Catalyst contact process

Sulphur trioxide, SO3, m.p. 17 C, b.p. 49 C. Formed SO2 plus O2 over a catalyst (contact process - see sulphuric acid). The solid exists... 

Since the catalyst is in the gaseous state, it is being continually removed from the mixing chambers. Its recovery, and the necessity of continual charging of the incoming gases with it, make the lead chamber plant complicated by comparison with that of the Contact process. 

In the finely divided state platinum is an excellent catalyst, having long been used in the contact process for producing sulfuric acid. It is also used as a catalyst in cracking petroleum products. Much interest exists in using platinum as a catalyst in fuel cells and in antipollution devices for automobiles. 

Thermal polymerization is not as effective as catalytic polymerization but has the advantage that it can be used to polymerize saturated materials that caimot be induced to react by catalysts. The process consists of the vapor-phase cracking of, for example, propane and butane, followed by prolonged periods at high temperature (510—595°C) for the reactions to proceed to near completion. Olefins can also be conveniendy polymerized by means of an acid catalyst. Thus, the treated olefin-rich feed stream is contacted with a catalyst, such as sulfuric acid, copper pyrophosphate, or phosphoric acid, at 150—220°C and 1035—8275 kPa (150—1200 psi), depending on feedstock and product requirement. 

In early years the contact process frequentiy employed only two or three catalyst stages (passes) to obtain overall SO2 conversions of approximately 95—96%. Later, four pass converters were used to obtain conversions of from 97% to slightiy better than 98%. For sulfur-burning plants, this typically resulted in sulfur dioxide stack emissions of 1500—2000 ppm. 

The contact process which replaced the chamber process reacts the products using a platinum or a vanadium catalyst. 

Contact process for SO3/H2SO4 patented by P. Philips of Bristol, UK (tlie original platinum catalyst was. subsequently replaced by ones ba.sed on V2O5). 

The newer process uses a solid catalyst for reaction (19). Either finely divided platinum or vanadium pentoxide, V205, is effective. Because catalysis occurs where the gas contacts the surface of the catalyst, this process is called the contact process. 

Sulfuric acid, H2S04, is produced commercially in the contact process, in which sulfur is first burned in oxygen and the S02 produced is oxidized to S03 over a V205 catalyst ... 

Today, sulfuric acid is produced by a method known as the contact process in which S02 is oxidized to S03, which then reacts with water to give the acid. Oxidation of S02 requires a suitable catalyst such as spongy platinum or sodium vanadate. In many cases, S03 is dissolved in 98% sulfuric acid to produce disulfuric acid oleum], which can be shipped, diluted, and still give 100% sulfuric acid. The concentration of S03 varies from 10 to 70% in commercial oleum. 

In the second stage, a mixture of sulphur dioxide and air is passed over a catalyst of vanadium (V) oxide, V205, at a temperature of about 430°C. This is called the Contact process. 

CAT-OX [Catalytic oxidation] An adaptation of the Contact process for making sulfuric acid, using the dilute sulfur dioxide in flue-gases. A conventional vanadium pentoxide catalyst is used. Developed by Monsanto Enviro-Chemical Systems, and operated in Pennsylvania and Illinois in the early 1970s. 

Mannheim (2) An early version of the Contact process for making sulfuric acid. Two catalysts were used ferric oxide, followed by platinum. The first Mannheim plant was built in Buffalo, NY, in 1903. 

Schroder-Grillo Also known as Grillo-Schroder. An early version of the contact process for making sulfuric acid. The catalyst was magnesium sulfate impregnated with platinum. The process was invented in 1899 by A. Hecksher at the New Jersey Zinc Company and first used at its plant in Mineral Point, WI, in 1901 this was the first use of the contact process in the United States. In the United Kingdom it was first used in Widnes in 1917. See also Mannheim (2). 

The production of sulphuric acid by the contact process, introduced in about 1875, was the first process of industrial significance to utilize heterogeneous catalysts. In this process, SO2 was oxidized on a platinum catalyst to S03, which was subsequently absorbed in aqueous sulphuric acid. Later, the platinum catalyst was superseded by a catalyst containing vanadium oxide and alkali-metal sulphates on a silica carrier, which was cheaper and less prone to poisoning. Further development of the vanadium catalysts over the last decades has led to highly optimized modem sulphuric acid catalysts, which are all based on the vanadium-alkali sulphate system. 

Some of its compounds, particularly the oxides, are used in chemical industries as catalysts to speed up organic chemical reactions. The yellow-brown vanadium pentoxide (V O ) is used as a catalyst to facilitate the production of sulfuric acid by the contact process. Vanadium pent-oxide is also used as a photographic developer, to dye textiles, and in the production of artificial rubber. When combined with glass, it acts as a filter against ultraviolet rays from sunlight. 

Sulfuric Acid. Essentially all sulfuric acid manufactured in this industry is produced by the contact process, in which SO2 and oxygen contact each other on the surface of a catalyst (vanadium pentaoxide) to form SO3 gas. Sulfur trioxide gas is added to water to form sulfuric acid. The sulfur dioxide used in the process is produced by burning elemental sulfur in a furnace. 

Conversion of sulfur dioxide to trioxide requires a suitable catalyst. Vanadium pentoxide, V2O5, is probably the most effective catalyst for the contact process. Vanadium and potassium salts supported on diatomaceous earth, platinized asbestos, platinized magnesium sulfate, and ferric oxide also have proved to be efficient catalysts. 

The lead-chamber process supplied the world s need for sulfuric acid for a century and a half. In the late nineteenth century, the contact process replaced the lead-chamber process. The contact process utilized sulfur dioxide, SOj, which was produced as a byproduct when sulfur-bearing ores were smelted. The contact process was named because the conversion of sulfur dioxide to sulfur trioxide, SO3, takes place on contact with a vanadium or platinum catalyst during the series of reactions ... 

This complex system would be difficult to solve directly. However, the problem is separable by taking advantage of the widely different time scales of conversion and deactivation. For example, typical catalyst contact times for the conversion processes are on the order of seconds, whereas the time on stream for deactivation is on the order of days. [Note Catalyst contact time is defined as the volume of catalyst divided by the total volumetric flow in the reactor at unit conditions, PV/FRT. Catalyst volume here includes the voids and is defined as WJpp — e)]. Therefore, in the scale of catalyst contact time, a is constant and Eq. (1) becomes an ordinary differential equation ... 

At present, almost all sulfuric acid is made by the contact process, which has been in use since 1831. The first step is exothermic air oxidation of SO2 catalyzed by vanadium pentoxide (V2O5) or platinum (reaction 10.5). The yield of SO3 is limited on the first pass to some 60% because the temperature rises to 600 °C or more usually, three more passes over the catalyst are made, and the yield can be increased to 98%. The SO3 vapor is then absorbed into 100% H2SO4 (reaction 10.6), and water is added to the resulting mixture of disulfuric (H2S207) and sulfuric acids (known as oleum) until the H2S2O7 is all hydrolyzed to H2SO4 (reaction 10.7). This obviates the aerosol problem. 

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