Energy storage and carbon capture and storage (Carben Capture and Storage, CCS for short) seem to be two areas that are irrelevant, but from Massachusetts Institute of Technology scientists Sahag Voskian and T. Alan Hatton changed this. They have developed a new type of CCS technology that separates carbon dioxide from a gas stream with a concentration as low as 0.6%-10% during the charging process through a charge and discharge process of an energy storage battery, and releases it pure during discharge. Carbon dioxide. The current efficiency of the battery exceeds 90%, and it takes 40-90 kJ of energy to separate one mole of carbon dioxide (44 g), and it can operate for a long time, and the capacity loss does not exceed 30% after 7000 charge and discharge cycles. The results were released on September 30th in Energy & Environmental Science, the top energy journal.
Introduction to CCS Technology
The threat posed by global warming caused by carbon dioxide is one of the major challenges facing humanity in this century. According to the IPCC Global Warming 1.5oC Special Report released by the IPCC of the Intergovernmental Panel on Climate Change in October 2018, if global warming is to be controlled within 1.5 °C, global carbon emissions will fall to 2030. At 55% in 2010, humans will achieve zero emissions by 2050. This requires removing carbon dioxide from the air to balance carbon emissions.
Related research has also been carried out. The more mature technology at present is oxyfuel combustion (burning the fuel by using pure oxygen instead of air to obtain a high carbon dioxide concentration exhaust gas for carbon dioxide storage) plus solution washing (usually amine washing). This process requires a carbon dioxide concentration greater than 10% and requires extensive modifications to the plant. Many technologies absorb carbon dioxide through chemical processes, which requires regeneration of the absorber for recycling. At present, the means of regeneration can be mainly divided into two types: "Termal-swing" and "Pressure-swing", but these two methods require a large amount of energy for heating the absorber or pumping the absorber. vacuum. Therefore, energy utilization efficiency is very low.
In addition, CCS applications should not be limited to the treatment of high concentrations of carbon dioxide. In some special environments, such as space stations, aircraft cabins, submarines, etc., it is necessary to separate carbon dioxide from air with very low carbon dioxide concentration. . Such technology can also be a tool for mankind to turn the tide after exhausting carbon emissions.
Therefore, although the research on CCS has been going on for many years, and carbon trading has made it possible for the economic application of CCS, the cost of implementing CCS for power plant emission reduction is still very high. According to IPCC estimates, the use of CCS in a coal-fired power station can reduce carbon emissions by 80%-90%, but it will increase energy consumption by 25%-40% and cost by 21%-91%. In 2015, the Ministry of Commerce referred to CCS as “an important solution to global warming” and also called it “an expensive experimental product”.
New technology principles and features
In this study, MIT scientists did not use the traditional "thermal change" or "pressure change" absorbers, but instead used an "Electro-Swing" absorber. Since the electrochemical process is nearly isothermal and isobaric, it can greatly improve its energy utilization efficiency. The core component of the entire unit is this "electrical change" absorber. The absorber consists of three parts: two electrodes coated with a ruthenium polymer nanotube coated with carbon dioxide, and an electrode made of a polyethylene ferrocene nanotube composite. Between the anode and cathode is an insulating material.
The next section involves a lot of chemistry, and the buddies who have phobias can skip it. When charging, the two oxygen atoms on the crucible get electrons, forming a negative electric center (or having sufficient Lewis base strength), attracting carbon atoms in the carbon dioxide near the positive electric center, and carboxylating the rhodium to capture carbon dioxide. Since neither nitrogen nor oxygen has such a Lewis acid strength, the reaction has a good selectivity. The higher the charging voltage, the more obvious the oxygen atoms are polarized, the faster the reaction rate, but the greater the energy loss. Therefore, from the energy point of view, the charging voltage should be slightly larger than the voltage required for the reaction, which is about 1 under pure nitrogen conditions. .21V or so, varies with the concentration of carbon dioxide.
The characteristics and difficulty of this technology lies in the selection and fabrication of electrode materials. First, it is necessary to selectively capture carbon dioxide; secondly, the surface of the electrode requires a large surface area and increases the reaction rate, which is especially important for capturing carbon dioxide from a low concentration of carbon dioxide source; finally, good conductivity is required, which is achieved by The delocalized π bond in 蒽醌 is realized.
The author did not mention too much about cost and energy storage density. However, it can be guessed that the economy of this technology will be better than the original technology. On the one hand, the electrodes are not used with rare metals, and the ruthenium and ferrocene used are also artificially synthesized, and the cost is not too high. On the other hand, this technology can be used for carbon trading, for peaking and filling of electric load, without heating or pressurizing in the reaction process, and also saving a lot of energy expenditure. The captured carbon dioxide can also be used in the production of urea and other industries. product. However, its energy storage density should not be large. On the one hand, part of the space needs to be reserved for the airway, which increases the volume of the device. On the other hand, only the surface layer of the concrete that actually reacts is limited, and the amount of electricity that can be stored is limited. Since capturing carbon dioxide ultimately requires energy, its single cycle is not efficient. However, this technology was originally developed as a carbon capture technology, and its energy storage characteristics can be used as a icing on the cake.
Currently, the research team has set up a company called Verdox to commercialize the system.