DE1621450A1 - Process to prevent metal corrosion - Google Patents

Description

Methods of preventing metal corrosion,

The present invention relates to the prevention of corrosion ·? »Ions in an inert atmosphere, i.e. in the absence of oxygen, by adding an aromatic aldehyde to the System in which the corrosion takes place. For this Aldehydes such as benzaldehyde are suitable for preventing corrosion and naphthaldehyde and their derivatives. Among others, Sahi empires The use of the aldehydes mentioned offers advantages maximum corrosion protection without harmful effects catalytic systems with which the aldehydes come into contact can come.

It is known that various organic and inorganic substances can cause severe shielding on metal surfaces with which they come into contact. Strongly destructive inorganic compounds; are for example HCl, vm $ HfJSOj ₁ . From the Omani. Prepare connections

for example acetic acid, phenol solutions and naphthenic acids cause considerable difficulties. The various organic chlorides, which are not naturally contained in crude oil , but are often added to it to remove paraffin deposits in boreholes and oil pipelines, are also quite corrosive. These corrosive substances belong to the compounds generally defined as "Brönsted acids". A Brönsted acid is a substance that can give off one or more protons .

In particular in the petroleum industry occur due to the presence of various corrosive compounds considerable material and time losses. Most crude oils contain numerous naturally occurring components and impurities which lead to significant corrosion of the metals from which conventional petroleum refining plants are built. This is primarily, of course, carbon steel.

Various inhibitors have already been used to prevent this corrosion. For example, benzaldehyde is oxidized to benzoic acid in the presence of oxygen. Benzaldehyde is therefore added in order to supply a system of oxygen with a particularly strong corrosive effect.

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free, with the oxygen for the oxidation of the eensaldehyde consumed to benzoic acid and thereby removed. The very insoluble benzoic acid is precipitated from the solution. In addition, many other means are available for Removal of corrosive substances in the presence known from oxygen. The prevention of corrosion in an inert atmosphere, "i.e. in the absence of oxygen, however, poses a completely different problem. This problem is so far practically unsolved, especially in the presence of catalytic systems, as most of the anti-corrosion agents have a deactivating effect on catalysts.

It has now surprisingly been found that the addition of aromatic aldehydes such as benzaldehyde, naphthaldehyde or their derivatives in an inert atmosphere prevents the corrosion of many metals by the various known corrosive substances. In this way, the destructive effect of strongly corrosive substances such as HgS, HCl _s chlorides of organic and inorganic nature and H ₂ SO ^ is successfully prevented. The organic acids whose corrosive effect is prevented by the present invention include, for example, acetic acid, fumaric acid, citric acid, succinic acid, naphthenic acids, organic acid halides, non-aqueous solutions such as formamide,

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Dimethyl sulfoxide and the like. The corrosion effect the various inorganic acids on metals is also prevented by the inhibitors according to the invention. These inorganic acids include, for example, hydrochloric acid, sulfuric acid, dilute nitric acid, sulphurous Acid * hydrofluoric acid, dilute perchloric acid, polyphosphoric acid etc.

The metals which are produced by the method according to the invention Corrosion-resistant steel may include carbon steel, nickel steel, copper and copper alloys, stainless steel, etc. However, the invention is most useful to prevent corrosion of carbon steel and in particular of carbon steel equipment in petroleum refineries.

Since the invention is to be used in an inert atmosphere, that is to say in an atmosphere in which oxygen - if at all - is only present in traces, it will first and foremost arrive at the point where chemical reactions or physical changes in an inert atmosphere such as nitrogen, Oxygen, CO, CO ₂ , K «, can be brought about with small amounts of SOg, SO, or mixtures thereof. Inert atmospheres are often encountered in the regeneration of catalysts for hydroforming or hydrotreating processes or other catalytic hydrogenation processes. It

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It is an essential part of the present invention that in all cases in which corrosion is prevented, no noticeable harmful influence on the catalysts with which the aromatic aldehyde, ie benzaldehyde, naphthaldehyde or their derivatives, comes into contact is observed. This is of particular importance for hydroforming and hydrotreating processes where the catalysts are expensive and their life has to be extended as much as possible. . %

The hydroforming process has been used industrially for a long time. In principle it consists in that: nan brings a Brdöl, either an unfractionated product or a Kraok product or Fischer-Tropsch product or a mixture thereof, into contact with a solid catalytic material. The catalyst used is generally platinum or palladium coated with aluminum oxide. The katalytisohe material temperatures at elevated temperature- _(and brought printing in the presence of added hydrogen with the AusgangsMtterial in contact.

The following reactions occur in the hydroforming process instead ofχ

1) Dehydrogenation of naphthanes to the corresponding aromatic hydrocarbons, e.g. dehydrogenation of methyl

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cyclohexane to toluene,

2) Isomerization of paraffins to branched chain Paraffins or isomerization of ring compounds, e.g. isomerization of ethylcyclopentane to methylcycloheJtane. which is then dehydrated to toluene, 30 dehydrogenation and cyclization of paraffins to aromatics, e.g. n-heptane ssu toluene and

4) Hydrocraken of the higher boiling components of the starting material to lower boiling components.

As already mentioned above, catalysts are used for the hydroforming process which contain 0.01 to 1.0 wt. JS platinum or 0.1 to 2.0 wt. £ palladium on a support of very pure aluminum oxide, with the aluminum oxide is obtained, for example, from aluminum alkoxide or an aluminum oxide hydrosol produced by hydrolysis of metallic aluminum with dilute acetic acid in the presence of small catalytic amounts of mercury. A suitable catalyst contains about 0.2 to 0.8% by weight of platinum, which is dispersed on alurainium oxide obtained from a suitable aluminum alcoholate in the η - or / "phase, and about 0.2 to 1.2% by weight of chloride and has an internal surface area of about 50 to 200 m / s . However, various other catalysts such as platinum on silica-aluminum oxide can also be used.

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The regeneration is carried out at least once a month for each hydroforming reactor, depending on the quality and processing difficulty of the starting material. In many cases, however, more frequent regeneration is required. During the regeneration, the coke deposited on the catalyst is burned off, whereby an atmosphere with a relatively high COg content and small amounts of SO ₂ and SO is obtained. During this treatment, the chloride content of the oasis phase increases, as the increase in the amount of water in the gas removes the chlorine in front of the catalyst. In the second stage, the water remaining on the catalyst is removed. This means thorough drying of the exhaust gases, which consist of a mixture of nitrogen, CO ₂ * CO, SOg, SO, and HCl. After most of the water has been removed, chlorination is started with the catalyst gradually taking up chlorine. During the subsequent revitalization of the catalyst with rearrangement of the crystal structure, some chlorine is still entrained with the exhaust gases. The final stage in regeneration is purging with nitrogen, an inert gas, to remove air from the system, which is then eventually pressurized with hydrogen. The inhibitor according to the invention is introduced into the system after this flushing process in order to prevent its oxidation by air at the high temperatures. Due to the presence of the inhibitor

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corrosion in the heat exchange system and in the Transports where a water condensate containing the acidic components mentioned above can accumulate « diminished or prevented. The corrosion inhibitors are adsorbed on the metal surface and attack the Corrosion by significantly slowing down the rate of corrosion reactions. As already mentioned was, is due to the presence of naphthaldehyde, benzene aldehyde or their derivatives in the absence of oxygen inhibited the corrosive effect of various corrosive substances on metals. In the case of the hydroforraing process described above, an inert gas atmosphere, namely nitrogen, is present and corrosive substances such as H ₂ S, HCl and HgSO ^ are also present. By adding an aromatic aldehyde such as naphthaldehyde, benzaldehyde or a derivative thereof, corrosion is kept to a minimum without any adverse effect on the platinum or palladium catalyst. For hydroforming processes, naphthaldehyde and its derivatives are preferred as corrosion inhibitors.

Another area in which corrosion occurs frequently in an inert gas atmosphere and has very negative effects is the hydrotreating process. In the hydrotreating process, three main groups of reactions take place. First there is a sulfur reduction, i.e. it becomes

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Sulfur in For® reduced by mercaptan, disulfide or thiophane. Furthermore, building material was removed from various compounds such as Ffeeaol 'and Peros ^ jrd. Finally, olefins are saturated with corresponding paraffins. These reactions require all® the presence and consumption of hydrogen »Si® kSnnsn in {fegenwsspt different catalysts have been carried out; Cobalt molybdate is probably the most frequently used. The presence of organic chlorides such as carbon tetrachloride and trichlorethylene is a major problem in the llydrotreating process. In addition, HCl is often present in the reactor, which can originate from organic chlorides or hydrofomoE ³ treatment gas. In any case, the presence of hydrogen chloride in the condenser and other parts of the plant above the reactor give rise to corrosion problems. In addition, of course, a considerable amount of H ₂ S is produced when sulfur is reduced in the reactor. This leads to considerable corrosion, especially in the presence of condensate water. The current leaving the reactor consists mainly of inert hydrogen gas and water vapor * KCl and HgS. Corrosion is avoided by adding benzaldehyde or naphthaldehyde or a derivative thereof to this stream. It is pointed out again here that "essentially no oxygen is present and the presence of acid

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substance the anti-corrosive effect of the substances mentioned impaired. It also has the presence of naphthaldehyde or benzaldehyde or derivatives thereof are not harmful Influence on the catalyst. POp hydrotreating process Benzaldehyde is preferred for price reasons All hydrotreating reactions can be carried out by the present process be improved; this includes auoh the unifining process of the Union Oil Company and UOP as well the Shell Oil Company's Trfckle Process and the Hydro · » fining method from Esso Research Company;

Ee is essential for the process according to the invention that the compound added as an anti-corrosive agent has a benzene ring bonded aldehyde group. The preferred compounds are benzaldehyde and naphthaldehyde. Benzaldehyde has a single aromatic ring and naphthaldehyde has two fused aromatic rings. Both Compounds have an aldehyde group attached to the aromatic nucleus. In addition, for the inventive Process a large number of derivatives of these compounds can be used. These can still be used, for example contain a third aromatic hanging «so long as one Aldehyde group bonded directly to an aromatic ring present 1st. Furthermore, the benzene ring of benzaldehyde or the rings of naphthaldehyde can also be used

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be substituted for other groups. For example an © alkyl group with 1 to 3 carbon atoms to any Carbon atom of the benzene ring be bonded; Likewise, a hydroxyl group can also be bonded to any carbon atom of the benzene ring. Preferably however, an alkyl or hydroxyl group is not added to more than one member of the benzene ring. Farther the alkyl or hydroxyl group is preferably not attached directly to the aldehyde group.

The amount of benzaldehyde, naphthaldehyde used or a derivative thereof can be very different and depends on the corrosive solution and the pH of the solution. To a corrosive solution one bit pH between 0 and 1 becomes 10 to 12,000 ppm and preferably 50 to 1000 ppm of the corrosion protection agent given. Corrosive solutions with a pH of 1 to 4 becomes about 10 to 1000 ppm and preferably 30 given up to 400 ppm of the corrosion inhibitor according to the invention. The haphthaldehyde, benzaldehyde or their derivatives can be added directly to the vapor or liquid stream. In the hydroforming process, the inhibitor given directly into the steam flow leaving the hydroforming vessel. The same applies to the hydrotreating process, in which the inhibitor is also fed directly into the das

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Hydrotreating vessel and leaving steam flow will.

The mechanism of action of the method according to the invention can be explained as follows, although not necessarily to be fixed on this theory. The additive, i.e. the naphthaldehyde, benzaldehyde or a derivative same, is adsorbed by the metal surface and. insulates the metal against the corrosive material. You Additive itself practically no thermal change takes place in the corrosive solution, since above the corrosive one Solution an inert atmosphere is maintained.

The additives according to the invention can be used in a very wide temperature range. Benzaldehyde "naphthaldehyde and its derivatives inhibit corrosion effective at temperatures between 4 and 100 ⁰ C and preferably between 4 and 9j5 ° C; In particular, the additives are used in a temperature range from 21 to 82.degree. They can also be used in a fairly wide pressure range, ie the method according to the invention can be used at pressures from 1 to 14 kg / cm. The Druok has no significant influence on this

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on the mode of action of the additives "because they can be used both in the liquid phase and in the vapor phase. The contact time of the additive with the corrosive solution can also vary within wide limits, for example between 0.1 and 2 minutes.

It is of crucial importance that the additives according to the invention are used in an inert gas atmosphere, ie in an atmosphere in which oxygen, if at all, is present in an amount of at most 0.5 to 1% by weight. Such inert gas atmospheres in which the process according to the invention is effective are, for example, nitrogen, hydrogen, CO ₂ , CO or exhaust gas in general and mixtures thereof. The presence of large amounts of oxygen oxidizes the aldehyde group with the formation of benzoic acid or naphthoic acid. Benzoic acid precipitates out of the solution and is then no longer effective for the purposes of the invention, ie the metal to be protected is no longer isolated. The additives can be used in the following amounts per liter of corrosive solution:

General area ΙΟ "* ¹ M / L to 10" * M / L

Preferred range 10 " ¹ M / L to ⁵ × 10 ~ 5 M / L

1 O

Particularly preferred range 10 M / L to 10 M / L.

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The invention is illustrated in more detail by the following examples:

example 1

This example demonstrates the ability of benzaldehyde to prevent corrosion of 1020 carbon steel, ie a 0.2 % carbon steel. Dec ^a carbon steel was placed in 0.1 η HCl , which had a pH of 1.0. For the experiment, a reaction vessel was used in glass. The atmosphere in the vessel consisted essentially of nitrogen.

Table 1

Protective effect of benzaldehyde to prevent the corrosion of carbon steel 1020 in 0, In HCl ( pH 1.0) at 25 ° C

Inhibitor Concentration Corrosion Rate% Inhibitor- (MoI Inhibitor Per liter rate (mean) in effect

Solution) fflre / dec. ² / day Blind attempt 1555 Benzaldehyde, 10 "*. M / L 1351 13.1 Benzaldehyde, 5xl0 ~ ⁵ M / L 418 72.9 Benzaldehyde, IxIO * " ¹ M / L 41 97.4

This table shows that benzaldehyde is an effective anti-corrosive agent. The effectiveness the benzaldehyde increases as the concentration approaches 1x10 moles per liter; at this concentration

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the protective effect is 97.4 % compared to 15.1 % at a concentration of 10 H / L,

Table 2 the 2950 • 75 - 97.5 - 88.9 - 84.5 - 85.8 Inhibitor corrosion % inhibitor
Concentration speed effect
Wh speed (mean) 296Ο temperature Protective effect of benzaldehyde for prevention
Corrosion of carbon steel 1020 in HCl Blind test 57 HCl conc
tration Benzaldehyde 528 57 0, ln 10 " ¹ H / L _ 1481 o, m Blind test 50 Benzaldehyde 255 50 0, ln 10 " ¹ H / L 4462 o, m Blind test 25th Benzaldehyde 655 25th 1, On ΙΟ " ¹ Vi / h 1, On Blind test 25th Benzaldehyde 25th 5.0η, ΙΟ " ¹ H / L 5, On

The values in this table are further evidence of that Effectiveness of benzaldehyde as an anti-corrosion agent. This table also shows that there is a change the HCl concentration and the temperature a certain amount

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Has an influence on the effectiveness of benzaldehyde in the concentration of 10 mol per liter of solution. In any case, however, the effectiveness remains extremely high compared to the «blind test. The experiments listed in Table 2 were carried out in a nitrogen atmosphere.

example 2

This example shows the effectiveness of the various naphthaldehydes in a nitrogen atmosphere.

Corrosion rate
age (medium)
mß / dec. ² / day Preventing the
ι 0.1η HCl Table 3 1555 % Inhibitor
effect Protective effect of naphthaldehydes for
Corrosion of carbon steel 1020 ir
at 25 ° C M / L 7 * 7 TnMbI tor concentration
(Mole inhibitor je
Liter of solution) N / L 7.5 52.0 Blind test M / L 1190 95.5 OC -naphthaldehyde 5x10 "^ M / L 176 23.5 * .- Naphthaaldehyde IxIO " ¹ M / L 11 88.7 fl-Naphthaldefayd lxlC ⁴ M / L 2.4 99.5 ß-maphthaldehyde 5x10 "* 99.8 ß-naphthaldehyde IxIO " ² fi-Caphthaldehyde 1x1 O * ¹

The above table 3 shows the anti-corrosion effect of naphthaldehydes in a nitrogen atmosphere on carbon off stole 1020 in OjIn HCl. The attempts were made in

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carried out in a glass vessel »These values also show that the inhibitory effect as the concentration approaches increases in laclO Hol / liter. In addition, the results show that under otherwise identical conditions ß-naphthaldehyde © is a better anti-corrosion agent than ^ -naphthaldehyde.

Table k Blind test Corrosive
speed
(Middle) 1481 # Inhibitor
effect - 97.7 Qk-caphthaldehyde 2950 I.
19.1 - temperature
⁰ C Blind test 73 97.5 98.7 37 Protective effect of naphthaldehydes for prevention
the corrosion of carbon steel 1020 in HCl 2960 37 HCl Concentrate Inhibitor
tration concentration
M / L ^ -Naphthaldehyde
ΙΟ " ¹ M / L 66.8 50 o, m Blind test 50 o, m ß-Naph thaldehyc
10 " ¹ H / L 25th o, in 25th 0, ln 1, On 1, On

The table above shows the percentage protective effect of nephthaldehyde at a concentration of 10 mol per liter. The protective effect was not significantly impaired by changing the temperature or the RCl concentration. .

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Claims (2)

1 K J 1 Esso Research and ή% (471 *) l Engineering Company Linden, NVJjf / V.Sfc-Λ Hamburg, October 30th 5-969 Godfather η "tan s ρ" rü ch © 1 »Procedure to prevent corrosion of metal surfaces that come into contact with liquids or vapors, -the at least one that corrodes the metal surface Contain substance, characterized in that the Liquids * or vapors with an aromatic aldehyde, especially with benzaldehyde * naphthaldehyde and / or their derivatives or a mixture of the same - ■ added: « 2. The method according to claim I _9, characterized in that mail in contact with the metal surface an inert gas atmosphere ^ preferably nitrogen C0 _s COp, hydrogen. Provides exhaust gas or mixtures thereof. 3> _a method according to claim i "characterized in that the metal surface is carbon steel and the corrosive / ■ Substance is hydrochloric acid. Documents (Art. 7 § 1 Para. A No. 1 Clause 3 of the amendment *. V. A. 9.18671 ■■■. ■■■ *. ^ß ÄQ ORfGfNAL 10 9820/1930 162H50 Process "according to claims 1 to Zh characterized *. That one. 1 χ 10 ** to 1 χ. 1Ό" ¹ mol! Corrosion Senutsraittel per lite? Liquid used., - ¥ iÄ ^J fal: iro £ i iifixiti aeo claims 1 to 4, ■ dadu ^ cli gekena « zvietoaek, ά & Β the 'metal surface from that of an il ^ drofoi?; Nlng -»' 5 ^; experienced " BAD 109820/1936