The use of carbon dioxide (CO₂) and calcium-containing by-products from industrial activities is receiving increasing interest as a route to valuable carbonate materials while reducing CO₂ emissions and saving natural resources. In this work, wet-chemical experimental data was assessed, which involved the carbonation of three types of materials in aqueous solutions, namely, 1) wollastonite, a calcium silicate mineral, 2) steelmaking slag, a by-product of steel production, and 3) paper bottom ash (PBA) from waste paper incineration. Aims were to achieve either a high carbonation degree and/or a pure carbonate product with potential commercial value. Producing a pure precipitated calcium carbonate (PCC) material that may find use in paper industry products puts strong requirements on purity and brightness. The parameters investigated were particle size, CO₂ pressure, temperature, solid/liquid ratio, and the use of additives that affect the solubilities of CO₂ and/or calcium carbonate. Temperatures and pressures were varied up to 180°C and 4 Mpa. Data obtained with the wollastinite mineral allowed for a comparison between natural resources and the industrial by-product materials, the latter typically being more reactive. With respect to temperature and pressure trends reported by others were largely confirmed, with temperatures above 150°C introducing thermodynamic limitations depending on CO₂ pressure. The influence of additives showed some promise, although costs may make recycling and reuse of additives a necessity for a large-scale process. When using steelmaking slag, magnetic separation may remove some iron-containing material from the process (although this is far from perfect), while the addition of bicarbonate supported the removal of phosphorous, aside from improving calcium extraction. The experiments with paper bottom ash (PBA) gave new data, showing that its reactivity resembles that of steelmaking slag, while its composition results in relatively pure carbonate product. Also, with PBA no additives were needed to achieve this.

Photocatalytic reduction of CO₂ on TiO₂ and Cu/TiO₂ photocatalysts was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under UV irradiation. The photocatalysts were prepared by sol-gel method via controlled hydrolysis of titanium (IV) butoxide. Copper precursor was loaded onto TiO₂ during sol-gel procedure. A large amount of adsorbed H₂O and surface OH groups was detected at 25°C on the TiO₂ photocatalyst after being treated at 500°C under air stream. Carbonate and bicarbonate were formed rapidly due to the reaction of CO₂ with oxygen-vacancy and OH groups, respectively, on TiO₂ surface upon CO₂ adsorption. The IR spectra indicated that, under UV irradiation, gas-phase CO₂ further combined with oxygen-vacancy and OH groups to produce more carbonate or bicarbonate. The weak signals of reaction intermediates were found on the IR spectra, which were due to the slow photocatalytic CO₂ reduction on photocatalysts. Photogenerated electrons merge with H⁺ ions to form H atoms, which progressively reduce CO₂ to form formic acid, dioxymethylene, formaldehyde and methoxy as observed in the IR spectra. The well-dispersed Cu, acting as the active site significantly increases the amount of formaldehyde and dioxymethylene, thus promotes the photoactivity of CO₂ reduction on Cu/TiO₂. A possible mechanism of the photocatalytic CO₂ reduction is proposed based on these intermediates and products on the photocatalysts.

In this paper, the effect of testing temperature on the performance of fixed carrier membrane for CO₂ separation were studied. The blend composite membranes were developed respectively with a blend of PEI-PVA (polyetheleneimine-polyvinyl alcohol) as separation layer and PS (polysulfone) ultrafiltration membranes as the substrates. The permselectivity of the membranes was measured with CO₂/CH₄ mixed gas. The effect of testing temperature on membrane separation performance was investigated. The results showed that both the permeances of CO₂ and CH₄ decreased with the increase of temperature, and the permeances decreased more quickly under low pressure than those under high pressure. At the feed pressure of 0.11MPa, the CO₂/ CH₄ selectivity of PEI-PVA/PS blend composite membrane reduced along with temperature increment. Under the feed pressure of 0.21MPa, as well as 1.11MPa, the selectivity decreased with the increase of temperature.

This work involves the production of magnesium in the form of Mg(OH)₂ from serpentinite rock (nickel mine tailing) material followed by conversion into MgCO₃ using a pressurised fluidised bed (PFB) reactor operating at 400°C–600°C and pressures up to 2.85MPa. Our approach is rooted in the thermodynamic fact that the reaction between Mg(OH)₂ and gaseous CO₂ forming MgCO₃ and water releases significant amounts of heat. The main problem is, however, the chemical kinetics; the reaction is slow and has to be accelerated in order to be used in an economically viable process for large-scale (~1Mt/a) CO₂ sequestration. We have constructed a lab-scale PFB reactor test-setup for optimising the carbonation reaction. At high enough temperatures and conversion levels the reaction should provide the heat for the proceeding Mg(OH)₂ production step, making the overall process energy neutral. So far we have been able to achieve a conversion degree of 26% at 500°C and 2.85MPa after 30min (particle size 125–212μm). In this paper the test facility and our latest results and progress on CO₂ mineral carbonation are summarised. Also, the possible integration of the iron as a feedstock for iron and steel production will be briefly addressed. An interesting side-effect of this carbon dioxide capture and storage (CCS) route is that significant amounts of iron are obtained from the serpentinite rock material. This is released during the Mg(OH)₂ production and can be of great interest to the iron- and steel producing sector, which at the same time is Finland’s largest CO₂ producer.

TiO₂-Al₂O₃ mixed oxides with different compositions ranging from 40wt-% to 95wt-% of TiO₂ were prepared by sol-gel method and impregnated with different amounts of VO_x. Supports and catalysts were characterized by X-ray diffraction (XRD), physisorption, temperature preprogrammed reduction (H₂-TPR), and ammonia temperature programmed desorption (NH₃-TPD). TiO₂ content in the support had obvious effect on the crystal structure, texture characteristic, acid property, and catalytic activity in dehydrogenation of ethylbenzene (EB) with carbon dioxide. The highest catalytic activity was acquired when the TiO₂ content was 50 wt-%.

A kind of new catalyst—carbonaceous catalyst—for CH₄-CO₂ reformation has been developed in our laboratory. The effect of both oxygen-bearing functional group such as phenolic hydroxyl, carbonyl, carboxyl, and lactonic, and ash such as Fe₂O₃, Na₂CO₃, and K₂CO₃ in the carbonaceous catalyst on the CH₄-CO₂ reforming has been investigated with a fixed-bed reactor. It has been found that the carbonaceous catalyst is an efficient catalyst on CO₂-CH₄ reforming. With the decrease of oxygen-bearing functional group, the catalytic activity of carbonaceous catalyst decreases quickly. The oxygen-bearing functional groups play a significant role in the carbonaceous-catalyzed CO₂-CH₄ reforming; the ash components in carbonaceous catalyst also have an important influence on the CO₂-CH₄ reforming. Fe₂O₃, Na₂CO₃, and K₂CO₃ in the ash can catalyze the CO₂-CH₄ reforming reaction; CaO has little effect on CO₂-CH₄ reforming reaction. CaO can catalyze the gasification between carbonaceous catalyst and CO₂; Al₂O₃ and MgO inhibit the CO₂-CH₄ reforming.

A kinetics model of CO₂ hydrogenation over iron-nickel catalysts was developed based on the detailed mechanism of alkenes re-adsorption and secondary reaction. The corresponding kinetical experiments are conducted in a continuous fixed bed reactor. The effect of reaction conditions on catalyst performance was analyzed according to the results of orthogonal experiments. The results of the experiments show that more methane in products can be obtained with iron-nickel catalysts, the trend of which is consistent with the thermodynamic analysis. However, the content of alkenes in products is equivalent with that of alkanes. This shows that the reaction is controlled by kinetics. In all, the results of the experiments also substantiate that the model can give a good representation of the reaction mechanism of CO₂ hydrogenation over iron-nickel catalysts. The parameters of this model give a better explanation for the question why the iron-nickel catalysts have a higher selectivity toward alkenes compared with other iron-based catalysts.

In this article, we present our research results on chemical fixation of CO₂ using organobismuth compounds. We fabricated bismuth biphenoate complex, Zn-Mg-Al composite oxides, and SBA-15 or Al-SBA-15 immobilized hydroxyl ionic liquid for CO₂ cycloaddition onto epoxides. The hypervalent bismuth compounds show good ability for association and dissociation with CO₂. The bismuth biphenolate complexes are catalytically effective for the cycloaddition reaction. The heterogeneous catalysts, viz. Zn-Mg-Al oxides and SBA-15 or Al-SBA-15 immobilized ionic liquid, are efficient for the synthesis of cyclic carbonate from CO₂ and epoxide. It is found that the presence of a trace amount of water can improve the catalytic activity of the immobilized ionic liquid.

If substantial amounts of CO₂, which according to actual scenarios may in the future be captured from industrial processes and power generation, shall be utilized effectively, scalable energy efficient technologies will be required. Thus, a survey was performed to assess a large variety of applications utilizing CO₂ chemically (e.g., production of synthesis-gas, methanol synthesis), biologically (e.g., CO₂ as fertilizer in green houses, production of algae), or physically (enhancement of fossil fuel recovery, use as refrigerant). For each of the processes, material and energy balances were set up. Starting with pure CO₂ at standard conditions, expenditure for transport and further process specific treatment were included. Based on these calculations, the avoidance of greenhouse gas emissions by applying the discussed technologies was evaluated. Based on the currently available technologies, applications for enhanced fossil fuel recovery turn out to be most attractive regarding the potential of utilizing large quantities of CO₂ (total capacity>1000 Gt CO₂) and producing significant amounts of marketable products on one hand and having good energy and material balances on the other hand (). Nevertheless, large scale chemical fixation of CO₂ providing valuable products like fuels is worth considering, if carbon-free energy sources are used to provide the process energy and H₂ being essential as a reactant in a lot of chemical processes (e.g., production of DME: ). Biological processes such as CO₂ fixation using micro-algae look attractive as long as energy and CO₂ balance are considered. However, the development of effective photo-bioreactors for growing algae with low requirements for footprint area is a challenge.

A significant proportion of power generation stems from coal-combustion processes and accordingly represents one of the largest point sources of CO₂ emissions worldwide. Coal power plants are major assets with large infrastructure and engineering units and an operating life span of up to 50 years. Hence, any process design modification to reduce greenhouse gas emissions may require significant investment. One of the best options to utilize existing infrastructure is to retrofit the power station fleet by adding a separation process to the flue gas, a practice known as postcombustion capture (PCC). This review examines the recent PCC development and provides a summary and assessment of the state of play in this area and its potential applicability to the power generation industry. The major players including the various institutes, government, and industry consortia are identified along with flue gas PCC demonstration scale plants. Of the PCC technologies reviewed, amine-based absorption is preeminent, being both the most mature and able to be adapted immediately, to the appropriate scale, for power station flue gas with minimal technical risk. Indeed, current commercial applications serve niches in the merchant CO₂ market, while a substantial number of smaller scale test facilities are reported in the literature with actual CO₂ capture motivated demonstrations now commencing. Hybrid membrane/absorption systems, also known as membrane contactors, offer the potential for the lowest energy requirements, possibly 10% of current direct scrubbers but are at an early stage of development. Other methods being actively pursued as R&D projects include solid absorbents, solid adsorbents, gas membrane separators, and cryogenic separation. The variety and different maturities of these competing technologies make technical comparison largely subjective, but useful insights could be gained through the development and application of econometric techniques such as ‘real options’ within this context. Despite these limitations, it is clear from this review that amine scrubbing is likely to be adapted first into the existing power station fleet, while less mature technologies will grow and become integrated with the development of future power stations.

The current studies on power plant technologies suggest that Integrated Gasification Combined Cycle (IGCC) systems are an effective and economic CO₂ capture technology pathway. In addition, the system in conventional configuration has the advantage of being more “CO₂ capture ready” than other technologies. Pulverized coal boilers (PC) have, however, proven high technical performance attributes and are economically often most practical technologies. To highlight the pros and cons of both technologies in connection with an integrated CO₂ capture, a comparative analysis of ultrasupercritical PC and IGCC is carried out in this paper. The technical design, the mass and energy balance and the system optimizations are implemented by using the ECLIPSE chemical plant simulation software package. Built upon these technologies, the CO₂ capture facilities are incorporated within the system. The most appropriate CO₂ capture systems for the PC system selected for this work are the oxy-fuel system and the postcombustion scheme using Monoethanolamine solvent scrubber column (MEA). The IGCC systems are designed in two configurations: Water gas shift reactor and Selexol-based separation. Both options generate CO₂-rich and hydrogen rich-gas streams. Following the comparative analysis of the technical performance attributes of the above cycles, the economic assessment is carried out using the economic toolbox of ECLIPSE is seamlessly connected to the results of the mass and energy balance as well as the utility usages. The total cost assessment is implemented according to the step-count exponential costing method using the dominant factors and/or a combination of parameters. Subsequently, based on a set of assumptions, the net present value estimation is implemented to calculate the breakeven electricity selling prices and the CO₂ avoidance cost.

With the rapid expansion of the global motor vehicle population, the transportation sector has taken up a growing proportion among all the carbon dioxide emission-related sectors. To contribute to solutions of the carbon dioxide-oriented problem in transportation, this paper proposes the “ALL FREE” concept that applies partial oxidation process instead of the conventional complete oxidation to vehicle engines. In such an engine, the fuels are partially oxidized into corresponding chemical products, which, as a result, enable the process to be theoretically free of CO₂, while the heat output of the partial oxidation could drive the vehicle. On the other hand, the resulting products are of great value, which could decrease or even counteract the cost of fuels in transportation. In this paper, the thermodynamic and kinetic data (e.g., the heat output and heat release rate) of five selected partial oxidation reactions were calculated at length to demonstrate and exemplify the theoretical feasibility of the “ALL FREE” concept. It turned out that the partial oxidation of n-butane to maleic anhydride has the most potential to meet the basic requirements of this concept. To sum up, this design concept is of significant application potential for the reduction of CO₂ emissions in the transportation industry, although there remain many technical challenges.

The syntheses of carbon dioxide (CO₂) based industrially important chemicals have gained considerable interest in view of the sustainable chemistry and “green chemistry” concepts. In this review, recent developments in the chemical fixation of CO₂ to valuable chemicals are discussed. The synthesis of five-member cyclic carbonates via, cycloaddition of CO₂ to epoxides is one of the promising reactions replacing the existing poisonous phosgene-based synthetic route. This review focuses on the synthesis of cyclic carbonates, vinyl carbamates, and quinazoline-2,4(1H,3H)-diones via reaction of CO₂ and epoxide, amines/phenyl acetylene, 2-aminobenzinitrile and other chemicals. Direct synthesis of dimethyl carbonate, 1,3-disubstituted urea and 2-oxazolidinones/2-imidazolidinones have limitations at present because of the reaction equilibrium and chemical inertness of CO₂. The preferred alternatives for their synthesis like transesterification of ethylene carbonate with methanol, transamination of ethylene carbonate with primary amine and transamination reaction of ethylene carbonate with diamines/β-aminoalcohols are discussed. These methodologies offer marked improvements for greener chemical fixation of CO₂ in to industrially important chemicals.

This paper presents an attempt to develop a new system for fixing carbon dioxide from the atmosphere. The proposed molecular system has been designed to have the capacity to spontaneously bind CO₂ from the atmosphere with high affinity. The molecular system is furthermore designed to have the ability to liberate CO₂ at a later stage in the process, i.e., in a separate compartment. The liberated CO₂ presents a carbon neutral way of obtaining pure CO₂. The proposed molecular system is based on a small stable organic molecule that potentially have two forms: one without bound CO₂ and one with bound CO₂. One class of molecules that undergo a reaction compatible with our purposal is the merocyanine dyes that exhibit photochromic properties. Based on this structural class of molecules, a system for the potential fixing of CO₂ has been developed.