their role and flow direction can be reversed during the course of the separation. This is the background of the concept of sequential centrifugal partition chromatography (sCPC) developed to perform a continuous separation in a cyclic manner. The feed is continuously introduced between two centrifugal partition chromatographic columns and two products are alternately collected at the opposite ends of the columns. In this work, a method is presented to select the operating parameters of an sCPC unit for the complete separation of a binary feed mixture. The method uses, as a basis, a restricted number of experiments needed to determine the distribution equilibrium of the components to be separated and to evaluate the column hydrodynamics. The method was validated experimentally for the separation of a binary mixture of hydroquinone and pyrocatechol.

Recent Advances in Microbial Fuel Cells Integrated with Sludge Treatment

Abstract: Microbial fuel cells (MFCs), which can directly convert chemical energy in organic matters into electricity, have drawn a lot of attention in the past decades. Recently, MFCs have been integrated with waste-activated sludge (WAS) treatment for recovering energy from WAS. Since 2004, a number of publications regarding this topic have been published. The recent advances in MFCs powered by WAS are critically reviewed. MFC reactor designs, MFC performances, and sludge degradation efficiencies are addressed based on the recent related publications. The challenges and corresponding enhancement measures of MFCs using WAS as fuel are also discussed.