Process for preparing organic isocyanates, which comprises the steps
(a) making available a first partial amount of chlorine, with the chlorine
of this first partial amount having a content of free and bound bromine and iodine
of <400 ppm;
(b) making available a second partial amount of chlorine;
(c) reacting the first and second partial amounts of chlorine with carbon
monoxide to form phosgene;
(d) reacting the phosgene from step (c) with one or more primary amines
to form the corresponding isocyanates and hydrogen chloride;
(e) separating off and, if necessary, purifying the isocyanates formed in
step (d);
(f) separating off and, if necessary, purifying the hydrogen chloride formed
in step (d);
(g) catalytically oxidizing at least part of the hydrogen chloride separated
off in step (e) by means of oxygen to form chlorine;
(h) separating off the chlorine formed in step (g) and using at least a
partial amount of the chlorine which has been separated off as second partial amount
of chlorine in step (b).
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