Catalytic purification of gas emissions
Increasing air pollution causesa serious concern, and therefore the purification of gas emissions every year becomes more urgent. The largest source of harmful gas emissions into the atmosphere are energy enterprises and road transport.
The purification of gas emissions is carried out by variousmethods, among which the most effective in many cases is the catalytic method of neutralizing and reducing the concentration of pollutants to the maximum permissible level. Catalytic purification is also preferable for economic reasons.
As a rule, catalytic methods areuniversal and can be used for deep cleaning of various process gases. With this method, industrial gases can be purified from nitrogen oxides and sulfur, carbon monoxide, harmful organic compounds and other toxic impurities. At the same time harmful impurities are transformed into less harmful and harmless, and sometimes even useful. The same method is used to purify exhaust gases. In fact, this method consists in realizing the processes of chemical interaction of substances in the presence of catalysts, which leads to the conversion of impurities to be rendered harmless to other products.
Special catalysts accelerate chemicalreactions, but they do not affect the energy level of the interacting molecules and do not shift the equilibrium of simple reactions. Catalytic purification is promising for multi-component mixtures of effluent gas streams. For the purification of gases in industry, iron, copper, chromium, cobalt, zinc, platinum and other oxides are used as catalysts. These substances are treated with a catalyst carrier placed inside the reactor apparatus. It is necessary to monitor the integrity of the outer layer of the catalyst, otherwise the catalytic cleaning will not be carried out in full, and the emission of harmful substances can exceed the permissible standards.
The main requirement for the catalyst- stability of the structure during the reaction. The search and manufacture of catalysts, not only suitable for long-term use, but also cheap enough, presents some difficulty that limits the application of the catalytic method. Modern catalysts must have selectivity and activity, resistance to temperature and mechanical strength.
Industrial catalysts are manufactured in the formblocks and rings of honeycomb structure. They have a small hydrodynamic resistance and a high external specific surface. Catalytic purification of gases in a fixed catalyst is most often used.
In industry, twofundamentally different ways of implementing gas cleaning processes - stationary and artificially created non-stationary regime. The transition to the predominant use of the non-stationary method is due to the higher processibility of the process, the increase in the reaction rate, the increase in selectivity, the reduction in the energy intensity of the processes, the reduction of the capital costs for installation, and the reduction in operating costs.
The main direction of development of catalyticmethods is to create cheap catalysts that can work at low temperatures and be resistant to various substances. For concentrations below 1 g / m³ and for large volumes of cleaned gases, the thermocatalytic method requires high energy inputs and a huge amount of catalyst, so it becomes necessary to develop the most energy-efficient technological processes and equipment that require low capital costs.
