Note: Descriptions are shown in the official language in which they were submitted.
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1 BACRGROUND OF T~E INVENl'ION
2 Field of the Invention
3 This invention relates to a dewaxing aid useful
4 in solvent dewaxing processes. More particularly, this
invention relates to an improved dewaxing aid useful in
6 solvent dewaxing processes wherein the improvement com-
7 prises a dewaxing aid comprising a mixture of (a) lithium
8 isostearate and (b) an acrylic ester polymer. Still more
9 particularly this invention relates to an improved de-
waxing aid for solvent dewaxin~ processes wherein the de-
11 waxing aid comprises a mixture of (a) lithium isostearate
12 and (b) a polymer of an ester of at least one aliphatic
13 alcohol with methacrylic acid or acrylic acid having an
14 average molecular weight ranging between about 300,000
to ~,000,000.
16 Description of the Prior Art
17 Waxes in wax-containing hydrocarbon oils are
18 removed therefrom by chilling tlle oil to precipitate out
19 the wax and then separating the solid wax particles from
the dewaxed oil by filtration or centrifugation. Indus~
21 trial dewaxing processes include press dewaxing processes
22 whexein the wax-containing oil, in the absence of solvent,
23 is chilled to crystallize out the wax particles which are
24 then pressed out by a filter. In general, only light hy-
drocarbon oil fractions (paraffinic fractions) obtained by
26 vacuum distillation are treated by press dewaxing proc-
27 esses due to viscosity limitations. More widely used are28 solvent dewaxing processes wherein a waxy oil is mixed
29 with solvent and then cnilled to precipitate the wax as
tiny particles or crystals there~y forming a slurry com-
31 prising solid wax particles and a solution of de~axed oil
32 containing dewaxing solvent. The slurry is then fed to a
33 wax filter wherein the wax is removed from the dewaxed oil
34 and dewaxing solvent. Solvent dewaxing processes are used
for heavier oil fractions such as lubricating oil frac--
36 tions and bright stocks. Typical dewaxing solvents include
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1 low boiling point, normally gaseous autorefrigerative hy-
2 drocarbons such as propane, propylene, butane, pentane,
3 etc., ketones such as acetone and MEK, MIBK, and mixtures
4 thereof, aromatic hydrocarbons such as benzene, toluene
xylene as well as mixtures of ke~ones and aromatic hydro-
6 carbons such as ME~/toluene and acetone/benzene and mix-
7 tures o ketones with autorefrigerants such as acetone/
8 propylene.
9 One of the factors tending to limit the capacity
of a solvent dewaxing plant is the rate of wax filtration
11 from the dewaxed oil, which in turn is strongly influenced
12 by the crystal structure of the precipitated wax. Although
13 the crystal structure of the precipitated wax is influenc-
14 ed by various operating conditions in the dewaxing process,
for any given feed, it is most strongly influenced by the
16 chilling conditions. The size and crystal structure of the
17 precipitated wax, occlusion of oil in the wax crystal and
18 the condition of the oil left in the crystal are extremely
19 varied and depend on the wax composition and precipitation
conditions. These conditions also affect the filtration
21 rate of the dewaxed oil from the wax and the ~ield of de-
22 waxed oil. In some cases, most notably when the waxy oil
23 is a bright stock, the wax crystals are of an extremely
24 fine size and not all are separated by filtration, but
some leave the filter with the dewaxed oil component which
26 creates an objectionable haze in the oil.
27 ~ne way of increasing the filtration rate and
28 minimizing haze formation is to add a dewaxing aid to the
29 wax-containing oil. Well-known in the art are dewaxing
aids such as ~ -olefin copolymers, mixtures of materials
31 such as a mixture of (a) an ethylene-vinyl acetate copoly-
32 mer and (b) an unsaturated ester of an aliphatic alcohol
33 having from 2 to 20 carbon atoms with acrylic or methacry-
34 lic acid, as well as polymeric dewaxing aids comprising
condensation products of chlorinated paraffins and naphtha-
36 lenes alone or mixed with acrylic ester polymers. However,
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1 in the case of heavy stocks these dewaxing aids are not
2 too efficient, thus requiring a relatively high concentra-
3 tion of the dewaxing aid in the oil. This is especially
4 true when a heavy oil raffinate or a bright stock is sol-
vent dewaxed. ~en tnese oils are solvent dewaxed, a
6 portion of the wax is precipitated as crystals so fine
7 that they pass through filter cloths, thereby creating a
8 haze in the dewaxed oil which greatly reduces the commer-
9 cial value of same. Also, because of the presence of so
many fine particles of wax, the filter rate of the dewaxed
11 oil tends to be lower than that obtained with lighter lube
12 oil stocks.
13 Haze may also appear when the dewaxed oil is
14 allowed to stand at room temperature for a long time. In
order to prevent the occurrence of haze, it is sometimes
16 necessary to filter the dewaxed oil through a filter of
17 sintered metal or polyvinyl alcohol a~ter the dewaxing
18 step. However, these process steps are complicated and
19 the dewaxing process becomes economically disadvantageous.
There~ore, there is a need for efficient dewaxing aids,
21 particularly for use with heavy stocks.
22 ~ A~
23 Accordingly, therefore, it has now been found
24 that an improvement results in processes for solvent de-
ZS waxing wax-containing hydrocarbon oils employing dewaxing
26 aids, if the dewaxing aid comprises a mixture of (a) lith-
27 ium isostearate and (b) a polymer ester of at least one
28 aliphatic alcohol with methacrylic acid or acrylic acid
29 having a number average molecular weight ranging from be-
tween about 300,00Q to 2,000,000. This combination de-
31 waxing aid results in increased wax filtration rates com-
32 pared to that obtained using the acrylic polymer alone.
33 Components (a) and (b) constituting the dewaxing
34 aid of this invention will be used in a weight ratio to
each other ranging from about 1/100 to 100/1 and prefer-
36 ably from 1/10 to 10/1 of (a)/(b)~ This dewaxing aid is
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1 added to the waxy oil feed in an amount ranging from about
2 0.01 to 0.50 wt. ~ and preferably from about 0.10 to 0.20
3 wt. % of the oil. It has been found to be advantageous to
4 prepare separate solutions of components (a) and (b) of the
dewaxing aid by dissolving each component in a mineral oil
6 or suitable solvent such as toluene, benzene, propane,
7 methylene chloride and the like. The separate solutions
8 of (a) and (b) can then be added to the wax-containing
9 hydrocarbon oil or they can be combined and the combined
solutions added to the wax-containing hydrocarbon oil.
11 The lithiu~ isostearate used as component (a)
12 in this invention was prepared by reacting equimolar quan-
13 tities of lithium hydroxide and isostearic acid. Thus, a
14 solution of 3 wt. % lithium hydroxide in water was mixed
with a solution of 15 wt. ~ isostearic acid in ethanol,
16 at room temperature and under agitation. A jelly-like pre-
17 cipitate of lithium isostearate was formed within a short
18 time. The lithium isostearate precipitate was washed with
19 water and dried in a laboratory oven at a temperature of
~0 about 105C. The dry lithium isostearate was then dissolv-
21 ed in toluene by heati.ng for from about 3 to 5 hours at a
22 temperature of about 95C to form a 2-3 wt. % solution of
23 lithium isostearate in toluene.
24 ~he pol~mer of the ester of an aliphatic alco-
hol with methacrylic or acrylic acid used as component (b)
26 in the present invention is a polymer of an ester of at
27 least one aliphatic alcohol having from about 6 to 30 car-
28 bon atoms and preferably from about 10 to 20 carbon atoms,
29 with methacrylic or acrylic acid. It has been found that
aliphatic alcohols having 5 to less carbon atoms or having
31 31 or more carbon atoms result in polymers which do not
32 give the desired dewaxing effect. Illustrative but non-
33 limiting aliphatic alcohol compositions suitable for use
34 in the instant invention include a mixture of (a) 0 to 30
wt. ~ of an alcohol having 10 carbon atoms, (b) about 10
36 to 40 wt. % of an alcohol having 12 carbon atoms, (c)
~ L.4i~
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1 about 10 to 40 wt. % of an alcohol having 14 carbon atoms,
2 (d) about 10 to 40 wt. % of an alcohol having 16 carbon
3 atoms, (e) about 10 to 40 wt. ~ of an alcohol having 18
4 carbon atoms, and ~f) about 0 to 30 wt. ~ of an alcohol
having 20 carbon atoms.
6 As hereinbefore stated, supra, the ester polymer
7 (b) will have a number average molecular weight ranging
8 from about 300,000 to 2,000,000 and preEerably from about
9 400 000 to 1,500,000. It has been found that known co~
polymers of aliphatic alcohols with methacrylic or acrylic
11 acid having an average molecular weight of less than about
12 300,000 or more than about 2,000,000 do not prevent naze
13 formation and do not yield increases in the amount of de-
14 waxed oil or dewaxing rate. Further, those having molecu-
lar weights less than about 5;000 have no effect as de-
16 waxing aids while those having molecular weights exceed-
17 ing 3,000,000 inhibit the dewaxing effect due to poor sol-
1~ vent solubility. One commercially available acrylic ester
19 polymer that has been found to be useful as component (b)
of this invention is Acryloid-150 available from the Rohm
21 and Haas Company.
22 The dewaxing solvent that is used in the present
23 invention is not particularly critical, provided that the
24 dewaxing aid stays in solution. Thus, any of the well-
known dewaxing solvents can be used. For example, there
26 may be used at least one member selected from linear hydro-
27 carbons having 2 to 10 carbon atoms in the molecule, such
28 as ethane, propane, butane, pentane, hexane, octane, ethy-
29 lene, propylenel butylene, pentene, hexene and octene, or
a mixture of at least one member selected from ketones
31 having from 3 to 6 carbon atoms, such as acetone, dimethyl
32 ketone, methylethyl ketone, methylpropyl ketone and methyl-
33 isobutyl ketone with at least one member selected from an
34 aromatic hydrocarbon such as benzene, xylene or toluene,
such as methylethyl ketone/toluene or methylisobutyl
36 ketone/toluene. Also useful are halogenated hydrocarbons
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l such as methylene chloride. Further, N~alkylpyrrolidones
2 such as N-methylpyrrolidone and ~-ethyl-pyrrolidone may be
3 used as the dewaxing solvent. Still further, mixtures of
4 autorefrigerative solvents and ketones can be used as the
dewaxlng solvent, suc~ as a mixture of acetone and propy-
6 leneO Solvents which have been found to be especially
7 preferred for practicing the process of the present inven-
8 tion include propane, other autoxefriger.ative solvents,
9 toluene, mixtures of a ketone and an aromatic hydrocarbon
such as MEK/toluene, methylene chloride and mixtures of
11 acetone and methylene chloride.
12 Any waxy petroleum oil stock or distillate frac-
13 tion thereof may be dewaxed employing the dewaxing aid of
14 this invention, although heavy feedstocks are preferred.
Illustrative but non-limiting examples of such stocks are
16 (a) distillate fractions that have a boiling range ~ithin
17 the broad range of from about 250 to 700C, with preferred
18 stocks including lubricating oil and specialty oil frac
l9 tions boiling within the range of from between about 300
and 650C and (b) bright stocks and deasphalted resids
~l having an initial boiling point above about 425C. Addi-
22 tionally, any of these feeds may be hydrocracked prior to
23 distilling or deasphalting. These may come from any
24 source such as paraffinic crudes obtained ~rom Aramco,
Kuwait, the Panhandle, North Louisiana, etc., naphthenic
26 crudes, such as Tia Juana, Coastal crudes, etc., as well
27 as the relatively heavy feedstocks such as bright stocks
28 having a boiling range of 565+C and synthetic feedstocks
29 derived from Athabasca tar sands, Cold Lake crude, coal.,
etc.
31 DESCRIPTION OF THE PREFERP~D EMBODIMENTS
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32 In a preferred embodiment of the process of this
33 invention, a solution of dewaxing aid comprising components
34 (a) and (b~ dissolved in an appropriate solvent such as a
light heating oil or a light mineral oil fraction is mixed
36 into the wax-containing oil and the mixture heated to a
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1 temperature higher than the cloud point of the oil (about
2 50 to 120C). This mixture is introduced, along with the
3 dewaxing solvent, into a chilling zone and chilled to a
4 temperature necessary to yield the desired pour point for
the resulting dewaxed oil. The chilling produces a slurry
6 comprising dewaxed oil and solvent along with solid parti-
7 cles of wax which contain the dewaxing aid. This slurry
8 is then sent to a wax filter to separate the dewaxed oil
9 and solvent from the wax particles. The dewaxing tempera-
ture or temperature to which the slurry is chilled varies
11 depending on the feed and conditions. In general, this
12 temperature will range from about 0 to about -50C. In
13 the case where the dewaxing solvent comprises a mixture of
14 a ketone and an aromatic hydrocarbon, such as methylethyl
ketone/toluene, the dewaxing temperature will range from
16 about -10 to about -30~C. Where propane is used as the
17 dewaxing solvent, the dewaxing temperature will generally
18 be from about -20 to about -40C. Preferred dewaxinc3 sol-
19 vents used in the process of this invention include pro-
pane, other autorefrigerative solvents, a mixture of a
21 ketone and an aromatic hydrocarbon as well as a mixture of22 a ketone and methylene chloride. The ratio of solvent to
23 waxy oil would generally range from about 0.5 to 10 and
24 preferably from about 2 to 7, by volume. The optimum
amount of dewaxing solvent employed is of course determined
26 by the wax content of the oil, viscosity, pretreatment and
27 and dewaxing conditions.
28 The invention will be more apparent from the Ex-
29 ample set forth below.
EXAMPLE
31 A bright stocl~ having a viscosity of 2500 SUS at
32 100F obtained from a light Arabian crude oil was charged
33 into an autoclave, along with dewaxing aid. Propane was
34 then added in the amounts shown in Table 1. The dewaxing
aid was added to the bright stock as a 3 wt. % solution in
36 a light heating oil. The mixture of bright stock, dewaxing
1 aid and propane was heated in the autoclave to 60C to form
2 a homogeneous solution and then prechilled to 16C via in-
3 direct, external heat exchange under agitation, at a chill-
4 ing rate of 6C per minute. The propane solvent was then
allowed to evaporate which chilled the mixture to -34C at
6 a chilling rate of 2.8C/min. to form a slurry of dewaxed
7 oil, solvent and solid particles of wax. After the chill-
8 ing operation, the slurry was fed to a wax filter where
9 filtration was conducted at a temperature of -34.4C and
at a filtration pressure differential of 34 KPA and the
11 filtration rate was determined. The results are shown in
12 Table I.
13 TABLE I
14 PROPANE DEWAXING OF ARABI~N LT. 2500 BRIGHT STOCK
~7ITH LITHIUM ISOSTEAR~TE/METHACRYLATE ESTER DEWAXING AID
16 Run ~lo. _ 2 _ 3_
17 Dewaxing Aid Acryloid-150 Lithium isostear-
18 ate/Acryloi.d-
19 150
20 amount, wt. % on feed 0.10 0.01/0.10
21 Propane dilution, vol. on feed 3.14 2.70
22 Feed Filtration Rate, 4.6 6.0
23 m8/m2 day
24 Wax Cake liquids/solids ratio, 2.4 2.8
25 weight basis
26 Thus, the data show that the feed filter rate
27 for the oil CQntaining the Acryloid-150 alone but no lith-
28 ium isostearate was 4.6, whereas when 100 wt. ppm (on waxy
29 oil feed) of lithium isostearate was present in the dewax-
ing aid, the feed filter rate was 6.0, thus yielding a 30%
31 improvement in feed filter rate.
