Process for preparing a chemical product or a chemical composition, wherein the process comprises the following steps and is conducted in a plant having plant sections corresponding to these steps: (I) reacting at least one substrate in a reactor to form at least one chemical product or a chemical composition, the at least one substrate being introduced into the reactor with a mass flow m 1 ; (II) working up the reaction mixture obtained in step (I) in a workup apparatus to obtain a crude product and at least one secondary stream comprising the constituents separated from the crude product; (III) purifying the crude product obtained in step (II) in at least one purifying apparatus to obtain a purified end product and at least one secondary stream comprising the constituents separated from the purified end product; and the optional steps (IV) to (V) (IV) working up the at least one secondary stream obtained in step (II) in a workup unit; (V) working up the at least one secondary stream obtained in step (III) in a workup unit, wherein in the event of a production shutdown lasting for 1 hour to 5 days for inspection, repair, cleaning or maintenance purposes in parts of the plant, one or more, but not all, plant sections from steps (I) to (V), if they are conducted, are put out of operation and an inspection, repair, cleaning or maintenance measure is conducted in these plant sections, and wherein the mass flow m 1 in step (I) is reduced to zero and, in each of the plant sections that has not been shut down, the output stream of the plant section is used again as input stream for the respective plant section or an upstream plant section, wherein, after the measure, the whole plant is started up again without delay. (I) reacting at least one substrate in a reactor to form at least one chemical product or a chemical composition, the at least one substrate being introduced into the reactor with a mass flow m 1 ; (II) working up the reaction mixture obtained in step (I) in a workup apparatus to obtain a crude product and at least one secondary stream comprising the constituents separated from the crude product; (III) purifying the crude product obtained in step (II) in at least one purifying apparatus to obtain a purified end product and at least one secondary stream comprising the constituents separated from the purified end product; and the optional steps (IV) to (V) (IV) working up the at least one secondary stream obtained in step (II) in a workup unit; (V) working up the at least one secondary stream obtained in step (III) in a workup unit, in the event of a production shutdown lasting for 1 hour to 5 days for inspection, repair, cleaning or maintenance purposes in parts of the plant, one or more, but not all, plant sections from steps (I) to (V), if they are conducted, are put out of operation and an inspection, repair, cleaning or maintenance measure is conducted in these plant sections, and wherein the mass flow m 1 in step (I) is reduced to zero and, in each of the plant sections that has not been shut down, the output stream of the plant section is used again as input stream for the respective plant section or an upstream plant section, wherein, after the measure, the whole plant is started up again without delay. <EOS>