WO1996009423A1

WO1996009423A1 - Organically-based agent for removing rust from surfaces, production and use of said agent

Info

Publication number: WO1996009423A1
Application number: PCT/EP1995/003670
Authority: WO
Inventors: Peter M. Kunz; Hans ZÄHNER; Monika Willrett; Stefan Dausmann; Michael Paul
Original assignee: Kunz Peter M; Zaehner Hans; Monika Willrett; Stefan Dausmann; Michael Paul
Priority date: 1994-09-20
Filing date: 1995-09-18
Publication date: 1996-03-28
Also published as: DE4433376C1; AU3607795A

Abstract

The invention concerns an agent, based on organic compounds obtained from micro-organisms, for removing rust from metal surfaces corroded with iron oxides. Rust is normally removed from metal articles using corrosive baths containing organic and/or inorganic acids which, owing to the concentrations used, must meet certain safety requirements and entail costly disposal procedures once the baths are depleted. Iron-absorbing products obtainable using biological methods are generally active in the neutral pH range, eliminating the salt production and contamination of the effluent associated with the neutralisation process normally required. Rust can be removed using reproducible intra- or extra-cellular products which have a high affinity with iron ions. The proposed agents are produced by culturing appropriate organisms in a suitable medium in such a way that they are stimulated to produce these agents. The articles requiring de-rusting are then treated by being dipped in or painted with the agent. Provision of appropriate supports to immobilise the articles facilitates use of the agents and permits recycling of the agent by suitable treatment.

Description

Means for the derusting of surfaces on an organic basis as well as their manufacture and application

description

The invention relates to agents for removing rust from surfaces (removal of corrosion products). The invention further relates to a process for forming and a process for using these rust removers.

By definition according to DIN 50900, 1. 1 is understood by corrosion to mean the "reaction of a metallic material with its surroundings, which causes a measurable change in the material and can impair the function of a metallic component or an entire system. In most cases, this reaction is of an electrochemical nature, in some cases, however, it can also be chemical (non-electrochemical) or metallophysical in nature. " [Meckelburg, E .: Corrosion behavior of materials, VDI Verlag]

The losses incurred by the global economy from corrosion damage and consequential costs are estimated by international material research and economic institutes to be many billions of dollars a year. This shows that signs of corrosion are of considerable economic interest. [Meckelburg, E .: Corrosion behavior of materials, VDI Verlag, Düseidorf 1 990]

The corrosion of a material is a very complex and multi-layered process, the exact course of which depends on the system of the material to be examined and its environment. Corrosion phenomena must therefore always be considered individually. However, some basic statements can be made that apply to all corrosion reactions. Corrosion reactions are always phase boundary reactions between the corrosive material and its immediate surroundings. The corrosive metal is oxidatively attacked in a redox reaction.

Me → Me ^{z +} + ze ' A metal is said to be passive with regard to its corrosion behavior if high corrosion speeds are expected under the given circumstances, but the corrosion takes place very slowly due to the (mostly oxidic) covering layers that form. These cover layers mostly arise from the corrosion itself.

An example is the high corrosion resistance of the base metal, which is very base with a normal potential of Eo = -1.66 V, which results from the formation of a stable, non-conductive oxide cover layer. [Kaesche, H .: The Corrosion of Metals, 3rd ed., Springer Verlag 1990].

In the case of iron, a passivating oxide layer can also be formed. The corrosion conditions are decisive here. The iron (II) hydroxide is much more soluble in water than Fe (OH) 3, which is a partial hydroxide of the formula FeO (OH) or Fe2θ3- * H2O. If pure iron immerses immovably in distilled water, the Fe ^{+ +} and OH "ions formed diffuse away from the metal surface and are only oxidized to Fe (OH) 3 (= rust) in a region of higher oxygen concentration Oxides that have precipitated on the metal surface do not form a protective layer on the metal and the corrosion progresses the samples do not corrode, but remain shiny [Kaesche, H .: The Corrosion of Metals, 3rd ed., Springer Verlag 1 990, Evans, UR: Introduction to Corrosion of Metals, Verlag Chemie, 1 965]

Iron is one of the base metals (Eo = -0.44 V) and is therefore particularly susceptible to electrochemical destruction. The main corrosion product of iron is rust. Rusting iron is a natural process. As a pure metal, iron is thermodynamically unstable and therefore tries to change to the thermodynamically more stable state, rust [Ute Rasemann: Examinations on rust layers to clarify their macroscopic and microscopic structure and some properties, the partial characterize the complex rust mechanism. Frei¬ berg, 1 975].

Chemically, rust is often described as hydrated iron (III) oxide (FeO (OH) = V2 Fe2θ3- * H2O). It is more precise, however, the rust as a mixture of different proportions of iron (II) oxide (FeO), iron (II, III) oxide (Fe3θ4), and as the most common component iron (III) oxide (Fe2θ3 ) to characterize. Water can be present as a hydrate or hydroxide.

By definition [Lexicon of Corrosion Volume 1: Mannesmannrhrenwerke, 1 970], film rust is understood to mean "the first easily removable rust that is created in the atmosphere on steel". Characteristic of the rust film is its initial appearance on metal surfaces as small pixels, which then grow together increasingly.

Extraneous rust is described as "deposits of corrosion products that did not arise at the point in question, but were carried from somewhere else. These deposits can create conditions for ventilation elements and cause rusting through".

The most common corrosion product of iron Fe2θ3 arises according to the following gross equation:

4 Fe + 3 O2 → 2 Fe2θ3 or for FeOOH

4 Fe (Me) + 3 0 ₂ (D + 2 H ₂ 0 (l) → 4 FeOOH (s)

Me = metallic, I = liquid, s = solid

The equation shows that it is not the free atmospheric oxygen but the one dissolved in the electrolyte that is responsible for the oxidation. The diffusion of soluble oxygen to the metal is therefore the rate-determining step of corrosion.

This equation can be broken down further, which explains the layered structure of the grate. First, the Formation of the unstable iron (II) oxide, which can be represented by the following redox equation:

Fe → Fe2 + + 2e "(Ox.) Vz O2 + 2e" → θ2- (Red.)

The very unstable FeO reacts further in the presence of water and oxygen to form Fe (OH) 2 _/ which is oxidized to Fe (OH) 3 by the dissolved atmospheric oxygen.

'Λ O2 + 2e "→ O ² ' θ2- + H2O → 2 OH '

Fe ² + + 20H- → Fe (OH) 2 2 Fe (OH) 2 + ' ₂ θ2 + H2O → 2 Fe (OH) 3 and

Fe (OH) 3 → FeOOH + H2O = y ₂ Fe2θ3 '* H2O + H2O

The middle mixed oxide layer made of Fe3θ4 arises from the fact that the formation of the iron (III) oxide layer partially blocks the oxygen supply to the lower layers. Thus, Fe ⁺ cannot be completely oxidized to Fe- * +. The formation of this protective layer explains the slowing rust formation over time. Therefore, a rust layer can basically be represented as follows:

■ hematite [ferric oxide]

■ magnetite [iron (II, III) oxide]

■ Wustite [iron (II) oxide]

■ iron

In practice, you will hardly find this clearly defined layer structure. The top layer of iron (III) oxide becomes brittle during drying and flakes off in places. As a result, the oxide layers or metallic iron lying further down are exposed, which means that they come into contact with O2 and can be oxidized. A microscopic examination of a rusted sample reveals a very jagged and porous structure. Thus, in terms of thickness and composition, it forms over time very uneven rust layer, which makes precise characterization difficult.

The current methods of derusting surfaces are based predominantly on the use of acids as pickling agents.

Since they are relatively highly concentrated, these must be treated with appropriate precautionary measures. The acid concentrations within the breathing air in the area of the pickling tanks should not be neglected. Despite the fact that they are recycled, the pickling baths become exhausted over time and have to be disposed of at great expense. Large amounts of correspondingly strong alkalis are required for this. There is generally no possibility of application for the salt formed in the process. It has to be deposited in a costly manner.

Mechanical methods for removing rust are also possible, but are used for technical and time reasons at most for small rust spots and flat surfaces. In addition, the metal surface is slightly damaged, which leads to new corrosion attack surfaces.

The object of the invention was to find a more environmentally friendly, efficient means which is capable of detaching the iron oxides from the corroded surfaces in approximately comparable periods of time from conventional rust removal baths and concentrating them to a high degree, so that, for example, one direct recovery from the complex becomes possible.

The object is achieved in that ferritin, as occurs in the human body for iron storage, is used. In addition, a large number of complexing agents, siderophores, chromatophores and other proteins can also be considered, all of which have an affinity for iron. Quantitatively rusted sheet metal, in order to demonstrate the effect of derusting by weight measurements, could be derusted with the mentioned means and thereby brought back to bare. The agents found will be produced by fermentation; they can be handled more safely and are easier to dispose of or recycle.

According to the invention, these agents are used in a more immobilized manner

Form on suitable carriers in order to increase the degree of utilization and to enable simple recovery from the application.

The metal parts to be derusted are then immersed in a bath mixed with these agents or coated with a correspondingly concentrated solution and removed again after a certain exposure time.

The agents found are briefly described below:

Ferritin is an iron-protein compound and, in addition to hemosiderin, serves as an important form of storage and transport of iron in the vertebrate organism. Ferritin is formed on polyribosomes freely present in the cytoplasm. The iron content in the compound is approximately 20%. The protein content of ferritin with a molecular weight of 480,000 is called apoferritin [Pschyrembel].

Ferritin is a hollow sphere with a diameter of 1 2 nm, which consists of 24 subunits of approx. 1 8,500 to 1 9,000 daltons each [Mann, S .; J .V. Bannister, R.]. P. Williams: Structure and composition of ferritin cores isolated from human spieen, limpet (Patella vulgata) hemolymph and bacterial (Pseudomonas aeruginosa) cells (published erratum appears in] .Mol.Biol, 1 986] ul 5, 1 90 (1) : 1 39) J. Mol.Blol 1 88, 225-232]. One molecule has a storage capacity of up to 4,500 iron atoms, which are linked to various amino acids of the protein coat [Massover, WH; J .M. Cowley: The ultrastructure of ferritin macromolecules. The lattice structure of the core crystallites. Proc. Natl. Acad. Be. Med ZΩ, 3847-385 1, (1 973)]. Most ferritins contain 1,000-3,000 iron atoms. The protein envelope encloses a dense matrix of hydrogenated iron hydroxide, Fe (OH) 3, with a Diameter of 7 nm. In addition, phosphorus is associated with this matrix in different proportions. Other sources speak of the storage form iron oxyhydroxide phosphate (FeOOH) β * (FeO * Pθ3H2) [Harrison, P .; F. Fischbach, T. Hoy, G. Haggis: Nature 2_l_ώ, 1 1 88 - 1 1 90, (1 967)]. Ferritin has ligands for ferrioxidase activity that enable it to oxidize Fe ⁺ to Fe ^ + and thereby initiate iron incorporation into the ferritin. The iron is extracted by reducing Fe ^ + to Fe ^{2 +} with the help of chiatants.

Hemosiderin is a water-insoluble iron-protein compound with about 37% iron. In addition to ferritin, it is a form of iron storage in the body.

Transferrin is a glycoprotein (MW around 90,000) that is located electrophoretically in the fraction of the ß-globulins. Normally, one third of transferrin is saturated with iron (as Fe- * +), the rest is called free iron binding capacity. The total binding capacity of the transferrin for iron is 45 - 73 / mol / l (250 - 41 0 g / dl).

To date, over 200 different siderophores have also been found. The variety of structures is quite large. They are divided into hydroxamate (e.g. desferrioxamine E), catechol (e.g. enterochelin) or phenol, oxazoline, polycarboxylate groups (e.g. rhizobactin) and mixed forms. Siderophores are classified as primary metabolites because they are synthesized in the logarithmic growth phase (trophophase).

Simmerochromes are iron-containing or iron-bound natural products which contain hydroxamic acid groups in one molecule in an arrangement which allows the formation of an iron hydroxamate complex. Here, Fe ^ + ions are selectively bound. The siderochromes with antibiotic properties are called sidermycins, those that can serve as growth factors are called sideramines. A distinction is made, for example, from acidic ferrioxamines: for example desferrioxamine H, ■ * basic ferrioxamines: for example desferrioxamine B, => amphoteric ferrioxamines: e.g. desferrioxamine G.

A ferrioxamine has been used for years to treat thalassemia patients who have too much iron in their blood, but also dialysis patients who receive too much aluminum from the treatment.

The ferrichrome was first isolated from Ustllago sphaerogena in 1952. There are many types of ferrichrome that are structurally related. These include ferricrocin, ferrichrysin, ferrirubin and ferrirhodin.

Sideramines are cyclic esters of 3 molecules of 2,3-dihydroxybenzoylserine. This includes enterochelin, also called enterobactin, which is used by e.g. E. coli or Salmonel la typhimurium is formed.

The following microorganisms can be used to produce the agent:

- Yersinia H 1 852. - Staphylococcus hyicus DSM 20459, yield up to 4.1 g / l

- E. coli AN 3 1 1

- E. coli 5050 Tu

- Staphylococcus aureus NCTC 1 4990

- Staphylococcus aureus NT 259 - Staphylococcus aureus 31 588

- Staphylococcus aureus G4

- Staphylococcus aureus BR 26

- Staphylococcus aureus Sau 3A

- Streptomyces olivaceus Tu 271 8

A modified nutrient solution according to Zahnner [Zahnner, H.; W. Keller-Schierlein, R. Hütter, K. Hess-Leisinger, A. Deer: Metabolic products of microorganisms, 40th middle Sideramine from Aspergillaceae. Arch. Microbiol. 45, 1 19, (1963)] uses:

0.5 g CaCl2 * 2 H2O 1.0 g K2HPO4

2 mg ZnSθ4 * 7 H2O

On hard disk: 1.5% agar

possibly 100 γ / l thlamine

20.0 g glucose

20 mg / 1 FeCl3 * 6 H2O

1 00 mg yeast extract

1 0 γ biotin 1000 ml dist. water

A suitable nutrient solution for E. coli AN 3 1 1 for the formation of boilers is

K2HP04 10.6 g

NaH2P0 ₄ * 2 H2O 6, 1 g

MgSO 4 * 7 H2O 0.2 g

(NH ₄ ) 2Sθ4 2.0 g

Ca (NO ₃ ) ₂ 0.01 g

FeSθ4 * 7 H2O 0.5 mg deion. Water ad 1 1

The fungal nutrient solution for sideramine formation can look like this:

Nutrient solution 4 normal medium

Glucose 20 g 20 g

Asparagine H2θ 5 g 5 g

NH4CI - 5 g

K2HPO4 1 g 1 g

MgSO 4 * 7 H2O 1 g 1 g

CaCl2 * 2 H2O 500 mg 500 mg

ZnSθ4 * 7 H2O 2 mg 2 mg

H2O 1 1 1 1 possibly with 20 mg / 1 Fe ⁽ = 13 '* 6 H2O.

Siderophores are characterized by

■ that they are heavily produced under iron deficiency. That they keep Fe (IIl) or Fe (II) in solution under physiological conditions,

■ that they transport Fe (III) or Fe (II) to or into the cell to an extent sufficient for growth [Neilands, J.B .; C. Radledge: Mcrobial iron transport compounds. In: CRC Handbook of microbiology, Vol IV. Eds. Laskin, A.I .; HA. Lechavalier, CRC Press, Boca Raton, Florida, 565-58 1, (1 982)] ..

In order to obtain the siderophores, it is generally necessary to work in an iron-free environment.

The siderochromes are excreted as iron deficiency compounds and form brown-red complexes with the iron bond, which are characterized by a broad absorption band with a maximum between 420 and 440 nm. Siderochromes formed by fungi and actinomycetes are trihydroxamates.

The crude siderochromes are isolated as follows: Add 5 ml of FeCl3 solution (100 mg / 1) to 500 ml of culture filtrate, saturate with solid NaCI, extract with 1/5 of the volume of chloroform-phenol (1: 1, V: G) , Centrifuge at 3000 rpm for 20 min, filter the organic phase, dilute with 2 vol. Ether, extract with water and lyophilize.

Ferricrocin production can be increased if there is a mutation in the ferricrocin uptake system, the strains are arginine auxotrophic, the ornithine δ-transaminase is mutated and / or the α-ketoglutarate dehydrogenase (auxotrophy for lysine) is changed. Production is optimized with glucose as the C source (8 g C / l) and asparagine as the N source (1 g N / 1). 10 mg l \ * h could be obtained over 60 hours [Kappner: Desferri-ferricrocin production in Aspergillus viridi-nutans. Ducker and Thrower, dissertation Tübingen, 1 978)].

The agents according to the invention are placed in a conventional immersion bath into which the surfaces to be rusted are immersed. They are brought into intimate contact with the surface by means of a stirring or circulation system. This can the surface renewal rate is kept high. The agents are retained in the bath by means of a simple sieve system. After a dwell time dependent on the rust strength - depending on the application, for example in wire drawing, hot-dip galvanizing, electroplating or painting plants - the immersion baths are filtered, the agents are concentrated, chelators are added and the iron released in this way is separated off.

After the chelators and agents have been separated, the agents are used again for their task according to the invention and the chelators are concentrated for the next workup. The processing can also be done externally.

According to the invention, the agents can also be applied to the surfaces by brushing or rolling or spraying. After an exposure time of, for example, 5 minutes, they are removed from the surface with the aid of spray or immersion or, if appropriate, wiping processes and, as described above, regenerated after the capacity has been exhausted.

According to the invention, the method is also to add the above-mentioned microorganisms with little or no risk level, which have extracellular products with a high iron binding capacity, directly to the immersion bath and to let them grow. The processing is carried out analogously to the explanations above.

Claims

Agent for the derusting of surfaces on an organic basis as well as its manufacture and application

1 . Agent for rust removal from surfaces, characterized in that it consists of organic compounds with a high affinity for divalent and / or trivalent iron and is obtained from biomass by the known methods of obtaining intra- and extracellular products and by dipping or brushing the rust ¬ facing surfaces is used.

2. Composition according to claim 1, characterized in that the organic component has a high iron binding capacity.

3. Composition according to claims 1 and 2, characterized in that it is complexing agents, siderophores, chromatophores, very general proteins, such as ferritin or other organic compounds occurring in cells with high affinity for iron .

4. Composition according to claims 1 and 3, characterized in that it is immobilized for use on spherical carriers with up to 3 mm diam.

5. A process for the preparation of an agent according to the preceding claims, characterized in that suitable microorganisms for the production of the active components according to claim 3 are grown in almost iron-free nutrient solutions.

6. A method for microbial rust removal according to claims 1 to 5, characterized in that the agents are given in a dip bath in concentrations of 1 g / l and more.

7. Device for carrying out the method according to the vorgenann¬ th claims, characterized in that the stirring means or Umwälzaniagen the means relative to the surfaces in a Wir- be brought to the fore and retained in the immersion bath via sieve systems.

8. A process for mlcrobial rust removal according to claims 1 to 5, characterized in that the agents are applied to the workpiece and are removed after an exposure time of 5 minutes by wiping or dipping in a rinsing bath.

9. A method for microbial rust removal according to claims 1 to 8, characterized in that the spent agent is separated from the immersion bath solution via a membrane separation system with specific retention depending on the carrier material and brought into contact with chelators which remove the iron from the agent release, and the regenerated agents are used again according to their task, while the iron ions are separately concentrated.

1 0. Process for microbial rust removal according to claims 1 to 3, characterized in that the suitable microorganisms are used directly in the conventional rust removal bath and, accordingly, optimal conditions are grown therein and treated analogously to claim 9.