NOVELTY - Reacting feed gas (FG) and separating product from unreacted FG, involves use of several serially connected compartments (CP) comprising reaction zone (RZ) and separation zone (SZ). First and last CP are joined to form loop. SZ outlet port (SOP) of CP (A) is connected to RZ inlet port of CP (B). FG is reacted in CP (A) and simultaneously unreacted FG is separated in SZ and ejected from SOP.    USE - For producing ethane and ethylene by metal oxide catalyzed reaction of methane in presence of oxygen, methanol by direct partial oxidation of methane in presence of oxygen, and for converting abundant natural gas reserves into useful feedstocks.    ADVANTAGE - The method and apparatus enables simultaneous and continuous reaction of feed gas to form product and separate product from unreacted feed gas. As the method is continuous, reactions which normally proceed to only very low conversions can be carried out efficiently when compared to conventional methods. The method and apparatus exhibit conversion of methane to ethane and ethylene (C2) of greater than 60 %, C2 yield of greater than 50 % and C2 selectivity of 80-90 %, and eliminate problems associated with solid handling, non-uniform solid flow, and solid breakdown. The apparatus also enables rapid separation of products formed.    DETAILED DESCRIPTION - Method for reacting feed gas to produce product and separate product from unreacted feed gas, involves use of serially connected compartments. The first and last compartment of the series are joined to form a loop. The compartments comprises reaction zone having reaction zone inlet port connected to feed gas line and carrier gas line, and separation zone having upstream section connected to downstream section with separation zone with recovery port for recovering product passing through the connection between the upstream and downstream sections. The downstream section includes separation zone outlet port(s). The compartments are connected such that separation zone outlet port of each compartment is connected to reaction zone inlet port of succeeding compartment in series. Pressurized feed gas is supplied to reaction zone inlet port of compartment (A) (first compartment in series) and pressurized carrier gas is supplied to reaction zone inlet port of preceding compartment upstream in series so that feed gas reacts in reaction zone of compartment (A) to form a mixture of product and unreacted feed gas. The mixture is passed to upstream section of separation zone of compartment (A) where product is separated from unreacted feed gas so as to effect simultaneous reaction and separation. The unreacted feed gas is ejected from separation zone outlet port, and transferred to reaction zone inlet port of compartment (B) (next compartment in series) along with carrier gas. After transfer of unreacted feed, product is recovered from separation zone recovery port of compartment (A). After product recovery compartment (A) is purged with carrier gas. Before transfer of unreacted feed, feed gas supply from reaction zone inlet port of compartment (A) to reaction zone inlet port of compartment (B) and carrier gas supply from reaction zone inlet port of preceding compartment to reaction zone inlet port of compartment (A), are switched so that feed gas and unreacted gas react in reaction zone of compartment (B) to produce mixture comprising product and unreacted feed gas. The mixture is passed to upstream section of separation zone of compartment (B) and product is separated from unreacted feed gas so as to effect simultaneous reaction and separation. The unreacted feed gas is ejected from separation zone outlet port. The feed gas transfer, product recovery, carrier gas purging into compartment (A) and switching of feed gas and carrier gas supply are performed in a continuous manner so that compartment in which the reaction and separation occurs advances sequentially around the series of compartment in closed loop.    An INDEPENDENT CLAIM is also included for apparatus used for reacting feed gas to produce reaction mixture, comprising serially connected compartments with first and last compartment connected to form a loop; connection between compartments which permit recovery of product ejected from separation zone outlet port; and unit for controlling introduction of feed gas, movement of unreacted feed gas and recovery of product so that the compartment in which reaction and separation occurs advances sequentially and continuously around series of compartment in closed loop.    DESCRIPTION OF DRAWING(S) - The figure shows the method for reacting feed to produce product and separating product from unreacted feed.    Separation zone (SZ1, SZ2, SZ3)    Reaction zone (RZ1)    Inlet port (IP1)    Outlet port (OP2, OP3)    Valve (1, 2, 3, 4)    Transfer line (5)    Recovery line (6,7)