Production of n-pentanal from low-butene feedstock mixtures

A process for producing n-pentanal comprising the steps of:

• a) providing a feedstock mixture having the following composition which sums to 100 wt %:
• n-butane:
• 70 wt % to 90 wt %;
• n-butene:
• 10 wt % to 30 wt %;
• 1-butene:
• 0 wt % to 3 wt %;
• isobutene:
• 0 wt % to 3 wt %;
• isobutane:
• 0 wt % to 3 wt %;
• 1,3-butadiene:
• 0 wt % to 1 wt %;
• other substances:
• 0 wt % to 1 wt %;
• b) mixing the feedstock mixture with a recyclate to obtain a feed;
• c) treating the feed with carbon monoxide and hydrogen in the presence of a first catalyst system to convert at least a portion of the n-butene present in the feed into aldehydes by hydroformylation to obtain a hydroformylation mixture;
• d) recovering a primary product fraction from the hydroformylation mixture, wherein the primary product fraction has the following composition which sums to 100 wt %:
• n-pentanal:
• 90 wt % to 98.5 wt %;
• 2-methylbutanal:
• 0 wt % to 5 wt %;
• 3-methylbutanal:
• 0 wt % to 3 wt %;
• other substances:
• 0 wt % to 2 wt %;
• e) recovering a subsidiary fraction from the hydroformylation mixture, wherein the subsidiary fraction has the following composition which sums to 100 wt %:
• n-butane:
• 80 wt % to 92 wt %;
• n-butene:
• 8 wt % to 20 wt %;
• other substances:
• 0 wt % to 1 wt %;
• f) subjecting the subsidiary fraction to a dehydrogenation in the presence of a second catalyst system to obtain a dehydrogenation mixture having the following composition which sums to 100 wt %:
• n-butene:
• 50 wt % to 60 wt %;
• n-butane:
• 40 wt % to 50 wt %;
• methane:
• 0 wt % to 4 wt %;
• ethene:
• 0 wt % to 3 wt %;
• propene:
• 0 wt % to 2 wt %;
• 1,3-butadiene:
• 0 wt % to 3 wt %;
• other substances:
• 0 wt % to 1 wt %;
• g) subjecting the dehydrogenation mixture to a selective hydrogenation in the presence of a third catalyst system to obtain a hydrogenation mixture having the following composition which sums to 100 wt %:
• n-butene:
• 50 wt % to 60 wt %;
• n-butane:
• 40 wt % to 50 wt %;
• 1,3-butadiene:
• 0 ppm by weight to 500 ppm by weight;
• other substances:
• 0 wt % to 5 wt %;
• h) direct use of the hydrogenation mixture as recyclate
• or
• purification of the hydrogenation mixture to obtain the recyclate.