Question

explain the preparation of sulphuric acid by contact process

Answer 1

Question #57817, Chemistry / Inorganic Chemistry

Explain the preparation of sulphuric acid by contact process.

The raw material for sulfuric acid is $\mathrm{SO}_2$ gas. It is obtained by:

(a) burning elemental sulfur with air

(b) smelting and roasting metal sulfide minerals

(c) decomposing contaminated (spent) sulfuric acid catalyst.

Sulfuric acid is made from this gases by:

(a) catalytically reacting their $\mathrm{SO}_2$ and $\mathrm{O}_2$ to form $\mathrm{SO}_3(\mathrm{g})$

(b) reacting (a)'s product $\mathrm{SO}_3(\mathrm{g})$ with the $\mathrm{H}_2\mathrm{O}(\mathrm{g})$ in 98.5 mass% $\mathrm{H}_2\mathrm{SO}_4$, 1.5 mass%

$\mathrm{H}_2\mathrm{O}$ sulfuric acid.

$\mathrm{O}_2$ does not oxidize $\mathrm{SO}_2$ to $\mathrm{SO}_3$ without a catalyst. All industrial $\mathrm{SO}_2$ oxidation is done by sending $\mathrm{SO}_2$ bearing gas down through 'beds' of catalyst,

$$\begin{array}{c c c c c} & & & 700-900 \mathrm{~K} \\ \mathrm{SO}_3(\mathrm{g}) & + & \frac{1}{2} \mathrm{O}_2(\mathrm{g}) & \rightarrow & \mathrm{SO}_3(\mathrm{g}) \\ \text{in dry } \mathrm{SO}_2, \mathrm{O}_2, & & \text{in feed gas} & \text{catalyst} & \text{in } \mathrm{SO}_2, \mathrm{SO}_2 \\ \mathrm{N}_2 \text{ feed gas} & & & & \mathrm{O}_2, \mathrm{N}_2 \text{ gas} \end{array}$$

At its operating temperature, 700-900 K, $\mathrm{SO}_2$ oxidation catalyst consists of a molten film of V, K, Na, (Cs) pyrosulfate salt on a solid porous SiO2 substrate. The molten film rapidly absorbs $\mathrm{SO}_2(\mathrm{g})$ and $\mathrm{O}_2(\mathrm{g})$ - and rapidly produces and desorbs $\mathrm{SO}_3(\mathrm{g})$

Catalytic oxidation's SO3(g) product is made into H2SO4 by contacting catalytic oxidation's exit gas with strong sulfuric acid

$$\begin{array}{c c c c} & & 350-380 \mathrm{~K} \\ \mathrm{SO}_3(\mathrm{g}) & + & \mathrm{H}_2\mathrm{O}(\ell) & \rightarrow \quad \mathrm{H}_2\mathrm{SO}_4(\ell) \\ \text{in } \mathrm{SO}_2, \mathrm{SO}_2, & & \text{in } 98.5\% \mathrm{H}_2\mathrm{SO}_4, & \text{in strengthened} \\ \mathrm{O}_2, \mathrm{N}_2 \text{ gas} & & 1.5\% \mathrm{H}_2\mathrm{O} & \text{sulfuric acid} \\ & & \text{sulfuric acid} \end{array}$$

Fig. 1.4. Double contact sulfuric acid manufacture flowsheet. The three main $\mathrm{SO}_2$ sources are at the top. Sulfur burning is by far the biggest source. The acid product leaves from two $\mathrm{H}_2\mathrm{SO}_4$ making towers at the bottom. Barren tail gas leaves the final $\mathrm{H}_2\mathrm{SO}_4$ making tower, right arrow.