JP2007520611A - A method for corrosion inhibition of purification units by acidic crude products. - Google Patents

Abstract

The process according to the invention for inhibiting the corrosion of the metal walls of the purification unit by naphthenic acid consists in using tertiary mercaptans of the general formula C _n H2 _{n + 1} -SH in which _n is in the range of 8-14.

Description

  The present invention relates to the field of processing acidic crude oil at refineries. A more specific subject matter of the present invention is a method for combating corrosion of a refinery that treats acidic crude products, including the use of specific sulfur compounds.

  Refineries can face serious corrosion problems when certain “acidic” crude products must be processed. These acidic crude products particularly contain naphthenic acid which is responsible for the very specific corrosion phenomenon that occurs in liquid media that do not conduct current. These naphthenic acids correspond to saturated cyclic hydrocarbons having one or more carboxyl groups. Crude acidity is described by measurements standardized according to the ASTM D 664-01 standard. The acidity of crude oil is expressed in mg of potassium hydroxide required to neutralize 1 g of oil and is expressed as TAN (total acid number). In the art, it has been found that crude oils with TAN greater than 0.2 are described as acidic and can lead to damage in the refiner.

  This corrosion reaction is highly dependent on local conditions such as, for example, wall temperature and metal properties in the affected device, hydrocarbon space velocities and the presence of gas-liquid interfaces. Thus, even after conducting a lot of research on the subject, refineries face many difficulties in determining the magnitude of the corrosion reactions and their location.

  One industrial solution to this corrosion problem consists of using equipment made from an alloy of stainless steel or iron with certain chromium and molybdenum. However, this solution is rarely used due to its high capital cost. Furthermore, this choice should preferably be considered during refinery design, since stainless steel exhibits mechanical properties that are inferior to those of commonly used carbon steel and requires a suitable substructure. .

  Thus, as a result of these technical difficulties in processing acidic crude products, these crude products are generally sold to refineries at a lower price level than that of standard crude products.

  Another solution to the problem of processing acidic crudes actually used by refineries is to dilute acidic crudes with other non-acidic crudes, for example to obtain an average acidity below the threshold for TAN of 0.2 Made up of. In this case, the concentration of naphthenic acid is low enough to produce an acceptable corrosion rate. However, this solution remains limited in scope. This is because some acidic crude products show a TAN value greater than 2, so their upper limit is at most 10% of the total volume of crude product entering the refinery. Furthermore, some mixtures of crude products sometimes have an effect opposite to that desired, even after dilution, i.e. acceleration of the naphthenic acid corrosion reaction.

  Another approach to combating this corrosion problem is to introduce chemical additives into the acid crude to be treated that inhibit or prevent impact on the metal walls of the affected equipment. This method is often very economical compared to those consisting of using the above-mentioned special alloys or special steels.

  In laboratory studies such as those of Tumbull (Corrosion, 1998, November, Volume 54, No. 11, page 922), a small amount of hydrogen sulfide (0. 1% order) was added. However, this solution is not applicable to refineries because hydrogen sulfide, which is a gas at ambient temperature, is very toxic and leaks have extremely serious consequences and its use is limited. In addition, at high temperatures, hydrogen sulfide itself becomes very corrosive and corrosion will generally worsen in other parts of the refinery.

  US Pat. No. 5,182,013 discloses the use of other sulfur compounds, ie polysulfides having alkyl radicals containing 6 to 30 carbon atoms, in solving this same corrosion problem.

  More recently, the use of sulfur and phosphorus based corrosion inhibitors has also been disclosed.

  Thus, EP 742 277 discloses the inhibitory action of the combination of a trialkyl phosphate and an organic polysulfide. US Pat. No. 5,552,085 recommends the use of thiophosphorus compounds such as organic thiophosphates or organic thiophosphites. Australian Patent No. 693 975 discloses a mixture of a trialkyl phosphate and a phosphorus ester of sulfurized phenol neutralized by lime as an inhibitor.

  However, organophosphorus compounds are very problematic for hurdles due to their high toxicity. In addition, organophosphorus compounds contaminate the hydrotreating catalyst used to purify the hydrocarbon fraction resulting from atmospheric distillation and vacuum distillation. For these two reasons, their use in the purification field is at least undesirable.

  Crude oil contains a variety of organic sulfur compounds including alkyl mercaptans. Surprisingly, certain families of alkyl mercaptans, compounds with tertiary carbon in the mercaptan functional group, can inhibit naphthenic acid corrosion more effectively than organic polysulfides without the need to add phosphorus-containing inhibitors. I understand.

  The subject of the present invention is therefore the formula:

（式中、同一又は異別である記号Ｒ_１、Ｒ_２、Ｒ_３、Ｒ_４、Ｒ_５、Ｒ_６、Ｒ_７、Ｒ_８及びＲ_９は、各々水素原子又は直鎖若しくは分岐鎖のアルキル基、アリール基又はアルキルアリール基を表し、これらの基が酸素又は硫黄などの１つ以上の複素原子を必要に応じて含むことが可能である。）
の、４ないし２０個の炭素原子を含む1つ以上の炭化水素化合物の有効量を、炭化水素流に添加することを含むことを特徴とする、酸素不在下で炭化水素流が処理される精製装置の金属壁のナフテン酸による腐食に対抗するための方法である。

(Wherein the symbols _R 1 are identical or _{different, R 2, R 3, R} 4, R 5, R 6, R 7, R 8 and _{R 9} are each a hydrogen atom or a linear or branched chain alkyl Represents a group, aryl group or alkylaryl group, these groups optionally containing one or more heteroatoms such as oxygen or sulfur.)
A process for treating a hydrocarbon stream in the absence of oxygen, comprising adding an effective amount of one or more hydrocarbon compounds containing 4 to 20 carbon atoms to the hydrocarbon stream A method for combating naphthenic acid corrosion of a metal wall of an apparatus.

The mercaptans preferably used according to the invention are tertiary mercaptans of the empirical formula C _n H _{2n + 1} -SH _where n is 8 to 14.

  The tert-dodecyl mercaptan may be isolated and collected, or may be collected in the form of a complex mixture containing tertiary mercaptans of 10 to 14 carbon atoms present in an amount greater than 50% by weight. Further particularly preferred compounds of Such mixtures are generally prepared industrially by the addition of hydrogen sulfide to an olefin fraction such as tetrapropylene and are sold under the name tert-dodecyl mercaptan.

  The amount of compound of formula (I) added to the hydrocarbon stream to be treated by the refiner is expressed as the equivalent weight of sulfur in said compound with respect to the weight of the hydrocarbon stream of 1 to 1000 ppm, preferably 5 to 200 ppm. Generally corresponds to a certain concentration. Within this concentration range, it would be possible to set a high content at the start of the process according to the invention and then subsequently reduce this content to a maintenance amount.

  With the process according to the invention, it is advantageously possible to treat hydrocarbon streams, in particular crude oil, having a TAN of greater than 0.2, preferably greater than 2.

  The temperature for carrying out the process corresponds to the temperature at which the corrosion reaction by naphthenic acid occurs, and is generally from 200 to 450 ° C., in particular from 250 to 350 ° C.

  The addition of the compound of formula (I) to the hydrocarbon stream can be carried out at the actual inlet of the device (at the same time as the hydrocarbon stream to be treated) or for local treatment for the overall treatment of corrosion. Therefore, it can be carried out in the part of the apparatus where the corrosion reaction occurs. This addition can be performed by any means known to those skilled in the art that provides injection flow rate control and good dispersion of the hydrocarbon and additive using, for example, a nozzle or mixer.

  The term “refiner metal walls” whose corrosion can be prevented by the method according to the invention is understood to mean all the walls in contact with the acidic hydrocarbon stream to be treated. Thus, the walls are equally well, suitable internal walls of equipment such as atmospheric distillation column and vacuum distillation column, and the surface of internal components relative to the vacuum distillation column such as plates or packings, or drawer and inlet piping or The parts can be vertical parts to a vacuum distillation column such as a pump or the like, as well as a preheating furnace or a heat exchanger, and these parts are provided at a local temperature of 200 to 450 ° C.

  The metal employed in the manufacture of the walls of the refiner is generally a carbon steel optionally containing up to 10% by weight of chromium and / or molybdenum, preferably up to 5%.

  Non-limiting examples of hydrocarbon streams treated according to the method described in the present invention are crude oil, atmospheric distillation residue, gas oil fraction resulting from atmospheric distillation and vacuum distillation, and vacuum residue and distillate resulting from vacuum distillation. It is.

  The following examples are given purely for the purpose of illustrating the invention and should not be construed as limiting the scope thereof.

(Example)
These examples use corrosion testing and the conditions are provided below.

Description of corrosion test

This inspection employs a mineral oil simulating an acidic crude product stream in which a mixture of iron powder and naphthenic acid simulating a metal surface is dissolved. The characteristics of these reactants are as follows. That is,
White oil having a density of 0.838,
Powder formed from spherical iron particles having a particle size of −40 + 70 mesh (ie about 212 to 425 μm),
A mixture of naphthenic acids having 10 to 18 carbon atoms, a boiling point of 270 to 324 ° C. and an average molecular weight of 244 g / mol.

The following is introduced into a 150 ml glass reactor equipped with a dropping funnel and a water-cooled reflux concentrator, and a stirring system and a temperature measuring system are attached.
70 ml of mineral oil (ie 58.8 g)
2g of iron powder,
2.8 g of naphthenic acid mixture

  The initial TAN initial value of the reaction mixture is 10.

  These reactants are left in contact at a temperature of 250 ° C. for 2 hours under a dry nitrogen atmosphere to prevent oxidation reactions.

  At the end of the test, the concentration of iron dissolved in the medium is determined by existing methods by which the sample is digested, the residue is placed in acidified water and the assay is performed using a plasma torch.

  This concentration of dissolved iron (expressed in ppm) is directly proportional to the rate of iron powder corrosion caused by the mixture of naphthenic acids present in the mineral oil.

(Comparative Example): Reference test in the absence of inhibitor The preceding test is repeated twice without the addition of the compound of formula (I).

  The results are shown in Table 1 below.

  Inspection in the presence of tertiary alkyl mercaptans.

  Example 1 is repeated while adding tert-nonyl mercaptan or tert-dodecyl mercaptan to the mineral oil introduced into the reactor. These products are mixtures of tertiary alkyl mercaptans individually concentrated on compounds containing 9 and 12 carbon atoms. The content of these derivatives is calculated so as to obtain a concentration of 500 ppm as the weight of sulfur in the mineral oil present in the reactor.

  The results summarized in Table 2 below are obtained.

  The degree of inhibition of corrosion caused by the naphthenic acid mixture is also shown in this table. This degree is expressed in%

により定義され、式中［鉄］は、阻害剤がある場合若しくはない場合に測定される溶解した鉄の濃度であり、阻害剤がない場合の鉄の濃度は実施例１にしたがって２０３．５ｐｐｍである。

Where [iron] is the concentration of dissolved iron measured in the presence or absence of an inhibitor, and the iron concentration in the absence of inhibitor is 203.5 ppm according to Example 1. is there.

Claims (8)

formula:

(In the formula, symbols R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ and R ₉ are the same or different and each represents a hydrogen atom or a linear or branched alkyl group. Represents a group, aryl group or alkylaryl group, these groups optionally containing one or more heteroatoms such as oxygen or sulfur.)
A process for treating a hydrocarbon stream in the absence of oxygen, comprising adding an effective amount of one or more hydrocarbon compounds containing 4 to 20 carbon atoms to the hydrocarbon stream A method for combating corrosion of metal walls of equipment by naphthenic acid. The process according to claim 1, characterized in that as the compound of formula (I) a tertiary mercaptan of the empirical formula _{CnH2n + 1-} SH _where n is 8 to 14 is used.   3. The process according to claim 1, wherein tert-dodecyl mercaptan is used as the compound of formula (I).   The amount of the compound of formula (I) corresponds to a concentration expressed as the equivalent weight of sulfur, relative to the weight of the hydrocarbon stream of 1 to 1000 ppm, preferably 5 to 200 ppm. The method according to claim 1.   Process according to one of claims 1 to 4, characterized in that the hydrocarbon stream to be treated has a TAN of greater than 0.2 and preferably greater than 2.   6. Process according to one of claims 1 to 5, characterized in that it is carried out at a temperature of 200 to 450 [deg.] C, and more particularly 250 to 350 [deg.] C.   The metal used in the manufacture of the wall of the refiner is a carbon steel optionally containing up to 10% by weight of chromium and / or molybdenum, preferably up to 5%. The method according to one item.   8. The hydrocarbon stream to be treated is selected from crude oil, atmospheric distillation residue, gas oil fraction resulting from atmospheric distillation and vacuum distillation, and the corresponding vacuum residue and distillate. The method according to one item.