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I was after some detail as to why the contact process was named as such.

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2 Answers 2

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The word "Contact process" has an historical origin.

Before the $18$th century, sulfuric acid was difficult to obtain. It was synthetized by first oxidizing pyrite $\ce{FeS2}$ in wet air, in order to obtain iron sulfate $\ce{Fe2(SO4)3)}$, which had to be later pyrolized according to : $$\ce{Fe2(SO4)3 + 3 H2O -> Fe2O3 + 3 H2SO4}$$ Unfortunately, the initial oxidation of pyrite in humid air was extremely slow and inefficient. A huge advance was made in the middle of the $18$th century, when a new process was invented, the so-called lead chamber process, although it was based on the incorrect phlogisticon theory. First sulfur $\ce{S8}$ or pyrite $\ce{FeS2}$ was burnt in air, producing gaseous $\ce{SO2}$ which was quickly oxidized by droplets of nitric acid $\ce{HNO3}$ falling like a mist or a shower in a chamber filled with the combustion gas $\ce{SO2}$. The reaction is quick and occurs according to : $$\ce{SO2 + 2 HNO3 -> H2SO4 + 2 NO2}$$ The chamber is made of lead, in order to resist to sulfuric acid. The advantage of this process is that the gas getting out of the reaction ($\ce{NO2}$) is not lost. It is pushed into another lead-chamber where droplets of water were injected in order to regenerate the original nitric acid according to the equation : $$\ce{4 NO2 + O2 + 2 H2O -> 4 HNO3}$$ This process was much quicker than the old process using iron sulfate. But it needs controls and maintenance of these two lead chambers, which is not easy.

A new progress happened in $1832$. The gas mixture containing $\ce{SO2}$ + air could be directly transformed into $\ce{SO3}$ without lead chambers, but with simple contact with a solid stuff, namely platinum wires, which had a catalytic effect in the reaction $$\ce{2 SO2 + O2 -> 2 SO3}$$. Then $\ce{SO3}$ is quickly transformed into sulfuric acid, according to $\ce{SO3 + H2O -> H2SO4}$. Lead chambers were replaced by a simple tube equipped with some wires. It was a big improvement. Later on, the platinum was replaced by vanadium oxides, which is not so sensitive to impurities. The process was named "contact process" at this time, when the catalysis was not yet well understood.

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According to this site:

The Hot gases( $\ce{SO2}$ ) evolved from burning of sulfur ore comes in contact with catalyst bed, So the name of this process is called contact process.

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