A device has a reaction chamber with at least one feed inlet (5) and at least one evacuation outlet (10). An outside jacket (2a) that is resistant to internal pressure is positioned around the device and contains at least one module (44) through which a reagent and formed products circulate. The module (44) has walls (11) and (12) made of refractory material that are included in a sealed jacket (40). The sealed jacket (40) is connected by a flexible connection to the jacket (2a) and to a heat exchanger that is also linked to the module (44) and to the jacket (2a) by a flexible connection.