The increase in atmospheric carbon dioxide is linked to climate changes; hence there is an urgent need to reduce the accumulation of CO2 in the atmosphere. The utilization of CO2 as a raw material in the synthesis of chemicals and liquid energy carriers offers a way to mitigate the increasing CO2 buildup. This review covers six important CO2 transformations namely: chemical transformations, photochemical reductions, chemical and electrochemical reductions, biological conversions, reforming and inorganic transformations. Furthermore, the vast research area of carbon capture and storage is reviewed briefly. This review is intended as an introduction to CO2, its synthetic reactions and their possible role in future CO2 mitigation schemes that has to match the scale of man-made CO2 in the atmosphere, which rapidly approaches 1 teraton.

The teraton challenge. A review of fixation and transformation of carbon dioxide

In recent years, Carbon Capture and Storage (Sequestration) (CCS) has been proposed as a potential method to allow the continued use of fossil-fuelled power stations whilst preventing emissions of CO2 from reaching the atmosphere. Gas, coal (and biomass)-fired power stations can respond to changes in demand more readily than many other sources of electricity production, hence the importance of retaining them as an option in the energy mix. Here, we review the leading CO2 capture technologies, available in the short and long term, and their technological maturity, before discussing CO2 transport and storage. Current pilot plants and demonstrations are highlighted, as is the importance of optimising the CCS system as a whole. Other topics briefly discussed include the viability of both the capture of CO2 from the air and CO2 reutilisation as climate change mitigation strategies. Finally, we discuss the economic and legal aspects of CCS.

Carbon capture and storage update

Beyond Oil and Gas: The Methanol Economy

Climate change and fossil fuel depletion are the main reasons leading to hydrogen technology. There are many processes for hydrogen production from both conventional and alternative energy resources such as natural gas, coal, nuclear, biomass, solar and wind. In this work, a comparative overview of the major hydrogen production methods is carried out. The process descriptions along with the technical and economic aspects of 14 different production methods are discussed. An overall comparison is carried out, and the results regarding both the conventional and renewable methods are presented. The thermochemical pyrolysis and gasification are economically viable approaches providing the highest potential to become competitive on a large scale in the near future while conventional methods retain their dominant role in H2 production with costs in the range of 1.34–2.27 $/kg. Biological methods appear to be a promising pathway but further research studies are needed to improve their production rates, while the low conversion efficiencies in combination with the high investment costs are the key restrictions for water-splitting technologies to compete with conventional methods. However, further development of these technologies along with significant innovations concerning H2 storage, transportation and utilization, implies the decrease of the national dependence on fossil fuel imports and green hydrogen will dominate over the traditional energy resources.

A comparative overview of hydrogen production processes

Progress and recent trends in biofuels

Methanol synthesis from carbon dioxide, water and nuclear fusion energy is extensively investigated. The entire system is analyzed from the point of view of process design of various processes. The main potential advantage of a fusion reactor (CTR) for this purpose is that it provides a large source of low cost, environmentally acceptable electric power based on an abundant fuel source. Carbon dioxide is obtained by extraction from the atmosphere or from sea water. Hydrogen is obtained by electrolysis of water. Methanol is synthesized by the catalytic reaction of carbon dioxide and hydrogen. The water electrolysis and methanol synthesis units are considered to be technically and commercially available. The benefit of using air or sea water as a source of carbon dioxide is to provide an essentially unlimited renewable and environmentally acceptable source of hydrocarbon fuel. Extraction of carbon dioxide from the atmosphere also allows a high degree of freedom in plant siting. The significant contribution of the present study is the evaluation of various methods of separation of carbon dioxide from air or sea water. Eight different methods of extraction of carbon dioxide from air are analyzed: (1) absorption and stripping of air by water at atmospheric pressure, (2) absorption and stripping of air by water at atmospheric pressure with a cooling tower as part of the absorption unit, (3) absorption and stripping of air by water at higher pressure, 20 atm, (4) absorption and stripping of air by methanol at 20 atm and −80°F, (5) removal of water vapor by adsorption on molecular sieves and subsequent extraction of carbon dioxide by refrigeration, (6) removal of water vapor by compression refrigeration and subsequent extraction of carbon dioxide by refrigeration, (7) absorption and stripping of air by a dilute aqueous potassium carbonate solution, and (8) removal of water vapor by adsorption on molecular sieves and adsorption/desorption of carbon dioxide from dry air by molecular sieves. A method of stripping of carbon dioxide from sea water is also presented. In order to compare these newly developed methods for CO2 separation with other conventional non-fossil sources of carbon, the calcination of limestone is also examined. For the extraction of carbon dioxide from air, the process of absorption/stripping of air by dilute potassium carbonate solution is found to require the least amount of energy. The total energy required for methanol synthesis from these sources of carbon dioxide is 3.90 kWh(e)/1b methanol of which 90% is used for generation of hydrogen. The process which consumes the greatest amount of energy is the absorption/stripping of air by water at high pressure and amounts to 13.2 kWh(e)/1b methanol. A subsequent paper will consider the important topic of economic evaluation.

Production of synthetic methanol from air and water using controlled thermonuclear reactor power—I. technology and energy requirement

A new complete solution for laminar flow with axial diffusion and first-order homogeneous and wall reactions in a tube is presented. The solution is in terms of an eigenfunction series expansion. Effects of axial diffusion, homogeneous reaction, and wall reaction on the concentration field are discussed. Comparison of the simplified results derived from the present analysis by neglecting axial diffusion and wall reaction with those of previous workers shows good agreement. Conditions are established for the necessity of applying the present results to describe the system accurately. 11 figures.

Convective diffusion with homogeneous and heterogeneous reactions in a tube

Quantitative relationships between chemical kinetics and differential thermal analysis (DTA) curves are studied for the reactions which follow the general rate expression: r = r/sub 0/e/sup -E/RT/(1 - x). Both the frequency factor and the activation energy can be derived from a single DTA curve. From the known kinetic parameters, the DTA curve can also be predicted. The rather simple models developed in this work have been tested by the oxidation reaction of nuclear graphite with CO/sub 2/ and by data in the literature on the thermal dehydration of clays. The results are satisfactory considering the complexities involved in DTA.

Meyer Steinberg

Papers

Production of synthetic methanol from air and water using controlled thermonuclear reactor power—I. technology and energy requirement

Convective diffusion with homogeneous and heterogeneous reactions in a tube

Reaction kinetics and differential thermal analysis

Preliminary design and analysis of recovery of lithium from brine with the use of a selective extractant

The Hy-C process (thermal decomposition of natural gas) potentially the lowest cost source of hydrogen with the least CO2 emission