# Patent

## Title
Dithiazine derivatives

## Abstract

Corrosion of metallic tubulars in an oil, gas or geothermal well may be inhibited by introducing into the well a dithiazine derivative of the formula:




wherein R14 is a C1-C24 straight chain or branched alkyl group; or a C6-C24 aryl or arylalkyl group; R15 is a C1-C6 alkyl or a C6-C30 aryl or alkylaryl group; and X is chlorine, bromine or iodine. The dithiazine may be isolated from a whole spent fluid (WSF) formed by reaction of hydrogen sulfide and a triazine. Alternately, the whole spent fluid containing dithiazine or dithiazine derivative and a corrosion inhibiting formulation may be used to inhibit corrosion in the well.

## Background
This application is a divisional application of U.S. patent application Ser. No. 13/236,332, filed on Sep. 19, 2011, now U.S. Pat. No. 8,354,361 which is a continuation-in-part application of U.S. patent application Ser. No. 12/862,582, filed on Aug. 24, 2010, now U.S. Pat. No. 8,022,018, which is a continuation-in-part application of U.S. patent application Ser. No. 12/643,521, filed on Dec. 21, 2009, now U.S. Pat. No. 8,022,017; all of U.S. Pat. Nos. 8,354,361, 8,022,018 and 8,022,017 being herein incorporated by reference.


FIELD OF THE INVENTION
The invention relates to methods of inhibiting corrosion in metallic surfaces during treatment of a well by introducing into the well a dithiazine or a dithiazine derivative.
BACKGROUND OF THE INVENTION
During the production life of an oil or gas well, the production zone within the well is typically subjected to numerous treatments. Corrosion of metallic surfaces, such as downhole tubulars, during such treatments is not uncommon and is evidenced by surface pitting, localized corrosion and loss of metal. Metallic surfaces subject to such corrosion are carbon steels, ferritic alloy steels, and high alloy steels including chrome steels, duplex steels, stainless steels, martensitic alloy steels, austenitic stainless steels, precipitation-hardened stainless steels and high nickel content steels.
Further, aqueous fluids, such as those used in drilling and completion, have a high salt content which causes corrosion. Gases, such as carbon dioxide and hydrogen sulfide, also generate highly acidic environments to which metallic surfaces become exposed. For instance, corrosion effects from brine and hydrogen sulfide are seen in flow lines during the processing of gas streams. The presence of methanol, often added to such streams to prevent the formation of undesirable hydrates, further often increases the corrosion tendencies of metallic surfaces.
Further, naturally occurring and synthetic gases are often conditioned by treatment with absorbing acidic gases, carbon dioxide, hydrogen sulfide and hydrogen cyanide. Degradation of the absorbent and acidic components as well as the generation of by-products (from reaction of the acidic components with the absorbent) results in corrosion of metallic surfaces.
The use of corrosion inhibitors during well treatments to inhibit the rate of corrosion on metal components and to protect wellbore tubular goods is well known. Commercial corrosion inhibitors are usually reaction mixtures or blends that contain at least one component selected from nitrogenous compounds, such as amines, acetylenic alcohols, mutual solvents and/or alcohols, surfactants, heavy oil derivatives and inorganic and/or organic metal salts.
Many conventional corrosion inhibitors used to reduce the rate of acid attack on metallic surfaces and to protect the tubular goods of the wellbore are becoming unacceptable in oilfield treatment processes. For instance, many conventional corrosion inhibitors have become unacceptable due to environmental protections measures that have been undertaken. In some instances, such as in stimulation processes requiring strong acids, high temperatures, long duration jobs and/or special alloys, the cost of corrosion inhibitors may be so high that it becomes a significant portion of total costs.
Efforts have been undertaken to find alternative corrosion inhibitors which are cost effective and which are capable of controlling, reducing or inhibiting corrosion.
SUMMARY OF THE INVENTION
Corrosion of metallic tubulars in a well may be inhibited from forming by introducing into the well a dithiazine or dithiazine derivative of the structural formulae (I)-(V):




wherein R is selected from the group consisting of a C1 to C12 saturated or unsaturated hydrocarbyl group or a C1 to C10 ω-hydroxy saturated or unsaturated hydrocarbyl group; R1 is selected from the group consisting of a C1-C24 straight or branched chain alkyl group or a C1-C24 arylalkyl group; R2 is a straight or branched alkylene group; R14 is a C1-C24 straight chain or branched alkyl group; or a C6-C24 aryl or arylalkyl group; R15 is a C1-C6 alkyl or a C6-C30 aryl or alkylaryl group; and X is chlorine, bromine or iodine.

The compounds of formula (II), (III) and (V) are quaternized derivatives of the dithiazine of formula (I) and (IV).
The dithiazine of structure (I) may be isolated from a whole spent fluid (WSF) formed by reaction of hydrogen sulfide and a triazine, such as a triazine of formula (VI):




wherein R is defined above in a hydrogen sulfide scavenger gas scrubbing operation. Alternatively, the whole spent fluid containing the dithiazine of structure (I) may be introduced into the well without isolation of the dithiazine.

Synergistic effects on inhibition of corrosion have further been noted when the dithiazine or dithiazine derivatives of formulae (I)-(V) are formulated with at least one corrosion inhibitor component selected from alkyl, alkylaryl or arylamine quaternary salts; mono or polycyclic aromatic amine salts; imidazoline derivatives; a mono-, di- or trialkyl or alkylaryl or arylalkyl phosphate ester; a monomeric or oligomeric fatty acid or salt; an alkyl or alkenyl substituted pyridinium; a polyamine amide; a polyhydroxy or alkoxylated amine or amide; a pyrazine derivative or a mercaptocarboxylic acid. Synergistic effects have further been noted when WSF is combined with a corrosion inhibiting formulation containing any one or more of these corrosion inhibitor components.



BRIEF DESCRIPTION OF THE DRAWINGS
In order to more fully understand the drawings referred to in the detailed description of the present invention, a brief description of the drawings is presented, in which:
FIGS. 1-7 demonstrate the effectiveness as whole spent fluids (WSF), formulated with additives defined herein.
FIGS. 8-12 demonstrate the effectiveness of quaternized reaction products of dithiazine compared to non-quaternized dithiazines.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Corrosion is inhibited during the treatment of a subterranean formation which is penetrated by an oil, gas or geothermal well by introducing into the well a dithiazine of the formula (I):




wherein R is selected from the group consisting of a C1 to C12 saturated or unsaturated hydrocarbyl group or a C1 to C10 ω-hydroxy saturated or unsaturated hydrocarbyl group; In a preferred embodiment, R is either (i) —R3—OH, wherein R3 is an alkylene group, preferably R is a C1-C6—OH group, most preferably —CH2CH2—OH; or (ii) a C1-C6 alkyl group, more preferably methyl or ethyl, and most preferably methyl.

The dithiazine of formula (I) is preferably that obtained from the homogeneous fluid which is produced during a hydrogen sulfide scavenger gas scrubbing operation. In such scrubbing operations, a scavenger is introduced to a stream of liquid hydrocarbons or natural gas (sour gas) which contains hydrogen sulfide. In addition, such gas scrubbing operations remove hydrogen sulfide from oil production streams as well as petroleum contained in storage tanks, vessels, pipelines, etc. The scavenger is most commonly a water soluble triazine such as those of formula (VI):




wherein R is defined above. Typically, the triazine is 1,3,5-tris(hydroxyethyl)-hexahydro-s-triazine. The production of dithiazines during a scrubbing operation using a triazine as scavenger is reported in U.S. Pat. No. 6,582,624 wherein the spent fluid is reported to contain amorphous dithiazine solids. Typically, dithiazines remain part of the whole spent fluid resulting from the scrubbing operation. Whole spent fluid is typically discarded.

In the method described herein, the dithiazine of formula (I) resulting from the scrubbing operation may be introduced into a gas, oil or geothermal well where it functions as a corrosion inhibitor.
The whole spent fluid containing the dithiazine may be introduced to the well or dithiazine. Alternatively, the dithiazine of formula (I) may be isolated from the whole spent fluid by processes known in the art.
In addition to the dithiazines of formula (I), excellent corrosion inhibition properties may be obtained by the use of dithiazine derivatives of either formula (II), formula (III), (IV) or (V):




wherein R and X are as described above; R1 is selected from the group consisting of a C1-C24 straight chain or branched alkyl group or a C1-C24 arylalkyl group; preferably a C1-C22 alkyl group, more preferably a C1-C12 alkyl group, most preferably a C1-C6 alkyl group; R2 is a C1-C6 straight or branched chain alkylene group; R14 is a C1-C24 straight chain or branched alkyl group; or a C6-C24 aryl or arylalkyl group; R15 is a C1-C6 alkyl or a C6-C30 aryl or alkylaryl group; and X is chlorine, bromine or iodine. R1 may also be substituted with an aryl group including benzyl and naphthyl. Alternatively, R1 may be a C1-C24 arylalkyl group, such as benzyl, wherein the alkyl portion of the arylalkyl group may be linear or branched and the aryl portion of the arylalkyl group may be substituted with a C1-C6 alkyl group, such as methyl. In a preferred embodiment, R2 is —CH2—CH2—CH2—CH2— or —CH2—CH2—CH2—CH2—CH2—. In a preferred embodiment, R of the compound of formula (III) is either —CH2CH2OH or —CH3, R14 of the compound of formula (IV) is either methyl or phenyl; and R14 and R15 of the compound of formula (V) is —CH3 and benzyl, respectively.

The quaternized product of formula (II) may be prepared by reacting a dithiazine of formula (I) with a halide of the formula R1X in approximately equimolar ratios. A representative quaternization reaction for the preparation of the compounds of formula (II) may be illustrated as follows:




In a preferred embodiment, the R1X used in the quaternization reaction is benzyl chloride or chloromethyl naphthalene and R is either —CH2CH2OH or —CH3. Most preferred are those reactants set forth in Table I below which is followed by the designated reaction schemes (B), (C), (D) and (E):









TABLE I





Reaction Scheme
R
R1X







(B)
—CH2CH2OH
Benzyl chloride


(C
—CH3
Benzyl chloride


(D)
—CH2CH2OH
Chloromethyl naphthalene


(E)
—CH3
Chloromethyl naphthalene

























The quaternized product of formula (III) may be prepared by reacting a dithiazine of formula (I) with a dihalide of the formula X—R2—X wherein each R2 is a C1-C6 straight or branched alkylene group, preferably —CH2—CH2—CH2—CH2— or —CH2—CH2—CH2—CH2—CH2—; and wherein X is chlorine, bromine or iodine.

A representative quaternization reaction for the preparation of the compounds of formula (III) may be illustrated by reaction scheme (F):




where R is —R3—OH, the dithiazine of formula (I) may be derivatized to form compounds of structural formula (IV) and (V). For instance, the compound of formula (IV) may be prepared by reacting the dithiazine of formula (I) with a stoichiometric amount of acid chloride, such as an alkyl, aryl or arylalkyl acid chloride or acid anhydride. In a preferred embodiment, the dithiazine is reacted with an acid chloride of the formula R14COCl. Typically, an alkyl amine, such as triethylamine, is used at the end of the reaction, especially when an acid chloride is used, in order to remove any halide salt. A representative reaction scheme for the production of the compound of formula (IV) wherein R14 is phenyl may be represented by the following:





The dithiazine derivative of formula (V) may be prepared by reacting the dithiazine of formula (I) with a stoichiometric amount of an alkyl, aryl or arylalkyl acid anhydride to form an ester of the dithiazine and then reacting the ester of the dithiazine with an alkyl, aryl or alkylaryl halide. A representative reaction scheme for the production of compounds of formula (V) where R14 is —CH3 and R15 is benzyl may be illustrated as:




The amount of dithiazine or dithiazine derivative introduced into the well is an amount sufficient to inhibit corrosion of the base materials, especially iron, of tubulars in the well. Typically, the amount of dithiazine or dithiazine derivative introduced into the well is in the range of from about 0.05% to about 5% by volume of the treatment fluid introduced.
In a preferred embodiment, the dithiazine of formula (I) or the dithiazines of formulae (II), (III), (IV) and (V) (all of which may be isolated or within whole spent fluid) may be formulated with at least one other component selected from the groups:
(i) an alkyl, hydroxyalkyl, alkylaryl arylalkyl or arylamine quaternary salt;
(ii) a mono or polycyclic aromatic amine salt;
(iii) an imidazoline derivative;
(iv) a mono-, di- or trialkyl or alkylaryl or arylalkyl phosphate ester;
(v) a monomeric or oligomeric fatty acid or salt thereof;
(vi) an alkyl or alkenyl substituted pyridinium;
(vii) a polyamine amide;
(viii) a polyhydroxy or alkoxylated amine or amide;
(ix) a pyrazine derivative; and
(x) mercaptocarboxylic acids.
In a more preferred embodiment, the dithiazine or dithiazine derivatives are formulated with the formulation component (a) through (x) such that the volume ratio of dithiazine to the additive component is typically between from about 1:0.5 to about 1:2.0, more typically between from about 1:0.8 to about 1:1. Formulating the dithiazine (or quaternized dithiazine) with the additive component may be effectuated by adding the additive to the whole spent fluid or by adding the additive to an alcohol containing solvent (for example methanol) containing the dithiazine or quaternized dithiazine.
Exemplary of the alkyl, hydroxyalkyl, alkylaryl arylalkyl or arylamine quaternary salts are those alkylaryl, arylalkyl and arylamine quaternary salts of the formula [N+R5R6R7R8][X−] wherein R5, R6, R7 and R8 contain one to 18 carbon atoms, X is Cl, Br or I. In a preferred embodiment, any or all of the R5, R6, R7 and R8 are a C1-C6 alkyl group or a hydroxyalkyl group wherein the alkyl group is preferably a C1-C6 alkyl or an alkyl aryl such as benzyl. The mono or polycyclic aromatic amine salt with an alkyl or alkylaryl halide include salts of the formula [N+R5R6R7R8][X−] wherein R5, R6, R7 and R8 contain one to 18 carbon atoms, X is Cl, Br or I.
Typical quaternary ammonium salts are tetramethyl ammonium chloride, tetraethyl ammonium chloride, tetrapropyl ammonium chloride, tetrabutyl ammonium chloride, tetrahexyl ammonium chloride, tetraoctyl ammonium chloride, benzyltrimethyl ammonium chloride, benzyltriethyl ammonium chloride, phenyltrimethyl ammonium chloride, phenyltriethyl ammonium chloride, cetyl benzyldimethyl ammonium chloride, and hexadecyl trimethyl ammonium chloride. Preferred are alkylamine benzyl quaternary ammonium salts, benzyl triethanolamine quaternary ammonium salts and benzyl dimethylaminoethanolamine quaternary ammonium salts.
In addition, the salt may be a quaternary ammonium or alkyl pyridinium quaternary salt such as those represented by the general formula:




wherein R9 is an alkyl group, an aryl group or an alkyl group having from 1 to about 18 carbon atoms and B is chloride, bromide or iodide. Among these compounds are alkyl pyridinium salts and alkyl pyridinium benzyl quats. Exemplary compounds include methyl pyridinium chloride, ethyl pyridinium chloride; propyl pyridinium chloride, butyl pyridinium chloride (such as N-butyl-4-methylpyridinium chloride), octyl pyridinium chloride, decyl pyridinium chloride, lauryl pyridinium chloride, cetyl pyridinium chloride, benzyl pyridinium, dodecylpyridinium chloride, tetradecylpyridinium chloride, N-methylpyridinium chloride, N-methylpyridinium bromide, N-ethylpyridinium chloride, N-ethylpyridinium bromide, 2-vinylpyridinium chloride, 2-vinylpyridinium bromide, 3-vinylpyridinium chloride, 3-vinylpyridinium bromide, 4-vinylpyridinium chloride and 4-vinylpyridinium bromide, and an alkyl benzyl pyridinium chloride, preferably wherein the alkyl is a C1-C6 hydrocarbyl group, as well as mixtures thereof.

The additive may further be an imidazoline derived from a diamine, such as ethylene diamine (EDA), diethylene triamine (DETA), triethylene tetraamine (TETA) etc. and a long chain fatty acid such as tall oil fatty acid (TOFA). Suitable imidazolines include those of formula (IV):




wherein R12 and R13 are independently a C1-C6 alkyl group more preferably hydrido, R11 is hydrido and R10 a C1-C20 alkyl, a C1-C20 alkoxyalkyl group. In a preferred embodiment, R11, R12 and R13 are each hydrido and R10 is the alkyl mixture typical in tall oil fatty acid (TOFA).

Suitable mono-, di- and trialkyl as well as alkylaryl phosphate esters and phosphate esters of mono, di, and triethanolamine typically contain between from 1 to about 18 carbon atoms. Preferred mono-, di- and trialkyl phosphate esters, alkylaryl or arylalkyl phosphate esters are those prepared by reacting a C3-18 aliphatic alcohol with phosphorous pentoxide. The phosphate intermediate interchanges its ester groups with triethyl phosphate with triethylphosphate producing a more broad distribution of alkyl phosphate esters. Alternatively, the phosphate ester may be made by admixing with an alkyl diester, a mixture of low molecular weight alkyl alcohols or diols. The low molecular weight alkyl alcohols or diols preferably include C6 to C10 alcohols or diols. Further, phosphate esters of polyols and their salts containing one or more 2-hydroxyethyl groups, and hydroxylamine phosphate esters obtained by reacting polyphosphoric acid or phosphorus pentoxide with hydroxylamines such as diethanolamine or triethanolamine are preferred.
The additive may further be a monomeric or oligomeric fatty acid. Preferred are C14-C22 saturated and unsaturated fatty acids as well as dimer, trimer and oligomer products obtained by polymerizing one or more of such fatty acids.
The additive may also be a polyamine amide such as products from the reaction of polyethyleneamines and carboxylic acids, such as polymethylenepolyaminedipropionamides as well as acylated derivatives of amino acids appended to a polyols, polyamine or hydroxylamine backbone.
Suitable polyhydroxy or alkoxylated amines or amides such as tallow-CONH(CH2)3NHCH2CH2OH and tallow-NH(CH2)3NH2 ethoxylated with 3 moles of ethylene oxide as well as deoxyglucityl derivatives of alkylamines.
Suitable pyrazine derivatives include methyl substituted derivatives such as 3,5-dimethylpyrazine, 2,3,5,6-tetramethylpyrazine and 2,4,6-trimethylpyridine reached with an aldehyde such as 1-dodecanal or ketone, such as 5,7-dimethyl-3,5,9-decatriene-2-one.
Further the additive may be a mercaptocarboxylic acid such as thioglycolic acid, 3,5′-dithiopropionic acid or potassium dimethyldithio carbamate.
A water soluble fluid containing the dithiazine, dithiazine derivative, or whole spent fluid and, optionally, one or more formulation components, is typically introduced into the wellbore or subterranean formation. The fluid of the water soluble fluid may be a hydrophilic solvent such as water (including fresh water, brackish water and brine, such as sodium chloride, potassium chloride and ammonium chloride brine). The hydrophilic solvent may further be a hydrophilic organic solvent, such as methanol or ethylene glycol.
In a preferred embodiment, the dithiazine is not separated and the whole spent fluid (containing the dithiazine or dithiazine derivative) is then combined with a corrosion inhibiting formulation containing at least one corrosion inhibitor of component (a) through (x). The weight ratio of spent fluid to the corrosion inhibiting formulation may be from 99:1 to 1:99 weight percent and typically is between from about 25:75 to about 75:25, preferably approximately 50:50.
In this embodiment, the whole spent fluid typically acts as a diluent to the corrosion inhibiting formulation. In a preferred embodiment, the corrosion inhibiting formulation is a commercial formulation containing one or more corrosion inhibitors. The corrosion inhibiting formulation may further contain water, an organic hydrophilic solvent, such as methanol. Suitable organic hydrophilic solvents include methanol and ethylene glycol, etc. Use of the whole spent fluid permits dilution of the corrosion inhibiting formulation by as much as 40 to 60 volume percent.
The whole spent fluid and corrosion inhibiting formulation exhibit a synergistic effect in the resulting blended fluid. For instance, a three to four fold decrease in corrosion inhibition has been noted from the blended fluid compared to the amount of corrosion inhibition seen in the whole spent fluid and corrosion inhibiting formulation individually. The synergism has been especially noted where the volume ratio of dithiazine (in the whole spent fluid) to corrosion inhibitor(s) (in the corrosion inhibiting formulation) is between from about 1:0.5 to about 1:2.0.
The use of a blend of whole spent fluid with corrosion inhibiting formulation has great commercial implications since it is not necessary to isolate the dithiazine from the whole spent fluid. As such, the whole spent fluid is combined with the corrosion inhibiting formulation. Since whole spent fluid is typically regarded as a waste material, the blend defined herein lessens the environmental impact created by the generation of whole spent fluid in the oil and gas service industry. In so doing, an otherwise useless waste product is converted to a product demonstrating superior corrosion inhibiting properties.
Since the dithiazine, dithiazine derivatives and synergistic blends dramatically reduce corrosion on metal, they may be used in a variety of industrial applications. Alternatively, the dithiazine or dithiazine derivatives may be introduced prior to or subsequent to, as well as during, a well treatment operation. For instance, the dithiazine or dithiazine derivatives as well as formulations containing the dithiazine or dithiazine derivative may be introduced into the well during stimulation.
Other embodiments within the scope of the claims herein will be apparent to one skilled in the art from consideration of the description set forth herein. It is intended that the specification, together with the examples, be considered exemplary only, with the scope and spirit of the invention being indicated by the claims which follow.
The following examples are illustrative of some of the embodiments of the present invention.
All percentages set forth in the Examples are given in terms of weight units except as may otherwise be indicated.
EXAMPLES
Example 1
The following are used to describe components of this Example.
The dithiazine refers to 5-hydroxyethyl-hexahydro-1,3,5-dithiazine of the formula I wherein R is —CH2CH2—OH.
Unspent fluid (“UF”) refers to the hexahydro-1,3,5-tri(hydroxyethyl)-s-triazine of the formula II above wherein each R is —CH2CH2—OH prior to any spending with hydrogen sulfide.
Whole spent fluid (“WSF”) refers to the homogeneous fluid produced in a hydrogen sulfide scavenger gas scrubbing operation wherein the tower was charged with a triazine[1,3,5-tris(hydroxyethyl)-hexahydro-s-triazine] containing fluid in water and methanol. The fluid contains a high level of the dithiazine, it still being in the WSF.
Isolated dithiazine (“iDTZ”) refers to dithiazine from the WSF that has been separated out of solution in its pure form.
Formulated products were paired using one of the following additives:

    
    
        Methyl/Ethylpyridinium benzyl quat (APBQ);
        Benzyldimethylcocoamine benzyl quat (ABQ);
        TOFA DETA Imidazoline derivative (“TDID”);
        Benzyl triethanolaminium quat (BTEAQ); and
        Benzyl dimethylaminoethanolaminium quat (BDMAEQ).
    
    
    Formulated WSF refers to the product formed by dissolving the additive in the WSF at a concentration of 12.2 weight percent with methanol at 10 weight percent.
    Formulated iDTZ refers to the product prepared by dissolving iDTZ in methanol at a concentration of 9.6 weight percent and then adding to the resultant the additive at a concentration of 19.2 weight percent. This product was then mixed for a brief period while heating to approximately 60° C.


Corrosion rate studies were performed using at ambient temperature a Gamry G Series potentiostat and the conventional Linear Polarization Resistance (LPR) module within the DC105TM corrosion technique software package (Rp/Ec trend). The instantaneous corrosion rate of the three electrode probe system was determined using voltage settings −0.2V to +0.02V versus open-circuit potential, Eoc. These studies were carried out during an approximately 20-24 hr run time. The treat rates of the corrosion inhibitors were between 50 and 200 ppm. A standard carbon dioxide saturated brine system comprised of 3 weight percent sodium chloride and 0.3 weight percent calcium chloride in 2 liter corrosion cells sparged with carbon dioxide was employed. LPR scans are shown in FIGS. 1-8 wherein:

    
    
        FIG. 1 contrasts the differences at a treatment rate of 500 ppm in corrosion rates between WSF and formulated WSF containing the additive APBQ. As shown, much higher corrosion rates are demonstrated with WSF than formulated WSF;
        FIG. 2 contrasts the differences at a treatment rate of 500 ppm in corrosion rates between formulated WSF and UF both containing the additive APBQ. As shown, formulated WSF is a better corrosion inhibitor than UF;
        FIG. 3 contrasts the differences at a treatment rate of 430 ppm of WSF and iDTZ. FIG. 3 shows that iDTZ is much more effective than WSF as a corrosion inhibitor;
        FIG. 4 contrasts the differences at a treatment rate of 430 ppm of Formulated iDTZ (with the additive APBQ) and iDTZ alone. FIG. 4 shows that Formulated iDTZ is a better corrosion inhibitor than iDTZ alone;
        FIG. 5 contrasts the differences at a treatment rate of 430 ppm in corrosion rates between iDTZ alone and Formulated iDTZ (with the additive ABQ), Formulated iDTZ (with the additive TDID) and Formulated iDTZ (with the additive APBQ). FIG. 5 shows the Formulated iDTZ (with APBQ) to be the best corrosion inhibitor. Formulated iDTZ (with TDID) and Formulated iDTZ (with ABQ) demonstrate similar results. All of the formulated iDTZs demonstrated better corrosion inhibition than iDTZ alone;
        FIG. 6 contrasts the differences at a treatment rate of 125 ppm in corrosion rates between Formulated iDTZ (with BTEAQ) and Formulated iDTZ (with APBQ). FIG. 6 demonstrates better corrosion results with Formulated iDTZ (with APBQ); and
        FIG. 7 contrasts the differences at a treatment rate of 125 ppm in corrosion rates between Formulated iDTZ (with APBQ) and Formulated iDTZ (with BDMAEQ). FIG. 7 demonstrates better corrosion results with Formulated iDTZ (with APBQ).
    
    


Example 2
A dithiazine quaternization reaction product was prepared in accordance with the following synthetic pathway:




by dissolving in 50 mls of methanol about 2.84 grams (17.2 mmols) of the dithiazine together with a 10% molar excess of the R1—X reagent (2.42 grams, 19.1 mmols). The solution was heated to 125° C. and stirred for 6 hrs in a Parr reactor. Upon cooling the solution was recovered as a dark red.

Corrosion rate studies were conducted using 35 parts of active species per million by mass at ambient temperature on a Gamry G Series potentiostat and the conventional Linear Polarization Resistance (LPR) module within the DC105TM corrosion technique software package (Rp/Ec trend) in accordance with the procedure set forth in Example 1. The instantaneous corrosion rate of the three electrode probe system was determined using voltage settings −0.2V to +0.02V versus open-circuit potential, Eoc. These studies were carried out during an approximately 20-24 hr run time. The treat rates of the corrosion inhibitors were between 50 and 200 ppm. A standard carbon dioxide saturated brine system comprised of 3 weight percent sodium chloride and 0.3 weight percent calcium chloride in 2 liter corrosion cells sparged with carbon dioxide was employed. LPR scans are shown in FIGS. 8-10 wherein:

    
    
        FIG. 8 contrasts the differences of compound (I) wherein R is methyl at 35 parts per million (ppm) (by mass) [or 0.26 ppm (by moles)] and compound (II) wherein R is methyl and R1 is benzyl at 35 parts per million (ppm) (by mass) [or 0.13 ppm (by moles)].
        FIG. 9 contrasts the differences of compound (I) wherein R is HO—CH2—CH2— 35 parts per million (ppm) (by mass) [or 0.21 ppm (by moles)] and compound (II) wherein R is HO—CH2—CH2— and R1 is benzyl at 35 parts per million (ppm) (by mass) [or 0.12 ppm (by moles)].
        FIG. 10 contrasts the differences of compound (I) wherein R is HO—CH2—CH2— at 35 ppm [or 0.21 ppm (by moles)] and compound (B) wherein R is HO—CH2—CH2— and R1 is naphthylmethyl at 35 parts per million (ppm) (by mass) [or 0.10 ppm (by moles)].

As shown, much better corrosion rate inhibition is demonstrated with the derivatized dithiazines represented by compound (II) than compound (I) especially considering that lower molar quantities of the derivatized dithiazines were used.

    
    


Example 3
A dithiazine quaternization reaction product was prepared in accordance with the following synthetic pathway:




by dissolving in 50 mls of methanol about 3 grams (18.2 mmols) of the dithiazine together with the X—R2—X— reagent (9.1 mmols). The solution was heated to 125° C. and stirred for 6 hrs in a Parr reactor. Upon cooling the solution was recovered as a dark red.

Corrosion rate studies were conducted at ambient temperature on a Gamry G Series potentiostat and the conventional Linear Polarization Resistance (LPR) module within the DC105TM corrosion technique software package (Rp/Ec trend) in accordance with the procedure set forth in Example 1. The instantaneous corrosion rate of the three electrode probe system was determined using voltage settings −0.2V to +0.02V versus open-circuit potential, Eoc. These studies were carried out during an approximately 20-24 hr run time. The treat rates of the corrosion inhibitors were between 50 and 200 ppm. A standard carbon dioxide saturated brine system comprised of 3 weight percent sodium chloride and 0.3 weight percent calcium chloride in 2 liter corrosion cells sparged with carbon dioxide was employed. LPR scans are shown in FIGS. 11 and 12 wherein:

    
    
        FIG. 11 contrasts the differences of the structure of formula (I) wherein R is HO—CH2—CH2— at 0.21 ppm (by moles) and the structure of formula (III) wherein R is HO—CH2—CH2— and R2 is C5H10 at 0.12 ppm (by moles).
        FIG. 12 contrasts the differences of the structure of formula (I) wherein R is HO—CH2—CH2— at 0.21 ppm (by moles) and the structure of formula (III) wherein R is HO—CH2—CH2— and R2 is C4H8 at 0.12 ppm (by moles).

As shown, much better corrosion rate inhibition is demonstrated with the derivatized dithiazines represented by compound (III) than the dithiazines represented by compound (I).

    
    


Example 4
5-(2-benzoyloxyethyl)hexahydro-1,3,5-dithiazine was prepared in accordance with the following synthetic pathway:




by dissolving in 1 ml of methylene chloride about 400 mg of 5-hydroxyethyl-hexahydro-1,3,5-dithiazine and a stoichiometric amount of benzoyl chloride in a sealed ReactiVial vessel at 100° C. and stirred for 8 hrs. About 400 mg of triethylamine was added to the resulting product and triethylammonium chloride salt was removed.

Example 5
5-(2-acetoxyethyl)hexahydro-1,3,5-dithiazine was prepared in accordance with the following synthetic pathway:




by dissolving in 1 ml of methylene chloride about 400 mg of 5-hydroxyethyl-hexahydro-1,3,5-dithiazine and a stoichiometric amount of acetic anhydride and heating the mixture at 100° C. for approximately 8 hours. The solvent was then removed from the resulting mixture and the ester of formula (XVI) was isolated. Above 200 mg of the ester was then dissolved in methanol and a stoichiometric amount of benzyl chloride was added to a sealed ReactiVial vessel. The solution was heated to approximately 120° C. for about 6 hours.

Example 6
Corrosion inhibition tests were conducted on the product solutions of Example 4 and Example 5 by ambient pressure linear polarization resistance (LPR) which was performed at ambient temperature in 2000 mL glass resin kettles. Corrosion rates were monitored using a linear polarization resistance instrument with 3 electrode probes. Tests were 24-hour exposures of AISI 1018 (UNS G10180) steel electrodes to stirred solutions at room temperature using a brine (3% NaCl, 0.3% CaCl2×2H2O) sparged with CO2. In each test, 50 ppm of compounds of formula (I), (II), (III) and (IV) in Examples 4 and 5 in the brine were evaluated. Corrosion rates after 23 hours were determined by weight loss of the reference electrode. Electrodes were cylindrical with a surface area of 9 cm2. Measured corrosion rates are set forth in Table I.










TABLE I








Corrosion,




Mils per year



Compound
(mpy)









(I)
1.60



(II)
0.60



(III)
0.18



(IV)
0.26










The compound of formula (II) exhibited more than 100% improved corrosion rate over the compound of formula (I). The corrosion rate of the compound of formula (I) was just over one tenth of the corrosion rate of the compound of formula (I). The compound of formula (IV) had better than 100% improvement in corrosion rate over the compound of formula (I).

Example 7
Whole spent fluid (WSF) produced in a hydrogen sulfide scavenger gas scrubbing operation was combined with commercially available corrosion inhibitor formulations—Technihib 366 (“A”) and Technihib 356 (“B”), both products of Baker Hughes Incorporated. Corrosion rates after 21 hours were determined as set forth in Example 6 and are set forth in Table II wherein 75 ppm of each of the formulations was tested:











TABLE II









Corrosion,





Mils per year



Formulation
Wt. Ratio
(mpy)









A
100
3.54



WSF/A
50/50
1.87



B
100
4.55



WSF/B
50/50
2.43










Table II illustrates that better results were obtained when a mixture of the whole spent fluid was used in combination with the commercial formulation than when the commercial formulation was used by itself.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concepts of the invention.

## Claims

1. A dithiazine of the formula:




wherein:
R14 is a C1-C24 straight chain or branched alkyl group; or a C6-C24 aryl or arylalkyl group.

2. The dithiazine of claim 1, wherein R14 is a C1-C12 straight chain or branched alkyl group.

3. The dithiazine of claim 1, wherein R14 is methyl.

4. The dithiazine of claim 1, wherein R14 is phenyl.