Asia-Pacific Journal of Chemical Engineering

Direct contact membrane distillation (DCMD) was operated at low temperatures from 25 to 40 °C to suit the purpose of thermally concentrating sensitive liquid foods, especially fruit juices to high solid content concentrate with most of the quality attributes preserved.

A lab scale DCMD unit has been set up at the Centre for Plant and Food Science, University of Western Sydney. Hollow fibre modules (HFM) using five types of fibres of polyvinylidene fluoride (PVDF) and Halar material, with mass transfer areas ranging from 281 to 573 cm² were employed. Experiments for concentration of glucose solutions from 30 to 60% (w/w) were carried out. Results indicated that not only the operating conditions were important, but also the membrane properties. It was found that Halar fibres were performing 2–3 times better than PVDF fibres in term of removing water from the feed, and 3–4 times better in term of energy saving. Results also showed that an increase of the feed inlet temperature from 25 to 40 °C improved the mass flux up to 6 times and energy efficiency (EE) up to 2.5 times depending on the feed concentration.

With flux up to 2.88 kg m⁻² h⁻¹ for PVDF and 5.83 kg m⁻² h⁻¹ for Halar fibres when concentrating 30% glucose solution at 40 °C, DCMD appeared to be an attractive concentration technique, when product quality is the priority. However, with EE from as low as 2.1–14.9%, PVDF fibres employed in the study seemed not to be very suitable for DCMD liquid food concentration under low temperature condition. DCMD in Halar fibres with EE up to 45.6% still encounters the challenge of energy and could only be cost competitive to osmotic distillation and evaporative concentration when cheaper energy sources or heat recovery measures are employed. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

The electroactivity of Pt₁Co₁(a/o)/C and Pt₃Cr₁(a/o)/C for the oxygen reduction reaction (ORR) in ethanol‐containing medium was studied. It was found that these cathodes present a high tolerance to this alcohol. The onset potential of the ORR decreased at 14 and 12 mV in the presence of 0.5 M ethanol on Pt₁Co₁/C and Pt₃Cr₁/C, respectively. The tolerance of the Pt alloys is one order of magnitude higher than that shown by Pt‐alone catalysts in previous works. Exceptionally, the Pt₁Co₁/C alloy maintained a very important electrocatalytic activity, i.e. a very small variation in current density at 400 mV in electrochemical cell measurements and improved performances in a direct ethanol fuel cell (DEFC). The current densities obtained from the DEFC equipped with a 10% Pt₁Co₁/C cathode were similar to those obtained when 20% Pt₃Cr₁/C was used. However, a higher performance in terms of Pt content was shown by PtCo/C. These electrochemical characteristics indicate the advantage of using PtCo alloys as cathodes in DEFCs. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

Studies have previously been done on efficacies of chitosan and zeolite in ammonium ion (NH₄⁺) removal. However, no study compares the adsorption performance of natural zeolite (NZ) and activated NZ (ANZ) with high molecular weight chitosan (HMWC) and low molecular weight chitosan (LMWC). Hence, this study investigates the potentials of NZ, ANZ, LMWC, and HMWC in NH₄⁺ removal. The characteristics of NZ, ANZ, LMWC, and HMWC such as functional groups, surface morphology, elemental composition, zeta potential, and particle size was also investigated. The deposition of NH₄⁺ on the surface of NZ and ANZ was confirmed with the absence of nitrogen by the adsorption spectrum of energy dispersive X‐ray (EDX) and supported by the presence of an Fourier transform infrared (FTIR) stretching band at ~3,500–3,300 cm⁻¹, as well as broader and less intense bands ~1,600 cm⁻¹ after the adsorption for all the adsorbents. The particle size of LMWC, HMWC, NZ, and ANZ were 98, 813, 22,354, and 9,826 nm, respectively. Meanwhile, after the activation process, the composition of O, Si, Al, Fe, Ca, and Na was reduced. NH₄⁺ batch adsorption was also studied. HMWC, NZ, and ANZ reached adsorption equilibrium at 15 h, meanwhile for LMWC, the equilibrium reached at t = 20 h. The adsorption capacity of LMWC, HMWC, NZ, and ANZ at an initial concentration of 50 mg/L was 0.769, 0.331, 2.162, and 2.937 mg/g, respectively.

The constant tightening of environmental regulations and the ongoing need to reduce operating costs have posed a challenge for the design of any chemical process. Process engineers use process simulators to help them perform calculations that will, ultimately, result in design parameters or operating conditions for a plant or process. Exergy is a potential indicator that can aid in the design of energy efficient chemical processes and plants. The exergy concept has been increasingly used as a tool to locate the critical energy use in many industrial processes, both chemical and non‐chemical. However, currently most process simulators in the market do not offer the capability of calculating the exergy of a process. An open‐source exergy calculator has been created by embedding the calculation procedure in an open‐source chemical process simulator. This improves process simulation by including a potential tool for design teams to quickly evaluate several process options in detail in order to understand their energy utilisation. A simple exergy analysis for a gas processing facility is used to demonstrate the capabilities of the tool. The analysis shows where the largest quantities of exergy are being consumed within the plant, thus pointing to areas where improvement in energy usage can be made. The use of exergy as a potential design and retrofit tool is also discussed. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

Many problems of process synthesis and design in chemical engineering can be modeled as mixed integer nonlinear programming (MINLP) problems. They include both the continuous (floating point) and integer variables. A common feature of this class of mathematical problems is the potential existence of nonconvexities due to a particular form of the objective function and/or the set of constraints. Owing to their combinatorial nature, these problems are considered to be difficult to solve. In the present study, a model based on an extension of conventional distillation is proposed for the synthesis of ethylene glycol using the nonequilibrium reactive distillation. The proposed model is simulated using the relaxation and homotopy‐continuation methods. The differential evolution (DE) algorithm is applied to find the minimum total annualized cost of the nonequilibrium reactive distillation for the synthesis of ethylene glycol, which is a MINLP optimization problem.

The optimization is performed with nonideal vapor–liquid equilibrium using ten strategies of DE, considering synthesis reaction on all trays. The results show that the optimized objective function values are better than those reported in the literature, and mostly independent of the number of trays and of the reaction distribution. It is shown that the proposed homotopy‐continuation method with DE strategy (DE/best/1/bin) is capable of providing optimized solutions which are close to the global optimum, and reveals its adequacy for the optimization of reactive distillation problems encountered in chemical engineering practice. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

Isolated energy systems seem to be a promising option for electrifying remote locations where grid extension is not feasible or economical. Integration of battery bank as means of energy storage with different renewable energy systems can enhance the system reliability and its overall performance. Therefore, appropriate choices of generator sizes and the battery bank capacity are critical to the success of such renewable‐based isolated power systems. In this article, the tools of pinch analysis are extended to design isolated renewable energy systems. The importance of setting targets before design is highlighted for designing renewable‐based isolated energy systems. The system sizing through the grand composite curve (GCC) representation of stored energy is proposed in this article. The set of all feasible solutions, defined as the design space for the system, is graphically represented for in‐depth visualization. The relation between the design space approach for designing and optimizing an isolated energy system and the principles of pinch analysis have been established in this article. The GCC representation also provides opportunity to the system designer for strategic load growth without affecting the system size. Copyright © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

The objective of this work was to perform simultaneous heat integration and the synthesis of biogas process based on the mixed‐integer nonlinear programming (MINLP) model. A synthesis model recently developed by Drobež et al. [R. Drobež, Z. Novak Pintarič, B. Pahor, Z. Kravanja. Chem. Biochem. Eng. Q, 2009; 23, 445–459] has been upgraded for simultaneous heat integration. An industrial case study was solved in order to describe the mathematical model and to illustrate the heat‐integrated MINLP synthesis approach. The optimal solution indicates that during the synthesis of biogas process and when selecting the best auxiliary facilities significant benefit can be obtained if the selected process and auxiliary facilities are heat integrated. In this way almost the complete consumption of hot utility and 1/3 of cold utility can be saved, and thus most of the electricity and heat produced in the cogeneration system from biogas can be sold as surplus to the distribution networks. The proposed optimal synthesis of heat‐integrated biogas process may improve a company's economic performance and significantly reduce its environmental impact by converting environmentally harmful organic and animal wastes into valuable products. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Bubble breakup in a four‐branched microchannel with carboxymethyl cellulose (CMC) solution was investigated by an improved coupled level set and volume of fluid (CLSVOF) method based on consideration of the rheological characteristic of the fluid. The validity of the numerical approach was satisfactorily verified by comparing with the experimental results. The regime and pattern of bubble breakup were evaluated by analyzing the evolution of bubble morphology. The effects of gas velocity, solution concentration, and subchannel width on daughter bubble length were examined, respectively. The results indicate that three split regimes at the branch comprising expansion, squeezing, and pinch‐off stage and three flow patterns including long slug, short slug, and bubble flows can be observed. Daughter bubble length increases with the gas velocity but decreases with the solution concentration. Particularly, the bubble length in the subchannel near the symmetry axis of main channel is always greater than that in the channel far from the axis. However, as the former channel shrinks, the bubble length in it will rapidly drop while the length in latter channel increases significantly. Finally, a scaling law to predict the daughter bubble length in two‐distanced channel is developed and agrees with the numerical results under present conditions.

Rotary cement kilns are widely used to convert calcineous raw meal into cement clinker, and are key components in the cement industry. In this article, we report a comprehensive computational fluid dynamics (CFD)‐based model to capture key transport processes in rotary cement kilns. Separate but coupled computational models were developed for the bed and the freeboard regions of the rotary kiln. The complex swirling airflow produced by kiln burners, coal combustion, gas‐phase combustion of volatile matter and radiative heat transfer in the freeboard region were modeled. The clinkerization reactions in the bed region were modeled assuming solids as pseudo fluids. Coating formation in cement kilns (for both bed and freeboard regions) was considered. Appropriate source and sink terms were developed to model transfer of CO₂ from the bed to the freeboard region due to calcination reaction in the bed region. The developed bed and freeboard models were coupled by mass and energy communication through common interface. These coupled computational models were able to quite satisfactorily predict the available data from industrial kilns and previously published results. The computational models were also able to capture the intricacies of the burning zones of rotary cement kilns for changing burner‐operational parameters like axial to swirl ratio and oxygen enrichment. The developed approach, computational models and simulation results will not only help in developing better understanding of cement kilns but also provide quantitative information about influence of burner design and other design parameters on kiln performance. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

In this study the CO₂ adsorption of three different diameters of multi‐walled carbon nanotubes (MWCNT) and single‐walled carbon nanotube (SWCNT) was investigated for a mixture of CO₂/Ar at a temperature of 70 °C and atmospheric pressure. The largest diameter of MWCNT showed the highest CO₂ uptake of 65.2 mg CO₂ adsorbed per g adsorbent. One of the MWCNTs were modified with urea (CH₄N₂O) under two different loading durations with the aim of improving adsorption capacity. After such a functionalization, the CO₂ uptake increased from 53.9 to 64.1 mg CO₂ adsorbed per g adsorbent after 4 h loading duration. These findings indicate considerable potential of functionalized carbon nanotubes in comparison with other silica and carbon adsorbents. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.