A review of chemical absorption of carbon dioxide for biogas upgrading

Increasing energy demand in the world leads to more electricity generation mainly at fossil fuel power plants. Greenhouse gases are thus produced and mostly emitted to the atmosphere directly, resulting in global warming and climate change. Carbon dioxide is believed to be a main pollutant among greenhouse gases responsible from global warming. Conventional systems using mostly amine solutions to capture carbon dioxide at the source have some disadvantages, and alternatives are constantly being searched. In this work, a benign system of aqueous calcium acetate solution was investigated for this purpose. Calcium acetate is easy to produce, relatively cheap, environmentally friendly, nonhazardous, and noncorrosive. These properties make it a great alternative for use in capturing carbon dioxide. This absorption process is accompanied by chemical reaction. Therefore, the reaction kinetics needs to be investigated before its use in absorbers. A stirred cell reactor was used in the experiments using aqueous calcium acetate solution of different concentrations (2‐20% w/w) and different carbon dioxide concentrations in gas mixtures (4.5‐100% v/v dry carbon dioxide) at temperatures ranging from 286 to 352 K. The Gibbs free energy change for the overall reaction between carbon dioxide and aqueous calcium acetate solution was found to be –2.75 kJ/mol that shows the reaction is exergonic and occurs spontaneously. It was also found out that the reaction is pseudo–first order with respect to carbon dioxide which was also proven by calculating the Hatta number. Activation energy and Arrhenius (frequency) constant were also determined experimentally.

Hydrodynamic analogy approach for modelling reactive absorption

Hitherto, boric is suggested and used as a promoter or catalyst for carbon dioxide capture in various chemical absorption reactions, such as, absorption by aqueous potassium carbonate solution to increase mass transfer rate. But in this study, a single step termolecular reaction mechanism is suggested for the chemical absorption of carbon dioxide directly by boric acid and water. The reaction thermochemistry and reaction kinetics for termolecular mechanism are investigated by using density functional theory calculations at the B3LYP/6-31G(d) level of theory by taking into account of the implicit solvent effects of water through the polarizable continuum model and dispersion corrections. The findings obtained from theoretical calculations indicate that it is possible to capture carbon dioxide with boric acid in the form of B(OH) 2 OCOOH.

Flexible Operation of the Potassium Taurate Solvent Absorption Section for CO2 Removal in a Coal-Fired Power Plant

Hydrogen is getting increasing attention as a medium for energy storage, and sodium borohydride is accepted as a suitable carrier for hydrogen. The main product of the process by means of which hydrogen is produced from sodium borohydride is sodium metaborate. Our aim was to find an alternative use for sodium metaborate and specifically investigating the feasibility to use it for carbon dioxide capture from flue gases. The products of this chemical absorption are sodium carbonate, sodium bicarbonate and boric acid, all of which are industrially important chemicals. A bubble column was used in the experiments. Oxygen desorption technique was employed to determine the liquid side physical mass transfer coefficient. Chemical mass transfer coefficient was determined by absorption of carbon dioxide from its mixture with nitrogen into sodium metaborate solution. Enhancement factor was then calculated and a correlation was developed for it.

Carbon dioxide was absorbed into non-aqueous solvents such as methanol, ethanol, n-propanol, n-butanol, ethylene glycol, propylene glycol, and propylene carbonate, and into water in a stirred semi-batch tank with a planar gas-liquid interface at 298 K and 101.3 kPa. Triethanoamine (TEA) was used as a reactant with carbon dioxide. The reaction rate constants of the reaction between carbon dioxide and TEA were estimated by the mass transfer mechanism, which was accompanied by a fast pseudo-first-order reaction. An empirical correlation between the reaction rate constants and the solubility parameter of the solvent is presented. In non-aqueous solutions of TEA, dissolved carbon dioxide is expected to react with solvated TEA to produce an ion pair.

Carbon dioxide was absorbed into the phenyl glycidyl ether (PGE) solution within a range of 0–2.0 kmol/m3 in a stirred batch tank with a planar gas-liquid interface at 333–363 K and 101.3 kPa. Trihexylamine-immobilized on chloropropyl-functionalized MCM-41 (THA-CP-MS41) was used as a mesoporous catalyst, dispersed in organic liquid for the reaction between carbon dioxide and PGE. The measured absorption rates were analyzed to obtain the reaction kinetics of the consecutive chemical reactions which consisted of two steps using the mass transfer mechanism based on film theory. The overall reaction kinetics, analyzed with the pseudo-first-order reaction constant in the consecutive reaction model, was equivalent to the consecutive reaction kinetics. Effects of polar solvent, such as N, N-dimethylacetamide, N-methyl-2-pyrrolidinone, and dimethyl sulfoxide, on the reaction rate constants were observed using the solubility parameter of the solvent.

CP-MS41 was synthesized by hydrolysis of tetraorthosilicate, as a silicon source, with 3-chloropropyltriethoxysilane as an organosilane using cetyltrimethylammonium bromide as a template. ID-CP-MS41 was synthesized by immobilization of imidazole on the CP-MS41 and was dispersed in organic liquid as a mesoporous catalyst for the reaction between carbon dioxide and oxirane. Phenyl glycidyl ether and glycidyl methacrylate were used as oxiranes. Carbon dioxide was absorbed into the oxirane solution in a stirred batch tank with a planar gas-liquid interface within a range of 0–2.0 kmol/m3 of oxirane and 333–363 K at 101.3 kPa. The measured values of absorption rate were analyzed to obtain the reaction kinetics using the mass transfer mechanism associated with the chemical reactions based on the film theory. The overall reaction of CO2 with oxirane, which is assumed to consist of two steps-i) a reversible reaction between oxirane (B) and catalyst of ID-CP-MS41 (QX) to form an intermediate complex (C1), and ii) irreversible reaction between C1 and CO2 to form QX and five-membered cyclic carbonate (C)-was used to obtain the reaction kinetics through the pseudo-first-order reaction model. Polar solvents such as N, N-dimethylacetamide, Nmethyl-2-pyrrolidinone, and dimethyl sulfoxide affected the reaction rate constants.

Chemical absorption and CO2 biofixation via the cultivation of Spirulina in semicontinuous mode with nutrient recycle

Chemical absorption of carbon dioxide into aqueous elastic xanthan gum solution containing NaOH

The search for improved CO2 capture solvents can be accelerated by deploying computer-aided molecular and process design (CAMPD) techniques to explore large molecular and process domains systematically. However, the direct solution of the integrated molecular-process design problem is very challenging as nonlinear interactions between physical properties and process performance render a large proportion of the search space infeasible. We develop a methodology that enables the direct and reliable solution of CAMPD for absorption–desorption processes, using the state-of-the-art SAFT-γ Mie group contribution approach to predict phase and chemical equilibria. We develop new feasibility tests and show them to be highly efficient at reducing the search space, integrating them in an outer-approximation algorithm. The framework is applied to design an aqueous solvent and CO2 chemical absorption–desorption process, with 150 CAMPD instances across three case studies solved successfully. The optimal solvents are more promising than those obtained with sequential molecular design approaches.

Overall mass transfer coefficients for physical desorption and chemical absorption of carbon dioxide in annular and dispersed two‐phase flow in a 1‐in. horizontal pipe have been measured. These coefficients have been correlated with gas and liquid flow rates and with the normality of the sodium hydroxide solutions used.A new method of analysis was used to separate overall coefficients into individual gas and liquid film coefficients. Penetration theory equations were used to calculate the effective inter‐facial surface area and the penetrotion contact time. Changes in these variables have been explained in terms of the changes in flow pattern.

A review: Desorption of CO2 from rich solutions in chemical absorption processes

Chemical absorption of carbon dioxide from flue or natural gas in hollow-fiber membrane contactors (HFMCs) has been one of the most beneficial techniques to alleviate its emission into the environment. A theoretical research study was done to investigate the change in membrane specifications and operating conditions on CO2 absorption using different alkanolamine solvents. The mathematical model was developed for a parallel counter-current fluid flow through a HFMC. The developed model’s equations were solved based on finite element method. The simulations revealed that the increase in membrane porosity, length and the number of fibers has a positive impact on CO2 removal, while the gas flow rate and tortuosity enhancement resulted in the reduction of CO2 absorption. Furthermore, it was found that 4-diethylamino-2-butanol (DEAB) with approximately 100% CO2 absorption is suggested as the best solvent in this system, but ethyl-ethanolamine (EEA) with only 46% CO2 absorption had the lowest capacity for CO2 absorption (DEAB>MEA>EDA>MDEA>TEA>EEA). It is worth pointing out that the CO2 absorption can be improved using EEA solvent via change in membrane specifications such as increase in membrane porosity, length and the number of fibres.

There are different measures to tackle the challenge of Climate Change. This includes weather modification techniques and climate engineering (CE). Especially the application of CE is very controversial. In this connection, one has to differentiate between carbon dioxide removal (CDR) techniques and solar radiation management (SRM) techniques. According to climate experts, CDR techniques – except from the controversial CO2 sequestration and some other risky CDR techniques – interfere less aggressively into the natural environment than SRM techniques. Additionally, CDR puts on the causes of Climate Change, whereas SRM merely treats the symptoms. Apart from possible negative side effects, environmental modification techniques and CE might also be abused and have already been abused for covert weather warfare or terrorism by the deliberate aggravation or creation of extreme weather patterns and natural disasters like droughts, blizzards, floods, and storms with the intention to cause property damages, health problems, injuries, or even fatalities in certain areas or nations to harm the enemy. Although weather and climate modification for military or other hostile purposes are expressly prohibited by the UN’s 1977 ENMOD Convention, this UN convention is repeatedly circumvented. In fact – additionally to the inadvertent anthropogenic climate change – deliberate anthropogenic Climate Change seems to be feasible nowadays by the use of existing technology, allowing a range of possibilities for targeted large-scale anthropogenic modification and manipulation of the weather and possibly even the climate.