Quaternary ammonium compounds and gas hydrate inhibitor compositions

Abstract

Quaternary ammonium compounds and compositions comprising the compounds are disclosed. The compositions are valuable as gas hydrate inhibitors in the oil and gas exploration, recovery and processing industries. The compounds and compositions may have improved biodegradability and reduced toxicity when compared with benchmark materials. Quaternary ammonium compounds of the present disclosure have the formula (I) in which R is C.sub.1-4 alkyl, C.sub.6-10 aryl, or C.sub.1-4alkyl-C.sub.6-10aryl; R.sup.1 is hydrogen or a group of formula C(O)X; and R.sup.2 is hydrogen or a group of formula C(O)Y, provided that R.sup.1 and R.sup.2 are not both hydrogen; X and Y are each independently a hydrogen, C.sub.1-6 alkyl or C.sub.1-6 alkenyl group, and Z is a C.sub.4-24 alkyl or C.sub.4-24 alkenyl group; each D is independently C.sub.1-4 alkylene; and A.sup. is an anion. ##STR00001##

Claims

1. A composition, useful for inhibiting gas hydrate formation during oil and gas exploration, recovery, or processing, said composition comprising: a quaternary ammonium compound of formula (I) ##STR00005## wherein: R is a C.sub.1-4 alkyl group, C.sub.6-10 aryl group, or C.sub.1-4alkyl-C.sub.6-10 aryl group, poly(C.sub.2-4 alkylene oxide), or poly(styrene oxide), any of which may be substituted by one or more groups selected from halide, C.sub.1-4 alkyl, OH, COOH, C(O)C.sub.1-4alkyl, or C.sub.1-4alkyleneOH; R.sup.1 is hydrogen or a group of formula C(O)X; and R.sup.2 is hydrogen or a group of formula C(O)Y, provided that R.sup.1 and R.sup.2 are not both hydrogen; X and Y are each independently a hydrogen, C.sub.1-6 alkyl or C.sub.1-6 alkenyl group; Z is a C.sub.4-24 alkyl or C.sub.4-24 alkenyl group; each D is independently a C.sub.1 to C.sub.4 alkylene group; and A.sup. is an anion, and organic solvent, the organic solvent being an aromatic organic solvent or a mixtures of aromatic organic solvents.

2. A composition according to claim 1, wherein R is a methyl group or benzyl group.

3. A composition according to claim 1, wherein the groups X and Y are identical.

4. A composition according to claim 3, wherein X and Y are C.sub.3 alkyl groups.

5. A composition according to claim 1, wherein Z is a C.sub.7-17 alkyl group or C(O)Z is the acyl unit derived from a fatty acid selected from caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, erucic acid, linoleic acid, linolenic acid, ricinoleic acid, isostearic acid, isopalmitic acid, eicosanoic acid, gadoleic acid, palmitoleic acid, arachidonic acid, clupanadonic acid, and behenic acid.

6. A composition according to claim 1, wherein D is CH.sub.2CH.sub.2.

7. A composition according to claim 1, wherein the anion A.sup. is selected from halides, methosulphate, methophosphate and ethosulphate.

8. A composition according to claim 1 in which the cation has formula II, III or IV. ##STR00006##

9. A composition according to claim 1 comprising a mixture of at least two quaternary ammonium compounds according to Formula I that differ at least in the identity of group C(O)Z.

10. A composition according to claim 9, wherein the ratio of different C(O)Z groups of the different quaternary ammonium compounds in the composition corresponds, to at least 90% correspondence, to the ratio of different carbon chain lengths in the acyl units of one of the mixtures of fatty acids selected from rapeseed oil fatty acids, soya oil fatty acids, tall oil fatty acids, tallow oil fatty acids, palm oil fatty acids, palm kernel oil fatty acids, coconut oil fatty acids, stripped coconut oil fatty acids, cottonseed oil fatty acids, wheat germ oil fatty acids, olive oil fatty acids, corn oil fatty acids, sunflower oil fatty acids, safflower oil fatty acids, and hemp oil fatty acids.

11. A composition according to claim 9, wherein at least 90% of the quaternary ammonium compounds in the composition have C(O)Z acyl groups with a carbon chain length selected from: C.sub.8 and C.sub.10; C.sub.10 and C.sub.12; C.sub.12 and C.sub.14; C.sub.14 and C.sub.16; C.sub.16 and C.sub.18; or C.sub.18 and C.sub.20.

12. A composition according to claim 1 comprising 10 to 99 volume percent of the quaternary ammonium compound according to Formula I and 1 to 90 volume percent of water, a water-miscible organic solvent, or both.

13. A composition according to claim 1 comprising 10 to 99 volume percent of the quaternary ammonium compound according to Formula I and 1 to 90 volume percent of the organic solvent.

14. A method of inhibiting gas hydrate agglomeration in a liquid, the method comprising contacting the liquid with a composition according to claim 1.

15. Use of a composition according to claim 1 as an anti-agglomeration hydrate inhibitor for an oil or gas processing application or a downhole application.

Description

EXAMPLES

Synthetic Example 1

(1) Esterification

(2) 300 g of butyric acid (2 moles) and 384 g of myristic acid (1 mole) were introduced in an inert atmosphere into a glass reactor, 263 g of triethanolamine (1.03 moles) were added with stirring. The mixture was heated for at least 24 h at 140-155 C. in order to remove the water of the reaction. The progress of the reaction was monitored by an acid/base assay which determines the residual acidity to obtain an esterification of at least 95% of the fatty acids.

(3) 855 g of a brown liquid product, referred to as esteramine 1 were recovered, consisting essentially of a mixture of unesterified fatty acids and mono-, di- and triesterified amine (small amount of unreacted triethanolamine).

(4) Quaternization

(5) 186 g of dimethyl sulphate were added with stirring at a temperature of 60-90 C. to 732 g of esteramine 1. After one hour of digestion, the virtually complete absence of residual amine was verified by acid/base assay.

(6) The product was then diluted to 90% by adding approximately 101 g of isopropanol. 1019 g of the product X3342-C14 were obtained.

(7) The product is predominantly a triester compound with smaller amounts of mono- and di-esters present.

(8) Compounds

(9) The following compounds in Table 1 were obtained for testing in gas hydrate inhibitor compositions. These compounds were produced by the same reaction as in Synthetic Example 1 but with the initial myristic acid component replaced by a fatty acid or fatty acid mixture having the relevant chain length. The references X, Y, Z, R, and A.sup. refer to the groups in Formula I above.

(10) TABLE-US-00002 TABLE 1 Fatty acid from which acyl Product group is derived Anion number X Y Z R A.sup. X3321 Stripped Butyric Butyric Me MS coco X3342 Coconut Butyric Butyric Me MS X3341 Stripped Butyric Butyric Salt with coco butyric acid X3343 Coconut Butyric Butyric Salt with butyric acid X3620 C16/C18 Butyric Butyric Me MS X3621 C8/10 Butyric Butyric Me MS X3622 C12/C14 Butyric Butyric Me MS X3342-C10 C10 Butyric Butyric Me MS X3342-C12 C12 Butyric Butyric Me MS X3342-C14 C14 Butyric Butyric Me MS Stripped coco = stripped coconut fatty acid Coconut = coconut fatty acid MS = methosulphate

(11) The distribution of the carbon chain lengths in the various fatty acid components used in table 1 is shown in table 2.

(12) TABLE-US-00003 TABLE 2 Fatty acid Carbon chain length distribution of fatty acids (%) mixture C6 C8 C10 C12 C14 C16 C18 C18:1 C18:2 C20 C22 Coco 7.6 6.1 46 18.7 10 2.9 6.8 1.4 Stripped 0.4 55.4 19.6 9.5 4.4 1.4 coco C16/C18 1.3 28.7 67.2 1.7 C8/C10 0.1 56.4 43.3 0.2 C12/C14 1 68 28 3 coco = coconut oil stripped coco = stripped coconut oil
Anti-Agglomeration (AA) Tests

(13) The AA performance was determined in a rocking cell systema RCS20 rig obtained from PSL Systemtechnik, Germany. The rig uses ten identical sapphire cells, each with an internal volume of 20 ml. Within each a stainless steel ball moves from end to end as the cells rock and sensors located at either end of the cell measure the run time of the ball. The rocking motion provides mixing and agitation. The rocking system is controlled by computer (rocking angle and rate) and pressure and temperature were logged along with the ball run time. The rocking angle was set to 40 and the frequency to 15 min.sup.1.

(14) A synthetic gas composition was used as shown in Table 3. This gas composition is predicted to form Type II gas hydrates.

(15) TABLE-US-00004 TABLE 3 Component Mol % Methane 80.40 Ethane 10.30 Propane 5.00 i-Butane 1.65 n-Butane 0.72 N2 0.11 CO2 1.82

(16) A standard procedure was adopted for all experiments. Cells were charged with brine, test chemical and liquid hydrocarbon (condensate or crude). They were then charged with gas and rocked for 5 minutes until the pressure drop was less than 210.sup.5 Pa (2 Bar). The gas charging to meet this target typically required several repetitions. Rocking then continued for 1 hour at 20 C. with a final repressurisation if the pressure had dropped. Cells were charged to a higher pressure at 20 C. than the required pressure at 4 C. to allow for the pressure drop associated with cooling.

(17) The cells were then cooled to 4 C. at a rate of approximately 4 C. per hour. Once the system reached the set temperature rocking was continued for 12 hours. A shut-in period of 6 hours then followed. During this time the cells were horizontally positioned. At the end of the shut-in the rocking was resumed for a further 6 hours.

(18) Brines were prepared using NaCl to provide the required salinity. Two liquid hydrocarbons were used. The first was an additive free condensate obtained from an offshore Netherlands field. The second was an additive free Norwegian crude oil. The crude oil was confirmed as not depositing wax at 4 C.

(19) The four different stages of the test (cooldown, flowing to shut-in, immediate start-up and end test) were assessed by visual inspection and a final overall rating given. The rating criteria used to evaluate the performance on each stage is based on one presented by Shell, which uses a scale from 1 to 5. A ranking of 5 is the best possible score and on occasion may mean there are no visible hydrates in the system at all. A ranking of 1 is a failure while a ranking of 2 represents a marginal hydrate control scenario at best.

(20) The factors used to generate the ranking include crystal morphology, liquid level, phase appearance, type of flow/apparent viscosity and ball movement. Many of these are visually assessed but the movement of the stainless steel ball between the two sensors for each sapphire cell is logged by computer and hence changes can be numerically determined. As an example the factors for a ranking of 1 (test failure) are as follows:

(21) Ranking 1System failure; pipeline is expected to plug

(22) Deposits on cell's interior surfaces and/or the ball

(23) Large agglomeration of hydrate particles

(24) Multiple phases; one of which will not disperse

(25) Hydrates do not disperse with strong agitation

(26) Low liquid level

(27) Exceedingly high viscosity liquids

(28) Possible stuck ball

(29) In contrast a ranking of 5 requires no deposits, hydrate particlesif presentare very fine, an easily dispersible liquid and rapid recovery of flow following the start-up.

Examples 1-5

Standard Conditions

(30) Compositions were tested under standard conditions of 8010.sup.5 Pa (80 Bar) gas pressure using the additive free condensate described above. The compounds were present at 2 volume % in a 3 wt. % per unit volume NaCl brine (30 g NaCl per liter). Results are presented in table 4. A benchmark compound, tributyl tetradecylphosphonium chloride (TTPC), was used for comparison.

(31) TABLE-US-00005 TABLE 4 Ranking Example Composition Stage 1 Stage 2 Stage 3 Stage 4 Reference TTPC 5 5 5 5 Example 1 Example 1 X3342 4 4 4 4 Example 2 X3622 4 4 4 4 Example 3 X3342-C10 4 3+ 4 4 Example 4 X3342-C12 2 3+ 4 3+ Example 5 X3342-C14 4 5 5 4 Stage 1 = Cooldown Stage 2 = Flowing and shut-in Stage 3 = Immediate restart Stage 4 = Restart to end test

(32) It can be seen in table 4 that all of these Example compounds perform at a similar level to the reference compound. The X3342-C12 compound is slightly lower in performance but is still sufficient to be useable in an LDHI composition.

Examples 6-10

Standard Conditions

(33) Further tests were performed under the same standard conditions as used for Examples 1-5 above. In these tests, one overall rating was given covering all of the stages. In some cases two ratings are given where the behaviour of the compound altered significantly during the test. The results are presented in table 5.

(34) TABLE-US-00006 TABLE 5 Example Composition Ranking Reference Example 2 X3343 1 Reference Example 3 X3341 1+ Example 6 X3342 4 Example 7 X3321 3 Example 8 X3620 2+ Example 9 X3621 5/2 Example 10 X3622 3+

(35) A number of comparisons can be drawn from the results in table 5. For example, comparison of examples 8-10 shows an effect of the length of the Z chain in formula I. The compositions in these examples differ only in the length of the Z chain in formula I. The performance seems to progress in the order example 8 (C16/C18)<example 9 (C8/C10)<example 10 (C12/C14). These results indicate that the C12/C14 chain length in example 10 is preferable.

(36) Comparison of example 7 with reference example 3 and also example 6 with reference example 2 highlights the difference in performance between compounds in which the R group in formula I is an alkyl group (Me in both examples 6 and 7) and those in which the group corresponding to R in formula I is H (reference examples 2 and 3).

(37) Comparison of examples 6 and 7 highlights the difference in performance between compounds in which the Z group of formula I is derived from coconut fatty acid (example 6) and those in which the Z group of formula I is derived from stripped coconut fatty acid (example 7). However despite these differences both examples 6 and 7 reflect behaviour of a useful LDHI composition.

Examples 11-13

Varying Conditions

(38) A range of conditions was used to determine performance as shown in Table 6. This range was chosen to represent typical conditions for which an anti-agglomerant composition should be suited.

(39) TABLE-US-00007 TABLE 6 Pressure 80 10.sup.5, 120 10.sup.5 Pa (80, 120 Bar) Water cut (% ratio of 10, 30, 50% water by volume compared to overall liquid components) Brine salinity 0, 1.5, 3% Liquid hydrocarbon Crude, condensate Composition dose rate 1, 2, 4%

(40) A range of tests were performed by systematically varying the parameters in table 6. The sets of conditions shown in table 7 were tested for a range of different compositions. Again TTPC was used as a reference AA composition.

(41) TABLE-US-00008 TABLE 7 Composition Water Condition dose rate cut Salinity set (%) (%) (%) Pressure (Pa) 1 1 10 1.5 120 10.sup.5 (120 Bar) 2 2 10 0 80 10.sup.5 (80 Bar) 3 4 50 1.5 80 10.sup.5 (80 Bar) 4 1 30 3 80 10.sup.5 (80 Bar) 5 2 50 3 120 10.sup.5 (120 Bar) 6 1 50 0 80 10.sup.5 (80 Bar) 7 4 30 0 120 10.sup.5 (120 Bar) 8 4 10 3 120 10.sup.5 (120 Bar)

(42) Compositions were tested in both crude oil and condensate as described above.

(43) Results were assessed by visual inspection as described above with an overall rating being given for each condition set.

(44) Compositions tested were X3342-C14, X3342, and X3622. For each composition, the number of rankings of level 3 or above was counted for each batch of 8 tests described in table 7. The results are provided in table 8.

(45) TABLE-US-00009 TABLE 8 Number of tests (out of 8) at ranking 3 or above Example Composition Condensate Crude oil Reference TTPC 5 4 example 4 Example 11 X3342-C14 6 4 Example 12 X3342 5 5 Example 13 X3622 4 4

(46) Examples 11-13 indicate that all three of the compounds tested show effective AA properties and similar behaviour to the TTPC reference example 4 in both crude oil and condensate environments.

(47) A trend was also seen in terms of the water cut. All of the tests apart from one scored a ranking of 2 or lower at water cut values of 50% irrespective of the other conditions. The exception was the X3342-C14 sample which scored a ranking of 3 under condition set 3 in table 7. The other test compounds and the reference compound TTPC scored a ranking of 2 or less under all condition sets in both crude oil and condensate. This is consistent with the behaviour of the test compositions being similar to that of the reference compound and also indicates that a water cut amount of less than 50% may be preferred to obtain the best anti-agglomeration results (although certain compositions may be useable at higher water cut values).

Examples 14-16

Environmental Compatibility

(48) Environmental experiments were performed to test biodegradation and toxicity. The biodegradation tests used the standard OECD Guideline for Testing of Chemicals TG 306 (Biodegradability in Seawater) 28 day method (version adopted 17 Jul. 1992) for testing biodegradation of chemicals in seawater.

(49) Toxicity was tested against Skeletonema costatum and EC.sub.50 values determined (over 72 hours). Results are presented in table 9.

(50) TABLE-US-00010 TABLE 9 Toxicity Biodegradation Example Composition EC.sub.50 after 28 days Reference TTPC 0.016 mg/l 11% example 5 Example 14 X3342-C14 1.9 mg/l 51% Example 15 X3342 2.3 mg/l 61% Example 16 X3622 2.4 mg/l 51%

(51) Examples 14-16 all show both lower toxicity and improved biodegradability when compared with reference example 5 (TTPC). Skeletonema costatum EC.sub.50 in all cases is less than 10 mg/l. The biodegradation data for examples 14-16 is much better than reference example 5; for example 15 the value exceeds 60%.