The present invention includes a removable microchannel unit including an inlet orifice and an outlet orifice in fluid communication with a plurality of microchannels distributed throughout the removable microchannel unit, and a pressurized vessel adapted have the removable microchannel unit mounted thereto, the pressurized vessel adapted to contain a pressurized fluid exerting a positive gauge pressure upon at least a portion of the exterior of the removable microchannel unit. The invention also includes a microchannel unit assembly comprising a microchannel unit operation carried out within a pressurized vessel, where pressurized vessel includes a pressurized fluid exerting a positive gauge pressure upon an exterior of the microchannel unit operation, and where the microchannel unit operation includes an outlet orifice in fluid communication with an interior of the pressurized vessel.