HEXAHYDROTRIAZINES, SYNTHESIS AND USE

!S _:; D OF I VENTION

[0001 J The invention pertains to methods and chemical compositions for reacting wiih hydrogen sulfide (¾S), and more particularly, for scavenging H?S from hydrocarbon streams in the petroleum and natural gas industries,

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[0002] Hydrogen sulfide, or ¾S, is a clear, toxic gas with a foul odor, it is also highly flammable. The Environmental Protection Agency and other regulatory agencies worldwide strictly control the release of J¾S into the environment. ¾S is often present in crude oil and natural gas reserves and must be removed before making commercial use of such reserves. The ¾S concentration in these reserves prior to treatment typically varies with location and is usually higher in natural gas than in crude oil reserves. In natural gas reserves, for example, ¾S may vary from less than 100 ppm to 3,000 ppm. Permitted H?S levels will also vary by location. The U.S. limits ¾S in natural gas pipelines to 4 ppm per 100 standard cubic feet (0.3 gr/100 sef).

[0003] Generally, hydrocarbon streams are treated to remove ¾S, mercaptans, or organic sulfides by using chemicals that will react with sulfide contaminants. These chemicals are called scavengers, or sweetening agents. Hexahyd.rotriazi.nes, commonly called "triazrnes," are frequently used as I feS. mercaptan. and organic sulfide scavengers. Triazines are a water-soluble species characterized as having a benzene ring structure in which three nitrogens with alky! radicals replace three carbon- hydrogen units. Triazines scavenge ¾S through the following reaction:

wherein R is a straight or branched alky! radical, including substituted alkyl radicals, with the genera! formula CJH n _* ..

[00041 Most hydrocarbon reserves are treated continuously near the wellhead, though treating hydrocarbons in a batch or similar application elsewhere is not uncommon. Continuous treatment installations near the wellhead inject scavengers, like triazines, directly into the hydrocarbon pipeline. The injection system typically includes a chemical injection pump and piping tees or atomization nozzles to introduce the triazines into the pipeline. Based on the stoichiometry of the scavenging reaction, a molar ratio of triazine to ¾S of 1 :2 is ideal. The amount, of triazine actually required, however, will vary depending on a variety of factors including the amount of ¾S in the well, permissible ¾S limits, the well flow rate, temperature, etc. and may be determined by those of ordinary skill in the art. Thus, to effectively treat the hydrocarbon stream, the triazine:H ₂ S molar ratio may vary from about 10: 1 to about 1 :2. A length of the pipeline is provided to allow for contact between the scavenger and the H ₂ S. At the end of the length, the spent scavenger is separated from the hydrocarbon stream and the hydrocarbon stream moves on for further processing or use.

10005! The most common method of making triazines, including those used in H?S scavenging applications is to add a primary amine to an aldehyde. The aldehyde may be either a water solution of formaldehyde or solid paraformaldehyde. Primary amines are compounds where one of three hydrogen atoms in ammonia is replaced by an alkyl. Examples of primary amines include meth l amine, ethanoiamine, monoeihanol amine and methoxypropylamine. The most commonly used triazines are made from monoethanolamine (MEA). The resulting triazine is hexahydro-1 ,3,5- tris(hydroxyefhyl)-s-triazine, or triazinetriethanoi, and has the structure:

The triazine structure can be altered through the use of different types of primary amines. Thus using methoxypropylamine (MOPA) results in hexahydro-1.,3,5- tris(niethoxypropyl)-s-tria2ine _; and has the structure:

1000 1 Hexahydro-KS^-trisihydroxyethyl^s-triazine triazine has a hig freezing point around -40 °F (-40 °C). This freezing point is not low enough for many hydrocarbon reserves in the northern hemisphere where winter temperatures may fall below -40 °F (-40 °C). Once temperatures reach below -40 °F (-40 °C) in scavenging applications t Sizing these triazirtes, they cannot be injected into the hydrocarbon stream using typical methods. This is true for the northern United States, Canada, Russia, Kazakhstan., northern China, and Norway. In these areas, the symmetrica! triazines are diluted with expensive and flammable soivents and antifreezes, such as methanol or ethylene glycol, to prevent freezing and achieve low temperature handling capability. This not only minimizes H S scavenging activity, but also increases the cost to purchase and ship the symmetrical triazines used in these areas.

[0007] Hexahydro~1 ,5 ris(methoxypropy!)~s-tria2:ine has a freezing point below -40 °F (-40 °C); however, it is less effective as an ¾S scavenger.

SUMMARY OF THE INVENTION

[0008] In one embodiment of the invention, a method of making at least one asymmetrical hexahydrotriazine or "triazine" is provided. The asymmetrical triazine is made by first forming a .mixture of at least two primary amines. Then the mixture of primary amines is reacted with an aldehyde compound. The aldehyde compound may be an aqueous formaldehyde solution or solid paraformaldehyde. In another embodiment of the invention, the primary amines include monoethanolamine (MEA) and methoxypropySarrime (MOP A) in a molar ratio of about 2 : 1.

[00091 In another embodiment of the invention, a method i provided for removing sulfides, including ¾S, mercaptaiis, and organic sulfides, from liquid or gaseous hydrocarbon streams. The method comprises contacting sulfides in the hydrocarbon stream with one or more asymmetric triazines. The method may be used in low temperature applications without adding solvents and antifreezes.

[001 Oj In yet another aspect of the invention, an asymmetrical triazine is provided. These asymmetrical triazines have different alkyi groups attached to the nitrogen atoms. The alkyi groups may be straight or branched, in yet another aspect of the invention, the asymmetrical triazine has both MEA and QPA primary amines incorporated into its structure.

[0011 J The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(00121 Exemplary embodiments include asymmetrical triazines and methods for manufacturing such triazines. Other embodiments utilize asymmetrical triazines to scavenge HjS at. low temperatures without adding expensiv and flammable solvents and antifreezes, such as methanol or ethylene glycol. The embodiments are described in conjunction with the following examples.

100I3j The first exemplary embodiment discloses a method for making asymmetrical triazine by first forming a mixture of two or more different primary amines. Examples of primary amines include methyl amine, ethanolamine, monoethanolamine and methoxypropylamine. The primary amine mixtiire may include MEA and MOP A. The molar ratio of the two primary amines may vary, hi one embodiment, the molar ratio is about 2:1. The mixture of primary amines is then reacted with an aldehyde compound. Aldehyde compounds include formaldehyde in a water solution and solid paraformaldehyde. The molar ratio of the ami ne mixture to the aldehyde compound is about 1:1. The resulting triazines have the general structure and formula I:

wherein R ₃ , R _2s and Ri are chosen from aJkyls, hydroxyi-substituted alkyls, and a!koxy- substituted alkyl of 1 to 10 carbon atoms, with the proviso that Rj., R ₂ , and R.¾ are not all the same. The alkyl groups may be straight or branched alkyl groups, including, but not limited to, methyl, ethyl, propyl, butyl, ethyl hydroxy!, and methoxypropyl.

|0 I 4| Another exemplary embodiment discloses using asymmetrical triazines to remove sulfides, including i¾S and mercaptans, from hydrocarbo streams. The hydrocarbon streams may be gaseous or liquid streams. The sulfides are contacted with at least one asymmetrical triazine, including triazines that incorporate both the MEA and MOPA structures. The asymmetrical triazines may be added in an asymmetrical triaz-ine:¾S molar ratio o about 10: 1. In another embodiment, the molar ratio of asymmetrical triazineTIiS is about 5:1 and in another embodiment, the molar ratio is about 1 :2.

[0015) In another embodiment, asymmetrical triazines are used to remove sulfides, including ¾S and mercaptans, from hydrocarbon streams at low temperatures without adding solvents or antifreezes. The hydrocarbon streams may be gaseous or liquid streams. The sulfides are contacted with at least one asymmetrical triazine, including triazines that incorporate both the MEA and MOPA structures. The amount of triazine added will depend on the application and amount of sulfide scavenging required and may vary from about 10: 1 to about 1 :2. The asymmetrical triazines are added in an asymmetrical triazine:i¾S molar ratio of about 10:1. in one embodiment, the molar ratio of asymmetrical triazine:l¾S is about 5: 1 and in another embodiment, the molar ratio is about 1 :2. In another embodiment., the ratio is about 2,5: 1 to about 3.5: 1. In another embodiment, the resulting tr.iazi.nes incorporate both the MEA and MOP A structures, producing asymmetrical triazines with at least one of the following formu!a and structures II or HI:

|0016| These asymmetrical triazines are beneficial hecause they have a freezing point around -60 °F (-5 i °C). The commonly used triazines have a high freezing point around -40 °F (-40 °C) and require dilution with expensive and flammable solvents and antifreezes, such as methanol or ethylene glycol, to prevent freezing and achieve low temperature handling capability. Thus, these asymmetrical triazines can be used for ¾S scavenging at Sow temperatures without adding expensive and flammable solvents and antifreezes, such, as methanol or ethylene glycol. EXAMPLES

[0017} The method of manufacture of an asymmetri cal triazine was compared to the method of manufacture of a symmetrical triaxine. The effects of these two types of triazines on a hydrocarbon stream containing ¾S were also compared. The following examples illustrate these comparisons.

10018| Example 1. Example I uti lizes a mixture of two or more primary amines, monoethanolamine (MEA) and methoxypropylamine (MOP A). The molar ratio of MEA to MOP.A is 2: 1 but the molar ratio may vary. in Example 1, the asymmetrical triazine was made in a flask equipped with a stirrer, condenser, and temperature control device. The flask wa charged with I Mole (31.25 gm) of 96% pure paraformaldehyde. The primary amines were preraixed in a separate container. The primary amine mixture included 0.66 Mole (40.26 gm) monoethanolamine (MEA.) and 0.34 (30.0 gm) of methoxyprop lamine (MOP A). The primary amine mixture was then added drop- wise to the flask containing the paraformaldehyde while controlling the temperature in the flask to below 50 °C. After the mixture was added, the contents of the flask were stirred for 1 hour while the temperature of the fiask was maintained at 80 °C. After one hour, 102 grams of asymmetrical triazine was collected. The product was a transparent single phase solution. The asymmetrical triazine that was produced had a freezing point of -60 °F (-51 " C }

[0019} Example 2. The efficacy of the product produced in Example 1 was tested in Example 2. In this example, 200 ml of a light hydrocarbon mixture having 2000 ppm of ¾S level in the head space was placed in a 1 -liter bottle. Next, 5500 ppm of the asymmetrical triazine produced in Example 1 was added to the 1 -liter bottle. After stirring for 30 minutes at room temperature, the J¾S level in the head space was reduced to 100 ppm..

[00201 Example 3. In this example, 200 ml of a light hydrocarbon mixture having 2000 ppm of H S level in the head space was placed in a 1 -liter bottle. Next. 6500 ppm of the asymmetrical triazine produced in Example 1 was added to the I -liter bottle. After stirring for 30 minutes at room temperature, the ¾S level in the head space was reduced to 6 ppm. [0021 J Example 4. For comparison to Example 1 , in Example 4, a symmetrical triazine was made in a flask equipped with a stirrer, condenser, and temperature control device. The flask was charged with 1 Mo!e (3 i .25 gm) of 96% pure paraformaldehyde. 1 Mole (61 gm) of monoethanolamine (MEA) was added drop-wise to the flask containing the paraformaldehyde while controlling the temperature in the flask to below 50 °C. After the all the MEA wa added, the contents of the flask were stirred for I hour while the temperature of the flask, was maintained at SO °C. After one hour, 92 grams of symmetrical triazine was collected. The symmetrical triazine that was produced with the above method had a .freezing point of -40 °F (-40 °C).

[0022J Example 5, For comparison to our Examples 2 and 3, the efficacy of the product produced in Example 4 was tested in Example 5. In this example, 200 ml of a light hydrocarbon mixture having 2000 ppm of ¾S level in the head space was placed in a 1 -liter bottle. Next, 5500 ppm of the symmetrical triazine produced in Example 4 was added to the 1 -liter bottle. After stirring for 30 minutes at room temperature, the ¾S level in the head space was reduced to 2 ppm.

[0023] Example 6. For comparison to the product produced in Example 1 , a mixture of hexahydro-l,3,5-tris(liydroxy ethyl )-s-triazine (MEA triazine) and hexahydro-i 3,5-tris(methoxypropyi)-s-tria2ine (MOPA triazine) was made. First a 75% MEA triazine solution in water was made. Added to that solution wa a 75% MOPA triazine solution in water. The solutions were stirred. Unlike Example i, which was a transparent single phase solution, the solutions in Example 6 separated into two immiscible layers. This clearly supports claims of an asymmetrical triazine with both MEA and MOPA structures.

[00241 This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated processes. These examples are merely illustrative and do not limit the invention in any manner. For example, although the asymmetrical triazine synthesis and scavenging conditions in the illustrative examples list specific temperatures, these reactions can occur at almost any temperature. The patentable scope of the invention is defined fay the claims, and may Include other examples thai occur to those skilled in the art. These other examples are intended to be w thin the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the clainis.

1 025] What is claimed is: