A first microchannel module comprises a first unit operation (22) having microchannels in fluid communication with a first inlet stream and a first outlet stream, and a second unit operation (26) having microchannels in thermal communication with the first unit operation and in fluid communication with a second inlet stream and a second outlet stream. A pressurized vessel (18) at least partially contains the first microchannel module and is occupied by a compressive medium (10) in thermal communication with the first microchannel module. The present invention also includes a removable microchannel unit including an inlet orifice and an outlet orifice in fluid communication with a plurality of microchannels distributed throughout the microchannel unit, and a pressurized vessel adapted to have the microchannel unit mounted thereto, where the pressurized vessel contains a pressurized fluid exerting a positive gauge pressure upon at least a portion of the exterior of the microchannel unit.