Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2000-03-31
2002-10-08
Carrillo, Sharidan (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S004000, C134S022100, C134S022110, C134S022120, C134S022140, C134S022190, C134S034000, C134S036000, C134S040000, C134S042000
Reexamination Certificate
active
06461440
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus which has a treated metallic surface and a process for treating the metallic surface and the use thereof.
BACKGROUND OF THE INVENTION
In the storage, preparation, working up or further processing of ethylenically unsaturated monomers, such as styrene, (meth)acrylic acid, (meth)acrylic esters and acrolein, the problem of the formation of deposits due to undesired polymer formation on the walls of the relevant plant components frequently occurs. Such polymer deposits can considerably reduce the heat transport in the relevant plant components, for example to container walls or to cooling means of reactors or distillation apparatuses. Polymer deposits in pipelines, for example in distillation apparatuses, can lead to pressure drops and/or blockages. The undesired polymer formation can finally result in complete polymerization and hence solidification of mixtures containing these monomers. In addition, the undesired polymer formation leads to losses of the relevant polymerizable compound, as a rule a compound capable of free radical polymerization. In syntheses in which polymerizable compounds are used as starting material (for example in the Michael addition), the undesired polymer formation leads to a reduction in the yield.
In order to suppress the undesired polymer formation, soluble polymerization inhibitors are usually used. Such polymerization inhibitors are on the one hand known free radical acceptors, such as phenothiazine or phenols such as pyrogallol, hydroquinone or hydroquinone monomethyl ether, and, on the other hand, the salts of reversibly reducible/oxidizable metal cations, such as the Cu
+
/Cu
2+
pairs.
Soluble polymerization inhibitors have the disadvantage that they cannot completely suppress the polymer formation on the container walls. In the distillation of monomers, high-boiling polymerization inhibitors remain in the vessel, so that the distillate is not protected from polymer formation.
The non-prior-published DE-A-19808179 of Feb. 26, 1998 describes inorganic coatings of process plants which are intended to prevent the adhesion of polymers to the relevant inner surfaces. The coated material contains immobilized metal ions and oxygen compounds of boron, aluminum, silicon or phosphorus.
Another possibility is to protect inner surfaces on which polymers can be deposited from undesired polymer deposition by modification with organic protective coats.
DE-A-196 48 811 describes the use of N-oxyl compounds of secondary amines for reducing the polymeric deposits in the polymerization of vinylically unsaturated compounds. The N-oxyl compounds however can be added to the polymerization mixture or, alternatively, the reactor surface can be wet with N-oxyl compounds before the addition of the polymerization mixture.
EP-B-0 606 013 relates to an inhibitor which is intended to reduce the deposition of polymer on reactor surfaces during the polymerization. It is a low molecular weight condensate of a stilbene compound and a quinone compound, which is applied to the reactor wall before the polymerization in an alkaline solution. After drying, a coating which is intended to provide protection from polymeric deposits during the polymerization forms. The disadvantage of the abovementioned methods for protecting a surface from undesired polymer deposition is that the protective coats produced on the surfaces are resistant only to specific media and moreover the protective coats lose their protective function in the course of time.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus with which polymerizable compounds, in particular compounds capable of free radical polymerization, e.g. acrylic acid, can be distilled, stored or reacted without polymer being deposited on the walls of the corresponding apparatus during the distillation, storage or reaction. It is intended to bring about this property of the apparatus by means of the material and/or by means of the surface of the apparatus. The material and/or the surface should not only be suitable for protecting plants for chemical processes from the adhesion of polymer but should moreover inhibit free radical polymerization in these plants.
DETAILED DESCRIPTION OF THE INVENTION
We have found that this object is achieved by an apparatus which is in the form of a process apparatus or container and has a metallic surface which contains Fe and/or Mo and/or V and/or Ti and/or Cr and/or Ni and/or Co. In the novel apparatus, at least a part of the metallic surface has been treated with polymeric complexing agent.
The metallic surface is to be understood as meaning the interface of a corresponding article, it also being possible for this interface to be regarded as a three-dimensional structure—the surface is then the uppermost thin layer of a corresponding article (the thickness of the surface is as a rule less than 1 mm). The treated metallic surface generally forms the total inner surface or a part of the inner surface of a process apparatus or of a container. Process apparatuses may be devices, components and apparatuses of all types, such as pipelines, reactors, stirrers, seals or apparatuses for separating substances (for example distillation apparatuses, filter presses, centrifuges). Containers may be, for example, storage containers or receivers.
Polymeric complexing agents are to be understood as meaning compounds whose average molecular weight is at least 1000, preferably from 3000 to 1.5 million, g/mol (number average—method of determination: gel permeation chromatography), which moreover have coordination sites at which heavy metals can be chemically bonded, on average at least 8, preferably at least 12, coordination sites (arithmetic mean) being present per molecule (per polymer). Coordination sites are to be understood as meaning ligands or ligand groups which form coordinate bonds with metal ions under the conditions of use—for example under the conditions of the treatment with polymeric complexing agents, under conditions of storage, chemical synthesis, purification or separation of substances. Coordinate compounds are complexes which have at least one central atom or central ion and at least one ligand or one ligand group (uncharged or negatively charged). In general, heavy metal ions act as central ions. Important examples of coordination sites are functional groups containing bonded oxygen, such as—COOH or —PO
3
H
2
, and furthermore nitrogen-containing functional groups, in particular nitrogen-containing heterocycles having five-membered or six-membered rings.
In particular, it is intended that cations of Fe and/or Mo and/or V and/or Ti and/or Cr and/or Ni and/or Co can be complexed, i.e. bonded by a coordinate bond. In principle, polymeric complexing agents may also be present in the form of salts. Polymeric complexing agents contain branched or straight backbones to which side chains having coordination sites are bonded.
In a preferred embodiment, the polymeric complexing agent contains phosphonoalkylated polyethyleneimines/polyvinylamines and/or carboxyalkylated polyethyleneimines/polyvinylamines and/or vinylimidazole polymers. The abovementioned groups of substances form basic types of suitable polymeric complexing agents. These basic types are to be described in more detail below.
Carboxyalkylated polyethyleneimines/polyvinylamines:
Carboxyalkylated polyethyleneimines/polyvinylamines are polyethyleneimines/polyvinylamines in which hydrogen atoms of the secondary or corresponding of the primary amino functions have been substituted by radicals which have carboxyl groups. Instead of the carboxyl groups, carboxylates too (deprotonated species) may be present at the corresponding sites, in which case the carboxyalkylated polyethyleneimines/polyvinylamines are present as salts. Polyethyleneimines may contain primary, secondary and/or tertiary amino functions. The primary or secondary amino groups can be completely or partially carboxyalkylated. In contrast to the secondary amino functions, in which o
Decker Jürgen
Jaworek Thomas
Keller Harald
Rahm Rainer
Schliephake Volker
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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