Volume 31, Issue 4

The continued great dependency on fossil fuels entails increasing SO 2 emissions to the atmosphere, with damaging consequences to both the local environment and the global climate. Thus, during the last years, the tightening of emission control policies has fostered the research over more efficient and sustainable removal technologies. The aim of this review is to present, as extensive as feasible, the origin and development of flue gas desulfurization (FGD) technology, especially of the wet type, using alkaline agents. From the early findings of the harmful effects of SO 2 to the gradual establishment of the current legislations worldwide, the deployment of FGD technology has been supported on understanding the mechanism of reaction and the nature of the desulfurization process, giving place to several configurations. A special analysis was made to the limestone/lime method as well as to the magnesium-based process, highlighting the main features and advances. The use of alternative absorbents is also presented along with a comprehensive analysis on the parameters and control variables affecting the process as well as on the management of residues and solid wastes.

A general review on correlations to evaluate mass transfer coefficients in liquid-liquid was conducted in this work. The mass transfer models can be classified into continuous and dispersed phase coefficients. The effects of drop size and interfacial area on mass transfer coefficient were investigated briefly. Published experimental results for both continuous and dispersed phase mass transfer coefficients through different hydrodynamic conditions were considered and the results were compared. The suitability and drawbacks of these correlations depend on the operating conditions and hydrodynamics. Although the results of these models are reasonably acceptable, they could not properly predict the experimental results over a wide range of designs and operating conditions. Therefore, proper understanding of various factors affecting mass transfer coefficient needs to be further extended.

Most of the oleochemical industries use glycerol as raw material for its adverse commercial applications in various fields. In spite of many available methods to produce glycerol from tallow, hydrolysis is one of the most feasible and widely used methods that draw the attention of doing more research for ensuring the safe operation, production level improvement, and accuracy of the synthesis process. The synthesis using biochemical methods in immobilized packed column lacks fastness compared to that of chemical means, which is enriched with more research problems. To attain inherent safety, improved process control methods need to be designed, which requires the knowledge of transient dynamics and sensitivity analysis of the process. This paper gives a state-of-the-art review of experimental analysis, mathematical modeling, parametric identification, and integrated control systems using sensors, actuators, and respective multiloop controllers for the production of glycerol and fatty acids from tallow fat through chemical/biochemical hydrolysis.

Fruit peel waste (FPW) is abundantly available from the agricultural and food processing industry and has been studied in recent past as an adsorbent. This paper critically reviews the reported work and investigates various FPW-pollutant systems. The study includes statistics of FPW generation, modification, characterization, adsorption ability, recovery/regeneration, and modeling (isotherms, kinetics, and thermodynamics) of batch adsorption. It is found that orange and banana peels are the most extensively studied adsorbents, whereas Pb 2+ and methylene blue are the most efficiently removed pollutants, the Langmuir and Freundlich adsorption isotherms provide the best fit in most of the cases, and in general, pseudo-second-order kinetics is followed. There are very limited column studies and no report on commercial plant. Though the reproducibility of the results is poor, FPW has a great potential in the wastewater treatment due to its abundant and cheap availability. FPW can be used for removal of heavy metals and dyes; however, removal of organic and gaseous impurities needs further investigation.

Concern has increased about climate change caused by carbon dioxide (CO 2 ) emissions through human activities in recent years. The Intergovernmental Panel on Climate Change predicts a 1.9°C rise in temperature by the year 2100, and this means a reduction in CO 2 is vital for human beings and all other life on earth. Therefore, there is an urgent need for the development of CO 2 separation processes to mitigate this potential problem. Post-combustion power plants can employ various types of separation technology. Among them, chemical absorption using aqueous amine is more developed and more reliable. The conventional solvents used in the chemical absorption process together with the use of absorbents, ionic liquid, alkanolamines and their blended aqueous solutions are reviewed in this work. Different ionic liquid-based solvents for CO 2 absorption and the most effective parameters on mass transfer phenomena between CO 2 and solvent are reviewed. The major concerns for this technology, including the physiochemical properties of ionic liquid-based solvents, Henry’s constant and mass transfer coefficient and their correlations, and various factors for effective CO 2 absorption, are addressed.