CS276140B6 - Aqueous solution of a catalyst for more perfect combustion of carbon- or/and hydrocarbon-containing compounds - Google Patents

Abstract

The invention relates to an aqueous catalyst solution for the improved combustion of materials containing carbon and/or hydrocarbon, such as fuel oils, fuel gases and solid fuels, and/or for the removal of deposits of soot or tar on surfaces of the combustion chamber, and it is characterised above all in that the aqueous catalyst solution has a pH of at least 7 and contains, in a catalytically active quantity, tetravalent cerium (Ce<4><+>) and alkali metal, alkali earth metal and/or magnesium compounds which, after combustion or thermal decomposition, show an alkaline reaction, and complexing agents for this Ce<4><+>. The invention also relates to a liquid or solid fuel, in particular fuel oil or coal, which is characterised in that it contains the aqueous catalyst solution in such a quantity that the cerium<4><+> content is between 1 and 100 ppm, preferably about 35 ppm, relative to the fuel quantity.

Description

The present invention relates to an aqueous catalyst solution for improved combustion of carbon and / or hydrocarbon-containing substances, such as fuel oils, fuel gases and solid fuels, and / or for the removal of soot and / or tar deposits from the surfaces of combustion chambers.

In order to prevent the formation of soot deposits on solid surfaces that come into contact with fire, the combustion of used fuels and the content of carbon or hydrocarbons must be as complete as possible. This can be achieved by supplying an excess of air, i.e. by supplying substantially more air to the fuels than the amount required to be combusted etechiometrically. While this results in improved complete combustion, there is also the disadvantage of inefficient use of fuels, since large amounts of air need to be heated unnecessarily and the amount of hot exhaust gases is also increased. On the other hand, it is desirable that the combustion of fuels containing carbon and hydrocarbons take place without the formation of soot deposits and at their minimum combustion formation at a ratio close to the etoichiometric ratio. However, this is not usually achieved in practice or hundreds do not always succeed. By gradually varying the nozzle feed of liquid fuels ae, it will also negatively affect the initial excellent combustion process and the formation of soot ae will increase.

The formation of soot disadvantages combustion both by the loss of heat generated and by reduced heat transfer, since the soot has a high thermal insulation effect.

Combustion catalysts have therefore been used for a long time in order to eliminate or minimize the formation of carbon dioxide and to cause the already formed carbon black or tar deposits to burn again at about the highest possible temperature. The improved combustion of already formed tars and soot is most effectively achieved by means of transition metal compounds which may be present in all of their known valences. Currently, copper, manganese, cobalt, zinc and chromium compounds are mainly used. In particular, the copper compounds, especially the metal powder, significantly reduce the combustion temperature of the carbon black and the tar. However, it defends the disadvantage that they are present in the waste gases in the form of poisonous proportions and cause a significantly greater degree of corrosion risk for ferrous objects. In the electro-chemical series, the stress is considerably more positive than iron, so that when precipitating copper compounds, local elements are formed on the iron articles commonly used in heating technology, which cause corrosion of the iron-containing structural elements. This phenomenon is even more intensified in the presence of sulfuric or sulfuric acid, which is formed when appealing sulfur-containing fuels.

Zinc compounds are less toxic than copper compounds and also do not pose any significant risk to the corrosion of the iron components of the device. However, as combustion catalysts for soot and tar, they are almost ineffective.

For the purposes described above, chromium is mainly used in the form of chromium, in which the catalytic effect of the metal ions for the combustion process and the oxidation potential of chromium to carbon are utilized. Due to the carcinogenic effects of some compounds of the astonishment, according to environmental protection requirements, we have practically eliminated them today. The same is true for nickel and cobalt compounds, although cobalt in particular has good combustion catalytic effects.

Also manganese, particularly in the form of permanganate has good combustion properties and catalytic -1.70 V as Mn0 ₂ + 2H ₂ 0 HNO ^ + 4H ⁺ + 3a has a high oxidation potential. However, manganese compounds are also toxic and are even classified as carclonogens.

The non-toxic transition metal is iron, which in the form of oil-soluble compounds (soaps, ferrooene, etc.) is often used as a combustion catalyst for liquid fuels. Iron salt solutions have also been designed and sprayed

CS 276140 Βδ to flame. Despite these suitable properties for catalytic combustion, iron is not a sufficient means to remove already formed tar and soot deposits. The reason lies in the relatively low oxidation potential of trivalent iron compounds, or?

- 0.77 V Pe ²⁺ - Pe ³⁺ + e '.

Also calcium compounds, although calcium as an alkaline earth metal is not a transition metal, have been recommended to remove deposited carbon black. However, calcium had little catalytic effect for combustion, even when hydroxyl ions were formed in the flame at high temperatures. However, as an alkaline earth metal, it has neutralizing effects on sulfuric acid and sulfuric acid, unless it is bound to thermally stable and non-flammable anions.

Until now, hydrogen peroxide has been used as a cleaning agent for the carbon black coating on the charred side of the combustion chamber, which does not contain metal ions. This oxidizing agent has also been recommended in conjunction with free alkali such as alkali hydroxides, alkali carbonates and silicates, the oxidation of the carbon black with H ₂ O ₂ and neutralization of acids with strong aqueous bases. The catalytic effect for combustion has not been demonstrated.

Examples of published publications are, for example, GB 1 252 624 for hydrogen peroxide and strong aqueous alkaline solutions, DE 3 023 520 for the addition of calcium compounds (calcium sulphates in powder form), DE 2 413 520 for a composition for removal of carbon black containing metallic compounds, U.S. Pat. No. 4,287,090 for aqueous, catalytically active metal salt solutions consisting of manganese acetate, calcium nitrate and copper acetate, DE 2 911 259 for cleaning agents exposed to fire by alkali iodides or solutions of alkali peroxides in admixture with tartrate carbonate as oxidizing agents and ammonia or alkaline nitrate to neutralize the acidic fractions of ash.

Potassium and ammonium nitrate are mentioned as biloba removers in DE 2 228 467 but do not have a catalytic effect for combustion. In GB 1 303 552 ammonium nitrate and potassium and / or calcium nitrate have been proposed for binding and condensing sulfuric acid in the appellation of waste gases.

In order to remove salts and tar fractions from the walls of the heating surfaces exposed to fire, according to DE-published application 1 810 424, ammonium nitrate, ammonium chromene or zinc and copper salts are used as support means or as catalytic auxiliary combustion means.

Swedish Nobel plants invented years ago a product called SP-SOTIN for cleaning heating surfaces, which, according to their own data, contains the main proportion of alkaline nitrates, but no combustion catalysts.

All these compositions aim to remove soot and tar deposits, but do not adequately meet today's environmental cleanliness requirements and minimize heat transfer losses. Catalytic combustion with suitable metals has the disadvantage, even with good efficiency, that toxic gases (Cu, Ni, Co, Cr, Mn) are present in the waste gases, and the oxidation potential of environmentally harmless metals such as iron and calcium is insufficient. The three uses of oxidizing agents, such as nitrates, periodates or peroxides, are only one-shot and, once the active oxygen has been consumed from them, soot and tar can settle unhindered and deteriorate the heat balance and destroy the environment with soot waste.

It should be noted here that, for example, a 1 mm thick carbon black layer may increase the temperature of the waste gases by a and 70 ° C and may increase fuel oil or fuel consumption by 5%.

It was therefore an object of the present invention to provide a combustion catalyst which is non-toxic, catalytically highly effective for burning soot and tar at as low temperatures as possible with air oxygen and exhibits a high oxidation potential at its highest valency. In addition, neutralization is required after combustion or thermal decomposition.

Suitable lanthanides, and in particular tetravalent cerium compounds, have proved to be such combustion catalysts. The water-soluble cerium compounds are not toxic and cerium nitrate bexahydrate or exhibits, for example, an LD ₅₀ value of 4 200 mg / kg, compared to a pure table salt having an LD 50 value of ≥ 3000 mg / kg.

The tetravalent cerium compounds are potent oxidizing agents, with an oxidation potential of Ce (IV) / Ca (HI) of about 1.6 V, i.e., only slightly below the oxidation potential of permanganate to manganese dioxide. which is about 1.7 V and is twice greater than the oxidation potential of ε (III) / Pe (II).

Oil soluble cerium compounds have been used as additives to fuel oils to improve combustion, as previously described in DE 2 729 363 and U.S. Pat. No. 4,462,810. However, these are solely oil soluble compounds, not aqueous solutions of cerium compounds. In addition, cerium is present in said three-valent form rather than in a four-valent form.

Both known uses of cerium are therefore not intended for cleaning soot and tar deposits from heating panels exposed to fire, nor are they suitable for this purpose.

For cleaning fire-exposed heating plates, it has proved to be advantageous if, after the formation of tar or soot, or after the thermal decomposition of the introduced tetravalent cerium compounds, an excess of alkali was present which neutralized the acids produced by the combustion of the fuels. This neutralization of inorganic acids, such as sulfuric and sulfuric acids, and organic acids, such as acetic, propionic, formic, reduces the deposition of wet and adherent carbon-containing coatings on solid surfaces, e.g. heat transfer surfaces, and prevents corrosion of these acids on the device. The use of aqueous solutions of tetravalent cerium in the presence of the above-mentioned excess alkali has the advantage that these solutions with catalytic effects for combustion can be adjusted to not close to neutral (pH 7), or may be present in weakly acidic or weakly basic aqueous solutions.

The aim has been achieved and the disadvantages of the known solutions have been eliminated with an aqueous catalyst solution for the complete combustion of the carbon and / or hydrocarbon-containing substances according to the invention, characterized in that the aqueous catalyst solution has a pH of at least 7 and contains tetravalent cerium ^. ) in an amount of 0.1 to 15% by weight, based on the total weight of the catalyst solution, of an alkali metal or alkaline earth metal and / or magnesium compound which, after combustion or thermal decomposition, react alkaline in an amount of 0.1 to 30% by weight, based on the content of metal ions in the total weight of the catalyst solution and further comprises a complexing agent for the tetravalent cerium (Ce ² ''') in an amount of 1%, by weight based on the total weight of the solution katakyzátoru.

As alkaline reacting compounds, the catalyst solution preferably contains organic salts or potassium, sodium or lithium soaps or organic calcium, magnesium and / or barium compounds. Furthermore, as the alkali reacting compound, the catalyst solution may advantageously contain alkali metal, alkaline earth metal and / or magnesium nitrates, carbonates, polycarboxylates and / or hydroxyl carboxylates.

The catalyst solution preferably contains from 2 to 10% by weight of the complexing agent.

In contrast to strongly acidic solutions, for example, cerium nitrate, the catalyst solution according to the invention has a corresponding corrosion protection effect for those metal surfaces which are in contact with it. Also, strongly alkaline reacting solutions present a risk of damage to metallic and especially mineral building materials such as fireclay, and there is also a risk of burns for those working with such a solution.

The invention is illustrated by the following examples, which are not intended to limit the scope and use of the invention in any way. The amounts are given in% by weight, based on the total weight of the resulting solution.

Example 1

6.19% by weight of cerium nitrate Ce (HO). δΗ ^ Ο was dissolved in 79.79% by weight of water and was converted to a tetravalent state by 2.27% by weight of a 35% aqueous hydrogen peroxide solution, corresponding to about 2% by weight of Ce Ce ^{+ in the} resulting solution. Furthermore, 3.09% by weight of citric acid and 2.06% by weight of the sodium salt of an acrylate maleic acid copolymer with an average molecular weight of 70,000 were added as a complexing agent to the above solution. The solution was adjusted to pH 9 with 4.54 wt% alkali (KOH).

To improve crosslinking on solid surfaces coated with carbon black and tar, 2.06% by weight of a C13 synthetic alcohol and 9 moles of an oxyethylene addition compound were added to the aqueous solution. The resulting solution was stable and clear and had a reddish brown color.

This solution was sprayed onto a carbon black and tar coated surface. After subsequent heating of these surfaces in normal use, burn-off of the coatings containing carbon and hydrocarbons (daze, tar) occurred with a favorable catalytic action.

The solution can also be advantageously used for mechanical cleaning of heat transfer surfaces, which is mandatory in many countries, and can also be applied to other surfaces that are at risk of soot coating. The solution serves as a corrosion protection agent but also in particular as a catalytically effective surface coating which prevents subsequent re-formation of carbon black and tar coatings.

After the organic matter (also citric acid and maleic acrylate copolymer) has burned, about 1.9% by weight of tetravalent cerium, predominantly CeOg, and about 5% of caustic alkali (of 4.4% by weight of KOH) are present and the rest are sodium salts of copolymer 100% by weight of the above solution for the catalytic combustion of salts and tars, as well as for the neutralization of mineral acids, in particular sulfuric and sulfuric acids, and organic acids, in particular acetic acid, formed during the appeal of wood.

Example 2

The aqueous catalyst solution of Example 1 was diluted 1:10 with water and was periodically applied to heat transfer surfaces and other surfaces from which soot should be removed by means of a mechanical built-in sprayer. Depending on the heating and the degree of soot contamination, it has been shown that periodic spraying at 2 to 24 hour intervals is sufficient to prevent the formation of soot deposits and to achieve the best possible heat transfer and fuel utilization.

This method is particularly suitable for large plants, ie industrial plants and thermal power plants.

Example 3

The aqueous catalyst solution of Example 1 was diluted 1:20 with water, indicating that the resulting dilution contained about 1000 ppm of tetravalent cerium ions. This solution was fed gently to the combustion air of larger heating and boiler systems at a ratio of 1% by weight of dilute aqueous solution to 50% by weight of residual fuel oil as the combustion catalyst. Due to its relatively low cerium content of about 20 ppm relative to heavy fuel oil, a reduction of three carbon blacks was achieved by Bacharach.

Example 4% by weight of water of the tetravalent cerium eoli dispersed in water was finely dispersed in 79% by weight of water. Here, 10% by weight of sodium polyacrylate having an average molecular weight of 4,000 and 1 part by weight of nonylphenol and 7 moles of oxyethylene separation of the compound were dissolved.

Cerium hydrate contains 89% _of CE0. The particle size was 15 microns, the crystal size (ΣΗ0 diameter measured by X-rays) was about 9 nanometers. The Ca * content was

7.2% by weight based on the weight of the dispersion.

The above-mentioned aqueous dispersion was sprayed onto tar deposits from the burned wood and burned with a short, amplified air stream. It has been shown that the catalytic action of the tetravalent cerium also in this form ae burns almost all health-damaging substances and combustible tar residues.

Example 5

9.66% by weight of cerium nitrate was dissolved in 67.74% by weight of water, which was oxidized to a tetravalent form by treatment with 2.90% by weight of hydrogen peroxide, corresponding to 3.4% by weight of Ce ⁴⁺ . Furthermore, 9.66% by weight of magnesium nitrate, 4.83% by weight of polyacrylate were dissolved in this solution, and the pH was adjusted to 8 by an average molecular weight of 2000 and sodium hydroxide or caustic soda.

This solution was applied to a soot and tar-contaminated surface, thereby improving combustion of these noxious coatings as in Example 1. The addition of crosslinking agents was also suitable for oily and fatty soot coatings. Preferably, nonionic or enionic surfactants have been used, such as ethylene oxidation products, alkylsulfonates, alkylarylsulfonates. Catalysts are also suitable, but often reduce the surface tension between the aqueous catalyst solution and the oil / debt residues to a small extent and are economically disadvantageous.

Magnesium nitrate is also thermally decomposed in the combustion of soot and tar and can neutralize mineral acids as alkaline oxide / hydroxides, but organic acids which are formed in the combustion of sulfur-containing fuel oils and coal or in the combustion of straw, wood, etc.

t

OS 276140 B6

Example 6

The solution of Example 5 was used analogously, substituting barium nitrate for magnesium nitrate. Here too, an excess of alkali was formed by thermal decomposition and catalytic combustion as described above.

Example 7

The procedure was the same as in Examples 5 and 6, but calcium nitrate was used instead of magnesium nitrate.

Example 8

The same solution was used as in Example 1, but the caustic liquor was replaced with lithium hydroxide monohydrate. Lithium hydroxide not only had acid neutralizing effects, but also had cerium-promoting effects in catalytic combustion.

Example 9

In 70.0% by weight of water, 4.55% by weight of Ca (NO.sub.2) 2 · 6 ^ 0 was dissolved and 1.82% by weight of 35% hydrogen peroxide was converted to its four-carbohydrate form corresponding to a cerium content of about 1%. % By weight. In addition, 22.72% by weight of a 40% solution of trisodium ethyleneamine tetraacetate (EDTA) and 0.91% by weight of a crosslinking agent were added. This solution was used as in the previous examples as an aqueous combustion catalyst.

Example 10

The composition of the solution used was the same as in Example 9, but sodium nitrilotriaoacetate (NTA) was used instead of EDTA.

Example 11% by weight of cerium nitrate was dissolved in 60% by weight of water and converted with 3% by weight of 35% hydrogen peroxide to a tetravalent form, corresponding to a content of about 3.3% by weight of Ce @ ⁺ . In addition, 7% by weight of potassium carbonate and 20% by weight of a 40% tetrakalium-EDTA solution were added. This solution was finely mechanically dispersed in a fuel oil in a 1: 1000 weight ratio. Water-in-oil emulsions have been burned to prevent further formation of a carbon black coating. SO3 or H2SO4 were preferentially bound by the neutralizing effect of KOH, which resulted in the formation of less acidic, and thus less aggressive and less corrosive, SO2 or sulfuric acid in the waste gases even when the sulfur-containing fuel oils were burned.

The content of Ca ^ ⁺ ions in the solution makes the catalyst of the invention from 0.1 to 15% by weight based on the weight of the catalyst solution. The metal ion content of the alkaline reacting compounds is 0.1 to 30% by weight based on the weight of the catalyst solution. In liquid or solid fuels, the Ce @ ^{+ +} ion content is then between up to 100 ppm by weight of the fuel.

The catalyst solution according to the invention has a pH of at least 7 and therefore lies in the neutral or basic region. It also has an effective corrosion protection. The complexing agent is included in the catalyst in an amount to prevent cerium hydroxide from falling out of solution. The amount of complexing agent is in the range of 1 to 40% by weight based on the total amount of catalyst, preferably between 2 and 10% by weight.

Claims (5)

An aqueous catalyst solution for improved combustion of carbon and / or hydrocarbon-containing substances, such as fuel oils, fuel gases and solid fuels, and / or to remove soot or tar deposits on surfaces of combustion chambers where the catalyst solution contains cerium salts; characterized in that the aqueous catalyst solution has a pH of at least 7 and contains a tetravalent cerium (Ce4 ⁺ ) in an amount of 0.1 to 15% by weight, based on the total weight of the catalyst solution, further alkali metal and / or alkaline earth metal compounds; and / or magnesium reacting alkaline after combustion or thermal decomposition in an amount of 0.1 to 30% by weight, based on the metal ion content of the total weight of the catalyst solution, and further comprising a complexing agent for the tetravalent cerium (Ce ^ ⁺ ) in an amount of 1. up to 40% by weight based on the total weight of the catalyst solution. 2. Catalyst solution according to claim 1, characterized in that the alkali-reacting compounds are organic salts or potassium, sodium, lithium soaps. 3. Catalyst solution according to claim 1, characterized in that it contains organic compounds of calcium, magnesium and / or barium as alkaline reacting compounds. Catalyst solution according to Claim 1, characterized in that it contains alkali metal, alkaline earth metal and / or magnesium nitrates, carbonates, polycarboxylates and / or hydroxylcarboxylates as alkali reacting compounds. 5. Catalyst solution according to any one of the preceding claims, characterized in that it contains a complexing agent in an amount of 2 to 10% by weight.