LOW CORROSION ALKANE SULFONIC ACIDS FOR CONDENSATION REACTIONS

Abstract

The present invention relates to methods for adding an aqueous solution of alkane sulfonic acids to a reactor via a pipe or container, wherein a condensation reaction takes place after addition of the aqueous solution of alkane sulfonic acid and to methods for reducing or limiting corrosion by adding said aqueous solution to a reactor. The present invention also relates to the use of aqueous solutions of alkane sulfonic acids in the reduction or limitation of corrosion and to the use of such aqueous solutions in condensation reactions.

Description

The present invention relates to methods for adding an aqueous solution of alkane sulfonic acids to a reactor via a pipe or container, wherein a condensation reaction takes place after addition of the aqueous solution of alkane sulfonic acid and to methods for reducing or limiting corrosion by adding said aqueous solution to a reactor. The present invention also relates to the use of aqueous solutions of alkane sulfonic acids in the reduction or limitation of corrosion and to the use of such aqueous solutions in condensation reactions.

Condensation reactions are reactions where two or more molecules or moieties of one molecule are combined to a single molecule accompanied by the loss of small molecules. Well known condensations comprise those where water is released during formation of the single molecule, but also other small molecules may be released. It is also possible that separate moieties within the same molecule may react with one another to reform the molecule (intramolecular condensation reaction) which is typically accompanied by the formation of a ring (Brückner, R., Reaktionsmechanismen, 2. Aufl.; Spektrum: Heidelberg, (2002), S. 388-389; Ullmann's Encyclopedia of Industrial Chemistry, 6. Aufl.; Wiley-VCH: Weinheim, (2002), 16, 241-245).

A typical example of a condensation reaction is an esterification between a carboxylic acid and an alcohol, producing an ester and one water molecule.

Condensations may occur intramolecular or intermolecular, either between only two molecules or more molecules to form a condensation polymer (polycondensation). Many condensations are acid catalyzed. For such acid catalyzed condensation reactions, a variety of acids is generally suitable, e.g., organic acids or inorganic acids. Strong acids like sulfuric acid, p-toluenesulfonic acid or methanesulfonic acid are often preferred since they enable a faster reaction. However, such strong acids have the disadvantage that they induce corrosion such as formation of iron oxides (rust) on metal surfaces which are contacted with such acids, either during the condensation reaction or when adding the acid catalyst to the reaction. Some strong acids are known to induce less corrosion than others. For example, alkane sulfonic acids such as methanesulfonic acid (MSA) are less corrosive towards stainless steel compared to sulfuric acid, and hence have become more popular in recent years. Methods for preparing alkane sulfonic acids are known in the art, e.g., WO 2000/031027, WO 2015/086645, WO 2011/054703, or U.S. Pat. No. 4,450,047.

If the acid catalyzed condensation reaction is an equilibrium reaction and involves the elimination of water, it is desirable to start the reaction with the lowest possible water content in order to shift the equilibrium more to the product side. That is, the acid catalysts should contain a minimum amount of water. However, higher acid concentrations in the catalyst solution normally lead to higher corrosion rates, especially in storage tanks, pipelines, fittings, etc., which are very often made of steel materials. Higher corrosion rates may also appear in the reactor, especially at the beginning of the reactant dosage. Accordingly, it is desirable to use as little acid catalyst as possible in order to minimize corrosion. On the other hand, a higher acid catalyst dosage normally leads to a faster reaction and hence a more efficient process.

Accordingly, there was a need to reduce the formation of corrosion in condensation reactions and maintain a high reaction rate with a suitable amount of catalyst dosage.

The objective technical problem resulting from the above has been addressed and resolved by the present invention as defined in the claims and described in the following description and examples.

The present invention relates to a method of adding an aqueous solution (A) to a reactor, wherein said aqueous solution (A) is added to the reactor via a pipe or a container, wherein said reactor, pipe and/or container has a corrosive surface (e.g., a surface containing iron), and

wherein said aqueous solution (A) contains about 80 to 99 w/w %, preferably about 80 to 98, 85 to 98, 88 to 98, 90 to 98, 92 to 97, 92 to 96, or 93 to 95 w/w of an alkane sulfonic acid, relative to the total weight of said aqueous solution (A).

In one embodiment of the present invention, a reaction takes place in said reactor after the addition of said aqueous solution (A) into the reactor, wherein said aqueous solution (A) is either a reactant (e.g., an educt), a solvent, a neutralizer, or a catalyst for said reaction. Such reaction is generally preferably a chemical reaction and may be of any kind where said aqueous solution (A) can be employed. Such reactions are known in the art and comprise inter alia alkylation reactions or condensation reactions such as esterifications and others as further exemplified herein. For example, said reaction is an acid or base catalyzed reaction. In this context, said aqueous solution (A) may be the catalyst for an acid catalyzed reaction or a neutralizer for a base catalyzed reaction; see, e.g., EP 2358851. In one embodiment of the present invention, the reaction which takes place in the reactor after addition of the aqueous solution (A) is a condensation reaction, for example an acid catalyzed condensation reaction.

As has been surprisingly found in context with the present invention, an aqueous solution (A) containing about 80 to 99 w/w % of an alkane sulfonic acid (relative to the total weight of said aqueous solution (A)) is able to drastically reduce the corrosion rate on a corrosive surface (e.g. a surface containing iron), compared to an aqueous solution comprising less than about 80 w/w % or more than about 99 w/w % of such alkane sulfonic acid. This result can even be improved at values of about 80 to 98, 85 to 98, 88 to 98, 90 to 98, 92 to 97, 92 to 96, or 93 to 95 w/w % of an alkane sulfonic acid. Also, as has been found in context with the present invention, the addition of small amounts of nitric acid or a salt thereof (e.g., an (earth) alkali metal salt of nitrate) can further reduce the corrosion rate.

Accordingly, the present invention also relates to a method for reducing the corrosion rate of the corrosive surface (e.g., an iron containing surface), comprising adding an aqueous solution (A) which contains about 80 to 99 w/w %, preferably about 80 to 98, 85 to 98, 88 to 98, 90 to 98, 92 to 97, 92 to 96, or 93 to 95 w/w % of an alkane sulfonic acid, relative to the total weight of said aqueous solution (A) to a corrosive surface (e.g., an iron containing surface). In one embodiment, the corrosive (e.g., iron containing) surface may be the surface of a reactor, a pipe and/or a container. For example, said aqueous solution (A) is added to the reactor via said pipe and/or container. In this context, the term “reducing” corrosion means that the corrosion rate is lower compared to when an aqueous solution containing more or less of the alkane sulfonic acid as defined herein is applied to said reactor, pipe and/or container. “Lower” in this context means that the formation of corrosion is at least about 1.2-fold, at least 1.5-fold, at least 1.8-fold, or at least 2-fold or even 2.5-fold lower.

Accordingly, the present invention relates to a method for limiting the corrosion rate of a corrosive surface (e.g., an iron containing surface) to a rate of max. about 0.3 mm/year, preferably max. about 0.25 mm/year, max. 0.2 mm/year, max. 0.15 mm/year, or 0.1 mm/year, comprising adding an aqueous solution (A) which contains about 80 to 99 w/w %, preferably about 80 to 98, 85 to 98, 88 to 98, 90 to 98, 92 to 97, 92 to 96, or 93 to 95 w/w % of an alkane sulfonic acid, relative to the total weight of said aqueous solution (A) to a corrosive surface (e.g., an iron containing surface). In one embodiment, the corrosive (e.g., iron containing) surface may be the surface of a reactor, a pipe and/or a container. For example, said aqueous solution (A) is added to the reactor via said pipe and/or container.

In context with the present invention, “corrosion” means any kind of chemical and/or electrochemical conversion of a metal to a chemically more stable form and particularly comprises the oxidation of a metal, particularly the oxidation of iron (rust formation). The “corrosion rate” as used herein means the degree of the formation of corrosion and can be measured by methods known in the art and as also described and exemplified herein. Typically, the corrosion rate is indicated in mm/year. Methods for measuring the corrosion rate are described for example in DIN 50905 (part 2) or ASTM G31-72 and as further described and exemplified herein.

In context with the present invention, the iron containing surface, e.g. that of a reactor, a pipe and/or a container which is/are contacted with an aqueous solution (A) as described herein, may be of any material containing iron. Particularly, such surface is of an iron containing material which has the general ability to corrode (e.g., to rust) when exposed to oxygenizing compounds (oxidants) such as oxygen, sulfur, or organic or inorganic acids (preferably organic acids such as, e.g., alkane sulfonic acid, sulfuric acid, citric acid, acetic acid, or others). In this context, such iron containing material may comprise any kind of iron alloys such as, e.g., cast iron alloys, austenitic steel alloys (see, e.g., Rompp Online, Version 3.5, Georg Thieme Verlag 2009), (stainless) steel alloys (e.g., steel alloys according to the SAE designation; see, e.g., Jeffus, Cengage Learning (2002), Welding: Principles and Applications), elinvar, fernico, ferroalloys, invar, kovar, staballoys, and others. Generally, iron alloys may comprise further (metal) compounds such as, e.g., nickel, chromium, cobalt, carbon, molybdenum, hydrogen, manganese, silicon, nitrogen, and/or others. For example, in context with the present invention, the iron containing surface may be an iron (e.g., steel) alloy comprising about 10 to 22, 12 to 20, or 13 to 17 w/w % chromium, and/or about up to 0.20 w/w % or about 0.02 to 0.15 w/w %, or 0.05 to 0.12 w/w % carbon, and/or about 15 to 22 w/w % chromium and about 9 to 15 w/w % nickel. In one embodiment, the chromium content may be about 16 to 20 w/w %, and/or the nickel content may be about 10 to 14 w/w %, and/or manganese in an amount of about 1 to 3 w/w %. Other metals may be contained in various amounts, for example about 1 to 5 (preferably 1.5 to 4 or 2 to 3) w/w % molybdenum, and/or about 0.1 to 2 or 0.5 to 1 w/w % titanium. It is also possible that such steel alloys do not contain chromium, nickel, or molybdenum, for example they do not contain nickel and/or molybdenum. In context with the present invention, such iron alloys may also be passivized by a passivation layer formed by, e.g., chromium in the presence of ambient air or oxygen. For example, the iron containing surface which is contacted with an aqueous solution (A) as described herein may be a steel alloy, e.g., a carbon steel alloy according to DIN EN 10088, AISI, SAE designation or others.

Examples of steel alloys in context with the present invention comprise those listed in Table 1, 2, 3, or 4.

TABLE 1
Steel alloy examples according to AISI and DIN EN 10088 classification including respective
selected contents of Cr, Ni, Mo, and C
			Cr	Ni	Mo	C
AISI	DIN EN 10088	DIN EN 10027-2	(w/w %)	(w/w %)	(w/w %)	(w/w %)
	1.4003	X2CrNi12	12	0.3-1		0.02
410	1.4006	X12Cr13	13			0.12
430	1.4016	X6Cr17	17			0.06
420	1.4021	X20Cr13	13			0.20
430F	1.4104	X14CrMoS17	17			0.14
304	1.4301	X5CrNi18-10	18	10		0.05
305	1.4303	X4CrNi18-12	18	12		0.04
303	1.4305	X8CrNiS18-9	18	9		0.08
304L	1.4306	X2CrNi19-11	19	11		0.02
304L	1.4307	X2CrNi18-9	18	9		0.02
301	1.4310	X10CrNi18-8	18	8		0.10
304LN	1.4311	X2CrNi 18-10	18	10		0.02
	1.4316	X1CrNi19-9	19	9		0.01
310LN	1.4318	X2CrNiN18-7	18	7		0.02
	1.4361	X1CrNiSi18-15-4	18	15	4	0.01
	1.4362	X2CrNiN23-4	23	4		0.02
316	1.4401	X5CrNiMo17-12-2	17	12	2	0.05
316L	1.4404	X2CrNiMo17-12-2	17	12	2	0.02
316LN	1.4406	X2CrNiMoN17-11-2	17	11	2	0.02
2507	1.4410	X2CrNiMoN25-7-4	25	7	4	0.02
316LN	1.4429	X2CrNiMoN17-13-3	17	13	3	0.02
316L	1.4435	X2CrNiMo18-14-3	18	14	3	0.02
316	1.4436	X2CrNiMo17-13-3	17	13	3	0.02
317L	1.4438	X2CrNiMo18-15-4	18	15	4	0.02
317LN	1.4439	X2CrNiMoN17-13-5	17	13	5	0.02
316L	1.4440	X2CrNiMo19-12	19	12		0.02
	1.4452	X13CrMnMoN18-14-3	18	14	4	0.13
329	1.4460	X3CrNiMoN27-5-2	27	5	2	0.03
2205	1.4462	X2CrNiMoN22-5-3	22	5	3	0.02
409	1.4512	X2CrTi12	12			0.02
926	1.4529	X1NiCrMoCuN25-20-7	20	25	7	0.01
904L	1.4539	X1NiCrMoCu25-20-5	20	25	5	0.01
321	1.4541	X6CrNiTi18-10	18	10		0.06
254SMO	1.4547	X1NiCrMoCuN20-18-7	18	20	7	0.01
alloy 31	1.4562	X1NiCrMoCu32-28-7	28	32	7	0.01
	1.4563	X1NiCrMoCu31-27-4	27	31	4	0.01
24	1.4565	X2CrNiMnMoNbN25-	25	18	4	0.02
		18-5-4
316Ti	1.4571	X6CrNiMoTi17-12-2	17	12	2	0.06
	1.4581	GX5CrNiMoNb19-11-2	19	11	2	0.05
Alloy 33	1.4591	XCrNiMoCuN33-32-1	33	32	1
	1.4841	X15CrNiSi25-21	25	21		0.15
321H	1.4878	X8CrNiTi18-10	18	10		0.08
304H	1.4948	X6CrNi18-10	18	10		0.06
	1.7218	25CrMo4				0.25
C-22	2.4602	NiCr21Mo14W	21		14
B-2	2.4617	NiMo28			28
C-276	2.4819	NiMo16Cr15W	15		16

Examples for iron containing surfaces as contacted with the aqueous solution (A) as described herein comprise steel alloys listed in Table 2 herein, e.g. those selected from the group consisting of 1.4401, 1.4404, 1.4541, 1.4571, 1.4462, 1.4539, 1.4016, and 1.4006 according to DIN EN 10088-3. Particular examples comprise 1.4401, 1.4404, 1.4541, 1.4571, 1.4462, 1.4539, 1.4016, and 1.4006, more particularly 1.4401, 1.4404, 1.4541, 1.4571, 1.4016, and 1.4006, more particularly 1.4016, and 1.4006 (all numbers according to DIN EN 10088-3).

As used herein, the term “reactor” which is contacted with the aqueous solution (A) containing an alkane sulfonic acid as described herein may be of any size and shape suitable to allow a (condensation) reaction to take place and has a corrosive surface (e.g., an iron containing surface) as defined herein above and below. Examples are batch reactors, stirred tank reactors or tubular reactors. The reactor can be operated in continuous, batch or semi-batch mode.

The “pipe” as used in context with the present invention has a corrosive surface (e.g., an iron containing surface) as defined herein above and below and is employed to add the aqueous solution (A) containing an alkane sulfonic acid as described herein to the reactor. The pipe may be of any size or shape suitable to add the aqueous solution (A) to the reactor, e.g., it may be round or contain edges (preferably it is round), it may be a tube which is closed except the entry and the outlet opening, it may be a channel, it may have a continuous diameter or be formed as a nozzle (i.e. with a larger diameter at one end and a reduced diameter at the other end), or have other or combined forms.

The “container” as used in context with the present invention has a corrosive surface (e.g., an iron containing surface) as defined herein above and below and is employed to add the aqueous solution (A) containing an alkane sulfonic acid as described herein to the reactor, either in addition or as an alternative to the pipe. The container may be of any size or shape suitable to add the aqueous solution (A) to the reactor, e.g., it may be a bottle, a flask, a container, a barrel, a tank, a can, or the like.

In one embodiment of the present invention, the corrosive (e.g., iron containing) surface, e.g. that of the reactor, pipe and/or container is contacted with the aqueous solution (A) in the presence of oxygen, e.g., in the presence of ambient air.

The aqueous solution (A) as described herein and to be employed in context with the present invention contains an alkane sulfonic acid in an amount of about 80 to 99 w/w %, preferably about 80 to 98, 85 to 98, 88 to 98, 90 to 98, 92 to 97, 92 to 96, or 93 to 95 w/w % of an alkane sulfonic acid, relative to the total weight of said aqueous solution (A). In one embodiment, the alkane sulfonic acid may be selected from methane sulfonic acid, ethane sulfonic acid, or higher alkane sulfonic acids (e.g., C₁ to C₂₀ alkane sulfonic acid, linear or branched, preferably linear).

In one embodiment of the present invention, the alkane sulfonic acid of the aqueous solution (A) is methane sulfonic acid (MSA). In context with the present invention, the aqueous solution (A) may further comprise nitric acid or salts thereof (e.g., (earth) alkali salts of nitrates such as Na-Nitrate, Mg-Nitrate, K-Nitrate, or others). In one embodiment of the present invention, the aqueous solution (A) may further comprise up to about 2000 ppm nitric acid or salts thereof, preferably about 100 to 1500 ppm, 300 to 1300 ppm, 500 to 1200 ppm, or 700 to 1000 ppm.

In context with the present invention, in accordance with the method of adding the aqueous solution (A) to a reactor, the aqueous solution (A) as described herein is added via a pipe and/or a container to the reactor wherein inter alia a(n) (acid catalyzed) condensation reaction may take place in said reactor after the addition of said aqueous solution (A) into the reactor. Such (acid catalyzed) condensation reaction may be of any kind. In context of the present invention, for example it may be selected from the group consisting of esterification, etherification, Aldol condensation, intramolecular condensation (cyclization), polycondensation, silica condensation, phosphate condensation, rearrangement, dehydration, and others. In context with the present invention, a typical example for a condensation reaction is a water releasing condensation reaction. A more particular example in this context may be an esterification, for example an esterification between a carboxylic acid and an alcohol, producing an ester and one water molecule. Examples comprise the production of dimethyl ether or diethyl ether.

Esterifications as used herein comprise generally reactions between an acid and an alcohol under elimination of water. Suitable acids can be inorganic or organic acids, preferably organic acids. Organic acids can be any kind of aliphatic or aromatic carboxylic acids. Aliphatic carboxylic acids can have linear or branched hydrocarbon chains, which might be saturated or unsaturated (e.g. double bonds or triple bonds), and might have additional functional groups. Alcohols can be monofunctional (e.g. methanol), diols (e.g. ethylene glycol) or polyols (e.g. glycerine). Examples for esterification reactions comprise the production of acrylates, plasticizers, acetates (solvent esters), oleochemical esters, cellulose acetate or polyesters. A specific example of oleochemical esters is the production of fatty acid methyl ester (FAME) from various fatty acid containing feedstocks, and methanol, which is an essential step in the production of biodiesel. In a specific case, the esterification might also be accompanied by an acid catalyzed transesterification, as described in WO 2011/018228. Such esterification reactions are known in the art and also exemplified herein, see, e.g., EP127104WO2015/063189, WO 2013/064775, or U.S. Pat. No. 6,673,959.

Polycondensations are a specific form of polymerization reactions. The polymers are produced from bifunctional or polyfunctional compounds (monomers) by elimination of small molecules (e.g. water, alcohols, hydrogen halides). Examples are the formation of polyesters, polyamides, polyacetales and resins (phenolic resins, furanic resins, epoxy resins, amino resins, etc.).

Accordingly, in one embodiment of the present invention, the reaction which takes place in the reactor as described herein is an acid catalyzed reaction, preferably an acid catalyzed condensation reaction. In a particular embodiment of the present invention, such condensation reaction is an esterification as known in the art and as also described and exemplified herein, for example an esterification of one or more carboxylic acids with one or more alcohols, an esterification of one or more fatty acids with one or more alcohols, or an esterification of one or more fatty acids with methanol.

In context with the present invention, specific examples of suitable condensation reactions in organic synthesis comprise acyloin condensation, aldol condensation, benzoin condensation, Claisen condensation, Claisen-Schmidt condensation, Darzens condensation, Dieckmann condensation, Guareschi-Thorpe condensation, Knoevenagel condensation, Michael condensation, Pechmann condensation, Rap-Stormer condensation, Ziegler condensation, or Beckmann rearrangement. As descried and shown herein, the use of an aqueous solution (A) as described herein leads to a reduced or limited corrosion rate on iron containing surfaces. Particularly acids are known to be corrosive to iron containing surfaces. Accordingly it is even more surprising that in the present invention it was found that relatively high concentrations (e.g., about 80, 85, 88, 90, 92, 93, 94, 95 w/w % relative to the total weight of the aqueous solution (A)) of alkane sulfonic acids (e.g., MSA) are able to reduce or limit the corrosion rates on iron containing surfaces, as long as the concentration stays below a certain limit, e.g., about 99, 98, 97, 96 or 95 w/w % relative to the total weight of the aqueous solution (A). However, also water (oxygen comprised by water) may contribute to the formation of corrosion, depending on the iron alloy which is contacted with the aqueous solution (A). Accordingly, as the amount of water in a water-releasing condensation reaction may increase over time, it is possible that the corrosion rate may increase as it exceeds the water amount which was initially comprised by the aqueous solution (A) which was added to the reactor. In one embodiment of the present invention, the total water content comprised by all components added to the reactor does not exceed about 20 w/w %, preferably about 15, 12, 10, 8, 7, 6, 5, 4, 3, 2 or 1 w/w % relative to the total amount of all components added to the reactor. In context with the present invention, if required, water formed by the condensation reaction over time may be removed in order not to allow the water content of the condensation reaction mixture to exceed the water which was added to the reactor by the addition of the aqueous solution (A), or not to allow the total water content comprised by all components added to the reactor to exceed about 20 w/w %, preferably about 15, 12, 10, 8, 7, 6, 5, 4, 3, 2 or 1 w/w % relative to the total amount of all components added to the reactor. Such water removal can be performed by methods known in the art, e.g., by evaporation, distillation, adsorption or phase separation.

In context with the present invention, as regards the (acid catalyzed condensation) reaction which may take place in the reactor after an aqueous solution (A) as described herein was added to the reactor, the educts and further components (e.g., catalysts, solvents, neutralizer, or reactants other than educts) for the (condensation) reaction may be added to the reactor before, during, or after the aqueous solution (A) is added to the reactor. The skilled person is aware of suitable educts and further components for respective (condensation) reactions and it is also described and exemplified herein. It is also possible to add one or more of the (condensation) reaction educts and further components together with the aqueous solution (A) to the reactor, i.e. in the same pipe and/or container as described herein, either at the same time or subsequently.

As has been shown also in context with the present invention, the corrosiveness of acids and/or water increases as temperature increases. That is, the effect which has been found in context with the present invention that the aqueous solution (A) as defined and to be employed as described herein leads to an reduced or limited corrosion rates on corrosive surfaces such as iron containing surfaces may be even higher at elevated temperatures. Accordingly, in one embodiment of the present invention, the temperature of the aqueous solution (A) as described herein or the temperature of any mixture comprising the aqueous solution (A) and further educts or further compounds as added to the reactor where the (condensation) reaction may take place is at least about 20° C., preferably at least about 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., or 80° C. when contacted with the corrosive (e.g., iron containing) surface, either during or after addition of the (mixture comprising) the aqueous solution (A) to the pipe, to the container, and/or to the reactor as described herein. That is, e.g., the (mixture comprising) the aqueous solution (A) may have a temperature of at least about 20° C., preferably at least about 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., or 80° C. when added to the reactor, pipe, and/or container, or when stored in the reactor, pipe, and/or container, or before or during any reaction as described herein takes place in said reactor.

As it is clear to the skilled person, the temperature may increase in the reactor once a (condensation) reaction as described herein has started and/or it may be intentionally increased in order to have such (condensation) reaction started. If a water releasing reaction (e.g., water releasing condensation reaction) takes place in the reactor, the water content of the mixture contained in the reactor may increase if not removed as known in the art and as described herein. In one embodiment, the temperature in the pipe, the container, and/or the reactor may be measured before, during or after (e.g., before) the (condensation) reaction starts, either during or after addition of the (mixture comprising the) aqueous solution (A) to the pipe, to the container, and/or to the reactor. For example, the temperature may be measured before the total amount of water contained in the reactor exceeds the amount of water comprised by the aqueous solution (A) as described and to be employed as described herein. For this purpose, it may be desirable that further components added to the reactor such as educts and/or other components (e.g., catalysts, solvents, neutralizer, or reactants other than educts) are substantially free of water, i.e. one or more or all of such further components do not comprise more than about 5 w/w %, preferably less than about 4, 3, 2, 1 or 0.5 w/w % water, either alone or all such components in total. In one embodiment, the temperature may be measured before the total amount of water contained in the reactor exceeds about 20 w/w %, preferably about 15, 12, 10, 8, 7, 6, 5, 4, 3, 2 or 1 w/w % relative to the total amount of all components added to the reactor. Preferably, the educts and/or other components (e.g., catalysts, solvents, neutralizer, or reactants other than educts) for the (condensation) reaction as added to the reactor are substantially free of water, for example they comprise water in an amount of less than about 5 w/w %, preferably less than 4, 3, 2, 1 or 0.5 w/w %. In this context, the pressure applied to the reactor for the condensation reaction may be inter alia up to about 200 bar, preferably up to about 100 bar, or up to about 10 bar. In one embodiment, the pressure is up to about 5 bar, for example up to about 2 bar, ambient pressure or below about 1 bar (e.g., about 0.5 bar).

In context with the inventive method of adding the aqueous solution (A) as described herein to a reactor in which an acid catalyzed (condensation) reaction may take place after addition of said aqueous solution (A), the aqueous solution (A) preferably acts as acid catalyst. In accordance with the present invention, the aqueous solution (A) may be added in amount suitable for the respective (condensation) reaction which takes place after addition to the reactor. For example, when acting as a catalyst—particularly but not only for a water-releasing condensation reaction such as, e.g., esterifications—the aqueous solution (A) may be added to the reactor in an amount of about 0.1 to 10 w/w %, preferably about 0.2 to 5, or 0.5 to 2 w/w %, relative to the total weight of all components added to the reactor.

Corresponding to the methods for reducing or limiting the corrosion rate of an iron containing surface as described herein, the present invention further relates to the use of an aqueous solution (A) as described herein for reducing or limiting the corrosion rate on an iron containing surface as defined herein.

Corresponding to the method of adding the aqueous solution (A) as described herein, the present invention further relates to the use of the aqueous solution (A) in a (condensation) reaction as described herein.

The present invention further relates to the condensation products obtained or obtainable by a condensation reaction as described herein.

It must be noted that as used herein, the singular forms “a”, “an”, and “the”, include plural references unless the context clearly indicates otherwise. Thus, for example, reference to “a reagent” includes one or more of such different reagents and reference to “the method” includes reference to equivalent steps and methods known to those of ordinary skill in the art that could be modified or substituted for the methods described herein.

Unless otherwise indicated, the term “at least” preceding a series of elements is to be understood to refer to every element in the series. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the present invention.

The term “and/or” wherever used herein includes the meaning of “and”, “or” and “all or any other combination of the elements connected by said term”.

The term “about” or “approximately” as used herein means within 20%, preferably within 10%, and more preferably within 5% of a given value or range. The term “about” or “approximately” as used herein also includes the exact respective values or ranges.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step. When used herein the term “comprising” can be substituted with the term “containing” or “including” or sometimes when used herein with the term “having”.

When used herein “consisting of” excludes any element, step, or ingredient not specified in the claim element. When used herein, “consisting essentially of” does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim.

In each instance herein any of the terms “comprising”, “consisting essentially of” and “consisting of” may be replaced with either of the other two terms.

The present invention particularly relates to the following items:

• 1. Method of adding an aqueous solution (A) as described herein to a reactor,
  • wherein said aqueous solution (A) is added to the reactor via a pipe or a container,
  • wherein said reactor, pipe and/or container has a corrosive surface, and
  • wherein said aqueous solution (A) contains about 80 w/w % to 99 w/w of an alkane sulfonic acid, relative to the total weight of said aqueous solution (A).
• 2. Method of item 2, wherein an acid catalyzed reaction takes place in said reactor after the addition of said aqueous solution (A) into the reactor.
• 3. Method of item 1 or 2, wherein said reaction is a condensation reaction.
• 4. Method of any one of the preceding items, wherein said reactor, container and/or pipe is contacted with said aqueous solution (A) in the presence of oxygen.
• 5. Method of any one of items 2 to 4, wherein educts for said reaction are added before, during or after said aqueous solution (A) is added to the reactor.
• 6. Method of any one of the preceding items, wherein the temperature of said aqueous solution (A) is at least about 20° C. when contacted with said iron containing surface.
• 7. Method of item 6, wherein said temperature is measured before the total amount of water within said reactor exceeds 20 w/w % relative to the total weight of all components added to the reactor.
• 8. Method of any one of the preceding items, wherein said alkane sulfonic acid is methane sulfonic acid.
• 9. Method of any one of items 2 to 8, wherein said reaction is selected from the group consisting of esterification, aldol condensation, polycondensation, etherification, intramolecular condensation, dehydration, and Beckmann rearrangement.
• 10. Method of any one of items 3 to 9, wherein said condensation reaction is a condensation reaction releasing water.
• 11. Method of any one of the preceding items, wherein said surface of the reactor, pipe and/or container containing iron is further containing chrome and/or nickel.
• 12. Method of any one of the preceding items, wherein said aqueous solution (A) further comprises nitric acid or salts thereof.
• 13. Method of any one of the preceding items, wherein said aqueous solution (A) is added to said reactor an amount of about 0.1 to 10 w/w %, relative to the total weight of all components added to the reactor.
• 14. Method of any one of the preceding items, wherein the pressure in said reactor is 0.5-10 bar.
• 15. Method for reducing the corrosion rate of an iron containing surface, comprising adding the aqueous solution (A) as described in any one of the preceding items to the iron containing surface.
• 16. Method for limiting the corrosion rate of an iron containing surface to a rate of max. 0.3 mm/year, comprising adding an aqueous solution (A) as described in any one of the preceding items to the iron containing surface.
• 17. Use of an aqueous solution (A) as described in any one of the preceding items for reducing or limiting the corrosion rate on an iron containing surface.
• 18. Use of an aqueous solution (A) as described in any one of the preceding items in a condensation reaction as described in any one of items 3 to 14.
• 19. A condensation product obtainable by a condensation reaction as described in any one of items 3 to 14.

The following examples are illustrating the present invention without limiting the scope of the invention which is defined by the claims.

EXAMPLES

The corrosion behavior of corrosive media by means of gravimetric and visual assessment of metal coupons was determined. It was tailored to the different and therefore comprised different types of coupons, media (from acidic to alkaline), test temperature (room temperature to 80° C.), potential corrosion inhibitors and test period of time.

Equipment and materials:

• • analytical balance
  • 125 ml beaker (PP) with screw cap, supplied by VWR (PA, USA)
  • metal coupon 50×20×1 mm*
    • *see Tables 2 to 4 for steel alloys used
  • test solution**
    • *** see Tables 2 to 4 for aqueous acid solutions
  • ethyl acetate for degreasing
  • deionized water (NH₃ free) to set up the test medium

Procedure:

• 1. The metal coupon was degreased in ethyl acetate and then rinsed with deionized water and dried. In order to avoid further contamination, the metal coupon was only touched with disposable gloves (e.g. Dermatril) after this treatment.
• 2. Weighing on an analytical balance.
• 3. The coupon was charged with 100 g of the test solution in a PP beaker and then closed.
• 4. The PP beaker with the coupon in the test solution was then stored at given temperatures (e.g., 40° C., 60° C., and 80° C.)
• 5. At predetermined time intervals 1 d, 3 d, 7 d, 14 d), the coupon was removed with forceps, rinsed, dried and weighed. In addition, visual changes of the coupon and the solution were recorded. Then the coupon was placed into the test solution again.
• 6. At the end of the test period, the annual corrosion was calculated. For each setting a double test was performed.
• 7. Calculation of the annual corrosion rate:

$\mathrm{CorrosionRate}\left[\mathrm{mm}\text{/}a\right]=\frac{\mathrm{MassLoss}·10·365}{\mathrm{Density}·\mathrm{Area}·\mathrm{Duration}}$

Mass Loss [g[

Density of metal coupon [g/cm³]

Area of metal coupon in [cm²]

Duration=Days of immersion [d] (for Tables 2 to 4: the respective values for 14 d are shown)

TABLE 2
Corrosion Rate 40° C. [mm/year]
	Aqueous		Aqueous	Aqueous
	solution with		solution with	solution with
	70 w/w %	Aqueous	94 w/w %	100 w/w %
Steel alloy	MSA	solution with	MSA and	MSA
according	(MSA70),	94 w/w %	900 ppm	(MSA100),
to DIN	comparative	MSA	nitric acid	comparative
EN 10088-3	example	(MSA94)	(MSA94 NA)	example
1.4401	0.00	0.00	0.00	0.0909
1.4404	0.00	0.00	0.00	0.4125
1.4541	0.00	0.00	0.00	0.2902
1.4571	0.00	0.00	0.00	0.0888
1.4462	0.00	0.00	0.00	0.25
1.4539	0.00	0.00	0.00	0.146
1.4016	2.9197	0.00	0.00	>6.5
1.4006	1.0256	0.00	0.00	>6.5

TABLE 3
Corrosion Rate 60° C. [mm/year]
Steel alloy
according
to DIN
EN 10088-3	MSA70	MSA94	MSA94 NA	MSA100
1.4401	0.1183	0.00	0.00	0.1587
1.4404	0.1368	0.00	0.00	0.3519
1.4541	0.5285	0.00	0.00	0.3447
1.4571	0.1616	0.00	0.00	0.1609
1.4462	0.00	0.00	0.00	1.5
1.4539	0.0013	0.00	0.00	0.25
1.4016	>6.5	0.00	0.00	>6.5
1.4006	>6.5	0.00	0.00	>6.5

TABLE 4
Corrosion Rate 80° C. [mm/year]
Steel alloy
according
to DIN
EN 10088-3	MSA70	MSA94	MSA94 NA	MSA100
1.4401	0.7335	0.00	0.00	0.3128
1.4404	2.4652	0.00	0.00	0.9946
1.4541	2.522	0.00	0.00	0.8023
1.4571	0.9175	0.00	0.00	0.3043
1.4462	1.4391	0.0003	0.00	>6.5
1.4539	0.1931	0.0948	0.00	>6.5
1.4016	>6.5	>6.5	0.00	>6.5
1.4006	>6.5	>6.5	0.00	>6.5

Claims

1-19. (canceled)

20. A method for reducing the corrosion rate of an iron-containing surface, comprising adding an aqueous solution (A) to the iron-containing surface,

wherein said aqueous solution (A) comprises 80 w/w % to 99 w/w % of an alkane sulfonic acid, relative to the total weight of the aqueous solution (A).

21. The method of claim 20, wherein the alkane sulfonic acid is methane sulfonic acid.

22. The method of claim 20, wherein the surface comprising iron further comprises chrome and/or nickel.

23. The method of claim 20, wherein the aqueous solution (A) further comprises nitric acid or salts thereof.

24. The method of claim 20, wherein the iron-containing surface belongs to a reactor, pipe and/or container.

25. The method of claim 24, wherein an acid catalyzed reaction takes place in the reactor after the addition of the aqueous solution (A) into the reactor.

26. The method of claim 25, wherein the reaction is a condensation reaction.

27. The method of claim 20, wherein a temperature of the aqueous solution (A) is at least about 20° C. when contacted with the iron-containing surface.

28. The method of claim 20, wherein the method limits the corrosion rate of an iron-containing surface to a rate of max. 0.3 mm/year.