Post-combustion CO2 capture from the flue gas is one of the key technology options to reduce greenhouse gases, because this can be potentially retrofitted to the existing fleet of coal-fired power stations. Adsorption processes using solid sorbents capable of capturing CO2 from flue gas streams have shown many potential advantages, compared to other conventional CO2 capture using aqueous amine solvents. In view of this, in the past few years, several research groups have been involved in the development of new solid sorbents for CO2 capture from flue gas with superior performance and desired economics. A variety of promising sorbents such as activated carbonaceous materials, microporous/mesoporous silica or zeolites, carbonates, and polymeric resins loaded with or without nitrogen functionality for the removal of CO2 from the flue gas streams have been reviewed. Different methods of impregnating functional groups, including grafting techniques and modifying the support materials, have been discussed to en...

Post-Combustion CO2 Capture Using Solid Sorbents: A Review

A Cook's tour is presented of the organosulfur chemistry of the genus Allium, as represented, inter alia, by garlic (Allium sativum L.) and onion (Allium cepa L.). We report on the biosynthesis of the S-alk(en)yl-L-cysteine S-oxides (aroma and flavor precursors) in intact plants and on how upon cutting or crushing the plants these precursors are cleaved by allinase enzymes, giving sulfenic acids—highly reactive organosulfur intermediates. In garlic, 2-propenesulfenic acid gives allicin, a thiosulfinate with antibiotic properties, while in onion 1-propenesulfenic acid rearranges to the sulfine (Z)-propanethial S-oxide, the lachrymatory factor (LF) of onion. Highlights of onion chemistry include the assignment of stereochemistry to the LF and determination of the mechanism of its dimerization; the isolation, characterization, and synthesis of thiosulfinates which most closely duplicate the taste and aroma of the freshly cut bulb, and additional unusual compounds such as zwiebelanes (dithiabicyclo[2.1.1]hexanes), a bis-sulfine (a 1,4-butanedithial S,S′-dioxide), antithrombotic and antiasthmatic cepaenes (α-sulfinyl disulfides), and vic-disulfoxides. Especially noteworthy in the chemistry of garlic are the discovery of ajoene, a potent antithrombotic agent from garlic, and the elucidation of the unique sequence of reactions that occur when diallyl disulfide, which is present in steam-distilled garlic oil, is heated. Reaction mechanisms under discussion include [3, 3]- and [2, 3]-sigma-tropic rearrangements involving sulfur (e.g. sulfoxide-accelerated thio- and dithio-Claisen rearrangements) and cycloadditions involving thiocarbonyl systems. In view of the culinary importance of alliaceous plants as well as the unique history of their use in folk medicine, this survey concludes with a discussion of the physiological activity of the components of these plants: cancer prevention, antimicrobial activity, insect and animal attractive/repulsive activity, olfactory–gustatory–lachrymatory properties, effect on lipid metabolism, platelet aggregation inhibitory activity and properties associated with ajoene. And naturally, comments about onion and garlic induced bad breath and heartburn may not be overlooked.

The Organosulfur Chemistry of the Genus Allium – Implications for the Organic Chemistry of Sulfur

The analysis of onion and garlic.

Supercritical CO2 extraction of essential oils is one of the most widely discussed applications in the supercritical fluid literature. Nevertheless, a comprehensive overview of the analytical, processing and modeling aspects has never been attempted. This is partly due to the difficulties involved in isolating essential oils from the other products which supercritical CO2 can dissolve. Moreover, only a limited number of studies provide quantitative data on the parameters governing this process.

In this review, solubility data on pure compounds belonging to essential oils are analyzed. Processes proposed to isolate and fractionate essential oils by supercritical CO2 and the corresponding modelling aspects are discussed critically.

Supercritical fluid extraction and fractionation of essential oils and related products

Upcoming bio-refineries will be at the heart of the manufacture of future transportation fuels, chemicals and materials. A narrow number of platform molecules are envisioned to bridge nature's abundant polysaccharide feedstock to the production of added-value chemicals and intermediate building blocks. Such platform molecules are well-chosen to lie at the base of a large product assortment, while their formation should be straightforward from the refined biomass, practical and energy efficient, without unnecessary loss of carbon atoms. Lactic acid has been identified as one such high potential platform. Despite its established fermentation route, sustainability issues – like gypsum waste and cost factors due to multi-step purification and separation requirements – will arise as soon as the necessary orders of magnitude larger volumes are needed. Innovative production routes to lactic acid and its esters are therefore under development, converting sugars and glycerol in the presence of chemocatalysts. Moreover, catalysis is one of the fundamental routes to convert lactic acid into a range of useful chemicals in a platform approach. This contribution attempts a critical overview of all advances in the field of homogeneous and heterogeneous catalysis and recognises a great potential of some of these chemocatalytic approaches to produce and transform lactic acid as well as some other promising α-hydroxy acids.

Lactic acid as a platform chemical in the biobased economy: the role of chemocatalysis

Introductory Chemical Engineering Thermodynamics

Adsorption of carbon dioxide near its critical point on DeGussa IV activated carbon is investigated in this study. A volumetric method was used to measure the adsorption/desorption isotherms at 284, 300, 305, 310, and 314 K over a large pressure range. At subcritical temperatures, adsorption isotherms display a discontinuity at the vapor pressure of carbon dioxide, and desorption hysteresis is observed. However, there is no desorption hysteresis if adsorption is terminated before vapor−liquid transition occurs. At supercritical temperatures, adsorption isotherms display a plateau, and the excess decreases beyond the critical pressure. No hysteresis occurs during the desorption process. The adsorption isotherms can be represented very well by the simplified local density model.

Adsorption and Desorption of Carbon Dioxide onto and from Activated Carbon at High Pressures

Physical adsorption of high-pressure fluids onto solids is of interest in the transportation and storage of fuel and radioactive gases; the separation and purification of lower hydrocarbons; solid-phase extractions; adsorbent regenerations using supercritical fluids; supercritical fluid chromatography; and critical point drying. A mean-field model is developed that superimposes the fluid-solid potential on a fluid equation of state to predict adsorption on a flat wall from vapor, liquid, and supercritical phases. A van der Waals-type equation of state is used to represent the fluid phase, and is simplified with a local density approximation for calculating the configurational energy of the inhomogeneous fluid. The simplified local density approximation makes the model tractable for routine calculations over wide pressure ranges. The model is capable of prediction of Type 2 and 3 subcritical isotherms for adsorption on a flat wall, and shows the characteristic cusplike behavior and crossovers seen experimentally near the fluid critical point.

Simplified local density model for adsorption over large pressure ranges

The reaction kinetics of the reversible esterification reaction of succinic acid with ethanol to form monoethyl and diethyl succinate are presented. The reaction was studied in batch isothermal experiments catalyzed by macroporous Amberlyst-15 ion-exchange resin. Experimental data were obtained between 78 and 120 °C at different mole ratios of ethanol to succinic acid and at ion-exchange resin catalyst concentrations from 1 to 5 wt % of solution. Kinetic modeling was performed using a pseudohomogeneous mole fraction model which acceptably fits the experimental data. The kinetic model is useful for the design and simulation of processes such as reactive distillation for diethyl succinate formation.

Carl T. Lira

Papers

Introductory Chemical Engineering Thermodynamics

Adsorption and Desorption of Carbon Dioxide onto and from Activated Carbon at High Pressures

Simplified local density model for adsorption over large pressure ranges

Reaction Kinetics for the Heterogeneously Catalyzed Esterification of Succinic Acid with Ethanol

Oligomer distribution in concentrated lactic acid solutions