DHD procedure

The DHD process ( dehydrogenation under H ₂ pressure ) is a chemical-technical process for converting non-aromatic components of gasoline such as naphthenes and paraffins into aromatics . The naphthenes present in raw gasoline are mostly substituted 5- or 6-membered cycloparaffins . The 5-membered naphthenes can be converted into 6-membered naphthenes by isomerization by ring expansion. The dehydrogenation of the 6-membered naphthenes leads directly to aromatic compounds. Paraffins can be converted into aromatics by dehydrocyclization . An undesirable side reaction is the dealkylation of substituted naphthenes by hydrocracking.

history

The DHD process was used, among other things, as a follow-up process to the Bergius Pier process to improve the octane number of hydrogenation fuels. In the course of the development of the process, it was found that the octane number of petroleum-based petrol with a higher concentration of paraffin or the Fischer-Tropsch synthesis can also be increased via the dehydrocyclization reaction .

Process parameters

The process operated at pressures of about 60 bar and the reaction temperature was about 510 to 530.degree. A contact composed of molybdenum oxide dispersed on aluminum oxide was used as the catalyst . The boiling limits of the petrol used were between about 85 and 185 ° C. The process increased the octane number of the gasoline from around 50 to 80.

A typical reaction of the DHD process is the dehydrogenation of methylcyclohexane to toluene, a strongly endothermic reaction (about −218 KJ / mol):

The starting material is first preheated to reaction temperature in a tube furnace and then pumped into a reactor with the appropriate contact. At the same time, the reactor is supplied with hydrogen, which is intended to delay the coking of the contact. The products are then cooled and the hydrogen separated and fed back into the process. The crude product is worked up by distillation. The main products of the process are the aromatics benzene , toluene and the xylenes .

Individual evidence

1. ^ Walter Krönig : The catalytic pressure hydrogenation of coal, tars and mineral oils (The IG process by Matthias Pier) . Springer Verlag, 1950, pp. 145–152. (Reprint: 2013, ISBN 978-3-642-50105-0 ).
2. ^ Karl Becker: Catalysts of the Leuna factory: a contribution to the history of technical heterogeneous catalysis - Part I: The developments from 1921 to 1945. In: Chemical engineering technology. 86, 2014, pp. 2105-2114, doi: 10.1002 / cite.201400051 .