Carbon Dioxide Utilization: Greening Both the Energy and Chemical Industry: An Overview

摘要

Carbon dioxide is the most abundant waste produced by human activities. Its further accumulation in the atmosphere must be avoided in order to prevent risky situations derived by the reinforcement of the greenhouse effect, to which CO_2 is estimated to be the major contributor. The energy production short- and medium-term scenarios, demonstrate that fossil fuels will be the major energy source for the coming 30-40 years. Therefore, our Society has to cope with the increase of the carbon dioxide emission, if more energy has to be used for ameliorating the standard of life of emergent and developing country populations. New technologies for carbon dioxide control are necessary, that imply its recovery from various sources. Effective separation technologies are available, and their cost is known to depend upon the concentration and quality of the source gas, and the required efficacy of separation. Also, the end use of recovered carbon dioxide depends on its quality. For example, use for the food (drink) sector, demands carbon dioxide characterized by a high degree of purity, without toxic pollutants. Only selected, pure sources can, thus, be used to this end. Supercritical carbon dioxide is now finding larger and larger utilization in several industrial sectors, as solvent and reagent. The use of CO_2 for methane reforming is an interesting application that would avoid CO_2 separation after extraction of LNG. In fact, should it be found a suitable catalyst or a technology for low temperature, effective conversion of CH_4 and CO_2 into syn-gas, the direct conversion of LNG at the extraction site into liquid fuels as methanol or gasoline would reduce the distribution costs with respect to methane separation and pumping. The utilization of carbon dioxide by other sectors of the chemical industry may contribute to implement greener synthetic technologies with respect to existing ones, and to reduce the carbon dioxide emission in terms of waste reduction at source, solvent shift, more direct synthetic procedures, energy saving. Mimicking natural processes for synthetic purposes can also address the development of innovative syntheses with CO_2 emission reduction. The fixation of CO_2 by algae (micro and macro) is a promising area that is worth to investigate for assessing the potential of aquatic biomass as soure of fuels. The assessment of the real amount of avoided carbon dioxide is not an easy and simple exercise. It is not only represented by the amount of recycled/fixed CO_2: the fraction of carbon dioxide not produced by implementing an innovative synthetic technology must also be taken into account. The Life Cycle Assessment methodology is the proper tool for such evaluation. Incentives are needed for running appropriate integrated programmes aimed at assessing the potential of the utilization option.