DE4032845C2 - Catalyst solution containing hydrophilic ceria compounds and their use for improved combustion of carbonaceous and hydrocarbonaceous materials - Google Patents

Description

The invention relates to hydrophilic, in particular aqueous Ver combustion catalysts for improved combustion of coals substance and / or hydrocarbon-containing substances, such as heating Oils, hot gases and solid fuels by air and / or to Removal of soot or tar deposits on surfaces of the Combustion chamber. Furthermore, the invention relates to the use of like catalyst solutions for improved combustion of carbon and hydrocarbon-containing substances and / or Removal of soot or tar deposits on surfaces of Combustion chambers.

To avoid soot deposits on fire side solid Surfaces is as complete a burn as possible used carbon and hydrocarbon fuels necessary substances. This can be due to a high excess of air be reached, d. H. that much more air the fuels is fed, as to their stoichiometric combustion necessary is. That brings an improvement to the full constant combustion, but at the same time the disadvantage an uneconomic use of the fuel with it, since unnecessarily large amounts of air must be heated and the Amount of hot exhaust gases is increased. One is therefore anxious, the Combustion of carbon and hydrocarbon Fuels without soot formation or minimize the same at to design near-stoichiometric combustion, which in the Naturally not completely or not always successful. Also by a gradual change in the nozzle injection with liquid fuels, an initially perfect Ver combustion device adversely affected and the formation of soot strengthened.

The soot formation deteriorates the combustion both by the Reduction of heat production, as well as by the reduced Heat transfer, since soot has a high thermal insulation effect having.  

For a long time, therefore, the use of Verbrennungskata lysatoren made to ver both the formation of soot prevent or minimize as well as already formed filing soot and tar at the lowest possible temperatures to burn down again. The improved combustion of already formed tars and soot is most effective by transition achieved metal compounds, which are known in various which valences occur. So far mainly used Metal compounds are those of copper, manganese, cobalt, Zinc and chromium (chromates). In particular copper compounds or metallic copper powders lower the combustion temperature considerably from soot and tars. However, they have the aftermath Part to act as toxic components in the exhaust, as well as a significantly increased risk of corrosion on iron materials effect. Copper is in the electrochemical series much more positive than iron, so that at copper boiler strikes on those commonly used in heating technology Ferrous materials form local elements that contain the ferrous Corroding construction parts. This is through the presence be of sulfuric acid or sulfuric acid, which are present combustion of sulphurous fuels, even more.

Also for ceramic materials, such as catalyst supports and carbon black the copper content can be used to lower the enamel points of such ceramic masses, which at higher Ab Gastemperaturen to deformations or change in the pores volume.

Zinc compounds are less toxic than copper and pose also no significant risk of corrosion for iron materials are, however, as a combustion catalyst for carbon black and tars practically hardly effective.  

Chromium has been used for present purposes mainly in Form of chromates used to burn both from benefit as well as catalytic effect of the metal ion to exploit the oxidation potential of chromates on carbon good. Due to the carcinogenic effect of some Chromver However, these compounds divorce according to today's environmental protection requirements. The same applies to nickel and cobalt ver although cobalt in particular is capable of to exert good combustion-catalytic effect.

Manganese, in particular as permanganate, has good combustion catalytic properties and with -1.70 volts as MnO₂ + 2 H₂O = MnO₄ ^- + 4 H⁺ + 3e ^- a high oxidation potential, but nevertheless manganese compounds are also toxic and even classified as carcinogenic suspected ,

A non-toxic transition metal is iron, which is frequently used in oil-soluble form (iron soaps, ferrocene, for example) as a combustion catalyst in liquid fuels. The injection of aqueous iron salt solutions, such as iron sulfate, in the flame has been proposed or handled. Despite these positive characteristics for the combustion catalysis, the iron compounds proved insufficient in their action to burn already formed soot and tars. One reason may also lie in the relatively low oxidation potential of 3-valent iron compounds, namely -0.77 volts Fe ⁺⁺ = Fe ⁺⁺⁺ + e ^- lie.

Also calcium compounds - whereby calcium is known as alkaline earth was not a transition metal - were eliminated recommended by soot deposits. Calcium has a low level Füige combustion-catalytic effect and should be such at all only at high combustion temperatures through education exert hydroxyl ions in the flame. As alkaline earth points However, it has a neutralizing effect on sulfuric acid and Sulfurous acid on, as far as not thermally stable  and incombustible anions is bound.

As a metal ion-free cleaning agent for fire-side coals Fabric coverings continued to use hydrogen peroxide. This Oxidant is also used in conjunction with free alkalis, as alkali metal hydroxides, carbonates and silicates recommended, wherein the oxidation of the soot by H₂O₂ and the acid neutralization tion is carried out by the strong aqueous alkali solutions; a combustion catalytic effect does not occur.

Examples of published publications are GB-PS 1,252,624 for hydrogen peroxide and strong aqueous alkali solutions gene, DE-OS 30 23 520 for the addition of calcium compounds (Calcium phosphate in powder form), DE-PS 24 13 520 for Ent based on metal compounds, the Copper powder, the US-PS 4,287,090 for aqueous catalytically active Metal salt solutions consisting of manganese acetate, calcium nitrate, and copper acetate, DE-OS 29 11 259 for means for fire side Purification with Alkalÿodat or Alkaliperjodatlösung together with copper carbonate as an oxidation aid and ammonia or Alkali carbonates for the neutralization of acidic ash constituents.

As a chemical soot killer were potassium nitrate and ammonium nitrate in DE-OS 22 28 467 (without catalytic combustion effect). In GB-PS 1 303 552 ammonium nitrate in addition to potassium nitrate and / or sodium nitrate for the formation and Condensation of sulfuric acid from the combustion exhaust gases recommended.

Also in a number of other fire-side cleaners from Heiz areas are used to remove soot and tar supporting oxidizing agents or catalytic combustion aids such as ammonium nitrate, ammonium chromate or zinc and copper salts (DE-OS 18 10 424) called.  

EP-A1-0 270 719 mentions water-soluble organic alkali metal salts together with those of rare earth reducing agents, in particular potassium acetate together with trivalent cerium acetate. The disadvantage of this combination lies in the acidic nature of such aqueous solutions with corresponding corrosion potential and the lack of direct oxidation of Cer ⁺⁺⁺ - compounds.

All the means mentioned have the elimination of soot and tars Goals, however, can meet today's demands for one environmentally friendly and possible without major losses insufficient heat transfer. The cataly table combustion through suitable metals has good Effectiveness the disadvantage of toxins in the exhaust gas (Cu, Ni, Co, Cr, Mn), while the oxidation potential in the environmentally friendly metals, such as Fe, Ca is insufficient. When using Oxidants, such as nitrates, iodates or peroxides, is only a one-time effect exists. It can be soot and Tar after consumption of active oxygen from this sub punch again unhindered deposit and the heat balance ver polluting and soot emissions pollute the environment.

It should be noted here that z. B. a soot thickness as a shelf increase the exhaust gas temperature by approx. 70 ° C only by 1 mm can and a fuel oil (fuel) more consumption of 5% after pulls.

Furthermore, some agents in aqueous liquids acidic Reactive solutions with a pH below 7. In the usual Combustion technology, however, exhaust gas temperatures are possible held so high that the dew point of corrosive gases exceeded will be. The feeder or injection is more acidic Components as soot killer would counteract this and in particular the corrosion of the commonly used ironworks feed materials.

The object of the invention is therefore to provide a hydrophilic Ver to create a combustion catalyst, the non-toxic and catalytic for combustion at the lowest possible temperature of Soot and tars by atmospheric oxygen is highly effective in its higher metal ions a high oxidation potential has and a pH of advantageously at least 7 or in the more alkaline areas, and certain To specify uses for this.

Surprisingly, the lanthanides, in particular cerium compounds in their tetravalent form, have been found to be suitable as such catalysts. Water-soluble cerium compounds are non-toxic, and cerium nitrate hexahydrate has z. B. an LD50 _(oral-rat) of 4200 mg / kg, compared to pure saline LD50 _(oral-rat) of only 3000 mg / kg.

Object of the invention, which solved the above problem is, the hydrophilic catalyst solution is according to Claim 1. Further advantageous features and types of use can be found in the claims 2 to 4.

Tetravalent cerium compounds provide strong oxidizing agents The oxidation potential of Ce (IV) / Ce (III) is approx. 1.6 volts, d. H. it is only slightly below the above from permanganate to manganese dioxide at about 1.7 volts and over twice as high as the Fe (III) / Fe (II) system.

Oil-soluble, d. H. hydrophobic lanthanide compounds, in particular those of trivalent cerium were already used as fuel oil used for improved combustion, as in the DE-OS 27 29 365, US Pat. No. 4,462,810 and EP-A1- 0 112 219 is described.  

However, these are exclusively oil-soluble (hydrophobic, hydrocarbon-soluble) and not hydrophilic or water-soluble lanthanide or cerium compounds; they are still present in the Ce ³⁺ form.

The aforementioned known applications were thus known as and fuel additives provided and not for the Feuersei cleaning of heat transfer surfaces, catalysts or Soot filtering of soot and tars deposited thereon suitable.

To avoid fire-side corrosion is provided that the hydrophilic catalyst solution has a pH of min at least 7 has the corrosion already described to avoid danger. As such hydrophilic catalyst solutions even after any mechanical release as a precautionary measure applied to the surface to be protected by soot and tars can be and advantageously at the same time a still should offer stand corrosion protection, it is recommended that aqueous catalyst solution more alkaline, z. B. on one Adjust pH of 8-10. Also higher alkalis are possible, but then increased precaution against skin and Eye contacts are taken.

Furthermore, it has been found that not only the Cer ⁴⁺ compounds have good decapping properties alone, but in particular also in synergistic combination with hydrophilic compounds of metal ions of the iron group.

Compared to the acidic solutions of z. Cerium nitrate, iron nitrate or combinations thereof provides the hydro according to the invention phile solution a corresponding corrosion protection of it treated metallic materials. The pH range is here so adjustable that even ceramic surfaces are not be attacked as well as safe handling without Ver Risk of corrosion is given.  

The weight relations between cerium and iron compounds can be varied, which showed that the kataly table combustion effect in the range from 1:10 to 10: 1 zwi cerium and iron show no major changes, and to 1: 20 or 20: 1 is advantageously possible. An optimum is likely be given at the ratio according to the following Example 1.

Citric acid, but also gluconic acid, can be used as complexing agents and ethylenediaminetetraacetic acid, nitrilotriacetic acid and Hydroxyäthylendiaminotriessigsäure be used.

Instead of iron, but also much more expensive, Compounds with ruthenium and / or osmium in their higher oxidation state can be used.

Instead of Cer ⁴⁺ , Praesodymium ⁴⁺ , Samarium ³⁺ , Europium ³⁺ , Terbium ⁴⁺ , Thulium ³⁺ and Ytterbium ^{3+ can also be used} from the Lanthanides. Since these elements are rare, their use will probably be advantageous only in special cases. Mixtures of said ions can also be used.

Example 1

In 59 parts by weight (GT) of water 3 GT trivalent cerium nitrate (Ce (NO₃) ₃ · 6 H₂O) are dissolved and brought by 2 GT 35% hydrogen peroxide in the tetravalent form of cerium. Furthermore, 12.5 GT citric acid and 9 GT trivalent iron nitrate (Fe (NO₃) · 4 H₂O) are dissolved and brought to a pH of about 9 with 14.5 GT monoethanol amine. The result is a clear, stable dark solution of complexed Cer ⁴⁺ and Fe ³⁺ .

This catalyst solution is tested for effectiveness by uniformly spraying carbon black in a platinum dish with this complexed Cer ⁴⁺ and Fe ³⁺ solution.

The mixture was placed in an oven at 120 ° C for 20 minutes dried, weighed and then the platinum dish with the Mixture heated in a muffle furnace at temperatures of 300-600 ° C. The shell of the remainder was re-weighed. The Difference is the residual soot (mean of several determinations).

The following values resulted:

This is clearly the strong catalytic effect on the Rußabbrand recognizable, especially in the field of 400-500 ° C, at which temperatures soot alone hardly any shows a burnup while the catalytically treated carbon black Residual values of less than 1/4 to 1/2 resulted.

The described test is a very critical one as it is when the gas black used was an aged product, while soot in statu nascendi through the catalyst Composition at even lower temperatures or too burned to a much higher extent.  

Comparative example

To compare the effect of the complexed alkaline Ce ⁴⁺ , Fe ³⁺ catalyst solution according to the invention, an acidic cerium nitrate solution was neutralized with lithium hydroxide. There are known Lich statements that lithium should also have a combustion-promoting property of carbon. Accordingly, 6 GT Ce (NO₃) ₃ · 6 H₂O were dissolved in 85.83 GT H₂O, oxidized with 2 GT 35% H₂O₂ to Ce ⁴⁺ and stabilized with 3 GT citric acid. This acid solution was made alkaline with 3.17 GT lithium hydroxide · monohydrate = LiOH · 1 H₂O.

The carbon black values determined analogously to Example 1 were:

Temperature (° C) Residue (%) 300 95 350 84 400 69 450 63 500 54 550 34 600 17

The combustion catalytic effect was in comparison to Example 1 despite twice as high cerium content dramatically bad ter, especially in the critical temperature range from 400-500 ° C.  

example 2

The solution according to Example 1 was based on sooty heat transfer applied by central heating systems and the Operation of the same continues normally. It shows up a 80% less soot layer after a few hours of burning time. To maintain this soot reduction, the injection of the Catalyst solution renewed periodically, depending on the present conditions a 48-hour to 30-day renewal showed as beneficial.

example 3

The solution according to Example 1 was according to the respective, in many Mandatory compulsory, mechanical cleaning on heat transfer surfaces and other soot-prone surfaces applied. During a subsequent shutdown of the heating or steam boiler plant gave the catalyst solution a Good corrosion protection, as the remaining acids neutralized and the solution itself was corrosion inhibiting property th.

After commissioning the plant showed the hydrophilic solution full combustion catalytic effect. It had an effect samer coating on the heat transfer and other surfaces educated. The sooting was due to longer periods postponed the increased burnup.

example 4

Similar problems as described above arise with the formation of soot particles in the operation of diesel engines. From the perspective of global CO₂ problem (greenhouse effect), the diesel engine is considered due to its good efficiency as one of the best engines. But special environmental problems cause the solid particles in the exhaust gas, which consist of carbon- or carbon-rich aromatic compounds in which a carcinogenic effect can not be excluded. To improve the pollutant contents in diesel engine exhaust, in particular the resulting NO _x and particulate emissions, various technologies are under development. For the above invention is particularly from the gas after-treatment with soot filters and with oxidation systems in NO _x -optimized combustion process of importance. Such soot filters must be heated to achieve a lasting effect, ie even at short distances and relatively low exhaust gas temperatures, with external energy sources or treated with Katalysatorflüssig opportunities for Rußabbrennung. One possibility is to add oil-soluble iron compounds in the diesel fuel to achieve complete combustion. The disadvantage is that form iron oxides in the engine, which act both abrasive on the piston chamber and can lead to disturbances in the sensitive injection and exhaust valve system.

Another system uses the spraying of copper acetyl solutions of acetonate on the soot filter itself to Catalysis easier to burn off. The disadvantage is here both in the Umweltedenklichkeit of copper oxide dusts as also the disposal of such soot filters. Also are acetyl acetone solutions flammable and very expensive.

It has been shown that the injection of a erfindungsge According to the solution according to Example 1, wherein the water or parts the same can also be replaced by hydrophilic solvents can, a strong reduction in the Rußabbrenntemperatur in the Filter - up to 300 ° C in the exhaust - causes and an environmentally friendly represents a practical and economical solution for soot filters.  

example 5

The catalytic solution according to Example 1 was sprayed onto solid fuels such as coal, coke, briquette, wood, straw and other biomasses. The combustion was significantly improved and the formation of soot already reduced at its formation. The combustion gases transport Cer ⁴⁺ and Fe ³⁺ particles to the heat transfer surfaces, so that this also leads to a significant reduction of the soot. Depending on the prevailing conditions, soot reductions could be measured by 45-90%. The aqueous solutions used in this case have no explosion limits, so that they can be used ge in all the usual conditions even during combustion GE.

example 6

The solution according to Example 1 is finely sprayed of the air stream with gaseous, liquid and / or or solid fuels supplied during their combustion. It has an analogous effect on improved combustion (Heat balance) and to reduce soot and solids in the exhaust and from the heat transfer surfaces instead. An advantage This method consists in the use of liquid fuels also in that the transition metals in this form the bearings stability - in contrast to the use of oil-soluble compounds - can not influence.

Claims (4)

1. Hydrophilic cerium compounds containing catalyst solution for improved combustion of carbon and carbon-containing materials and / or to remove soot or tar deposits on surfaces of combustion, characterized in that the solution in addition to cerium compounds in which the cerium is present as a 4-valent cerium , Compounds of dreiwerti conditions iron in a weight ratio of Cer ⁴⁺ - and iron ³⁺ ions of 1:20 to 20: 1 and optionally complexing agent for these metal ions and that the pH of the solution at least 7, preferably 8-10 , is. 2. A catalyst solution according to claim 1, characterized in that the Ce ⁴⁺ ions are replaced by Pr ⁴⁺ , Sm ³⁺ , Eu ³⁺ -, Tb ⁴⁺ -, Tm ³⁺ - or Yb ³⁺ -ions , 3. Catalyst solution according to claim 1 or 2, characterized, that they are citric acid, hydroxyethylenediaminetriacetic acid, Ethylenediaminetetraacetic acid, nitrilotriacetic acid or Contains gluconic acid as a complexing agent. 4. Use of the catalyst solution according to any one of claims 1 to 3, for the improved combustion of carbon and hydrocarbonaceous substances and / or Ent removal of soot or tar deposits on surfaces of Combustion chambers.