Apparatus, methods, and processes are provided for a tube reactor including multiple, substantially parallel reaction tubes arranged within a tube reactor shell, the reaction tubes spaced apart such that a thermal fluid can flow between the tubes and transfer heat between the tubes and the thermal fluid during operation; an inlet head defining an inlet head space, where the inlet head space is in fluid communication with an inlet end of the reaction tubes, and an outlet head including an outlet head shell and at least one insert positioned within an outlet head space defined by the outlet head, where the insert defines a reduced volume outlet head space relative to that defined by the outlet head, and where the reduced volume outlet head space is in fluid communication with an outlet end of the reaction tubes and in fluid communication with a reactor outlet.