Acrylic copolymers as additives for inhibiting paraffin...

Details Acrylic copolymers as additives for inhibiting paraffin... Acrylic copolymers as additives for inhibiting paraffin...

2002-12-19

2004-06-15

Pezzuto, Helen L. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S319000, C526S328500, C524S555000, C524S560000

Reexamination Certificate

active

06750305

ABSTRACT:

FIELD OF THE INVENTION
The invention pertains to crude oil and additives intended to improve exploitation conditions.
Crude oil can contain large fractions of waxes, the exact nature and quantity of which vary from oilfield to oilfield. At the temperature of the well, the waxes are liquid and dissolved in the crude oil. As the oil rises to the surface, its temperature drops and the waxes crystallise to form a three-dimensional network of needles and flakes. This results in a loss of fluidity and renders production, transport, storage and even treatment of such oil very difficult. Pipeline and unit blockages are frequent.
PRIOR ART
A number of processes have been proposed to overcome the problem, such as mechanical scraping or heating the walls. Such processes are expensive and they cannot always be carried out.
SHELL has pioneered improving the rheology of crude oil: its French patent FR-A-1 575 984 discloses macromolecular “comb” type compounds constructed on a model of a principal hydrocarbon chain onto which are grafted side chains, themselves fairly long hydrocarbons, i.e., at least 14 carbon atoms and at most 30 carbon atoms, to perturb crystallisation of the heavy waxes. That property is well developed in macromolecules with a mass average molecular mass Mn (the definition of which, of course, is: Mn=&Sgr;
i
NiMi/&Sgr;
i
Ni, where Mi is the molecular mass of individual species Ni present in the polymer) in the range 1000 to 1000000, preferably in the range 4000 to 100000.
The prior art then suggested the use of additives, usually polymeric additives the role of which was to retard or modify wax crystallisation and thus to improve the flow properties of the oil and prevent agglomeration of the crystals formed on the walls.
A number of studies then attempted to improve the efficiency of these first polymeric additives either by synthesis or by formulation, to adapt them to the different types of crude oils encountered, and to successively overcome the difficulties with synthesis and/or manipulation of the different generations of products, the most efficient examples of which are copolymers of C
18
-C
30
acrylates, preferably mainly C
20
-C
22
, with a heterocyclic monomer, in particular vinylpyridine (U.S. Pat. No. 2,839,512 (1958) and FR-B-2 128 589 (1972) from SHELL).
It was shown that the presence of polar moieties endowed the copolymer with a dispersing nature, which prevented deposition of the waxes on the walls. Because of the higher reactivity of long chain acrylates compared with that of polar co-monomers, incorporating the latter is generally very difficult and the dispersing effect, linked to the degree of incorporation of the polar co-monomer, thus usually remained very low.
Despite such successive improvements, prior art additives could not be universally applied to crude oil as each type is a special case with its own problems.
International patent application WO-A-97/34940 proposed particularly high performance wax inhibitors of an alkyl (meth)acrylate copolymer type or alkyl (meth)acrylate and vinyl pyridine (2-vinylpyridine and/or 4-vinylpyridine) copolymer type, but manipulating the vinylpyridines, which are particularly toxic, during their preparation constituted a hurdle to their industrial development despite excellent inhibiting properties.
DISCLOSURE OF THE INVENTION
It has just, unexpectedly, been discovered that alkyl (meth)acrylate copolymer type wax inhibitors perform as well as the wax inhibitors described in WO-A-97/34940 and have the added advantage of not containing any residual reactant in their final composition with associated dangers of high toxicity; these wax inhibitors are copolymers of alkyl acrylates and/or methacrylates and N-vinylpyrrolidone, wherein a portion of the alkyl acrylates and/or methacrylates monomers participating in the polymeric chain can be represented by the formula:
where R is H or CH
3
, Ri represents residues of saturated linear aliphatic alcohols Ri—OH, wherein the number of carbon atoms is from about 10 to about 50 and originates from an acrylic cut with a particular distribution of alkyl chains, denoted a “U” distribution for the purposes of the present patent. The term “U distribution” means that the distribution of alkyl chains as a function of the chain length, in this case all with an even number of carbon atoms, wherein the envelope is very regular, wherein the mass average molecular weight Mw is in the range 375 to 700, wherein the number average molecular weight Mn is in the range 375 to 840, and wherein the polydispersity factor Pd=Mw/Mn is in the range 1.0 to 1.2 (Mw is the mass average molecular weight the formula for the calculation of which is Mw=&Sgr;
i
NiMi
2
/&Sgr;
i
NiMi, where Mi is the molecular mass and Ni the individual species present in the polymer).
FIG. 1
shows the distribution of alkyls distributed in accordance with such a “U” distribution law with a mean molecular mass of 425 (to produce the corresponding alcohols, see U.S. Pat. No. 4,426,329). The polymeric acrylates or methacrylates obtained by a single polymerisation of monomers with a “U” distribution are not particularly distinguished from those obtained from arbitrary monomers, meaning the products normally available to the skilled person and in which no particular distribution for the pendent chain length is sought; in other words wherein the distribution is of any type, in any case not a “U” distribution. Surprisingly, and from this the Applicant draws all advantageous consequences, a powerful synergy is developed as regards inhibition of the crystallisation of waxes in crude oil when products of the “U” class and of the “non U” class are distributed in the same (meth)acrylate/N-vinylpyrrolidone copolymer. Like any synergy in mixtures which may be highly variable in composition, the rules are difficult to discern, but the directing principles can be stated and are of great importance to the skilled person: the “U” components are centred on average lengths of the pendent chains i
u
that are longer than those i
ni
of the “non U” components and the mass in the copolymer of the ensemble of moieties with “U” chains is relatively low compared with that of the ensemble of “non U” moieties. The copolymers of the invention contain 1% to 10% of N-vinylpyrrolidone.
It should be noted that in the copolymers of the invention, the N-vinylpyrrolidone can be at least partially replaced by other vinyllactames, such as vinylbutyrolactame or vinylcaprolactame.
Regarding a structural description, it can be said that the invention is constituted by alkyl (meth)acrylate/N-vinylpyrrolidone copolymers with a mass average molecular weight Mw in the range 5000 to 500000, preferably in the range 40000 to 350000, wherein the acrylate or methacrylate monomer moieties that participate in the polymer chain are moieties representable by the formula:
where R is H or CH
3
, Ri are residues of saturated linear aliphatic alcohols Ri—OH where i represents the number of carbon atoms of said residues and is in the range 10 to 50 and follow a distribution law that is the superimposition of a “U” distribution law, where numbers i are even numbers developed over the high 24-50 portion of the interval, wherein the centred value is i
u
, and a “non-U” distribution law where i are even or odd numbers developed over the low portion 10-22 of the interval and wherein the centred value i
nu
is such that i
nu
<i
u
, the weight ratio of the ensemble of moieties with formula:
to Ri distributed in accordance with the “U” law to the ensemble of moieties distributed in accordance with the “non-U” law being 1:99 to 50:50, preferably 5:95 to 50:50.
Formulations for wax inhibitors incorporating these copolymers as essential components overcome the disadvantages cited above and enable a series of additives to be produced with a broad spectrum of use endowed with good solubility in crude oil, which have an effect both on wax crystallisation and on the dispersion of crystals that have already formed. They retard the crystallisation of waxes wherein the

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