Sublimate vapors are recovered from gases in a heat-pipe exchanger system, operating alternately in a condensing mode and a melting mode, for condensing on the exchanger tube surfaces such sublimable vapors as phthalic anhydride, maleic anhydride, naphthalene and fatty acids from gases containing said vapors thereof during the condensing mode, and for melting out the accumulated sublimate solids during the melting mode. Multiple, such as two or more units may be used to provide continuous processing of the sublimate vapor-laden gas stream, at least one operating in the condensing mode while simultaneously at least one may operate in the alternate mode. The cooling of opposite heat-pipe exchanger ends to recover sublimate solids is economical and efficient with ambient air, either alone or with some warm recycle exchanger air to adjust the cooling temperature; and the heating to melt out the accumulated solids is effective with heated air or hot waste gases, such as combustion gases, preferably by incineration of residual sublimate tail gas from which the sublimate was condensed, or other hot combustion gases, but other sources of heating the air or gases may be optionally substituted. Important advantage is present in superior heat exchange efficiency using the heat-pipe exchanger for this service, in the ease of switching from heating to cooling of such exchangers for alternate operation in both condensing and melting modes, in the elimination of intermediary heat transfer media and the separate auxiliary equipment required for the heating and cooling cycles, in the utilization of waste heat from combustion gases, and in the great economy for sublimate storage tank vent condensers through elimination of both cooling water and steam requirements.