Abstract: A method for cracking and shifting a synthesis gas by the steps of providing a catalyst consisting essentially of alumina in a reaction zone; contacting the catalyst with a substantially oxygen free mixture of gases comprising water vapor and hydrocarbons having one or more carbon atoms, at a temperature between about 530.degree. C. (1000.degree. F.) to about 980.degree. C. (1800.degree. F.); and whereby the hydrocarbons are cracked to form hydrogen, carbon monoxide and/or carbon dioxide and the hydrogen content of the mixture increases with a corresponding decrease in carbon monoxide, and carbon formation is substantially eliminated.

Abstract: A method and apparatus are provided for reducing the concentration of carbon monoxide in a gaseous reactant stream comprising carbon monoxide and water vapor. The catalyst bed of a water gas shift reactor is preferably divided into two sections. Alternatively, an assembly which includes two sequential reactors can be employed. The first section or reactor operates in an adiabatic fashion whereas the second section or reactor is cooled, thereby facilitating the further conversion of carbon monoxide in the second section or reactor. The gaseous reactant stream exiting the second section or reactor typically has a carbon monoxide concentration in the range from about 0.06% to about 0.14% by volume.

Abstract: A catalyst for the conversion of carbon monoxide which before reductive activation, has the chemical composition which corresponds to the formulaCu.sub.0.04-6 AlMg.sub.0.1-10.sup.O.sub.X,wherein x denotes the number of oxygen atoms required to maintain electroneutrality per formula unit; and wherein the intensity ratio between the x-ray diffraction lines of the spinels CuAl.sub.2 O.sub.4 and MgAl.sub.2 O.sub.4 at d=0.244 nm and copper oxide at d=0.232 nm, determined as the ratio of reflex heights is about 0.05 to 0.5.

Abstract: A compact structure for a hydrogen generator is disclosed using a porous metal layer instead of conventional evaporators, thus reducing the size of the generator. This invention further includes a catalyst used in the water-shift reaction which reduces the toxic carbon monoxide in the product.

Abstract: This invention relates to the production of hydrogen-rich gas by the partial oxidation of a saturated gaseous hydrocarbonaceous fuel or a mixture of saturated gaseous hydrocarbonaceous fuel and a liquid hydrocabonaceous fuel in a gas generator. In the process, a saturated gaseous hydrocarbonaceous fuel from a subsequent fuel gas saturator is preheated by indirect heat exchange with a portion of shifted process gas stream from a catalytic water-gas direct shift conversion zone and reacted in said partial oxidation gas generator. The process gas stream from the noncatalytic partial oxidation gas generator is quench cooled and scrubbed with water and preheated by indirect heat exchange with a second portion of the process gas stream from the shift conversion zone prior to catalytically reacting the CO and H.sub.2 O in the process gas stream in the shift conversion zone to increase its H.sub.2 content.

Abstract: A process for producing high purity hyrogen is disclosed. Specifically, the process includes (1) partially oxidizing a gaseous hydrocarbonaceous feedstock to produce a synthesis gas mixture of carbon monoxide and hydrogen, (2) reacting the synthesis gas mixture with steam to convert the carbon monoxide into a raw gas mixture which primarily includes carbon dioxide and hydrogen, and (3) subjecting the raw gas mixture to pressure swing adsorption to purify the raw gas mixture, thereby producing high purity hydrogen and a reject gas mixture of impurities.The gaseous hydrocarbonaceous feed is specific, inasmuch as it is characterized by containing a major component which includes at least one C.sub.1 -C.sub.3 hydrocarbon and which has an average molecular weight of up to about 30.

Abstract: A process for producing high purity hydrogen is disclosed. Specifically, the process includes (1) partially oxidizing a refinery offgas feedstock to produce a synthesis gas mixture of carbon monoxide and hydrogen, (2) reacting the synthesis gas mixture with steam to convert the carbon monoxide into a raw gas mixture which primarily includes carbon dioxide and hydrogen, and (3) purifying the raw gas mixture to produce high purity hydrogen and a reject gas mixture of impurities. In a preferred embodiment, the purification step occurs in a pressure swing adsorption unit.Alternative embodiments are also described, each of which essentially involve the optional treatment and/or use of the reject gas mixture of impurities.

Abstract: A two-stage process for converting synthesis gas to higher alcohols includes an alkali metal-containing cobalt synthesis gas conversion catalyst in a first stage and a copper-containing catalyst in a second stage. The process allows great flexibility in selecting the product mix by changing catalyst compositions and process conditions.

Abstract: The conversion of CO/H.sub.2 O mixtures, in particular water gas, is carr out in the presence of solid, polymer rhodium complex catalysts which are insoluble in aqueous and organic solvents and are obtainable by polycondensation of one or more rhodium complexes having at least one ligand which contains at least one group capable of coordinating to rhodium and at least one group forming an inorganic network in the polycondensation, either with itself or with one or more inorganic network-forming agents capable of undergoing polycondensation. Novel rhodium complexes of this type are also described.

Abstract: Carbon monoxide is reacted with water vapor and converted into hydrogen and carbon dioxide, in the presence of a thio-resistant catalyst which comprises an active phase deposited onto a support, said active phase comprising molybdenum, vanadium or tungsten, and a cobalt and/or nickel promoter therefor, and said support comprising cerium oxide or zirconium oxide. The reaction mixture advantageously includes carbon monoxide, hydrogen, water and compounds of sulfur, wherefrom hydrogen is selectively produced in increased amounts.

Abstract: A gas stream containing hydrogen, carbon monoxide, and steam, and having a steam to dry gas molar ratio below 0.5 and a steam to carbon monoxide molar ratio above 0.5, and that has been formed at a temperature above 700.degree. C., is passed, at a temperature within the range 550.degree. to 650.degree. C., over an iron-free catalyst effective at such temperatures to catalyze the shift reaction. This effects some shift reaction thus increasing the amount of high grade heat that can be recovered from the gas. Also the hydrogen content of the gas is increased and the carbon monoxide to carbon dioxide ratio of the gas is decreased, thus decreasing the risk of hydrocarbon formation if the gas is subsequently subjected to a further shift reaction using an iron-oxide containing catalyst. Suitable catalysts comprise palladium and/or an oxide of an alkali, or alkaline earth, metal on a refractory support.

Abstract: The present invention concerns a process for carrying out the water gas shift reaction in the presence of carbon monoxide and water in contact with an alkali-doped catalyst.

Abstract: The present invention relates to a water-gas shift process which is carried out in a non-aqueous, high boiling liquid medium, either in an ebullated or slurry mode. The function of the liquid is to provide a heat sink for the exothermic reaction thereby allowing for better performance and longer catalyst life. The process, termed "liquid phase shift" (LPS) preferably uses commercially available vapor-phase low temperature shift (LTS) catalysts to accomplish the shift reaction. Because of the isothermality of the LPS process and its ability therefore to take advantage of higher catalyst activity, the average operating temperature is typically 260.degree. C. (500.degree. F.). This compares favorably to the lower average operating temperature for the conventional vapor-phase LTS process, which is typically 240.degree. C. (465.degree. F.). In addition, the LPS process can handle high carbon monoxide content feeds, e.g. 75 vol % carbon monoxide on a dry basis, without experiencing excessive catalyst deactivation.

Abstract: Oxides having the spinel structure of .gamma.-Fe.sub.2 O.sub.3 /Fe.sub.3 O.sub.4 type, substituted by trivalent and monovalent metals, or doped with non-spinel derivatives thereof, more particularly iron/aluminum/potassium oxides well suited as dehydrogenation catalysts, e.g., for dehydrogenating ethylbenzene into styrene, are prepared by thermally decomposing mixed iron, aluminum and potassium salts, notably the oxalates thereof, in the presence of air, then reducing the product of thermal decomposition at a temperature of less than 400.degree. C., advantageously in the presence of steam and hydrogen, and optionally oxidizing the product of reduction; oxides of .beta.-alumina structure are also produced.

Abstract: A catalyst for conversion of carbon monoxide in water gas reaction, which comprises iron oxide, chromium oxide and magnesium oxide in the proportions of the from 40 to 85% by weight computed as Fe.sub.2 O.sub.3, from 12 to 45% by weight computed as Cr.sub.2 O.sub.3 and from 3 to 15% by weight computed as MgO, respectively.

Abstract: Carbon monoxide is reacted with water vapor and converted into hydrogen and carbon dioxide, in the presence of a thio-resistant catalyst which comprises an active phase deposited onto a support, said active phase comprising molybdenum, vanadium or tungsten, and a cobalt and/or nickel promoter therefor, and said support comprising cerium oxide or zirconium oxide. The reaction mixture advantageously includes carbon monoxide, hydrogen, water and compounds of sulfur, wherefrom hydrogen is selectively produced in increased amounts.

Abstract: Carbon monoxide is reacted with water vapor and converted into hydrogen and carbon dioxide, in the presence of a thio-resistant catalyst which comprises an active phase deposited onto a support, said active phase comprising molybdenum, vanadium or tungsten, and a cobalt and/or nickel promoter therefor, and said support comprising cerium oxide or zirconium oxide. The reaction mixture advantageously includes carbon monoxide, hydrogen, water and compounds of sulfur, wherefrom hydrogen is selectively produced in increased amounts.

Abstract: Catalysts susceptible to deactivation by free oxygen or to reactions involving free oxygen are protected by scavenging the oxygen in the presence of an oxidation catalyst, so as to remove commingled oxygen from the reactants to be converted in the presence of the catalyst suscepticle to oxygen attack.

Abstract: An improved catalyst for the high temperature shift reaction especially suited for low steam to gas ratio applications is made by dipping an iron oxide-chromium oxide catalyst in an aqueous copper salt solution, drying the catalyst and calcining it.

Abstract: The present invention relates to a method of activation of a CuO/ZnO/Al.sub.2 O.sub.3 catalyst slurried in a chemically inert liquid. Successful activation of the catalyst requires the use of a process in which the temperature of the system at any time is not allowed to exceed a certain critical value, which is a function of the specific hydrogen uptake of the catalyst at that same time. This process is especially critical for activating highly concentrated catalyst slurries, typically 25 to 50 wt %. Activation of slurries of CuO/ZnO/Al.sub.2 O.sub.3 catalyst is useful in carrying out the liquid phase methanol or the liquid phase shift reactions.

Abstract: Catalytic shift is effected in a reactor provided using a copper catalyst in indirect heat exchange with boiling water at a gas flow rate of 200 to 800 kg mol per hour per m.sup.3 of catalyst. The shift is effected using an outlet temperature in the range 230.degree. to 280.degree. C. that is preferably 10.degree. to 30.degree. C. below the maximum, or inlet, temperature. The heat exchange surface is 30 to 200 m.sup.2 per m.sup.3 of catalyst.

Abstract: A process for the production of hydrogen with simultaneous formation of carbon dioxide by reacting carbon monoxide with steam at elevated temperatures in the presence of a catalyst which essentially consists of a refractory oxidic carrier having a high specific surface area loaded with metallic copper of a purity of more than 90% by weight, a fraction of at least 1% by weight of said metallic copper calculated as % by weight of the total weight of the copper and carrier being present as particles of a size of less than 20 nm.

Abstract: This process relates to the upgrading of at least one stream of condensate water by removing water soluble gaseous impurities from the group consisting of HCN, COS, HCOOH, and mixtures thereof as produced in a process for the production of synthesis gas by the partial oxidation of solid carbonaceous fuel and/or liquid hydrocarbonaceous fuel. In the process, at least one internally produced condensate stream of water containing the aforesaid water soluble gaseous impurities is mixed with and vaporized into a stream of synthesis gas. The vaporized mixture is then introduced into at least one bed of catalyst where the gaseous impurities are removed by hydrolysis. The upgraded water stream is then recycled in the process for use in cooling and/or scrubbing the hot raw effluent gas stream from a partial oxidation gas generator.

Abstract: The water gas shift reaction can be advantageously carried out in the presence of catalyst-poisoning, chloride-containing compounds by utilizing a catalyst comprising copper, zinc, a rare earth element and an alkaline earth element wherein such alkaline earth element is present in an amount from about 10 to about 30 atomic weight percent of the total metals present.

Abstract: C.sub.4.sup.- hydrocarbons are converted into syngas with a H.sub.2 /CO molar ratio between 0.25 and 2.25 by reforming at a pressure above 10 bar in the presence of specified amounts of carbon dioxide and steam followed by conversion of the syngas into C.sub.5.sup.+ hydrocarbons over a cobalt-containing catalyst or a catalyst combination comprising a cobalt-containing catalyst and having CO-shift activity.

Abstract: Reaction mass containing mixed oxides of iron with one or more metals of groups IV to VII of the periodic table of the elements, wherein the mixed oxides are deposited in finely divided form on an inert refractory substrate with a high specific surface area. The invention also relates to methods for the manufacture of this reaction mass as well as the use thereof as a catalyst for the shift reaction of carbon monoxide with steam, forming carbon dioxide and hydrogen at an elevated temperature, and/or the removal of sulphur compounds from gases.

Abstract: Iron oxide-chromium oxide catalyst of increased mechanical strength (lateral crushing strength) for high-temperature water-gas shift reaction. The catalyst contains as an additional component magnesium oxide and/or magnesium spinels in the form of discrete particles.

Abstract: Process for the reaction of carbon monoxide with steam, with formation of carbon dioxide and hydrogen at elevated temperature in the presence of iron-containing catalysts (shift reaction), in which a catalyst is used, which contains finely divided iron oxide on an inert, thermostable carrier having a high specific surface.

Abstract: The shift reaction of carbon monoxide with steam to give carbon dioxide and hydrogen is carried out over a catalyst comprising iron oxide and at least one further metal oxide that is difficultly reducible to metal, contains metal exerting a valency of at least 2 and is incapable of forming a mixed oxide having the spinel structure M.sup.II M.sup.III M.sub.2 O.sub.4 where M.sup.II is a divalent metal and M.sup.III is a trivalent metal.

Abstract: A process is disclosed for preparing a hydrogen-rich gas, which is carried out by reacting a carbon monoxide-containing gas with steam in the presence of a catalyst. The catalyst contains a spinel whose composition is expressed by the formula Li.sub.x Cu.sub.(1-x) Fe.sub.5 O.sub.8 in which 0<x<1. Preferably a compound of an alkali metal is added to the catalyst.

Abstract: Desulfurized hydrocarbons are reacted with water vapor on catalysts at temperatures of 700.degree. to 1200.degree. C. to form a high-hydrogen product gas, which is separated in a pressure-swing adsorber into purified hydrogen and a separated gas, which contains substantially carbon oxides and methane. The purified hydrogen is supplied to a hydrogenating plant, which is operated at temperatures in the range of 250.degree. to 500.degree. C. and pressures of 200 to 400 bars. High-hydrogen gas from the hydrogenating plant flows in a pipeline through a heater and is then recycled to the hydrogenating plant. The heater consists of a fuelfired reheater, in which the separated gas is used as a fuel. The pipeline in which the high-hydrogen gas is recycled between the hydrogenating plant and the heater consists of an alloy steel, in which the carbon is combined in carbides with at least one of the alloying constituents chromium, molybdenum, tungsten or vanadium.

Abstract: A process is disclosed for the conversion of carbon monoxide in sour synthesis gas mixtures in the presence of a catalyst which is active in the presence of sulfur compounds. The catalyst comprises known sulfactive metal oxides or sulfides supported on a shaped carrier. The catalytically active oxides or sulfides are doubly promoted with an alkali metal compound and an oxide or sulfide of manganese. The two promoters combined in proper ratio provide a synergistic effect on the activity of the catalyst which is enhanced beyond that of the singly promoted catalyst. The catalysts are active at relatively low temperatures of less than 500.degree. F., even in the presence of sulfur compounds. The equilibrium for the conversion of steam and carbon monoxide to hydrogen and CO.sub.2 is favored at lower temperatures.

Abstract: A process is disclosed for the conversion of carbon monoxide in sour synthesis gas mixtures in the presence of a catalyst which is active in the presence of sulfur compounds. The catalyst comprises known sulfactive metal oxides or sulfides supported on a shaped carrier. The catalytically active oxides or sulfides are doubly promoted with an alkali metal compound and an oxide or sulfide or manganese. The two promoters combined in proper ratio provide a synergistic effect on the activity of the catalyst which is enhanced beyond that of the singly promoted catalyst. The catalysts are active at relatively low temperatures of less than 500.degree. F., even in the presence of sulfur compounds. The equilibrium for the conversion of steam and carbon monoxide to hydrogen and CO.sub.2 is favored at lower temperatures.

Abstract: In an ammonia production process a hydrocarbon steam mixture (16) is preheated (18, 24) and reacted in an adiabatic catalyst bed (22, 26), the resulting methane-containing gas is reacted (30) with air (32) to introduce more than 1 N.sub.2 per 3H.sub.2 and purified (44, 48, 54) the purified gas is passed to ammonia synthesis (66) in admixture with a hydrogen-rich stream (82) separated at 80 from reacted synthesis gas, and the rate of flow of that stream is controlled so that the H.sub.2 :N.sub.2 ratio of the gas entering the synthesis catalyst is in the range 1.0 to 2.5. Preferably methane is purged at 86 to the extent of 5-15% of the hydrocarbon feedstock.

Abstract: Crude gas obtained through partial oxidation of carbon-containing material is subjected to catalytic conversion in an apparatus containing a moistening-demoistering system connected by means of a combined water circulation. To reduce the required amount of steam and process heating, a partial stream of water coming from the moistener is branched off, heated by indirect heat exchange with converted, hot synthesis gas, and then united with the partial stream of water coming from the demoistener for re-delivery to the moistener.

Abstract: Hydrogen-rich gas is produced by reacting gas mixtures comprising CO and H.sub.2 O in a reactor containing an improved unsupported catalyst comprising an alkali-metal promoted partially reduced mixture of at least one copper uranate and at least one oxide of copper. The weight percent uranium present in the activated catalyst, based on total weight of catalyst composition, is in the range of over 50 to about 90.

Abstract: The invention concerns a process for the purification of a hydrogen-containing gas mixture comprising up to 45% by volume of hydrogen, together with carbon oxides, hydrogen cyanide and impurities including nitrogen oxides and/or oxygen. The process comprises passing the gas over a sulphur-resistant hydrogenation catalyst at a temperature of from 120.degree. C. to 250.degree. C. and at a pressure of from 0.5 to 250 bar to remove the nitrogen oxides and/or oxygen therefrom while substantially avoiding hydrogen cyanide removal. The gas may be obtained from a Koppers-Totzek gasifier and may be used for the production of ammonia after further purification. The sulphur-resistant catalyst may be a nickel molybdate or cobalt molybdate catalyst or a metal from Group VI and/or Group VIII of the Periodic Table.

Abstract: A solution containing nitrates of iron and chromium is produced by reacting metallic iron or an iron alloy with nitric acid in the presence of a hexavalent chromium compound. The solution is the starting material for making an iron-chrome oxide catalyst for the shift reaction of carbon monoxide with steam.

Abstract: An outer enclosed pressure container is formed of a simple steel material. An inner enclosed container is positioned within the pressure container such that there is an intermediate space therebetween. Catalyst layers are provided within the inner container. A gas containing a reducing component and water vapor are introduced into the inner container and are therein reacted by means of the catalyst to perform a desired reducing reaction. At least part of the water vapor is alone introduced into the intermediate space to thereby pressurize the intermediate space to substantially the same pressure as occurs within the inner container. The water vapor in the intermediate space operates to protect the wall of the pressure container from the temperatures occurring due to the catalytic reaction within the inner container. The water vapor is removed from the intermediate space and is at least partially added to the gas containing a reducing component before the introduction thereof into the inner container.

Abstract: Catalyst for producing hydrogen by reaction of carbon monoxide with water or for producing methanol by reaction of carbon monoxide with hydrogen, containing by weight 10-60% of copper oxide, 5-40% of zinc oxide, 1-20% of a rare earth metal oxide, 30-70% of aluminous cement and optionally 0.01-1% of a noble metal from group VIII.

Abstract: A process for the conversion of carbon monoxide in synthesis gas mixtures to hydrogen and CO.sub.2 utilizes a catalyst which is active in the presence of sulfur compounds, and which comprises the oxides or sulfides of cobalt and molybdenum, supported on a shaped, relatively high surface area aluminous carrier. The carrier is stabilized by admixture with one or more rare earth metal oxides while the alumina is in the hydrated condition. The mixture of hydrated alumina and rare earth metal oxide is formed into a desired shape and calcined to convert the hydrated alumina to the oxide. Thereafter, the calcined, high surface area alumina is impregnated with the desired salts of cobalt and molybdenum and the impregnated catalyst is thereafter calcined and placed into service. The stabilized catalyst exhibits good activity at relatively low temperatures with synthesis gas mixtures containing sulfur compounds and retains its surface area and the aluminous carrier is not converted over to the alpha phase.

Abstract: In a method for producing high quality hydrogen, the carbon monoxide level of a hydrogen stream which also contains hydrogen sulfide is shifted in a bed of iron oxide shift catalyst to a desired low level of carbon monoxide using less catalyst than the minimum amount of catalyst which would otherwise be required if there were no hydrogen sulfide in the gas stream. Under normal operating conditions the presence of even relatively small amounts of hydrogen sulfide can double the activity of the catalyst such that much less catalyst may be used to do the same job.

Abstract: The life of copper-containing catalysts in the low temperature shift reaction of carbon monoxide with steam is limited as a result of slow poisoning by halogen and/or sulphur compounds. It has been found that the poisoning reaction and the shift reaction occur almost entirely on the surface of the catalyst pellets, and that the rate at which a catalyst charge loses activity can be decreased by having the catalyst in an inlet zone in a form more accessible to the reacting gas than that catalyst downstream thereof. The inlet zone catalyst pieces can be smaller and/or formed with indentations or protrusions and/or more macroporous in order to provide better access.

Abstract: Catalyst compositions and an improved process for converting carbon monoxide and water to hydrogen and CO.sub.2 are disclosed.

Abstract: Hydrogen-containing gas mixtures including saturated and unsaturated hydrocarbon gases, carbon monoxide and organic sulfur contaminants are purified by passing them over a hydrogenation catalyst containing phosphorus with the addition of predetermined limited amounts of water. The process makes it possible to produce hydrogen-containing gases which can be used for hydrogenation processes with the elimination or reduction of carbon monoxide, olefins and organic sulfur, all brought about simultaneously by passing the gas mixture over the same catalyst and in the same reactor.

Abstract: A carbon monoxide shift process at a pressure of at least 15 atm. abs. is carried out over an oxidic and/or sulphidic catalyst of a specified level of activity in a 2-zone bed. The upstream zone has an outlet temperature in the range 350.degree.-400.degree. C. and the downstream zone has a higher outlet temperature, for example up to 550.degree. C. The catalyst in the upstream zone differs from the catalyst in the downstream zone by containing more catalytic material per unit volume and/or by having a lower area/volume ratio and/or by having a lower porosity.

Abstract: An oxidic catalyst for the conversion of water gas which consists of oxides of the metals aluminum, lanthanum, cobalt, nickel and uranium, with the aluminum oxide being present predominantly as .alpha.-Al.sub.2 O.sub.3. The lanthanum and cobalt content is 5 to 30% by weight, that of nickel, 0.1 to 4% by weight and of uranium, 0.1 to 2% by weight, related to the total weight of the catalyst.

Abstract: A catalyst containing metallic copper, especially a low temperature shift catalyst containing also zinc oxide, is made from a corresponding catalyst precursor by reduction in two stages. In the first stage a steam and/or CO.sub.2 -diluted reducing gas is used and in the second a more strongly reducing gas mixture such as ammonia synthesis gas or even 100% hydrogen. The resulting catalyst is substantially more active than one reduced according to previous one-stage steam-reduction practice and similar to catalyst made by the less convenient dry-reduction using nitrogen or natural gas as diluent.

Abstract: Catalyst for the conversion of carbon monoxide in the presence of water, to produce hydrogen, or in the presence of hydrogen, to produce methanol, said catalyst containing 10 - 60% by weight of copper oxide, 5 - 40% by weight of zinc oxide and 30 - 70% by weight of aluminous cement, the total content of copper oxide and zinc oxide being from 30 to 70% by weight.

Abstract: Catalysts having a high degree of thermal stability, comprising alumina and one or more of the iron group metals are prepared from aqueous solutions containing a dissolved aluminum salt, a salt of at least one of the iron group metals and a delayed precipitant such as urea. The solution is heated to a temperature sufficient to hydrolyze the delayed precipitant with resultant liberation of ammonia and carbon dioxide homogeneously throughout the solution, until the pH of the solution rises sufficiently to effect coprecipitation of the metal salts as hydroxides and/or carbonates. The resulting coprecipitate is then recovered, washed, dried, shaped and calcined in conventional fashion to obtain a final product which, after hydrogen-reduction is very active, and displays much greater thermal stability than corresponding prior art catalysts prepared by non-homogeneous coprecipitation with alkaline, ionic reagents such as sodium carbonate, ammonium hydroxide, or ammonium carbonate.