Abstract: To protect a plate-type heat exchanger (1) against corrosion due to the attack of sulfuric acid, it is proposed in accordance with the invention that the region through which flows sulfuric acid has at least one metal cathode (16, 17) and one reference electrode (27), that at least half the metal plates (7) have an electric contact (23) which is connected with the anode (21) of an electric d.c. voltage source of variable electric voltage, that the metal cathode (16, 17) likewise is electrically connected with the d.c. voltage source, and that the d.c. voltage source belongs to a potentiostat (20) which is electrically connected with the reference electrode (27).

Abstract: To protect a plate-type heat exchanger (1) against corrosion due to the attack of sulfuric acid, it is proposed in accordance with the invention that the region through which flows sulfuric acid has at least one metal cathode (16, 17) and one reference electrode (27), that at least half the metal plates (7) have an electric contact (23) which is connected with the anode (21) of an electric d.c. voltage source of variable electric voltage, that the metal cathode (16, 17) likewise is electrically connected with the d.c. voltage source, and that the d.c. voltage source belongs to a potentiostat (20) which is electrically connected with the reference electrode (27).

Abstract: A gas mixture comprising molecular oxygen and 15 to 60 vol-% SO2 flows through a first catalyst layer which contains a catalyst containing vanadium pentoxide, and directly subsequently through a second catalyst layer which contains a catalyst containing iron. With an inlet temperature of 350 to 600° C., the gas mixture is introduced into the first catalyst layer which contains a granular V2O5 catalyst and 20 to 80 wt-% catalytically inactive inert material. Directly subsequently, the gas mixture is introduced into the second catalyst layer with a temperature of 500 to 750° C. Preferably, the catalyst of the second catalyst layer contains 3 to 30 wt-% arsenic oxide. There is produced an SO3-containing product gas with a volume ratio of SO2: SO3 of not more than 0.1.

Abstract: The electrolytic cell has a trough-like container with a bottom, with side walls and with at least one inlet and at least one outlet for the electrolyte. Numerous plate-like electrodes are disposed in the container and are partly immersed in an electrolyte bath. The bottom of the container which is in contact with the electrolyte bath has numerous openings for the passage of electrolyte, and below the bottom there is disposed at least one distribution chamber for recirculated electrolyte. At least one of the side walls of the container is equipped with at least one recirculation chamber for recirculating electrolyte from the electrolyte bath into the distribution chamber, the upper portion of the recirculation chamber being connected with the electrolyte bath and the lower portion of the recirculation chamber communicating with the distribution chamber.

Abstract: The electrolyte is supplied from a reservoir through at least one supply line to an electrolysis area including anodes and cathodes and at least one electric d.c. voltage source, and used electrolyte is at least partly recirculated from the electrolysis area back to the reservoir through at least one discharge line. Between a first contact point in the electrolyte of the supply line and a second contact point in the electrolyte of the discharge line there is a bridge line containing electrolyte, where the ohmic resistance R1 of the electrolyte in the bridge line between the first and the second contact point is not more than 10% of the ohmic resistance R2 which exists between the first and the second contact point in the electrolyte flowing through the reservoir. The amount of electrolyte flowing through the bridge line per unit time is not more than 5% of the amount of electrolyte flowing in the supply line in the vicinity of the first contact point.

Abstract: This invention concerns a process in which gases or gas mixtures are reacted in the presence of an ion-conductive liquid in an electro-chemical cell. The cell has at least one anode (2) and at least one cathode (3) to which an external electrical constant potential is applied so that a direct current flows through the ion-conducting liquid. In the lower region of the cell a sump (4) of ion-conductive liquid is located into which the electrodes are partially immersed. At least 20% of the entire surface of at least one of the electrodes is located outside the sump in an upper region through which gas flows. This upper region of the cell is sprayed or irrigated with the ion-conductive liquid and the electrode surface at least partially wet. During this wetting process, the gas flows across the electrode surface.

Abstract: An electrolytic cell is disclosed which comprises: (a) an electrolyte; and (b) a plurality of bipolar electrodes surrounded by the electrolyte and electrically connected in series during operation of the cell, the bipolar electrodes each comprising a cathode side, an anode side, and an electrically conductive connection between the cathode side and the anode side, wherein the cathode side and the anode side of at least one of the bipolar electrodes are movable and mechanically separable with respect to each other so that one of the two electrode sides can be removed from the cell, while the other electrode side remains in the cell.