INNOVATIVE APPLICATIONS OF IONIC LIQUIDS AS “GREEN” ENGINEERING LIQUIDS

Over the past decade, ionic liquids (ILs) have become one of the fastest growing “green” media for chemists and engineers due to their superb physicochemical properties. The applications of these remarkable salts in reactions and extraction processes have been extensively investigated and reviewed. This review, however, highlights recent advances of ILs as versatile “green” engineering liquids in a variety of industrial applications including heat transfer fluids, azeotrope-breaking liquids, lubricants, electrolytes, liquid crystals, supported IL membranes, plasticizers, and more. This review is not intended to be comprehensive, but rather to discuss the potentials of ILs for diverse industrial applications.     

ESTIMATION OF EFFECTIVE SHEAR RATE FOR AERATED NON-NEWTONIAN LIQUIDS IN AIRLIFT BIOREACTOR”“

Effective shear rate is one of the indispensable parameters for the design of aerobic fermentors using a viscous non-Newtonian system. The estimation of effective shear rate in airlift loop bioreactors has been investigated with liquid circulation velocity. An empirical correlation of effective shear rate in airlift loop reactors is proposed.

γ_eπ= 3.26-3.51 ; 10²U_G + 1.48 10⁴U²_G

It is found that the effective shear rate is lower in airlift reactors than in bubble columns. This equation can be used for the cultivation of cells sensitive to shear stress.     

Development of a problem-based learning elective in “green engineering”

Green engineering is the design of products and processes that maximise resource and energy efficiency, minimise waste and cause reduced harm to the environment. In modern society, engineers equipped with the skills to develop these sustainable technologies are particularly valuable. In 2004 the University of Sydney offered an elective course in ‘green engineering’ for the first time in Australia, during which students were introduced to cutting edge examples of sustainable technologies relevant to chemical and biomolecular engineering. Five assessable case studies were delivered using a problem-based learning (PBL) methodology which involved substantial group work as well as self-directed learning. This learning approach was a challenge for the majority of students who had not previously been exposed to it. Student feedback was overwhelmingly positive. In particular, overall student satisfaction with the course, measured during the formal evaluation, had a mean score of 4.43 (out of 5) with all students agreeing or strongly agreeing with the statement “Overall I was satisfied with the quality of this unit of study”. Students were also satisfied with the way the course helped to develop valuable generic attributes (4.43). Individual students commented that the ‘think outside the box’ nature of the unit was a highlight they would like to see incorporated more widely into their degree programme.     

“GENERALIZED” ENTROPY PRODUCTION RATE ASSOCIATED TO ONE-DIMENSIONAL HEAT CONDUCTION- EXTREMUM POINTS AND APPLICATIONS

In previous papers, the author considered the critical or the extremum points of the entropy production rate in insulations with one-dimensional heat conduction, either alone or associated with other refrigerating systems necessary to maintain the steady state.

The aim of this paper is to obtain a general formulation for the presence of critical or extremum points of the (generalized) entropy production rate in a more ample domain that includes the previous cases as particular ones.

Homogeneous and more than one component systems are considered; for homogeneous systems, the necessary and sufficient condition for the minimum of the (generalized) entropy production rate in the system is obtained, while for two or more component systems only the necessary condition for a relative extremum is stated. In the latter case one can have also a particular state which is not an extremum and can be known as a “saddle point” state from analogy.

This general formulation can be used for the thermodynamic optimization of cryogenic plants, extensively used in large-scale superconducting plants operating at liquid helium temperatures.     

THE “UCKRON-1” TEST PROBLEM FOR REACTION ENGINEERING MODELING

Testing kinetic models against a “true” and detailed kinetic expression was the aim of the Workshop on Kinetic Model Development at the Denver AIChE Meeting in August, 1983. For this purpose an artificial reaction mechanism was created, based on the known thermodynamics of the methanol synthesis as a framework. The kinetic rate laws, that were derived from this mechanism, were made thermodynamically consistent by achieving agreement between equilibrium constants calculated at various temperatures from the given, real original thermodynamic relationship and those calculated from the detailed reversible kinetic expressions.

Using the artificial kinetics as the "true" one, CSTR experiments were simulated. The results of a statistically designed set of experiments were published after 5% random error was added to the data. Participation was invited for all interested to correlate the data, develop kinetic models and to calculate the performance of the specified reactor.

The results of 19 submitted entries are summarized with the conclusion that the models had more differences than were expected, but their predictive values were not as different as was anticipated, if the extreme high production rates due to thermal runaways are not considered. This in turn points out the necessity to check models experimentally, in pilot plant, not only for predicted optimum, but also for calculated runaway conditions. Models which did not capture the true character of this reaction failed to predict the onset of runaway reactions.     

Gas-liquid mass transfer in “dead-end” autoclave reactors

Gas-liquid volumetric mass transfer coefficients, (k_La), have been obtained for “dead-end” autoclave reactors operated in two different modes: (a) gas introduced into the gas phase, and (b) gas introduced through a dip-tube in the liquid. Three different methods of k_La determination have been compared. Effects of agitation speed, impeller diameter, gas to liquid volume ratio (V_g/V_L), position of the impeller and reactor size on k_La have been investigated. The k_La data were found to be correlated as: k_La = 1.48 × 10^?3 (N)^2.18 (V_g/V_L)^1.88 (d_I/d_T)^2.16 (h₁/h₂)^1.16 The critical speed of surface breakage, at which transition from the surface convection to the surface entrainment regime occurs, was also determined for different impeller positions, impeller diameters and gas to liquid volume ratios.     

Interrogation of “surface,” “skin,” and “core” orientation in thermotropic liquid‐crystalline copolyester moldings by near‐edge X‐ray absorption fine structure and wide‐angle X‐ray scattering

Injection molding thermotropic liquid‐crystalline polymers (TLCPs) usually results in the fabrication of molded articles that possess complex states of orientation that vary greatly as a function of thickness. “Skin‐core” morphologies are often observed in TLCP moldings. Given that both “core” and “skin” orientation states may often differ both in magnitude and direction, deconvolution of these complex orientation states requires a method to separately characterize molecular orientation in the surface region. A combination of two‐dimensional wide‐angle X‐ray scattering (WAXS) in transmission and near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy is used to probe the molecular orientation in injection molded plaques fabricated from a 4,4′‐dihydroxy‐α‐methylstilbene (DHαMS)‐based thermotropic liquid crystalline copolyester. Partial electron yield (PEY) mode NEXAFS is a noninvasive ex situ characterization tool with exquisite surface sensitivity that samples to a depth of 2 nm. The effects of plaque geometry and injection molding processing conditions on surface orientation in the regions on‐ and off‐ axis to the centerline of injection molded plaques are presented and discussed. Quantitative comparisons are made between orientation parameters obtained by NEXAFS and those from 2D WAXS in transmission, which are dominated by the microstructure in the skin and core regions. Some qualitative comparisons are also made with 2D WAXS results from the literature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Comparison study of a chiral stationary phase based on cellulose derivatives prepared by “grafting from” and “grafting to” methods

Chiral stationary phase (CSP) with cellulose derivatives was synthesized using the “grafting from” and “grafting to” methods. The “grafting to” method involves the bonding of a preformed end‐functionalized polymer to reactive surface amine groups on the silica gel. The “grafting from” involves the immobilization of initiator onto the aminated silica gel followed by atom transfer radical polymerization (ATRP) to generate the chiral polymer chains. The successful preparation of the CSP with cellulose derivatives prepared by ATRP was confirmed by FE‐SEM, XPS, EA, and thermal analysis. The chiral resolution of the CSP with cellulose derivatives was evaluated by high‐performance liquid chromatography using 10 racemates with various mobile phases that consisted of hexane/alcohol, hexane/THF, and hexane/chloroform. Furthermore, the CSP with cellulose derivatives prepared by “grafting from” and “grafting to” were compared and discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Performance Evaluation of a Novel Concept “Open Plate Reactor” Applied to Highly Exothermic Reactions

The implementation of chemical reactions in batch or semibatch reactors is strongly limited by the constraints linked to the dissipation of the heat generated by the reactions. A novel concept of heat exchanger reactors offers enhanced thermal performances in a continuously operating reactor. A study program is proposed to assess the feasibility and potentialities of this concept. Two kinds of reactions are carried out to characterize simultaneously the reactor performances in terms of reaction and heat exchange: the oxidation of sodium thiosulfate by hydrogen peroxide and an acidobasic reaction (NaOH/H₂SO₄). The resultant experimental data emphasize a significant thermal efficiency: the reactant concentrations and therefore the heat generation can be increased without risk of thermal runaway.     

Treatment of gases and dust using “droplet columns”

The properties of the air-water state diagram, representing the liquid holdups according to gas velocities, in a 0.075 m diameter column are restated. After measurement of the interfacial areas and mass-transfer coefficients, the part of the diagram corresponding to high gas velocities and low liquid contents (10 < U_G < 14 m/s and 0.005 < U_L < 0.04 m/s) was chosen for the treatment of polluted gas streams. Under these conditions, it was shown that a “droplet column” is very efficient for the treatment of gases polluted by acid vapors (SO₂, HCl) and dust (iron oxide, talc, etc.). The cost of energy appeared more favorable than for classical bubble columns.     

STRUCTURAL AND PARAMETRIC SENSITIVITY OF “UCKRON-1” TEST PROBLEM

The sensitivity of a specified tabular reactor to thermal runaway is simulated using a model for the UCKRON-1 Test Problem. Parametric sensitivity was increased by the increase of coolant temperature and by the increase of inlet temperature and pressure. Extension of the Test Problem by the water-gas shift reaction reduced the productivity and sensitivity of the reactor. Addition of the water-gas reaction represents the sensitivity for runaway to the structure of the model. These observations lead to a strategy for maximizing the methanol production within a range where thermal runaway does not occur.     

Comments to the paper “The need to reconsider tradional free volume theory for polymer electrolytes”

The specific free volume V_f is calculated from the Simha–Somcynsky equation (S–S eos) of state analysis of pressure–volume–temperature (PVT) data of Bendler et al. [Electrochim. Acta 48 (2003) 2267], for poly(propylene glycol) (PPG) containing LiCF₃SO₃. We found that, due to the compressibility of the occupied volume, V_f is not constant for a constant specific total volume V but depends on the pathway in the P–T plane on which the V is reached. From this it follows that the observation of different relaxation properties for the same total volume in variable temperature, high-pressure experiments does not necessarily contradict the free volume theory. We show that the traditional free volume theory is consistent with the electrical conductivity data for Bendler et al. for 20:1 PPG:LiCF₃SO₃ when V_f is calculated from the S–S eos. Moreover, we derive an empirical function for describing the temperature and pressure dependence of the electrical conductivity which contains, beside the three parameters of the Vogel–Tammann–Fulcher law, only two additional parameters, both control the effect of pressure on the electrical conductivity.     

ADDITION OF PORE DIFFUSION LIMITATION TO THE “UCKRON-I” KINETIC RATE OF METHANOL SYNTHESIS

Kinetic data with pore diffusion limitation on methanol synthesis were generated by extending the “UCKRON-I” kinetic rate expression. The best fit model and the extended “true” model were compared using their respective rates to simulate temperature profiles in a non-isothermal plug flow tubular reactor.

The objective of this work was to add pore diffusion resistance to the UCKRON-1 kinetic rate for methanol synthesis (Berty, et al. 1983). Kinetic modeling of the data with 5% experimental error added, showed the best model to be that developed from a previous kinetic model (Shalabi, et al. 1983) with apparent activation energy approximately one-half the activation energy at no pore diffusion.

Methods used in this work to determine and evaluate pore diffusion parameters can be utilized for other reaction systems where pore diffusion may play a role in reaction rate.

Temperature profiles estimated from reactor simulation studies showed good argeement between ideal and predicted models for temperature.     

Computational investigation of the mechanisms of particle separation and “fish‐hook” phenomenon in hydrocyclones

The motion of solid particles and the “fish‐hook” phenomenon in an industrial classifying hydrocyclone of body diameter 355 mm is studied by a computational fluid dynamics model. In the model, the turbulent flow of gas and liquid is modeled using the Reynolds Stress Model, and the interface between the liquid and air core is modeled using the volume of fluid multiphase model. The outcomes are then applied in the simulation of particle flow described by the stochastic Lagrangian model. The results are analyzed in terms of velocity and force field in the cyclone. It is shown that the pressure gradient force plays an important role in particle separation, and it balances the centrifugal force on particles in the radial direction in hydrocyclones. As particle size decreases, the effect of drag force whose direction varies increases sharply. As a result, particles have an apparent fluctuating velocity. Some particles pass the locus of zero vertical velocity (LZVV) and join the upward flow and have a certain moving orbit. The moving orbit of particles in the upward flow becomes wider as their size decreases. When the size is below a critical value, the moving orbit is even beyond the LZVV. Some fine particles would recircuit between the downward and upward flows, resulting in a relatively high separation efficiency and the “fish‐hook” effect. Numerical experiments were also extended to study the effects of cyclone size and liquid viscosity. The results suggest that the mechanisms identified are valid, although they are quantitatively different. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Solid—liquid mass transfer in a shaking vessel for a bioreactor with “current pole”

A shaking vessel with “current pole”, which is a center pole installed at the bottom, had shorter mixing time than a shaking vessel with a cone at the bottom. The mass transfer rate on the suspended particles was also measured in the shaking vessel where ion-exchange resin beads were used as the suspended particles. The dependence of the solid-liquid mass transfer coefficient on the circulating frequency changed at the critical circulating frequency for complete suspension N_JS. For a circulating frequency higher than N_JS, the mass transfer coefficient was correlated with the power consumption per unit volume, regardless of presence or not of the current pole.     

“Smart” membrane materials: Preparation and characterization of PVDF‐g‐PNIPAAm graft copolymer

In this research, a smart membrane material of graft copolymer of poly(vinylidene fluoride) with poly(N‐isopropylacrylamide) (PVDF‐g‐PNIPAAm) was synthesized by atom transfer radical polymerization (ATRP) using poly(vinylidene fluoride) (PVDF) as a macroinitiator and direct initiation of the secondary fluorinated site PVDF facilitates grafting the N‐isopropylacrylamide comonomer. The copolymers were characterized by Fourier transform infrared (FTIR), ¹H NMR, gel‐permeation chromatography (GPC), and X‐ray photoelectron spectroscopy (XPS). The temperature‐sensitive membrane was prepared from the PVDF‐g‐PNIPAAm graft copolymers by the phase inversion method. The effects of temperature on the flux of pure water of membrane was investigated. The results showed that alkyl fluorides were successfully applied as ATRP initiators in the synthetic condition and the flux of pure water through the PVDF‐g‐PNIPAAm membrane depended on the temperature change. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1482–1486, 2007     

Synthesis of NR‐g‐PMMA by “grafting from” method using ATRP process

Grafting poly(methyl methacrylate) or PMMA from natural rubber (NR) using ATRP process, NR has to be transformed into bromoalkyl‐functionalized NR (NRBr) acting as ATRP macroinitiator. The NRBr was prepared by two‐step chemical modification i.e., epoxidation and epoxide ring opening reaction using a nucleophile containing bromine atom such as 2‐bromopropionic acid ( A1 ) and 2‐bromo‐2‐methylpropionic acid ( A2 ). The fixation of A1 and A2 on 4‐methyl‐4‐octene, a model representing one repeat unit of NR, modified by epoxidation was prior studied and it was found that the resulting addition products from A2 using as ATRP initiator for MMA gave a better control of M _n,exp and low PDI of PMMA than that from A1 . Then, the NR was transformed into ATRP rubber macroinitiator via epoxidation, followed by epoxide ring addition with only A2 . ¹H NMR was employed to determine the amount of A2 addition units on NR, which is considered to be the same amount of grafting sites for ATRP of MMA. The grafting of PMMA was then successfully carried out from the NR backbone by ATRP process. The PMMA grafts of the NR‐g‐PMMA were indeed linked to the NR backbone via ester linkage of the A2 unit. The PMMA grafts could be cleaved from the NR backbone by acid hydrolysis, while PMMA grafting by other conventional radical reaction could not be done. Then, the average MW of PMMA grafts after separation using acetone extraction was evaluated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Use of ionic liquids as ‘green’ solvents for extractions

This review summarizes recent applications of ionic liquids (ILs) as ‘green’ solvents in extractions of a variety of substances, including metal ions, organic and bio‐molecules, organosulfur from fuels, and gases. ILs could also be used along with another ‘green’ technology, supercritical fluid extraction (SFE), for a more effective separation of products from ILs. In addition to their environmentally‐benign feature, ILs have other favorable properties over organic solvents used for extraction, such as adjustable hydrophobicity, polarity and selectivity. Copyright © 2005 Society of Chemical Industry