Abstract: A method of maintaining a given content of a substance A in an aqueous solution where it is continuously consumed and where the redox potential E, at least within the range of concentration used, approximately satisfies the equation:E=G+F(x)wherein x is the content of A, F is a function of x whose derivative dF/dx approaches zero when x assumes a high value, and G on the whole is independent of x but is influenced by other parameters, such as pH, temperature or the like. The addition of A is controlled in such manner that a set value of the redox potential is maintained. The set value is determined by increasing or decreasing the addition of A in a predetermined manner, whereupon the redox potential is measured, and the measured value is used for determining the set value.

Abstract: During the pickling, etching, chemical shaping etc. of steels, stainless steels, special alloys and special metals and the dissolution of those metals, metalliferous solutions of the acids employed arise in the course of such processes which must either be disposed of by neutralization or be used for the recovery of the acids and metals by expensive processes. According to the invention the production or recovery of nitric acid or a mixture of nitric acid and hydrofluoric acid takes place by spray-roasting the solutions at temperatures of 200.degree. to 500.degree. in a reactor (1) and subsequent absorptions or condensation of the gases generated in column means (7, 8) at temperatures of 0.degree. to 70.degree. C.

Abstract: A method for the removal of nitrogen oxides from waste gases and for obtaining nitric acid is described. The waste gas is charged with the required amount of hydrogen peroxide, converted into the gas phase, and the gas mixture is reacted on a solid catalyst to hydrogen nitrate, which is either withdrawn for further use or is converted into nitric acid either by condensation or by scrubbing with water. The method permits the removal of NO.sub.x at low concentrations below 2000 ppm with efficiencies above 90%.

Abstract: In a process for the removal of nitrogen oxides (NO.sub.x) from pretreated flue gases having a nitrogen oxide content which is low by means of a multi-stage washing process employing a nitric acid (HNO.sub.3) solution to which is added hydrogen peroxide (H.sub.2 O.sub.2), the process including a first stage in which the pretreated flue gases are received and contacted with nitric acid (HNO.sub.3) vapor to at least partially oxidize nitrogen monoxide (NO) present in the pretreated flue gases to nitrogen dioxide (NO.sub.2) and result in a first stage flue gas, and a second stage in which the first stage flue gas in received and washed with an aqueous nitric acid (HNO.sub.3) solution to which is added H.sub.2 O.sub.2 to remove nitrogen dioxide (NO.sub.2) and any remaining nitrogen monoxide (NO) from the first stage flue gas and result in a second stage flue gas, wherein the pretreated flue gases have been treated to free the flue gases of contaminants including at least one of sulfur dioxide (SO.sub.

Abstract: The mixture of aqueous nitric and nitrous acids which is produced by the absorption of nitrogen oxides with water in the manufacture of nitric acid is conducted to a closed vessel, where the acid mixture is reacted with oxygen, preferably under pressure, and is then returned to the absorber. This treatment has been found to enhance the absorption of the nitric oxide (NO) component of the gas mixture of NO and NO.sub.2 which is supplied to the absorber in the production of nitric acid. Normally, nitric oxide has a low solubility in the mixture of nitric and nitrous acids. Because nitric oxide oxidation is the controlling factor in the operation of nitric acid plants, this enhanced absorption provides for more efficient and economic nitric acid manufacture, as well as for the reduction of emissions of nitrogen oxides in the acid plant tail gases.The same invention is also applicable to the removal of nitrogen oxides from emissions generated in processes other than nitric acid manufacture.

Abstract: A process for the generation of mechanical energy in the ammonia oxidation step of process for the production of nitric acid is disclosed, whereby the utilization of process heat is improved, particularly the exploitation of heat contained in NO.sub.x gases and including process heat recovered at low temperature. The process involves evaporating and superheating liquid ammonia upstream of the oxidation step, at a pressure which is a multiple of the pressure required for the combustion, using the process heat of the NO.sub.x gases formed during the the combustion and then expanding the superheated ammonia in a turbine, thus generating mechanical energy.

Abstract: A process is provided for removing nitric oxide from effluent vent or flue gas by subjecting the gas cyclically to scrubbing with a nitric acid stream and to electrolysis of the resulting nitric acid stream containing dissolved nitric oxide to oxidize the dissolved nitric oxide to nitric acid, for purposes of economy, for achieving a useful by-product, and for minimizing environmental pollution.

Abstract: A method for regenerating an aqueous liquid comprising nitrous acid and/or oxides of nitrogen is characterized by feeding the liquid to a column such that the liquid descends through the column. An aqueous solution comprising nitric acid is heated to its boiling point such that the heated nitric acid refluxes into the packed column. An oxygen-containing gas is passed into the liquid, whereby the liquid is converted substantially to nitric acid as it descends in the column.

Abstract: The invention relates to a method of manufacturing bismuth germanate (Bi.sub.4 Ge.sub.3 O.sub.12) crystals using the Bridgman technique. A high degree of crystal perfection and an acceptable level of inclusions are obtained by changing the stoichiometry of the starting mixture in favor of Bi.sub.2 O.sub.3, such that the starting mixture contains between 40.2 and 40.5 mol. % of Bi.sub.2 O.sub.3 and between 59.8 and 59.5 mol. % of GeO.sub.2.

Abstract: An oxido-reduction process for nitrogen oxides contained in a gas stream also containing oxygen, in a countercurrent gas-liquid contact device. In this process,(a) for values of the ratio NO/NO.sub.2 greater than 1, in that section of the gas-liquid device where the NO.sub.x content in the gas stream is less than about 6000 vpm, the ratio K, which is the ratio of the liquid retention volume in m.sup.3 to the flow rate of the gas stream in Nm.sup.3 /hour, is increased so that the NO.sub.x are preferentially absorbed according to the reaction: NO+NO.sub.2 +H.sub.2 O.fwdarw.2HNO.sub.2 (liquid phase); and(b) oxidation is then induced, to reduce the value of the ratio NO/NO.sub.2 and to restore the conditions of stage (a).In practice, the operating point describes a curve A.sub.0 A.sub.2 B.sub.1 A.sub.3 B.sub.2 A.sub.4, as shown in FIG. 1.

Abstract: The present invention involves a process for removing nitrogen oxides from an off gas stream, such as nitric acid plant tail gas. The off gas is scrubbed with concentrated nitric acid to remove nitrogen oxides to a concentration below about 200 ppm. The nitric acid used in the scrubbing step is subsequently stripped of recovered nitrogen oxides which can be recycled back to a nitric acid plant. The oxidized nitric acid is recovered as concentrated nitric acid which can be used in the initial scrubbing step and/or recovered as product.

Abstract: A process for making fuming nitric acid involving the reacting of nitrogen dioxide gas with dry hydrogen chloride gas to produce the fuming nitric acid directly, and to produce as a co-product nitrosyl chloride gas; separating the formed liquid fuming nitric acid from the reaction gases and co-product gas; and stripping the liquid product and demisting the gaseous product to complete their separation.

Abstract: This invention relates to a continuous process for the recovery of nitrogen oxides from a gaseous mixture containing, with other chemicals, said nitrogen oxides and in general some oxygen. This process is characterized by the fact that this gaseous mixture flows simultaneously with an aqueous liquid which may be pure water or an aqueous nitric acid solution over a carbonaceous adsorbing layer which may be made of activated carbon.

Abstract: Nitric oxide is prepared by the oxidation of ammonia produced by the Haber-Bosch synthesis technique by (a) vaporizing and heating water to superheated steam; (b) electrolyzing the superheated steam in a high temperature electrolysis cell to oxygen and hydrogen; (c) reacting said hydrogen with atmospheric nitrogen thereby forming ammonia by the Haber-Bosch process; and (d) oxidizing said ammonia to nitric oxide and water vapor in the anode of said electrolytic cell with the oxygen produced by said electrolysis.

Abstract: A cyclic process for removing lower valence nitrogen oxides from gaseous mixtures includes treating the mixtures in a first stage with an acidic aqueous media including a peroxygen oxidant to form nitric acid and higher valence nitrogen oides and to capture these oxides as alkali metal salts, especially nitrites and nitrates, in a carbonate/bicarbonate-containing product aqueous media in a second stage. Highly selective recovery of nitrates in high purity and yield may then follow, as by crystallization, with the carbonate and bicarbonate alkali metal salts strongly increasing the selectivity and yield of nitrates. The product nitrites are converted to nitrates by oxidation after lowering the product aqueous media pH to below about 9.Where the gas mixtures include both sulfur dioxide and lower valence nitrogen oxides, the processes for removing lower valence nitrogen oxides and sulfur dioxide may be combined into a single removal/recovery system, or may be effected in sequence.

Abstract: To remove nitrous gases from gas mixtures there is needed a process and apparatus by which they can be eliminated quickly, without formation of secondary waste and as cheaply as possible. This is done by scrubbing the nitrous gases out of the gaseous mixture with 15-50% nitric acid solution and treating this solution additionally with gaseous oxygen, especially atmospheric oxygen.

Abstract: Nitric oxide, NO, and nitrogen peroxide, NO.sub.2, are facilely removed from gaseous admixtures comprising the same, together with gaseous oxygen, advantageously in a plate tower for the commercial production of nitric acid, by countercurrently oxidizing/absorbing said gaseous feedstream in aqueous solution, in a gas/liquid phase contactor, and wherein that section of said phase contactor the NO.sub.x content in the gaseous feedstream is less than 6000 vpm, the improvement which comprises that the residence time in said less than 6000 vpm section of said phase contactor, is increased to a value such that the ratio K, of the liquid retention volume in cubic meters in said phase contactor to the rate of flow therein of said gaseous feedstream in Nm.sup.3 /hour, in excess of 5.10.sup.-4 hour.

Abstract: The invention is regeneration and recirculation of nitrogen oxides in the exhaust gas of a nitric acid plant without using any material current and heat energy other than that generated in the process of producing nitric acid. Nitrogen oxide is recovered by at least two adsorbers each containing an acid resistant zeolite molecular sieve and operating in an alternate heat cycle; adsorption occurring at 20-40 degrees C. and regeneration at 300-350 degrees C. The hot gas exiting from the oxidation unit used in the production of nitric acid is used to regenerate the adsorbers and the nitrogen oxides set free during the said regeneration are introduced into the main feed stream of the nitric acid plant. In the final stage of the regeneration the adsorbers are cooled by rinsing them with exhaust gas or air at a temperature of 20-40 degrees C.

Abstract: Nitrogen oxides are removed from gaseous mixtures by treatment with an aqueous solution of nitric acid having a concentration by weight from about 35% to about 58% and containing by weight at least 0.001% but less than 25% of hydrogen peroxide whereby the nitrogen oxides are converted to nitric acid.

Abstract: There is described a process for the reconstitution of NO.sub.X gases produced by the thermal decomposition of metal nitrates to nitric acid comprising the steps of:1. contacting the NO.sub.X gases in counter-current relationship in one or more packed columns with cooled 50 to 60 percent nitric acid to remove as nitric acid a major portion of the originally introduced NO.sub.X values and provide an acid solution leaving the column having a temperature below about 180.degree. F. to remove as nitric acid a major portion of the originally introduced NO.sub.X values;2. compressing the residual gases from step 1 to from about 2 to about 6 atmospheres absolute;3. contacting the compressed gases from step 2 with from about 50 to about 60 percent nitric acid in a packed absorption column in counter-current relationship to remove substantially all of the remaining NO.sub.X values from the gas stream as HNO.sub.3 ; and4. recovering 50-60% nitric acid as it accumulates.

Abstract: Nitric oxides can be absorbed from gas mixtures containing nitric oxides (NO and NO.sub.2) and oxygen by absorption with aqueous solutions. According to the invention, the absorption is effected in bubble columns, superficial velocities of 2 to 30 cm/second being maintained. It is advantageous to connect several bubble columns in series such that the gas and absorption liquid pass in counter-current to one another. In this embodiment, considerably less counter-current stages are required to achieve a high degree of absorption of NO.sub.x than in the case of conventional processes. At superficial velocities of 10 to 30 cm/second, large bubbles of gas can rapidly form from the gas introduced and can interact with the absorption liquid only with difficulty. In this case, gas distributor devices are incorporated in the bubble column. Since NO.sub.2 is more readily absorbed than NO, it is advantageous to connect flow reactors, in which NO.sub.2 is formed from NO and O.sub.2, upstream of the bubble columns.

Abstract: A process for the manufacture of nitric acid comprises contacting a mixture of starting gas, containing oxygen, nitrogen oxides and, possibly water, this mixture being previously cooled, oxidized and, optionally dried, with cooled nitric acid aqueous solution to provide a solution of nitrogen oxides in nitric acid aqueous solution, consisting fundamentally in that the said solution is reacted according to the reaction:2 NO.sub.2 (and/or N.sub.2 O.sub.4)+1/2 O.sub.2 +H.sub.2 O.fwdarw.2 HNO.sub.3with the air previously contacted with the solution of nitrogen oxides in the highly concentrated nitric acid resulting from the said reaction, so as to rid the said highly concentrated acid of the nitrogen oxides dissolved therein.

Abstract: A process for preparing manganese nitrate solution by leaching manganese ore containing manganese dioxide in an aqueous slurry containing dissolved nitrogen dioxide gas. The reaction is controlled by monitoring the pH of the aqueous slurry, and adjusting the relative concentration of the manganese ore containing manganese dioxide and/or the rate of addition of nitrogen dioxide containing gas, to establish and maintain the leaching reaction.

Abstract: The invention relates to a process for the production of nitric acid with a concentration of 50-65% by weight by compression of a reaction gas and its absorption in water, said reaction gas originating from an ammonia combustion process, containing nitrogen oxides and being under pressure. The nitric acid produced by the process according to the invention is particularly suitable for further processing to fertilizer.

Abstract: In a process for producing nitric acid, a mixture of oxygen, nitrogen, nitric oxide, nitrogen dioxide, and dinitrogen tetroxide is introduced into an absorption column into which cold oxygen (below 0.degree. C.) is introduced. H.sub.2 O is introduced into the upper reaches of the column and reacts with the nitrogen dioxide and dinitrogen tetroxide to form nitric acid. The low oxygen temperature helps to shift the equilibrium between nitric oxide and oxygen to dinitrogen tetroxide and in favor of reacting the latter with water to form nitric acid.

Abstract: An improved process for preparing nitric acid. The process is characterized by the steps of (1) contacting gaseous nitrogen dioxide with feed water to yield aqueous liquid nitric acid and a gaseous by-product; (2) contacting the gaseous by-product with ammonia and water to yield a decontaminated gaseous effluent and an aqueous liquid by-product comprising aqueous ammonium nitrate, ammonium nitrite and nitric acid, and (3) feeding the liquid product to the first step above and reducing the amount of said feed water up to an amount equivalent to the water fed in the liquid product. The process is characterized by substantially reduced water consumption and improved pollution control economics and by the innocuous disposal of the hazardous ammonium nitrite.

Abstract: An improved process for the manufacture of nitric acid involving catalytic oxidation of ammonia and passage of the resulting nitric oxide through columnar absorption zones, the improvement particularly comprising oxygen-enrichment of that gas passing through the absorption zones at one or more regions of the zones wherein the absorption reaction is from 50 to 90% complete. Further, the invention contemplates the oxygen-enrichment of bleaching air and a reduction in the rate at which bleaching air or other air is taken to form secondary air. The invention results in improved production rates of nitric acid and reductions in the concentration of nitrogen oxides in vent gas.

Abstract: This invention relates to an improved process for preparing cyanogen chloride by reacting chlorine and hydrogen cyanide in a manganous chloride-containing aqueous medium to form gaseous cyanogen chloride and dissolved hydrogen chloride and to the subsequent conversion of the hydrogen chloride to chlorine employing manganese dioxide and nitric acid as cyclic reagents.

Abstract: This invention is based on the factors that both oxygen gas and nitrous oxides as gas are paramagnetic; as well as are quite soluble in saturated halogenated hydrocarbon liquids; whereas nitrogen is not paramagnetic; thus providing a means of separation of the oxygen and nitrous oxide from the nitrogen by high intensity magnetic forces created by an electromagnet.The absorber liquid, saturated with dissolved oxygen and nitrous oxides, or ammonia is then ozonated using the solvent or absorber liquid dielectric as the dielectric in an ozone generator.The effluent is stripped of nitric oxide with water to form nitric acid or by reduced pressure to recover nitric oxide.

Abstract: Nitric oxide may be removed from gases with which it is admixed by contacting the gases with aqueous solutions containing nitrate ions in sufficient concentration to oxidize the nitric oxide to nitrous acid and to retain it in the solution under stable conditions. Other oxides of nitrogen can also be absorbed producing nitrous acid which is retained in the aqueous solution in a similar manner. Thereafter, the scrubbing solution is regenerated under controlled conditions, producing a gas stream which contains the recovered nitrogen oxides in relatively high concentration and a scrubbing solution which can be recycled. The recovered nitrogen oxides may be used in the manufacture of nitric acid or other compounds or decomposed into harmless gases.

Abstract: A method for the removal of nitrogen oxides from the off-gases of a nitric acid manufacturing facility. The off-gases containing the nitrogen oxides are first contacted at atmospheric pressure and at a temperature below about 90.degree. F with a countercurrently flowing stream of about 10 to about 35% by weight nitric acid to absorb the nitrogen oxides. The rate of flow of the nitric acid is controlled so that the partial pressure of the nitrogen oxides absorbed in the nitric acid is lower than the partial pressure of the nitrogen oxides in the off-gas feed stream. The nitric acid containing the absorbed nitrogen oxides is then countercurrently contacted with a small amount of air at a temperature between about 60.degree. and about 120.degree. F to liberate the absorbed nitrogen oxides so that they can be returned to the reactor section of a nitric acid plant. The nitric acid being recycled to absorb more nitrogen oxides.

Abstract: The present invention provides a novel process for treating a fluid stream carrying various components including nitrogen oxides, wherein the stream is subjected to oxidative reactions under gaseous and absorptive conditions to convert a portion of the nitrogen oxides to nitric acid and thereby simultaneously reduce the concentration of nitrogen oxides in the stream discharge.

Abstract: A method of treating raw materials containing components of metals of the group IVb of the Periodic Table, which comprises heat-treating a raw material of a component of a metal of the group IVb of the Periodic Table containing coloring poisonous metal components such as Mn, V and Cr components in the presence of a flux composed mainly of an alkali metal nitrate or an alkali metal peroxide which is a thermal decomposition product of the alkali metal nitrate in an amount 2 to 5 times the amount of the raw material on the weight basis in a non-reducing atmosphere to thereby effect fluxing reaction, and subjecting the resulting fluxing reaction product to a leaching treatment of at least one stage in an aqueous medium to separate the fluxing reaction product into said coloring metal components and a concentrate of the component of the group IVb of the Periodic Table which is acid-soluble and substantially free of said coloring poisonous metal components.

Abstract: The present invention relates to a process for obtaining nitric acid of a concentration higher than the azeotropic concentration by means of the absorption of nitrogen oxides in water or diluted nitric acid and the partial pressure of the nitrogen oxides before absorption is raised partly by compression of the gases that contain the nitrous gases and partly by means of a cycle of diluted nitric acid which is decomposed by the action of the NO contained in the gases, enriching them in NO.sub.2 and which subsequently reform by absorption of NO.sub.2 in water when the partial pressure of the nitrogen oxides is low.

Abstract: A method of generating electricity and fixing nitrogen oxides is disclosed in which coal is gasified at high pressure to produce a mixture of carbon monoxide and carbon dioxide, with a minimal amount of hydrogen and water, as a gas stream. This high pressure gas stream is mixed with an oxidant to introduce mixtures of nitrogen and oxygen and then completely combusted. The high temperature combustion gas is then further ionized to form a plasma and its velocity is increased, while its high pressure is maintained. The high pressure, high velocity plasma is fed into an MHD generator to produce electricity and where it is adiabatically expanded to fix the nitrogen oxides contained therein. The final gas stream, with the fixed nitrogen oxide compounds therein, is thereafter reacted to form nitric acid.

Abstract: A process for the preparation of nitric acid from nitrogen oxides, oxygen and water which utilizes an aqueous stripping liquid having a nitric acid content within a specified range which passes through a reaction zone. By controlling the process parameters within specified ranges three regions are provided with the reaction zone.

Abstract: Nitric oxide may be removed from gases which it is admixed by contacting the gases with aqueous solutions containing nitrate ions in sufficient concentration to oxidize the nitric oxide to nitrous acid and to retain it in the solution under stable conditions. Other oxides of nitrogen can also be absorbed producing nitrous acid which is retained in the aqueous solution in a similar manner. Thereafter, the scrubbing solution is regenerated under controlled conditions, producing a gas stream which contains the recovered nitrogen oxides in relatively high concentration and a scrubbing solution which can be recycled. The recovered nitrogen oxides may be used in the manufacture of nitric acid or other compounds or decomposed into harmless gases.

Abstract: Dinitrotoluene and nitric acid are concurrently produced by continuously roducing toluene, nitrogen dioxide and oxygen in a molar ratio of at least 4 mols nitrogen dioxide and 1 mol oxygen per mol toluene into a reaction zone containing a reaction medium comprising dinitrotoluene and 93-103% nitric acid, maintaining the resulting mixture of toluene, nitrogen dioxide, oxygen and reaction medium under a pressure of at least 100 psig and at a temperature up to about 100.degree. C. until a reaction product containing dinitrotoluene and 93-103% nitric acid in the ratio of about 1 mol dinitrobenzene and 2 mols nitric acid is produced, and continuously removing said reaction product from the reaction zone.

Abstract: Waste gas containing sulfur oxide (SO.sub.x) and nitrogen oxide (NO.sub.x) is mixed with an ozone-containing gas to have the value x of NO.sub.x fall in the range of 1.2 to 2.5 and thereafter brought into contact with an aqueous solution containing sulfuric acid, nitric acid and an iron compound to be deprived of SO.sub.x and NO.sub.x. To the solution with which the waste gas has been brought into contact, air or oxygen is added to effect oxidation of the part of said oxides still remaining therein in an unoxidized state and regenerate the activity of the iron compound functioning as a catalyst. Part of the solution to which the addition of air or oxygen has been made is recycled as the solution for the purpose of contact with waste gas.

Abstract: A process for reducing the level of nitrogen oxide contaminants in an industrial effluent gas comprises (a) oxidizing said gas to convert the contaminants substantially to a mixture of N.sub.2 O.sub.3 and NO.sub.2 and (b) passing the oxidized gas through an aqueous medium containing an amount of hydrogen peroxide maintained at a level just sufficient to oxidize the N.sub.2 O.sub.3 and NO.sub.2 to HNO.sub.3.

Abstract: A process for efficiently removing nitrogen oxides with a very high rate from waste gas is provided wherein nitrogen monoxide contained in the gas is oxidized by chlorine dioxide or ozone, and then the oxidized gas is brought into contact with sodium chlorite in water solution in an absorption column.

Abstract: Process for removing nitrogen oxides from a gaseous mixture comprises contacting the mixture with an aqueous liquid in the presence of a knitted wire mesh packing material of stainless steel containing at least 8% Ni and having a diameter of from 0.003 to 0.015 inches.