WO2021061903A1

WO2021061903A1 - Anhydride-based copolymers

Info

Publication number: WO2021061903A1
Application number: PCT/US2020/052383
Authority: WO
Inventors: Larisa Mae Q. REYES; Michael T. PETR; Joseph Manna; Xiangyi Zhang; Shane L. Mangold; Raghunath ROY
Original assignee: Dow Global Technologies LLC; Rohm and Haas Co; Dow Silicones Corp
Current assignee: Dow Global Technologies LLC; Rohm and Haas Co; Dow Silicones Corp
Priority date: 2019-09-27
Filing date: 2020-09-24
Publication date: 2021-04-01
Anticipated expiration: 2022-03-27

Abstract

A grafted poly(a-olefin-maleic anhydride) copolymer for use as a wax inhibitor in crude oils having the following general chemical formulae of Structure (I), where R₁ is a substituent having, for example, from 1 carbon atom to 10 carbon atoms (C1-C10); R₂ is a substituent having, for example, from 22 carbon atoms to 42 carbon atoms (C24-C42); and X is an atom including, for example, oxygen, nitrogen, or sulfur; and a process of wax inhibition of crude oil using the above grafted copolymer.

Description

ANHYDRIDE-BASED COPOLYMERS

FIELD

Embodiments relate to maleic anhydride-based copolymers and a process for producing such copolymers; and to maleic anhydride-based copolymers useful as inhibitors of paraffin wax buildup in crude oil to improve the flow of the crude oil.

INTRODUCTION

Crude oil is a mixture of many hydrocarbons and substituted hydrocarbons including long-chain n-paraffins or waxes, and different crude oils have different proportions of waxes. Depending on the type of crude oil, the proportion of such paraffins may typically be from 1 wt % to 30 wt % of the crude oil. Generally, high melting point portions of the paraffins present in the crude oil mixture stay dissolved in lower melting point portions of the paraffins in the crude oil at high temperatures (e.g. > 40 °C). However, upon cooling to a temperature of, for example, < 25 °C, the high melting point components crystallize to form solid wax or wax networks. Therefore, in the production of crude oil, fouling of pipes and equipment occurs from bringing hot crude oil from an underground well beneath the earth to a much cooler surface above ground because, as crude oil cools upon exiting a well, the paraffins can crystallize, typically in the form of platelets that impede the flow of the crude oil. The precipitated or crystallized paraffins (i.e., solid wax or wax networks) on surfaces of equipment considerably impair the flowability of the crude oil and can block filters, pumps, pipelines and other installations, thus requiring a high frequency of cleaning. The lowest temperature at which a sample of a crude oil still flows in the course of cooling is referred to as the pour point ("yield point"). Certain crude oils have pour points above room temperature, and, as such, may solidify in the course of or after production. It is known that the pour point of crude oils can be lowered by additives pumped into a pipeline or well, such as wax inhibitors and pour point depressants (PPDs). Therefore, commercial wax inhibitors and PPDs are added to the crude oil to slow down crystallization and/or to hinder crystalline adherence to walls or network formation in the crude oil flow as described in Yang et ah, J Disper Sci Technol, 2015, 36, 213.

Because crude oils have a broad range of compositions, there are a number of different types of conventional wax inhibitors for the various crude oil compositions. One class of known wax inhibitors are grafted copolymers. The long grafts on these “bottle brush” type polymers can extend into growing wax crystals; and the long grafts can interfere with crystallization, prevent aggregation; or prevent adherence to walls as described in Jang et ah, J Phys Chem B, 2007, 111, 13173. Grafted copolymers are often synthesized by grafting long alkyl chain alcohols and amines onto anhydride or acid functionalized copolymers, which are themselves synthesized with traditional chain growth processes. Typically, grafted copolymers have a molecular weight of around 10 kg/mol, as disclosed in Kelland, Malcolm A.; Production Chemicals for the Oil and Gas Industry, Second edition ed.; CRC Press: Boca Raton, 2014. Some of the additives typically used as wax inhibitors and PPDs include, for example, ethylene polymers and copolymers thereof with vinyl acetate, acrylonitrile, or a-olefins, such as propylene, butene, octene and the like; comb polymers with alkyl side chains such as methacrylate ester polymers, maleic olefinic ester copolymers, and maleic-olefinic amide copolymers; and branched copolymers having alkyl side chains such as alkylphenol formaldehyde copolymers and polyethyleneimines.

A typical process for producing grafted copolymers is described in, for example,

PCT publications W02018064270A1 and WO2018064272A1; and U.S. Published Patent Application Nos. 2018/0086862A1, and 2018/0086968A1 which disclose paraffin inhibitors, paraffin suppressant compositions and methods for producing such materials.

The above patent applications describe materials where the Ri group of the grafted copolymer is 10 carbon atoms to 30 carbon atoms (C10-C30); and the R2 group of the grafted copolymer is 10 carbon atoms to 50 carbon atoms (C10-C50). U.S. Published Patent Application Nos. 2018/0086862 and 2018/0086968 disclose polymers comprising a- olefins with C10-C50 alkyl chains and esters derived from maleic anhydride (MAH) and functionalized with a C10-C50 alkyl group. Similarly, U.S. Published Patent Application No. 2009/0233817 discloses the use of poly (octadecene-co- MAH) grafted with alkyl amines as wax inhibitors.

U.S. Patent No. 6,174,843 B1 discloses a composition and method for a lubricant wax dispersant and a pour point improver. This patent discloses various materials where the Ri group of the grafted copolymer is 4 carbon atoms to 34 carbon atoms (C4-C34), and the R2 group of the grafted copolymer is 2 carbon atoms to 20 carbon atoms (C2-C20).

Attempts to treat waxy crude oils include synthesizing comb-type copolymers derived from styrene-co-3-maleic anhydride (styrene-co-MAH) copolymer functionalized with an alcohol, that is an R-OH group having 8 carbon atoms to 18 carbon atoms (C8-C18) as disclosed in Journal of Petroleum Science & Eng. 2009, 65, 139-146. The article in Journal of Petroleum Science and Eng. 2009, 65, 139-146 discloses styrene-maleic anhydride copolymers grafted with alcohols having C8-C18 to provide styrene-maleic anhydride copolymer esters as flow improvers for waxy crude oil. Additionally, poly (octadecene-co-MAH) functionalized with an R-OH group having 12 carbon atoms to 22 carbon atoms (C12-C22) has been used as well as disclosed in Journal of Petroleum Science and Eng. 2014, 122, 411-419. This article discloses modified maleic anhydride-co-octadecene copolymers as flow improvers for waxy Egyptian crude oil. The article also describes octadecene-maleic anhydride copolymers grafted with alcohols having 12 carbon atoms to 22 carbon atoms (C12-C22).

SUMMARY

An embodiment is directed to a crude oil wax inhibitor including grafted poly(a- olefin-MAH) copolymers, having the following general chemical formulae of Structure (I):

(A) (B)

Structure (I)

The grafted poly(a-olefin-MAH) copolymers represented by the above Structure (I) typically includes two possible structures (regioisomers) as shown in Structures (IA) and (IB). In Structures (IA) and (IB) above, Ri is a substituent having from 1 carbon atom to 10 carbon atoms (C1-C10) in one embodiment, from 1 carbon atom to 8 carbon atoms (C1-C8) in another embodiment and from 1 carbon atom to 6 carbon atoms (C1-C6) in still another embodiment; R2 is a substituent having from 22 carbon atoms to 42 carbon atoms (C22- C42) in one embodiment; from 24 carbon atoms to 40 carbon atoms (C24-C40) in another embodiment; and from 36 carbon atoms to 38 carbon atoms (C26-C38) in still another embodiment; and X is an atom including, for example, oxygen (O), nitrogen (N), or sulfur (S); and the like.

Another embodiment includes a process for synthesizing a crude oil wax inhibitor, said process comprising reacting a poly(olefin-MAH) having the chemical formula of Structure (II) as follows:

with a molecule having the following chemical formula of Structure (III):

R2-XH Structure (III); wherein Ri is a substituent having from 1 carbon atom to 10 carbon atoms (Cl -CIO) in one embodiment, from 1 carbon atom to 8 carbon atoms (C1-C8) in another embodiment; and from 1 carbon atom to 6 carbon atoms (C1-C6) in still another embodiment; wherein R2 is a substituent having from 22 carbon atoms to 42 carbon atoms (C22-C42) in one embodiment; from 24 carbon atoms to 40 carbon atoms (C24-C40) in another embodiment; and from 26 carbon atoms to 38 carbon atoms (C26-C38) in still another embodiment; and wherein X is O, N or S; and n is a number that provides the above poly(olefin-MAH) with a molecular weight (Mw) of from 10 kg/mol to 100 kg/mol in one embodiment; from 20 kg/mol to 80 kg/mol in another embodiment; from 30 kg/mol to 60 kg/mol in still another embodiment; from 30 kg/mol to 50 kg/mol in yet another embodiment; and from 30 kg/mol to 40 kg/mol in event still another embodiment. In the above process for synthesizing a crude oil wax inhibitor, when R2-XH, such as an alcohol, reacts with poly(olefin-MAH) under the reaction conditions described herein, the final product includes the two regioisomers of chemical Structures (IA) and (IB); and there should be no selectivity for either of the two structures.

Another embodiment includes a process of inhibiting paraffin wax buildup in crude oil; said process includes the step of treating a crude oil with an effective amount of the above wax inhibitor. In the present invention, the alcohols having from 22 carbon atoms to 42 carbon atoms (C22-C42) grafted through maleic anhydride (MAH) chemistry on a polymer backbone produces an effective additive system to treat crude oil for wax inhibition. The polymer resulting from the addition of an alcohol to poly(olefin-MAH) has the necessary hydrocarbon chain length to prevent wax crystallization and aggregation.

Advantageously, the use of the above wax inhibitor provides more effective wax inhibition of waxy crude oils than previously known wax inhibitors.

DETAILED DESCRIPTION

As used throughout this specification, the abbreviations given below have the following meanings, unless the context clearly indicates otherwise: “=” means “equal to”;

@ means “at”; “<” means “less than”; “>” means “greater than”; g = gram(s); mg = milligram(s); kg = kilograms; kg/m³ = kilograms per cubic meter; “kg/mol” = kilograms per mole; g/mol = grams per mole; L = liter(s); mL = milliliter(s); g/L = grams per liter; rpm = revolutions per minute; Mw = weight average molecular weight; “Mn” = number average molecular weight; m = meter(s); pm = micrometers: pL = microliters; mm = millimeter(s);

% = percent; cm = centimeter(s); min = minute(s); s = second(s); hr = hour(s); °C = degree(s) Celsius; vol % = volume percent; mPa.s = millipascals-seconds; kPa = kilopascals; Pa.s/m² = pascals-seconds per meter squared; mg KOH/g = hydroxyl value in terms of milligrams of potassium hydroxide per gram of polyol; cells/mm² is pore density value in terms of the number of cells per millimeter squared; and wt % = weight percent.

All percentages stated herein are weight percentages (wt %), unless otherwise indicated.

Temperatures are in degrees Celsius (°C), and "ambient temperature" means between 20 °C and 25 °C, unless specified otherwise.

"Polymer" generally refers to a polymeric compound or "resin" prepared by polymerizing monomers, whether of the same or different types. As used herein, the generic term "polymer" includes polymeric compounds made from one or more types of monomers.

“Copolymer” means a polymer comprising more than one monomer, in other words a polymer comprising two or more comonomers, three or more comonomers, four or more comonomers, four or more comonomers, etc.

“Pour point depressants” are compositions that reduce the pour point of crude oils, mineral oils and/or mineral oil products. The pour point ("yield point") refers to the lowest temperature at which a sample of an oil, in the course of cooling, still just flows. For the measurement of the pour point, standardized test methods are used, for example ASTM D- 97 “Standard Test Method for Pour Point of Petroleum Products.”

“Graft copolymers” are segmented copolymers comprising (1) a linear backbone polymer, and (2) branches of another polymer.

“Wax inhibitor” herein means an additive that reduces the deposition of wax from crude oil.

In one broad embodiment of the present invention, the wax inhibitor includes grafted poly(a-olefin-MAH) copolymers, having the following general chemical formulae of Structure (I):

Structure (I) where in Structures (IA) and (IB) above, Ri is a substituent having from 1 carbon atom to 10 carbon atoms (C1-C10) in one embodiment, from 1 carbon atom to 8 carbon atoms (Cl-

C8) in another embodiment and from 1 carbon atom to 6 carbon atoms (C1-C6) in another embodiment; R2 is a substituent having from 22 carbon atoms to 42 carbon atoms (C22- C42) in one embodiment; from 24 carbon atoms to 40 carbon atoms (C24-C40) in another embodiment; and from 26 carbon atoms to 38 carbon atoms (C26-C38) in still another embodiment; and X is an atom including, for example, O, N, or S; and the like.

Exemplary of the grafted poly (a-olefin- MAH) copolymers of Structure (I), include for example: poly(l-octene-co-MAH-g-dotriacontane); poly(diisobutylene-co-MAH-g- dotriacontane); poly(styrene-co-MAH-g-dotriacontane); and mixtures thereof. In a preferred embodiment, the grafted poly(a-olefin-MAH) copolymers may include, for example, poly(l-octene-co-MAH-g-dotriacontane).

The inhibitor is at least about 5 % graft copolymer in one embodiment, at least about 10 % graft copolymer in another embodiment, at least about 50 % graft copolymer in still another embodiment, and at least about 90 % graft copolymer in yet another embodiment.

The grafted poly(a-olefin-MAH) copolymers of the present invention have a molecular weight of from 5 kg/mol to 50 kg/mol in one embodiment, and from 10 kg/mol to 30 kg/mol in another embodiment.

The inhibitor of the present invention may consist of the copolymer alone; or in another embodiment, the inhibitor of the present invention may consist of the copolymer in combination with a wide variety of other optional additives. The additives in combination with the wax inhibitors of the present invention may be formulated to enable performance of specific functions while maintaining the excellent benefits/properties of the present wax inhibitors. For example, the following additives may be blended with the wax inhibitor to form a formulation including: dewaxing auxiliaries, corrosion inhibitors, asphaltene inhibitors, scale inhibitors, antioxidants, lubricity additives, dehazers, conductivity improvers, cetane number improvers, sludge inhibitors, surfactants, dispersants, flow improvers, and the like; and mixtures thereof.

The optional additive, when used in combination with the grafted poly(a-olefin- MAH) copolymers, can be present in an amount generally in the range of from 0 wt % to about 99 wt % in one embodiment; from about 0 wt % to about 50 wt % in another embodiment; and from about 0 wt % to about 25 wt % in still another embodiment.

The polymerization of the poly(a-olefin-MAH) can be carried out by free radical solution polymerization of the a-olefin and MAH in an appropriate organic solvent using conventional processes and equipment.

The grafting of another molecule, such as an alcohol, can be carried out by a ring opening reaction of MAH, to afford a grafted poly(a-olefin-MAH) copolymer. In one preferred embodiment, the grafted polymer, effective for wax inhibition when used in crude oil production, is synthesized according to the following reaction Scheme (I):

For example, in a broad embodiment of the process of synthesizing a crude oil wax inhibitor, such as a grafted poly(a-olefin-MAH) copolymer includes, for example, the general step of reacting:

(A) a poly(olefin-MAH) having the chemical formula:

Structure (II); and

(B) a molecule having the chemical formula:

R2-XH Structure (III).

In the formula of Structure (II), component (A) above, Ri is a substituent having from 1 carbon atom to 10 carbon atoms (C1-C10); and n is a number that provides the above poly(olefin-MAH) with a Mw of from 10 kg/mol to 100 kg/mol in one embodiment; from 20 kg/mol to 80 kg/mol in another embodiment; from 30 kg/mol to 60 kg/mol in still another embodiment; from 30 kg/mol to 50 kg/mol in yet another embodiment; and from 30 kg/mol to 40 kg/mol in event still another embodiment.

In the formula of Structure (III), component (B) above, R2 is an alcohol, amine, thiol or mixtures thereof wherein R2 includes a substituent having from 26 carbon atoms to 38 carbon atoms (C26-C38); and X is an atom selected from the group consisting of O, N or S (i.e., an alcohol, amine, or thiol having the chemical formula R2-X, wherein X is O, N or S).

In a preferred embodiment, the above synthesis process which includes the step of

(I) reacting a poly(olefin-MAH) with an alcohol further includes, for example, the steps of:

(II) optionally, drying said poly(a-olefin-MAH) to a temperature of 160 °C in a vacuum oven for a time of from 12 hours to 48 hours;

(III) heating said poly(a-olefin-MAH) and said alcohol at 150 °C, in the presence or absence of a solvent; and in the presence of a catalyst to form a grafted polymer; wherein said catalyst is selected from the group consisting of p-toluene sulfonic acid; 4- dimethylaminopyridine; l,8-diazabicyclo(5.4.0)undec-7-ene; urea, and 1,5,7- triazabicyclo[4.4.0]-dec-5-ene;

(IV) holding said polymer at 100 °C to 200 °C for 4 hours to 48 hours;

(V) diluting said polymer with a solution selected from the group consisting of aromatic-150, toluene, and xylenes;

(VI) isolating said polymer in alcohol; and

(VII) drying said polymer in a vacuum.

More specifically, the poly(a-olefin-MAH) is heated to a temperature of 160 °C in a vacuum oven for 12 hours to 48 hours in one embodiment, and 24 hours in another embodiment. The above heating is carried out to remove water and drive any acid functionality back to the anhydride. Poly(a-olefin-MAH) and the long chain alcohol (between C22-C42) are then heated to melt at 150 °C in the presence of a catalyst. For example, the catalyst useful in the present invention can include, but is not limited to: (i) strong acids such as p-toluene sulfonic acid (PTSA); (ii) strong bases such as 4- dimethylaminopyridine (DMAP or pyridine DMAP), l,8-diazabicyclo-(5.4.0)undec-7-ene (DBU or amidine DBU), and l,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD or guanidine TBD); and (iii) hydrogen bonding donors such as urea; and (iv) mixtures thereof. Poly(octene-alt- MAH) and the long chain alcohol are then held at 100 °C to 200 °C in one embodiment and at 140 °C in another embodiment, for 4 hours to 48 hours in one embodiment, and for 20 hours in another embodiment, during which the long chain alcohol reacts with the poly(octene-alt-MAH) and grafts onto the polymer. The graft polymer is then diluted with a solution. For example, the solution can include, but is not limited to, Aromatic- 150 solvent (heavy aromatic solvent naphtha), toluene, xylenes, and mixtures thereof. The polymer graft is isolated by precipitation in alcohol, further washed with alcohol, and dried under vacuum to yield the final grafted poly(a-olefin-MAH) copolymer product. The purification alcohol can include, but is not limited to, for example, methanol.

If desired, other optional step(s) can be used to make the wax inhibitor. For example, one optional step useful in the present invention process includes heating the a- olefin MAH solution to promote polymerization and also precipitation of the final wax inhibitor into methanol. The grafting step of the process can also be performed in a solvent such as toluene or Aromatic 150.

One of the advantageous/beneficial properties exhibited by the polymer wax inhibitor produced according to the above-described process can include, for example, the present invention wax inhibitor exhibits a high grafting content (or grafting density) than known paraffin inhibitors. The grafting efficiency, i.e., the grafting level of the polymer, affects the wax inhibition efficiency of a polymer wax inhibitor. Typically, high grafting levels (i.e., a high grafting efficiency) indicate that the high grafting content could enable better perturbation of the wax crystal and give a high inhibition efficiency. For instance, in the Examples discussed herein below, Inventive Examples 1 and 2 that showed relatively high grafting efficiency of 60 % and 100 %, respectively, yielded the highest wax inhibition efficiency. As an illustration and not to be bound thereby, the grafting level, as determined by NMR spectroscopy, of various wax inhibitors of the present invention include, for example: (1) a grafting level of from 50 % to 70 % when R1 in Structure (I) is C16 (octadecene); (2) a grafting level of from 30 % to 70 % when R1 in Structure (I) is C6 (styrene); (3) a grafting level of from 30 % to 50 % when R1 in Structure (I) is C6 (diisobutylene); and (4) a grafting level of from 80 % to 100 % when R1 in Structure (I) is C6 (octene).

The higher inhibition efficiency of the wax inhibitors of the present invention can be compared to conventional wax inhibitors such as the olefin/maleic anhydride (OMAC) polymer wax inhibitors described in U.S. Patent Application Publication No.

US2018/0086862.

For example, the molecular weight (Mw) of the grafted poly(a-olefin-MAH) copolymers is generally from 1 kg/mol to 100 kg/mol in one embodiment; from 10 kg/mol to 50 kg/mol in another embodiment; and from 15 kg/mol to 35 kg/mol in still another embodiment. If a grafted poly(a-olefin-MAH) copolymer with a Mw of greater than 1 Mg/mol or less than 1 kg/mol is used, less wax inhibition will occur. The Mw of the grafted poly(a-olefin-MAH) copolymer is measured by gel permeation chromatography.

The grafted poly(a-olefin-MAH) copolymers also have a graft content of at least 5 % graft copolymer in one general embodiment; at least 10 % graft copolymer in another embodiment; at least 50 % graft copolymer in still another embodiment; and at least 90 % graft copolymer in yet another embodiment. In other embodiments, the graft polymer content of the inhibitor is from 5 % to 100 % graft copolymer in one general embodiment; from 10 % to 100 % graft copolymer in another embodiment; from 50 % to 100 % graft copolymer in still another embodiment; and from 90 % to 100 % graft copolymer in yet another embodiment. The greater graft polymer content of the grafted poly(a-olefin-MAH) copolymer is beneficial because greater grafting efficiency means greater incorporation of the long alkyl chain in to the wax inhibitor polymer which means the polymer has better compatibility with the wax. Better compatibility increases the chance of incorporation and perturbation of wax.

The graft content of the grafted poly(a-olefin-MAH) copolymer is measured by NMR spectroscopy based on the signal of the -CH2- adjacent to the alcohol chain end.

This -CH2- in the alcohol appears as a triplet at 3.66 ppm, which shifts to 4.12 ppm and becomes broad upon grafting onto MAH copolymers. The integral ratio of the two peaks resulting from the NMR spectroscopy is used to determine the grafting efficiency.

Another advantageous property exhibited by the wax inhibitor of the present invention is significantly higher wax inhibition, where the prior art has little to none. For example, the wax inhibitor provides inhibition of from 10 % to 100 % in one embodiment; from 20 % to 100 % in another embodiment; and from 40 % to 100 % in still another embodiment. The greater inhibition of the grafted poly(a-olefin-MAH) copolymer is beneficial because a greater inhibition property shows the effectiveness of the polymers to inhibit the formation of wax; and therefore, the build-up or deposition of wax on pipelines and other crude oil production is avoided. Build-up or deposition of wax is detrimental to the flow of crude oil in the production process of crude oil. The greater wax inhibition exhibited by the grafted poly(a-olefin-maleic anhydride) copolymer is measured by the testing technique referred to as a “cold finger” method described in the Examples present herein below in % inhibition units. In the Examples, the measured % inhibition of a crude oil sample containing a wax inhibitor (i.e., the grafted poly (a-olefin- maleic anhydride) copolymer of the present invention) is compared to the measured % inhibition of a crude oil sample without any wax inhibitor. The grafted poly(a-olefin-maleic anhydride) copolymer of the present invention is used as a wax inhibition additive and a pour point depressant additive. As aforementioned, the wax inhibitor of the present invention is particularly useful, for example, in the field of crude oil production to provide wax inhibition for the crude oil when being extracted from underneath the ground to the surface of the earth or as the crude oil is being transported in pipelines.

The grafted poly(a-olefin-maleic anhydride) copolymer of the present invention is particularly useful for readily treating waxy crude oils that are known to be difficult to prevent wax deposition. In one embodiment, an effective amount of the graft copolymer is added to the crude oil. An “effective amount" is that amount of the graft copolymer necessary to inhibit wax precipitation. "Inhibit" means to retard the precipitation of wax to prolong the period of maximal efficiency of equipment. The effective amount of graft copolymer added to the crude oil may vary depending upon the temperature of the crude oil along with the concentration of contaminants in the crude oil, as well as field conditions. In most applications, the effective amount of graft copolymer ranges from 5 ppm to 10,000 ppm in one embodiment, from 10 ppm to 7,500 ppm in another embodiment, and from 25 ppm to 5,000 ppm in still another embodiment.

Another advantageous/beneficial property exhibited by the polymer wax inhibitor of the present invention can include, for example, the present invention wax inhibitor exhibits enhanced

asphaltene inhibition” and enhanced

solids inhibition”. For example, the asphaltene inhibition” of the present invention polymer wax inhibitor is generally from 10 % to 100 % in one embodiment, from 10 % to 50 % in another embodiment, and from 10 % to 30 % in still another embodiment. The

solids inhibition” of the present invention polymer wax inhibitor is generally from 10 % to 100 % in one embodiment, from 10 % to 50 % in another embodiment, and from 10 % to 30 % in still another embodiment. If the % asphaltene and/or % solids inhibition is below 10 % more frequent cleaning of the wax buildup in the process equipment will be required. In some instances, mechanical cleaning of equipment such as pipes may be needed which would include higher costs, greater risk to facilities, more downtime in production, and other economic losses; or in a worse case instance, the entire pipes may need to be changed.

The Examples which follow herein below provide a method for determining the

asphaltene fraction” and

solids content” of the polymer wax inhibitor of the present invention. The properties of

asphaltene inhibition” and

solids inhibition” of the present invention polymer wax inhibitor are measured after the polymer wax inhibitor is subjected to a cold finger experiment, described in the Examples herein below. For example, after conducting the cold finger experiment, the deposits on the cold finger are analyzed for insoluble solids and asphaltene content. In general, the process of determining insoluble solids and asphaltene content includes the steps of: (i) scraping off the deposits formed on the cold finger; (ii) initially washing the deposits scraped off the cold finger with hexanes (pentanes can also be used) to remove n-alkane soluble fractions/entrapped crude oil; (iii) weighing the remaining deposit that did not dissolve, after the initial washing step (ii), to obtain a first weight (Wl); (iv) further washing the deposit W1 with xylene to dissolve the asphaltene fraction from the W 1 ; and (v) weighing the remaining deposit, after the washing step (iv), to obtain a second weight (W2). The first weight Wl includes insoluble solids plus asphaltene fraction. The second weight W2 includes the insoluble solids. The asphaltene fraction is determined by the following formula:

W2 - Wl = asphaltene fraction.

Asphaltenes are large highly polar components made up of condensed aromatic and naphthenic rings, which also contain heteroatoms. In one case, asphaltenes may precipitate and can lead to an increase in viscosity of the crude oil; and in another case, asphaltenes can deposit on surfaces which can lead to choking of valves, lines and tubing. In both cases, the presence of asphaltenes can negatively impact oil production.

Insoluble solids are sediments or suspended solids that are not part of the crude oil itself. However, such insoluble solids follow the crude oil from the reservoir. Knowledge about the insoluble solids is important to be able to treat the crude oil and avoid problems in downstream operations such as refining and processing.

The treatment of the crude oil with the inhibitor of the present invention can be carried out using various methods. For example, in one embodiment, the inhibitor of the present invention can be added to an oil pipeline by batch or continuous injection or squeezing, upstream or downstream of the location of any potential cold area likely to result in deposition of wax, gelation, thickening, sludging, and the like. In another embodiment, the copolymer composition can be added at the cold area (reservoir, tank, container, and the like) to decrease the pour point of the oil.

In a preferred embodiment, the injection of the inhibitor into the crude oil can be affected at the oilfield, i.e., at the start of the crude oil pipeline. In another embodiment, the injection can also be affected at another site. More particularly, the pipeline may be one leading onshore from an offshore platform. The cooling of crude oil in underwater pipelines leading onshore from an offshore platform is naturally particularly rapid, especially when the pipelines are in cold water, for example, wherein the temperature of the water is less than 10 °C.

In another embodiment of the present invention, the oil is crude oil and the inhibitor is injected into a production well where oil is flowing from an underground formation into the production well. Here too, the production well may be a production well leading to an offshore platform. In a preferred embodiment, the injection of the inhibitor is affected approximately at the site where oil from the formation flows into the production well. In this way, the solidification of the crude oil in the production well or an excessive increase in the crude oil’s viscosity can be prevented.

The use, application and benefits of the present invention will be clarified by the following discussion and description of exemplary embodiments of the present invention.

EXAMPLES

The following examples are presented to further illustrate the present invention in detail but are not to be construed as limiting the scope of the claims. Unless otherwise stated all parts and percentages are by weight.

Various materials used in the examples are explained as follows:

“Aromatic- 150” is a commercially available aromatic mixture with a boiling point around 180 °C.

Various terms and designations used in the examples are explained herein below.

“MAH” stands for maleic anhydride.

“M„” stands for number average molecular weight.

“Mw” stands for weight average molecular weight.

“N2” stands for nitrogen gas.

“C32” stands for a carbon chain with a number average of around 32 carbons. Examples 1 - 3 and Comparative Examples A and B

For this Inventive Example 1, 40.2 g of a solution of 11.3 wt % MAH and 12.3 wt % styrene in toluene was fed over 2 hr to 4.2 g of a 9.1 wt % solution of 2,2'-azido(2- methylbutyronitrile) in toluene at

60 °C, and the resulting solution was then held at 60 °C for 30 min. Next, the toluene from 20 g of solution was removed by rotary evaporation at 50 °C to give 4.6 g solid product. To this product were added 10.3 g of the C32 alcohol (polyethylene monoalcohol M_n -460), 45 mg para-toluene sulfonic acid, and 15 mL toluene. The mixture was heated to 100 °C under nitrogen (N2) for 4 hr, and then 3 mL anhydrous dimethyl formamide was added. The temperature was maintained at 100 °C for another 64 hr before the mixture was cooled to 85 °C, at which point 5 mL toluene was added and the whole solution was precipitated into methanol. Finally, the recovered solid was dried in a vacuum oven at 55 °C for 24 hr.

For Inventive Examples 2 and 3 and Comparative Examples A and B, to 49.6 g of a solution of either 21.5 wt % MAH and 29.7 wt % octene or 18.2 wt % MAH and 33.0 wt % diisobutylene (see Table I) in aromatic-150 was fed 1.0 g of a solution of 23.3 wt % tert- butyl peroxy-2-ethylhexanoate at 100 °C and 170 kPa (10 psig) over 1.5 hr followed by another 1.0 g of the same solution over 15 min. The resulting solution was then heated to 134 °C for 30 min before cooling to room temperature. Next, the aromatic- 150 was removed by rotary evaporation at 50 °C, and to 6 g of this solid product were added either 7 g stearyl alcohol, 11 g of the C32 alcohol (polyethylene monoalcohol M_n -460), or 18 g of the C50 alcohol (polyethylene monoalcohol M_n -700); 49 mg para-toluene sulfonic acid; and 15 mL aromatic- 150. The mixture was heated to 135 °C, cooled to 100 °C, and then maintained at 100 °C for 64 hr under N2 before the mixture was cooled to 85 °C, at which point 5 mL toluene was added and the whole solution was precipitated into methanol. The recovered solid was then dried in a vacuum oven at 55 °C for 24 hr.

For all Examples, the weight average molecular weight of the backbone was measured by gel permeation chromatography (GPC) on an Agilent 1100 Series High Pressure Liquid Chromatograph (HPLC) with two 20pm MIXED-A columns using tetrahydrofuran as the mobile phase and diluent at lmL/min and room temperature. The weight average molecular weight of the final grafted copolymer was measured by gel permeation chromatography on a PolymerChar GPC-IR maintained at 160 °C. The sample was eluted through a PLgel 20 pm 50 mm x 7.5 mm guard column and four PLgel 20 pm Mixed A LS 300 mm x 7.5 mm columns with 1,2,4-trichlorobenzene (TCB) stabilized by 300 ppm of butylated hydroxyl toluene (BHT) at a flowrate of 1 mL/min. Approximately 16 mg of the polymer sample was weighed out and diluted with 8 mL TCB by the instrument. For molecular weight, a conventional calibration of polystyrene (PS) standards (Agilent PS-1 and PS -2) was used with apparent units adjusted to homo-polyethylene (PE) using known Mark-Houwink coefficients for PS and PE in TCB at this temperature.

Decane was used as an internal flow marker, and retention time was adjusted to this peak.

A South Asia Crude Oil (SACO) was used in the Examples for evaluation. Before evaluation of Examples, the composition of SACO was determined via a common analysis technique known as “saturates, aromatics, resins, and asphaltenes” (“SARA”) analysis and the SARA analysis of the crude oil is set forth in Table I. Table I

Table I notes: *“LC” stands for “liquid chromatography”.

Cold Finger Test

A cold finger apparatus was used to evaluate the effectiveness of the novel grafted poly(a-olefin-maleic anhydride) copolymers of the present invention as wax inhibitors for SACO. The SACO was placed in a glass jar that was immersed in a silicone bath at 60 °C, which was above the wax appearance temperature of SACO. A cold finger was then immersed in the jar such that approximately one-third of the cold finger was submerged in the oil. The temperature of the finger was maintained at 40 °C, and the cold finger apparatus was stirred at 200 rpm for 18 hr, such that sufficient wax would deposit on the finger. The wax was then removed and weighed.

The above cold finger analysis was then repeated with SACO combined with 38 pL of the wax inhibitor samples described in the Examples as 50 wt % solutions in aromatic- 150 at 60 °C. Using a pipette, the inhibitor was added into the jar with the crude oil. A stir bar was placed in the jar to mix the crude oil and inhibitor (200 rpm). The cold finger test was subsequently ran for 18 hr in an effort to deposit wax on the finger. After the cold finger test was complete, the wax containing the inhibitor was removed and weighed. A percent inhibition (“% inhibition” of wax) was then calculated according to the following formula:

Weight of wax without additive — Weight of wax with additive

% Inhibition = Weight of wax without additive x 100 %

The wax inhibitors described in the Examples having the following general chemical formulae of Structure (I). The results of wax inhibition for the various wax inhibitor samples described in Table II clearly show that R2 carbon lengths of 32 make effective wax inhibitors, and other R2 lengths do not.

(A) (B)

Structure (I) Structures (IA) and (IB) are generally alternating backbone structures of the wax inhibitors useful in the present invention.

Table II - Wax Inhibition Results

Table II notes: denotes styrene; and “+” denotes diisobutylene.

Pour Point Depressant Test To measure the pour point of sample, an analyzer named Scientifique de Laboratoire

MPP 5Gs Pour Point Analyzer was used. The crude oil was first heated to 50 °C in a water bath and shaken well. Then the sample was prepared for testing by placing 1 pL of the wax inhibitor into a vial followed by 0.5 mL of crude oil. The vial containing the wax inhibitor and crude oil was closed with a stopper and placed in the hot water bath at 50 °C to digest for one hour. The solution in the sample vial was shaken well before and after digesting. Once digested, the stopper was removed and replaced with a top insert. The vial was then positioned in the pour point analyzer for measurement. The above method for measuring the pour point was patterned after ASTM D5853 (Standard Test Method for Pour Point of Crude Oils). The results of the above test method are described in Table III. Table III

The Inventive Examples 1-3 in Table III show an effectiveness as pour point depressants. This means the chemistries disrupt the formation of networks of paraffin crystals which traps crude oil and prevents the crude oil from flowing freely. Percent Asphaltene/Percent Solids Measurements

After the cold finger experiment described above, the deposits on the cold finger were further analyzed for insoluble solids and asphaltene content. The deposit was scraped off the cold finger and initially washed with hexanes to remove n-alkane soluble fractions/entrapped crude oil. The remaining deposit that did not dissolve was then weighed (Wl). W1 includes insoluble solids plus asphaltene fraction. W1 was then further washed with xylene to dissolve the asphaltene fraction. The remaining deposit is the insoluble solids (W2). The asphaltene fraction is determined by the formula: W2-Wl=asphaltene fraction.

Table IV describes the results of measuring the amount of asphaltene and insoluble solids for Comparative Example C and Inventive Example 2. The results surprisingly show that when no inhibitor is added to the cold finger experiment (Comp. Ex. C), the amount of asphaltene and insoluble solids was found to be 0.128 g which translates to 38 % inhibition. However, when an inhibitor is added to the cold finger experiment (Inv. Ex. 2), the amount of asphaltene and insoluble solids decreased substantially with only 0.036 g in the deposit which translates to 51 % inhibition, a significant improvement. This means that, aside from inhibiting the formation of waxes, the wax inhibitor of the present invention also inhibits the deposition of solids and asphaltenes on surfaces. Table IV

OTHER EMBODIMENTS

As aforementioned, in one embodiment the wax inhibitor added to the crude oil includes a polymer having the formula of Structure (IV):

Where in Structure (IV) above, X is an atom including, for example, O, N, or S; and the like. In the above chemical structure, n is a number that provides the above poly(olefin- MAH) with a Mw of from 10 kg/mol to 100 kg/mol in one embodiment; from 20 kg/mol to 80 kg/mol in another embodiment; from 30 kg/mol to 60 kg/mol in still another embodiment; from 30 kg/mol to 50 kg/mol in yet another embodiment; and from 30 kg/mol to 40 kg/mol in event still another embodiment. In the above chemical Structure (IV), Ri is a substituent having from 1 carbon atom to 10 carbon atoms (C1-C10), a substituent having from 1 carbon atom to 8 carbon atoms (C1-C8), a substituent having from 1 carbon atom to 6 carbon atoms (C1-C6), a linear alkyl chain of 6 carbon atoms (C6), or neopentyl. In the above chemical Structure (IV), R2 is a substituent having from 22 carbon atoms to 42 carbon atoms (C22-C42), a substituent having from 24 carbon atoms to 40 carbon atoms (C24-C40), a substituent having from 26 carbon atoms to 38 carbon atoms (C26-C38), a substituent having from 30 carbon atoms to 34 carbon atoms (C30-34), or a hydrocarbon chain of 32 carbon atoms (C32). In the above chemical Structure (IV), R3 is R2, H, or mixtures thereof. In another embodiment, the wax inhibitor of present invention is at least 5 weight percent of the polymer of the above chemical Structure (IV), at least 10 % of the polymer, at least 50 % of the polymer, or at least 90 % of the polymer.

In still another embodiment, the wax inhibitor of the present invention has a molecular weight of between 1 kg/mol and 1,000 kg/mol, a molecular weight of between 10 kg/mol to 50 kg/mol, or a molecular weight of between 15 kg/mol to 35 kg/mol.

In yet another embodiment, the present invention includes a method of synthesizing a crude oil wax inhibitor, and the method includes reacting a poly(olefin-MAH) having the following chemical formula of Structure (II):

Structure (II) with a molecule having the chemical formula of Structure (III):

R2-XH Structure (III).

In the above chemical Structure (III), X is an atom selected from the group consisting of O, N, or S; and the like. In the above chemical Structure, n is a number that provides the above poly(olefin-MAH) with a Mw of from 10 kg/mol to 100 kg/mol in one embodiment; from 20 kg/mol to 80 kg/mol in another embodiment; from 30 kg/mol to 60 kg/mol in still another embodiment; from 30 kg/mol to 50 kg/mol in yet another embodiment; and from 30 kg/mol to 40 kg/mol in event still another embodiment. In the above chemical Structure (II), Ri is a substituent having from 1 carbon atom to 10 carbon atoms (C1-C10), a substituent having from 1 carbon atom to 8 carbon atoms (C1-C8), a substituent having from 1 carbon atom to 6 carbon atoms (C1-C6), a linear alkyl chain of 6 carbon atoms (C6), or neopentyl. In the above chemical Structure (III), R2 is a substituent having from 22 carbon atoms to 42 carbon atoms (C22-C42), a substituent having from 24 carbon atoms to 40 carbon atoms (C24-C40), a substituent having from 26 carbon atoms to 38 carbon atoms (C26-C38), a substituent having from 30 carbon atoms to 34 carbon atoms (C30-34), or a hydrocarbon chain of 32 carbon atoms (C32). The poly(olefin-MAH) of the above chemical Structure (II) has a molecular weight of from 30 kg/mol to 50 kg/mol in one embodiment, and the alcohol has a molecular weight of between 200 g/mol to 800 g/mol in one embodiment and a molecular weight of between 350 g/mol to 750 g/mol in another embodiment. The effective amount of the above inhibitor produced is between 50 ppm to 10,000 ppm in one embodiment. In a preferred embodiment, the present invention includes a process of inhibiting paraffin wax buildup in crude oil, comprising treating a crude oil with an effective amount of a crude oil wax inhibitor comprising a grafted poly(a-olefin-MAH) copolymer having the following general chemical formulae of Structure (I):

Structure (I) where in Structures (IA) and (IB) above, Ri is a substituent having from 1 carbon atom to 10 carbon atoms; R2 is a substituent having from 22 carbon atoms to 42 carbon atoms; and X is an atom including, for example, oxygen, nitrogen, or sulfur.

In another embodiment, the above treatment process includes treating a system comprising crude oil and the system is selected from the group consisting of an above ground oil pipeline, an underwater oil pipeline, an offshore platform, and a production well.

In still another embodiment, the above treatment process includes using the inhibitor in an effective amount of between about 50 ppm to about 10,000 ppm.

In still another embodiment, the above treatment process is carried out at a temperature of from about -40 °C to about 60 °C.

Claims

WHAT IS CLAIMED IS:

1. A crude oil wax inhibitor comprising a grafted poly(a-olefin- maleic anhydride) copolymer having the following general chemical formulae of Structure (I):

Structure (I) where in Structures (IA) and (IB) above, Ri is a substituent having from 1 carbon atom to 10 carbon atoms; R2 is a substituent having from 22 carbon atoms to 42 carbon atoms; and X is an atom selected from the group consisting of oxygen, nitrogen, and sulfur.

2. The inhibitor of claim 1, wherein Ri is a substituent having from 1 carbon atom to 8 carbon atoms; and R2 is a substituent having from 24 carbon atoms to 40 carbon atoms.

3. The inhibitor of claim 1, wherein Ri is a substituent having from 1 carbon atom to 6 carbon atoms; and R2 is a substituent having from 26 carbon atoms to 38 carbon atoms.

4. The inhibitor of claim 1, wherein Ri is selected from the group consisting of: phenyl, neopentyl, and a linear Ce alkyl chain.

5. The inhibitor of claim 1, wherein the inhibitor is at least 5 weight percent of said copolymer.

6. The inhibitor of claim 1 , wherein the inhibitor has a weight average molecular weight of from 10 kg/mol to 100 kg/mol.

7. The inhibitor of claim 1, wherein said inhibitor further comprises an additive selected from the group consisting of dewaxing auxiliaries, corrosion inhibitors, asphaltene inhibitors, scale inhibitors, antioxidants, lubricity additives, dehazers, conductivity improvers, cetane number improvers, sludge inhibitors, and mixtures thereof.

8. A process for synthesizing the crude oil wax inhibitor of claim 1, said process comprising:

(I) reacting:

(a) a poly(olefin-maleic anhydride) having the following chemical formula of Structure (II):

Structure (II); wherein Ri is the substituent having from 1 carbon atom to 10 carbon atoms; and wherein n is a number that provides the above poly(olefin-maleic anhydride) with a molecular weight (Mw) of from 10 kg/mol to 100 kg/mol; and

(b) an alcohol, amine, thiol or mixture thereof having the following chemical formula of Structure (III):

R₂-XH Structure (III); wherein R₂ is the substituent having from 22 carbon atoms to 42 carbon atoms; and X is the atom selected from the group consisting of oxygen, nitrogen, and sulfur.

9. The process of claim 8, wherein the process further comprises the steps of: (II) optionally, drying said poly(a-olefin-maleic anhydride) to a temperature of

160 °C in a vacuum oven for 12 hours to 48 hours;

(III) heating the poly(olefin-maleic anhydride) and the alcohol at 150 °C, in the presence or absence of a solvent; and in the presence of a catalyst to form a polymer; wherein the catalyst is selected from the group consisting of (i) a strong acid; (ii) a strong base; and (iii) a hydrogen bonding donor

(IV) holding the polymer at 100 °C to 200 °C for 4 hours to 48 hours;

(V) diluting the polymer with a solution selected from the group consisting of aromatic- 150, toluene, and xylene;

(VI) isolating the polymer in alcohol; and (VII) drying the polymer in a vacuum.

10. A process of inhibiting paraffin wax buildup in crude oil, said process comprising treating a crude oil with an effective amount of the crude oil wax inhibitor of claim 1.