An apparatus for recovering a desired gas from the effluent of a chemical process reactor that utilizes two or more separate gas compositions in sequence, the apparatus comprising; (a) the chemical process reactor provided with at least one inlet and one or more lines for introducing two or more separate gas compositions into the chemical process reactor; (b) an effluent line from the chemical process reactor capable of removing effluents of the two or more separate gas compositions introduced into the chemical process reactor; (c) a check valve in the effluent line allowing removal of the effluent from the chemical process reactor, the check valve having a set cracking pressure and preventing any substantial flow of effluent to the chemical process reactor; (d) a recovery line, having a connection to the effluent line upstream of the check valve in the effluent line, capable of removing a desired gas from the effluent line; (e) an automatic valve in the recovery line; (f) a process controller or controllers (94, 104) capable of controlling introduction of two or more gas compositions in sequence into the chemical process reactor and capable of controlling operation of the automatic valve in the recovery line so that the automatic valve is open during at least a portion of the time when the desired gas is in the effluent line as a part of a gas composition, where the process controller or controllers (94, 104) are capable of generating and receiving process signals by signal connections (95, 96, 98, 99) with the automatic valve and with one or more of the chemical process reactor and the inlet(s) and/or line(s) for introducing the gas compositions into the chemical process reactor; and, (g) a compressor in the recovery line capable of removing the desired gas from the effluent line in sufficient flow to close the check valve in the effluent line by reducing the pressure at the check valve below the check valve's cracking pressure setting. (a) the chemical process reactor provided with at least one inlet and one or more lines for introducing two or more separate gas compositions into the chemical process reactor; (b) an effluent line from the chemical process reactor capable of removing effluents of the two or more separate gas compositions introduced into the chemical process reactor; (c) a check valve in the effluent line allowing removal of the effluent from the chemical process reactor, the check valve having a set cracking pressure and preventing any substantial flow of effluent to the chemical process reactor; (d) a recovery line, having a connection to the effluent line upstream of the check valve in the effluent line, capable of removing a desired gas from the effluent line; (e) an automatic valve in the recovery line; (f) a process controller or controllers (94, 104) capable of controlling introduction of two or more gas compositions in sequence into the chemical process reactor and capable of controlling operation of the automatic valve in the recovery line so that the automatic valve is open during at least a portion of the time when the desired gas is in the effluent line as a part of a gas composition, where the process controller or controllers (94, 104) are capable of generating and receiving process signals by signal connections (95, 96, 98, 99) with the automatic valve and with one or more of the chemical process reactor and the inlet(s) and/or line(s) for introducing the gas compositions into the chemical process reactor; and, (g) a compressor in the recovery line capable of removing the desired gas from the effluent line in sufficient flow to close the check valve in the effluent line by reducing the pressure at the check valve below the check valve's cracking pressure setting.