Tubular reactor with expandable insert

A tubular reactor having a tubular reactor inlet and a tubular reactor outlet downstream of the tubular reactor inlet, the tubular reactor comprising:

• a tube having a tube wall, and
• an insert, wherein the insert comprises:
• a catalyst;
• and
• a plurality of metal structures consecutively arranged in a lengthwise direction of the tube, each of the plurality of metal structures having an upstream end, a downstream end and a radially expandable side wall enclosing a central space between the upstream end and the downstream end, wherein the upstream end defines an inlet to the central space, wherein the central space is at least partially blocked at the downstream end, and wherein the radially expandable side wall defines a plurality of orifices for passing a fluid from the central space toward the tube wall, the plurality of orifices characterized by a hydraulic diameter, d, and a spacing, h, from the tube wall, wherein h/d for the plurality of orifices ranges from 0.05 to 10, and wherein each of the plurality of metal structures form an outer space having a plurality of hollows between the radially expandable side wall of each of the plurality of metal structures and the tube wall, wherein the outer space is at least partially blocked at the upstream end, and wherein the outer space is in fluid flow communication with the inlet of an adjacent downstream metal structure and/or the tubular reactor outlet.