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

Abstract

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.