Catalysts & Fine Particle In Industry
Catalysis, alteration of the speed of a chemical reaction, through the presence of an additional substance, known as a catalyst, that remains chemically unchanged by the reaction. Enzymes, which are among the most powerful catalysts, play an essential role in living organisms, where they accelerate reactions that otherwise would require temperatures that would destroy most of the organic matter.
A catalyst in a solution with-or in the same phase as-the reactants is called a homogeneous catalyst. The catalyst combines with one of the reactants to form an intermediate compound that reacts more readily with the other reactant. The catalyst, however, does not influence the equilibrium of the reaction, because the decomposition of the products into the reactants is speeded up to a similar degree. An example of homogeneous catalysis is the formation of sulfur trioxide by the reaction of sulfur dioxide with oxygen, in which nitrogen dioxide serves as a catalyst. Under extreme heat, sulfur dioxide and nitrogen dioxide react to form sulfur trioxide and the intermediate compound nitric oxide, which then reacts with oxygen to re-form nitrogen dioxide. The same amount of nitrogen dioxide exists at both the beginning and end of the reaction.
A catalyst that is in a separate phase from the reactants is said to be a heterogeneous, or contact, catalyst. Contact catalysts are materials with the capability of adsorbing molecules of gases or liquids onto their surfaces. An example of heterogeneous catalysis is the use of finely divided platinum to catalyze the reaction of carbon monoxide with oxygen to form carbon dioxide. This reaction is used in catalytic converters mounted in automobiles to eliminate carbon monoxide from the exhaust gases.
Catalysts are substances that trigger or speed up chemical reactions (without chemically altering the catalysts in the process). A catalyst combines with a reactant to form an intermediate compound that can more readily react with other reactants. An example of this is the formation of sulfur trioxide (SO3), which is an important ingredient for producing sulfuric acid (H2SO4). Without a catalyst, sulfur trioxide is made by combining sulfur dioxide (SO2) with molecular oxygen: 2SO2 + O2 2SO3. Because this reaction proceeds very slowly, manufacturers use nitrogen dioxide (NO2) as a catalyst to speed production of SO3:
Step 2: NO (from Step One) + O2 NO2 (catalyst that is reused in step one)
In the above reactions, nitrogen dioxide (NO2) acts as a catalyst by combining with sulfur dioxide (SO2) to form both sulfur trioxide (SO3) and nitrogen monoxide (NO). The sulfur trioxide is removed from the process (to be used in the production of sulfuric acid). Nitrogen monoxide (NO) is subsequently combined with molecular oxygen (O2) to produce the original catalyst, nitrogen dioxide (NO2), which can be continually reused to catalyze sulfur trioxide (SO3).
Applications And Uses To Particular Industries:
Hydrotreating is a process used in the oil industry to remove objectionable elements from petroleum distillates. Oil refinery produces such as jet fuels, naptha, kerosene and diesel contain sulphur and nitrogen molecules, and have to be hydrotreated to reduce the concentration of these contaminants in order to meet specifications associated with emission standards and for odour and colour improvement. The permitted concentration of contaminants in diesel fuel were reduced in 1996 and will be significantly further reduced in the years 2000 and 2005 under stringent new EU legislation, forcing oil companies to upgrade their hydrotreating processes to comply with the new regulations.
The hydrotreating process involves reacting the contaminated fuel with hydrogen in the presence of a catalyst, which serves to promote the reaction. Some types of hydrotreating process are operated with reactants in the vapour phase. The process chemistry involves the controlled breaking of the molecular chain or ring at the point where the sulphur or nitrogen is joined to the carbon atoms of the fuel. Hydrogen sulphide or ammonia respectively are liberated, which can be safely disposed of, generally as elemental sulphur or nitrogen respectively.
The catalyst used in the reactor is made of porous alumina, and has metals such as nickel, cobalt or molybdenum attached to its surface, generally as their sulphides. An important feature of the catalyst is its high internal surface area, as reacting molecules must diffuse into the pores and adsorb to the surface in order to react with each other. In order to optimise processing conditions, oil companies such as BP-Amoco, need to know how fluids interact with the catalyst under reacting conditions. In particular they need to know how the process is affected by condensation of vapour reactants to liquid inside the catalyst pores. Pockets of liquid block off areas of the catalyst pore structure, reducing the efficiency of the process, a phenomenon known as capillary condensation.
The objective of this research is to investigate the conditions under which capillary condensation occurs in catalyst pores. From these processes, we hope to make suggestions to the sponsors, BP-Amoco, as to how they could optimise their reactors and thereby increase the efficiency of their processes. Some possible solutions may-be to modify the catalyst properties such as the distribution of pore sizes, or reaction conditions such as temperature and pressure. One aspect of the work involves simulating the diffusion of reactants into the catalyst pores, and capillary condensation by constructing computer models of the processes occurring at the catalyst scale. A further aspect of the work is an experimental investigation using magnetic resonance methods, in order to gain an insight into the way that different molecular species interact with each other in the pores of the catalyst.
Fine Particles And Their Safety Aspects:
During the ‘1950s and ‘1960s, stringent authorities assumed there was a threshold or some amount of polycyclic aromatic hydrocarbons (PAH’s: combustion processes, whereby most fine particles are coated with toxic materials, metals like lead and mercury, or some toxic organic material) that was safe. However, after 1975, a greater understanding of fine particles and health was achieved. In 1979, the National Research Council of the National Academy of Sciences, and the United Nations, both published book-length studies of the dangers of small particles to humans. It stated the current view: humans evolved in an environment where dust was made up of large particles. Humans therefore evolved means for protecting themselves against large particles. Large particles are filtered out by hairs inside the nose, mucous membranes in the throat and airways, and other mechanisms. However, modern combustion machines produce small particles which pass right by these natural protections and then enter the deep lung. In the deep lung, air comes into contact with a person’s blood stream; this is where oxygen passes into the body and carbon dioxide passes out with each breath we take. Putting tiny particles of pollution directly in contact with the surface of the deep lung is a recipe for trouble. . So fine particles provide a uniquely efficient carrier, giving dangerous toxins direct entry into the blood stream.
No epidemiological study can prove a cause and effect relationship because it is always possible that some major factor was left out. Until recently, skeptics could say smoking might explain why death rates increase as PAH’s concentrations increase. But the studies looking at 8111 adults in six American cities and showed that smoking did not explain the increased death rate observable when PAH’s concentrations rise. Smoking has now been ruled out.
Eight studies of air pollution in U.S. cities have now shown that fine particles (the invisible soot emitted by incinerators, automobiles, power plants and heating units) are presently killing about 60,000 Americans each year. More than a dozen studies have, in one way or another, confirmed this relationship. Furthermore, there appears to be no threshold, no level below which effects disappear. This means that people are being killed by air pollution levels well within existing federal standards. To summarize bluntly, any increase in fine particles in the atmosphere kills someone.