A catalyst will change or influence or effect three major parameters which are:
1. The rate of a reaction
2. The energy required for a chemical reaction
3. The sequence of mechanism steps of a chemical reaction
However, it does not change the equilibrium of the reaction. Bulk production of the chemical will depend on the choice of catalysts for example,
- Raney Nickel: used in the hydrogenation of vegetable and animal oils
- Platinum-on-alumina: Reforming of petroleum naphtha
- Promoted Iron: Ammonia synthesis
Some of the images of the catalysts used for some specific reactions and the selection of the catalyst depending on the shape, activity; surface area etc.
The iron-based catalyst which is mostly used for ammonia synthesis reaction of Nitrogen and Hydrogen reactants, its optimum dimensions are about 1.5 to 3 mm diameter and have a lifetime from 5 to 10 years
The catalyst for water shift reactions:
For a high-temperature shift conversion reaction where Carbon dioxide is produced from Carbon monoxide on the catalyst of Iron /Chromia which has the optimum shape of tablets and has dimensions with a diameter of 6 mm and height of 6 mm, its lifetimes can be expected to greater than 5 years.
For further reducing carbon-monoxide and thereby increasing the H2 yield for Ammonia synthesis. The Low-Temperature shift catalyst is a combination of copper and zinc oxide and is active at a lower temperature where restrictions in conversion due to equilibrium are minimized. But LT shift catalyst is very sensitive to high temperature, poisoning and contamination by water. It is made of a tablet shape and has dimensions of 4.3mm diameter and 3.2mm height, with a lifetime expected to be more than 5 years.
The catalyst for Hydrogenation reactions:
In most hydrogenation reactor where hydrogen will be reacted with the reactant on a catalyst made from Nickel- Molybdate its shape are designed as a ring structure having dimensions, 5 mm outer diameter and 2.5 mm inner diameter, about greater than five years of life is expected in the production services.
Every petroleum product has impurities, toxic or poisonous material where sulphur is one of them, which is present in a higher percentage of all other, so for removing sulphur content, which may be in the form of hydrogen sulphide trace, are mostly absorbed in the solid surface after maximum removal in pretreatments operations, for absorption process a Zinc oxide is used as absorbent, it made into cylindrical shaped extrude which is used to absorb Hydrogen Sulphide into its small pores, and the dimensions of the cylinder would be about 4mm diameter and 8 mm height.
The catalyst used for the Methanation process:
The process gas composition contains small traces of CO and CO2. Removal of carbon oxide is accomplished in methanation where CO + CO2 are converted in the presence of a nickel-based catalyst into CH4. The shape of the nickel-based catalyst is made in the formation of a ring having dimensions of about 5 mm outer diameter its lifetime is expected to be about more than 10 years
CO + 3H2 → CH4 + H2O Δ H = -49.2Kcal/mol
CO2 + 4H2 → CH4 + 2H2O Δ H = -39.4Kcal/mol
The temperature rise for one per cent of CO converted is 74oC and for one per cent of CO2 converted, it is 60oC. The performance of methanol where catalyst Rx takes place is directly related to the efficiency of co-conversion and CO2 removal sections. High concentrations of carbon oxides can cause temperature runaway in the methanation catalyst and it is necessary to protect both the reactor vessel and the catalyst from serious damage. The vessel should be isolated, depressurized and purged with nitrogen. At a temperature below 204oC Nickel in presence of CO forms nickel carbonyl which is very poisonous.
The catalyst used in the Reforming process:
In the reforming process were mostly high chain hydrocarbon can be reformed or rearranged for the desired products, this reaction becomes a primary step in most petrochemical process plants the best catalyst used for this is a Nickel based catalyst with a cylindrical shape having seven holes with dimension having 16mm outer diameter and 11 mm height and each hole is of 3.5mm diameter, when coming to its lifetime it would about in the range 3 to 5 years.
And another type of platinum-on-alumina-based catalyst has the same shape but different dimensions which are 20 mm outer diameter and 18 mm height with each hole diameter of 4 mm, its lifetime is greater than 10 years.
These catalysts can be made from natural and synthetic materials, such as most widely used natural catalyst is clay and Zeolites whereas crystalline aluminosilicates are an example of synthetically prepared catalyst. This is what a catalyst used and prepared.
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