Abstract: The present invention is concerned with a process and a plant for the production of sulphuric acid wherein a sulphur dioxide-containing feed gas is converted, at least in part, with oxygen in at least two contact stages of main contacts arranged in series, to generate sulphur trioxide, and wherein generated sulphur trioxide-containing gas is conducted to an absorber and converted therein to sulphuric acid. In order to be able to economically process feed gases of a sulphur dioxide content of between 13 and 66% by volume to sulphuric acid, using conventional catalysts, it is suggested to withdraw from a contact stage connected upstream of the last main contact stage, a partial stream of the sulphur dioxide- and sulphur trioxide-containing gas, to mix the said partial stream with the feed gas to generate a contact gas of a sulphur dioxide content of more than 13% by volume, and to return the same to the first contact stage.

Abstract: This invention relates to a method for the thermal treatment of granular solids in a fluidized bed (3, 3a) which is located in a fluidized-bed reactor (1, 1a), wherein microwave radiation is fed into the fluidized-bed reactor (1, 1a) through at least one wave guide (5), and to a corresponding plant. To improve the efficiency of the microwave irradiation, the irradiation angle of the microwaves is inclined by an angle of 10° to 50°, in particular 10° to 20°, with respect to the principal axis (11) of the fluidized-bed reactor (1, 1a).

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: This invention relates to a method for the protection against corrosion of steel parts made of austenitic or semi-austenitic steel during the production of sulfuric acid. To improve the corrosion resistance of the steel parts which are in contact with the sulfuric acid, it is proposed to use austenitic or semi-austenitic steel which has a Cr content of 15 wt-% to 36 wt-% and an Ni content of 9 wt-% to 60 wt-% and in which the ratio of the chemical elements (Cr+Si)/(Ni+Mo) lies in the range from 0.9 to 1.9 or in which the ratio of the chemical elements Cr/(Ni+Mo) lies in the range from 0.8 to 1.5, and to additionally provide this steel part with an anodic corrosion protection.

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: An electrolyte line extends from the outlet of an electrolysis device to a collecting tank and from the same back to the inlet of the electrolysis device. The electrolyte is passed from the outlet of the electrolysis device to a first container which is disposed at a higher level than a second container. Electrolyte collected in the first container is periodically discharged through a first syphon line into the second container, and electrolyte collected in the second container is periodically discharged through a second syphon line into the collecting tank which is disposed at a lower level than the second container. The outlet end of each syphon line is disposed at a distance above the liquid level of the container disposed thereunder, so that electrolyte always flows only in one of the two syphon lines or in none of the syphon lines. When electrolyte flows in none of the two syphon lines, electrolyte is preferably supplied from the collecting tank into the second container.

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: A catalyst for reacting SO2 with molecular oxygen to form SO3 is suited for a continuous operation at temperatures of 700° C. and above, when the same consists of a carrier and an active component connected with the carrier, the active component consists of 10 to 80 wt-% iron, the carrier has a BET surface of 100 to 2000 m2/g and an SiO2 content of at least 90 wt-%, and the weight ratio carrier:active component is 1:1 to 100:1.

Abstract: An electrolyte line extends from the outlet of an electrolysis device to a collecting tank and from the same back to the inlet of the electrolysis device. The electrolyte is passed from the outlet of the electrolysis device to a first container which is disposed at a higher level than a second container. Electrolyte collected in the first container is periodically discharged through a first syphon line into the second container, and electrolyte collected in the second container is periodically discharged through a second syphon line into the collecting tank which is disposed at a lower level than the second container. The outlet end of each syphon line is disposed at a distance above the liquid level of the container disposed thereunder, so that electrolyte always flows only in one of the two syphon lines or in none of the syphon lines. When electrolyte flows in none of the two syphon lines, electrolyte is preferably supplied from the collecting tank into the second container.

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.

Abstract: An electrolytic cell comprising bipolar electrodes is employed for electrochemical deposition of copper, zinc, lead, nickel or cobalt. An interior space is provided between the cathode side and the anode side of a bipolar electrode. The electrolyte can flow substantially without an obstruction through the interelectrode space between adjacent electrodes. The current densities in the interelectrode space amount to 800 to 8000 A/m.sup.2. Gas is evolved on the anode side of the bipolar electrodes and causes liquid to flow along the anode side. In the middle of the height of the anode side that liquid flow has a vertical component having a velocity of 5 to 100 cm/second. Electrolyte solution flows from the upper edge portion of the anode side to a return flow space, in which the solution flows downwardly. From the return flow space the solution is returned to the lower portion of the interelectrode space.

Abstract: The anode comprises a substantially horizontal carrying bar, which is disposed outside the electrolyte and serves to supply electric current. Two substantially parallel metal surfaces (anode grids) are electrically conductively connected to the carrying bar and with at least one-half of their surface extending into the electrolyte. The carrying bar comprises a copper conductor, to which at least one vertical copper rod is joined. There is a direct electrically conducting connection between the copper conductor and the copper rod. The copper rod is surrounded by a titanium sheath and is an interference fit in that sheath. The copper rod provided with the titanium sheath is disposed between the two anode grids and is electrically conductively connected to said grids.

Abstract: The ammonium polysulfide is produced in at least one electrochemical cell, to which an aqueous ammonium sulfide solution is supplied as electrolyte. The cell comprises an anode, a gas diffusion cathode, and between the anode and the cathode an electrolyte chamber, where the cell voltage is 0.01 to 5V. The cathode has an electrically conductive, gas-permeable carbon layer, over which flows gas containing free oxygen, and which is in contact with the electrolyte. O.sub.2 -containing gas is introduced into the electrolyte chamber, thereby forming hydroperoxide anions (OOH.sup.-) in the electrolyte chamber. From the electrolyte chamber a solution containing ammonium polysulfide and a residual gas are withdrawn.

Abstract: An aqueous solution which contains ammonium polysulfide is proportionally added to the sour water, which contains cyanide ions, ammonium ions, and sulfide ions. At least part of the cyanide ions contained in the sour water is converted to thiocyanate ions by the ammonium polysulfide. The solution which contains ammonium polysulfide is prepared from an aqueous solution by oxidation in an electrochemical cell. That aqueous solution may consist entirely or in part of sour water.