Raschig trial

The Raschig process is a chemical process for the production of hydroxylamine , which is required annually on a multi-ton scale, for example for the production of caprolactam . It is named after the German chemist Fritz Raschig .

The starting materials are oxygen , sulfur dioxide , ammonia , carbon dioxide and water. First, ammonia is catalytically partially oxidized to nitrogen monoxide and nitrogen dioxide :

${\displaystyle \mathrm {2\ NH_{3}\ +\ 3\ O_{2}\longrightarrow \ NO\ +\ NO_{2}\ +\ 3\ H_{2}O} }$

This gas mixture is then introduced into an ammonium carbonate solution:

${\displaystyle \mathrm {H_{2}O\ +\ NO\ +\ NO_{2}\longrightarrow \ 2\ NO_{2}^{-}\ +\ 2\ H^{+}} }$

The ammonium carbonate required is obtained by introducing carbon dioxide into an ammonia solution:

${\displaystyle \mathrm {2\ NH_{3}\ +\ CO_{2}\ +\ H_{2}O\longrightarrow \ (NH_{4})_{2}CO_{3}} }$

In the nitrite-containing solution , ammonia is converted to ammonium nitrite , with carbon dioxide and water being formed:

${\displaystyle \mathrm {(NH_{4})_{2}CO_{3}\ +\ 2\ NO_{2}^{-}\ +\ 2\ H^{+}\longrightarrow \ 2\ NH_{4}NO_{2}\ +\ CO_{2}\ +\ H_{2}O} }$

Ammonium nitrite is now reduced to hydroxylamine with sulfur dioxide , with sulfur dioxide being oxidized to sulfuric acid in an aqueous medium . The resulting hydroxylamine is converted directly to its salt hydroxylamine sulfate (NH ₃ OH) ₂ SO ₄ :

${\displaystyle \mathrm {2\ NH_{4}NO_{2}\ +\ 2\ SO_{2}\ +\ 4\ H_{2}O\longrightarrow \ 2\ (NH_{3}OH)_{2}SO_{4}} }$

The net equation of the overall process is thus:

${\displaystyle \mathrm {4\ NH_{3}\ +\ 3\ O_{2}\ +\ 2\ SO_{2}\ +\ 2\ H_{2}O\longrightarrow \ 2(NH_{3}OH)_{2}SO_{4}} }$

Hydroxylamine can be released with the help of a base :

${\displaystyle \mathrm {2\ (H_{3}NOH)_{2}SO_{4}+2NH_{3}\ \rightleftharpoons \ 2(NH_{4})_{2}SO_{4}+2H_{2}NOH} }$

A major disadvantage of the process is the high proportion of "waste". 4 tons of ammonium sulfate are produced per ton of hydroxylamine . In 1967, BASF and Inventa introduced a process that produces only half as much waste. In 1970, Stamicarbon completely eliminated ammonium sulfate ( Stamicarbon process ).

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1. ^ ^{A b} Menachem Lewin: Handbook of Fiber Chemistry . Marcel Dekker Inc; Edition: 0003 (November 15, 2006), ISBN 0-8247-2565-4 ( Google-books ).