NOVELTY - A pseudo-isothermal flow reactor (100) comprises greater than or equal to 2 reaction enclosures (108, 114) having outer surface which is in thermal contact with cooling medium and contains reaction enclosure inlet (110) and reaction enclosure outlet (112), and cooling medium enclosure (102) which holds cooling medium under pressure at boiling point of cooling medium and has cooling medium inlet and cooling medium outlet in which inlets and outlets are connectable.    USE - A pseudo-isothermal flow reactor used for production of synthetic natural gas, methanol and formaldehyde (all claimed).    ADVANTAGE - Capital cost is reduced. By-products such as ethanol, ketones and aldehydes and carbon deposits are reduced.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) reactor section comprising reactor (100) having 1st and 2nd reaction enclosures (108, 114), cooler and gas/liquid separator having inlet, gas outlet and liquid outlet in which cooler inlet is connected with 1st reaction enclosure inlet, cooler outlet is connected with separator inlet and separator gas outlet is connected with 2nd reaction enclosure inlet;    (2) production of synthetic natural gas in multiple reaction enclosure pseudo-isothermal reactor which involves directing synthesis gas to contact 1st material catalytically active in methanation inside 1st methanation reaction enclosure, withdrawing 1st gas rich in methane and water from 1st methanation reaction enclosure, cooling 1st gas rich in methane and directing to gas/liquid separator, withdrawing condensate and methane rich gas from separator, directing methane rich gas to contact 2nd material catalytically active in methanation inside 2nd methanation reaction enclosure and withdrawing synthetic natural gas from 2nd reaction enclosure;    (3) production of methanol which involves directing synthesis gas to contact 1st material catalytically active in methanol synthesis inside 1st reaction enclosure, withdrawing 1st gas rich in methanol from 1st methanation reaction enclosure, cooling 1st gas rich in methanol and directing to gas/liquid separator, withdrawing condensate and intermediate process gas from separator, directing intermediate process gas to contact 2nd material catalytically active in methanol inside 2nd methanation reaction enclosure and withdrawing 2nd product gas rich in methanol from 2nd reaction enclosure; and    (4) production of formaldehyde which involves directing feed gas containing methanol and oxygen to contact 1st material catalytically active in formaldehyde synthesis inside 1st reaction enclosure, withdrawing 1st product gas rich in formaldehyde from 1st reaction enclosure, combining product rich in formaldehyde with feed containing methanol forming intermediate process gas, directing intermediate process gas to contact 2nd material catalytically active in formaldehyde synthesis inside 2nd reaction enclosure and withdrawing 2nd product gas rich in formaldehyde from 2nd reaction enclosure.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the pseudo-isothermal reactor.    Pseudo-isothermal flow reactor (100)    Cooling medium enclosure (102)    Reaction enclosures (108, 114)    Reaction enclosure inlet (110)    Reaction enclosure outlet (112)