Abstract: An exhaust gas containing nitrogen oxides is efficiently purified without the necessary use of catalysts by contacting the exhaust gas with a nitrile compound at high temperature in the presence of oxygen, whereby the nitrogen oxides and the nitrile compound are selectively decomposed into harmless materials.

Abstract: Industrial exhaust gas containing nitrogen oxides is treated with an aqueous solution of an iron chelate complex salt which contains essentially a sulfite salt at the time of treatment whereby nitrogen oxides which have been difficult to catch can be absorbed with a high absorbing rate even when the concentration of nitrogen oxides is low in the exhaust gas or sulfur dioxide is included in the gas, and simultaneous desulfurizing can be attained in this case. Said aqueous solution has a large absorbing capacity and may contain an ion or ions of alkali metal, alkali earth metal or ammonium.

Abstract: A continuous procedure is disclosed for the wet-process manufacture of phosphoric acid in a reaction zone and continuously cooled by means of evaporation into air circulating at the surface of the reaction zone. The evaporated gases are scrubbed by using part of the water needed for the methodic washing of the calcium sulfate, whereby the solution obtained is collected and passed into the reaction zone in such a way as to cause the soluble gaseous products to return to the reaction medium, from which they are collected with strong acid, which constitutes production. The procedure gives rise to no liquid pollutants, particularly fluorine, and does not increase the amount of water consumed.

Abstract: A process for the selective removal of nitrogen oxides from waste gases containing sulfur oxides as well as nitrogen oxides, which comprises contacting the waste gases with a catalyst comprising active metal oxides consisting of vanadium oxide and at least one of molybdenum oxide and tungsten oxide as a catalytically active component and .alpha.-alumina having a specific surface area of 0.3 to 12 m.sup.2 /g and a pore volume of 0.1 cm.sup.3 /g or more as a carrier wherein the atomic ratio of the vanadium, molybdenum, tungsten and aluminum contained in the carrier alumina isV.sub.12-x-y Mo.sub.x W.sub.y Al.sub.zwherein 0.ltoreq.x.ltoreq.8, 0.ltoreq.y.ltoreq.5, 0.3.ltoreq.x + y.ltoreq.8 and 40.ltoreq.z.ltoreq.480, in the presence of ammonia of 0.3 to 4 mol on the basis of 1 mol of nitrogen oxides contained in the waste gases at a temperature of 150.degree. to 700.degree. C.

Abstract: A process for converting nitrogen dioxide into nitrogen monoxide which comprises bringing a gas containing nitrogen dioxide into contact at a temperature ranging from 50.degree. C. to 400.degree. C. with a carbide of a metal selected from the group consisting of chromium, molybdenum, tungsten, vanadium, titanium, tantalum, silicon and boron or a composite carbide of such metals, thereby reducing nitrogen dioxide contained in the gas to nitrogen monoxide.

Abstract: A process is provided for removing ammonia, hydrogen sulfide and hydrocyanic acid from gases such as coke oven gas. In carrying out the process, the gas to be cleaned is first washed with an alkaline solution to remove the hydrogen sulfide and hydrocyanic acid. The hydrogen sulfide is oxidized by air to produce elemental sulfur, which is removed, and the alkaline solution is recirculated for reuse, a portion of the solution carrying cyanide and other compounds being diverted for further treatment. The gas to be cleaned is subjected to a second washing operation with an inorganic acid solution which removes the ammonia from the gas by formation of an ammonia salt solution. The salt solution is regenerated to recover the acid which is recirculated for reuse.

Abstract: In a process for preparing phosphoric acid by contact of sulphuric acid and phosphate rock with filtration of the gypsum slurry and recycle of the rest for contact with fresh rock, a fraction of the recycle slurry is treated with sulphuric acid to convert at least some of the gypsum to calcium sulphate hemihydrate and the slurry comprising hemihydrate is returned to contact the mixture of phosphate rock, phosphoric acid and recycle gypsum slurry. The process gives an easily filtered gypsum slurry with low phosphate losses in the gypsum filter cake.

Abstract: A process for selective removal of nitrogen oxides from waste gases containing 1,500 ppm or less (gas volume) of nitrogen oxides by contacting the waste gases with a metal oxide catalyst containing vanadium oxide and at least one of molybdenum oxide and tungsten oxide with an atomic ratio of the oxide forming elements of:V.sub.12-x-y Mo.sub.x W.sub.yWherein 0.ltoreq.x.ltoreq.8, 0.ltoreq.y.ltoreq.5 and 0.3.ltoreq.x + y.ltoreq.8, at a temperature of 150.degree. to 700.degree. C in the presence of 0.3 to 4 mol of ammonia (on the basis of 1 mol of the nitrogen oxides).

Abstract: A process for removing sulfate ions from extracted phosphoric acid which is substantially free of metallic ion impurities and which has been prepared by extracting wet process phosphoric acid with an organic solvent which comprises:A. adjusting the extracted phosphoric acid concentration to a concentration greater than 70%;B. adding an amount of a barium compound which is less than the stoichiometric equivalent amount of barium relative to the amount of dissolved sulfate ion to form barium sulfate crystals; andC. separating said barium sulfate from the resulting slurry at a temperature less than 80.degree. C and recovering purified, extracted phosphoric acid;Wherein the amount of barium compound added is such that said purified extracted phosphoric acid contains at least 5 ppm of sulfate ions.

Abstract: An aqueous urea solution is concentrated to a substantially water-free molten urea by conducting successively a first step of concentrating said aqueous urea solution under the conditions forming a urea slurry and a second step of concentrating said urea slurry under conditions forming a substantially water-free molten urea free from crystalline urea.

Abstract: Magnesium chromites promoted with aluminum have been found to be superior to chromia-alumina type dehydrogenation catalysts, for example, in the dehydrogenation of n-butane. The aluminum is either added to the preformed magnesium chromite or is incorporated into the spinel structure of the chromite itself or added in both ways. The aluminum will be present in the catalyst from all sources in an atomic ratio of Al:Cr of 0.0004 to 1.2:1. The atomic ratio will more usually be 0.04 to 0.8:1, Al:Cr.

Abstract: A method of forming a silicon carbide article is disclosd. Selected weight percentages of silicon carbide particles, graphite particles, if desired, and a thermosetting binder are mixed together and molded into an article by molding techniques which operate on the basis that the thermosetting binder forms a continuous medium about all the particles supported therein. The molded article is heated in the absence of oxygen and the thermosetting binder breaks down to form a low density, vitreous carbon phase. The article is heated in the absence of oxygen to a selected temperature at which the article is maintained for a period of time in a gaseous environment consisting of nitrogen preferably with a small amount of hydrogen therein. The hydrogen-nitrogen treatment is effective to cleanse the article and insure that there is an adequate pore structure through the article for a later siliciding operation to be carried out thereon.

Abstract: A method for the removal of fluorine compounds from admixture with phosphoric acid in which the mixture in organic solvent is contacted with an aqueous solution of a compound of Al, Fe, Ti or Zr whereby the phosphoric acid remains in the organic solvent phase while the fluorine compounds are extracted in the aqueous phase, and then regenerating the organic solvent phase with water to remove phosphoric acid from the solvent phase.

Abstract: An aqueous solution of a mineral acid is freed of dissolved or colloidally dispersed organic matter by admixing to the solution an aldehyde or an aldehyde oligomer and a compound copolymerizable with an aldehyde, allowing a polymerization reaction to occur and separating the resulting polymer. The polymer that forms removes selectively from the solution the said organic matter and any suspended organic matter is also removed. The aldehyde and the compound copolymerizable therewith may be added in the form of a pre-condensate.

Abstract: Nitrogen oxides, or both sulfur oxides and nitrogen oxides are efficiently and economically removed from exhaust gas containing the same with an aqueous scrubbing suspension of alkaline earth metal compounds. The aqueous scrubbing suspension of alkaline earth metal compounds further contains (a) thiourea or thiosulfates or mixtures thereof and (b) copper ion or iron ion or a mixture thereof.

Abstract: A method for the recovery of ammonia from liquor from the filters of ammonia-soda plants, which contains free ammonia and ammonium chloride. In this method the liquor is heated to release the free ammonia, and the remaining liquor is then treated successively in a prelimer with lime in an amount insufficient to decompose the whole part of the ammonium chloride and in a still with steam and an alkali metal hydroxide in an amount sufficient to decompose the remaining part of ammonium chloride.

Abstract: In a process for the reaction of phosphate rock and sulfuric acid in the presence of potassium ion to form a mixture of phosphoric acid and a precipitated gypsum wherein the presence of the potassium ion causes precipitation of fluorides from the phosphate rock as potassium silicofluoride as a coprecipitate with the gypsum, and the phosphoric acid is separated from the gypsum slurry, the potassium silicofluoride is separated from the gypsum by extraction with phosphoric acid which may contain from 0-25 weight percent of sulfuric acid based on the amount of gypsum to be extracted or such phosphoric acid which may contain some fluorine. This extraction procedure provides a substantially fluoride-free gypsum product and an extraction solution containing recoverable potassium silicofluoride.

Abstract: In the synthesis of ammonia with recycle of unreacted nitrogen and hydrogen to the reactor, a purge gas stream is removed from the recycle stream and partially condensed using refrigeration provided by the expansion and subsequent vaporization of the condensate. After partial condensation the condensate is rich in methane and argon while the gaseous phase is hydrogen enriched. The gaseous stream from the partial condensation is returned to the reactor and a bleed stream is removed from this gaseous stream at a temperature not exceeding 30.degree. C above the subambient temperature of the condensation. At least a part of the bleed stream is then expanded and injected into the expanded condensate prior to vaporization in the refrigeration step. Accumulation of helium, argon and methane impurities in the reactor can thus be prevented and expanded vaporized combined condensate and bleed can be recovered at a suitable pressure for use as a fuel gas stream.

Abstract: A method of removing nitrogen oxides from a gas containing nitrogen oxides and converting same to a salt of imidodisulfonic acid, wherein the gas containing nitrogen oxides is brought into contact with an aqueous solution which contains at least one ferrous salt and at least one sulfurous acid alkali salt to absorb the nitrogen oxides in solution in the form of imidodisulfonic acid alkali salts.

Abstract: A process for removing nitrogen oxides including nitrogen monoxide from a gaseous mixture such as industrial waste gases is provided. The gaseous mixture is contacted, first, with an aqueous solution of a chlorate and, then, with water, an aqueous solution or dispersion of a basic compound or an aqueous alkaline solution or dispersion of a reducing agent.