Catalyst Essay Research Paper Catalysts

Catalyst Essay, Research Paper

Catalysts & Fine Particle In Industry

Catalyst:

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.

Examples:

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 1: NO2 (catalyst) + SO2 NO + SO3 (SO3 is extracted and combined with steam to produce sulfuric acid)

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:

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. Fr