Title: Production of esters
Abstract: Disclosed is a process for the production of esters. In particular, the process includes contacting an olefin or an ether with carbon monoxide and an acid composition comprising BF3.2CH3OH to from a product composition, adding an alcohol to the product composition, and separating the BF3.2CH3OH from the ester. The separated BF3.2CH3OH may then be recycled to the reaction unit.
Patent Number: 7,005,537 Issued on 02/28/2006 to Mozeleski, et al.
| Inventors:
|
Mozeleski; Edmund J. (Califon, NJ);
Beck; Carl R. (Greenwell Springs, LA);
Nadler; Kirk C. (Houston, TX);
Schlosberg; Richard H. (Bridgewater, NJ)
|
| Assignee:
|
ExxonMobil Chemical Patents Inc. (Houston, TX)
|
| Appl. No.:
|
750567 |
| Filed:
|
December 26, 2000 |
| Current U.S. Class: |
560/233; 560/232; 560/240 |
| Current Intern'l Class: |
C07C 67/36 (20060101); C07C 67/38 (20060101); C07C 67/24 (20060101) |
| Field of Search: |
560/233,322,240,232
|
References Cited [Referenced By]
U.S. Patent Documents
| 2967873 | Jan., 1961 | Koch et al.
| |
| 4311851 | Jan., 1982 | Jung et al.
| |
| 4894188 | Jan., 1990 | Takahashi et al.
| |
| 5552080 | Sep., 1996 | Bolmer.
| |
| Foreign Patent Documents |
| 1 232 317 | May., 1971 | GB.
| |
| 0 017 441 | Oct., 1980 | WO.
| |
| PCT/US99/09885 | May., 1999 | WO.
| |
Other References
J. Falbe, "New Synthesis with Carbon Monoxide," Springer-Verlag, Sec. 5.7, pp.
406-413, 1980.
40 C.F.R. 80.27, "Controls and Prohibitions on Gasoline Volatility."
Carter, W.P.L., "Preliminary Report to California Air Resources Board under Contract
No. 95-308," Aug. 6, 1998.
"Toxicology," Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed.,
vol. 24, pp. 456-490.
"Table 2: Physical Properties of Common Industrial Solvents," Kirk-Othmer
Encyclopedia of Chemical Technology, 4th Ed., vol. 22, pp. 536-548.
Dante et al., "Program Calculates Solvent Properties and Solubility Parameters,"
Modern Paint and Coatings, Sep., 1989.
|
Primary Examiner: Tsang; Cecilia J.
Assistant Examiner: Oh; Taylor Victor
Parent Case Text
CROSS REFERENCE
This application claims priority to U.S. Provisional Application Ser. No. 60/173,504
filed Dec. 29, 1999, which is incorporated herein in its entirety.
Claims
What is claimed is:
1. A method of making an ester comprising:
(a) contacting an olefin selected from the group consisting of ethylene propylene,
isoolefins, normal butenes, and C
5 to C
18 olefins with carbon
monoxide and a BF
32ROH acid composition to form a product composition;
(b) adding ROH to the product composition of (a); and
(c) separating a BF
32ROH acid product from the ester, wherein ROH
is selected from methanol; n-propanol; n-butanol; 2-propanol 2-ethyl hexanol; isohexanol;
isoheptanol; isooctanol; isononanol; 3,5,5-trimethyl hexanol; isodecanol; isotridecanol;
1-octanol; 1-decanol; 1-dodecanol; 1-tetradecanol and mixtures thereof.
2. The method of claim 1 further comprising recycling a portion of the separated
said product to contact the olefin.
3. The method of claim 1 wherein the olefin is an isoolefin.
4. The method of claim 2 wherein the olefin is isobutene.
5. The method of claim 1 wherein the olefin is contacted with carbon monoxide
and a BF
32ROH acid composition at a temperature fern about 60°
C. to about 200° C.
6. The method of claim 5 wherein said temperature is from about 110° C.
to about 160° C.
7. The method of claim 1 wherein the olefin is contacted with carbon monoxide
and a BF
32ROH acid composition at a pressure from about 30 atm to about
200 atm.
8. The method of claim 7 wherein said pressure is from about 110 atm to about
16 atm.
9. The method of claim 1 wherein ROH is methanol.
10. The method of claim 1 further comprising contacting the olefin with a saturated
linear or bunched hydrocarbon having at least six carbons.
11. The method of claim 1 further comprising adding to the product composition
a saturated linear or branched hydrocarbon having at least six carbons.
12. The method of claim 11 further comprising separating the hydrocarbon and
ROH from BF
32ROH and directing a of the separated hydrocarbon and the
separated ROH to a unit selected horn the group consisting of a separation unit,
a reaction unit, and a combination thereof.
13. The method of claim 1 further comprising contacting the olefin with phosphoric acid.
14. The method of claim 1 wherein the acid product is separated by concentrating
the acid product such that the molar ratio ROH:BF
3 in the concentrated
acid product is from about 2:1 to about 4:1.
15. The method of claim 14 wherein said molar ratio of ROH:BF
3 is
from about 2:1 to about 3:1.
16. The method of claim 1 wherein the acid composition has a molar ratio of ROH:BF
3
from about 1.6:1 to about 3:1.
17. The method of claim 16 wherein said molar ratio is from about 1.9:1 to about 3:1.
18. The method of claim 1 wherein the product composition contains less than
3% by weight carboxylic acid.
19. A method of making methyl pivalate comprising:
contacting methyl-t-butylether with carbon monoxide and a BF
32CH
3OH
acid composition to form a methyl pivalate product composition
adding methanol to the product composition; and
separating a BF
32CH
3OH acid product from the methyl pivalate.
20. The method of claim 19 wherein the methyl-t-butylether is contacted with
carbon monoxide and a BF
32CH
3OH acid composition at a temperature
of about 110° C. to about 160° C.
21. The method of claim 19 wherein the methyl-t-butylether is contacted with
carbon monoxide and a BF
32CH
3OH acid composition at a pressure
from about 30 atm to about 200 atm.
22. The method of claim 19 further comprising contacting the methyl-t-butylether
with a saturated linear or branched hydrocarbon having at least six carbons.
23. The method of claim 19 further comprising contacting the product composition
with a saturated linear or branched hydrocarbon having at least six carbons.
24. The method of claim 23 further comprising separating the hydrocarbon and
the methanol from the methyl pivalate and directing a portion of the separated
hydrocarbon and the separated methanol to a unit selected from the group consisting
of a separation unit, a reaction unit, and a combination thereof.
25. The method of clam
19 further comprising contacting the methyl-t-butylether
with phosphoric acid.
26. The method of claim 19 wherein the acid product is separated by concentrating
the acid product such that the molar ratio ROH:BF
3 in the acid product
is from about 2:1 to about 4:1.
27. The method of claim 26 wherein said molar ratio of ROH:BF
3 is
from about 2:1 to about 3:1.
28. The method of claim 19 wherein the acid composition has a molar ratio of
ROH:BF
3 from about 1.6:1 to about 3: 1.
29. The method of claim 28 wherein said molar ratio is from about 1.9:1 to about3:1.
30. The method of claim 19 wherein the product composition contains nonanoic
methyl esters such that the molar ratio of methyl pivalate to nonanoic methyl esters
is about 4 or greater.
31. A method of making an ester comprising:
(a) contacting an olefin selected from the group consisting of ethylene, propylene,
isoolefins, normal butenes, and C
5 to C
18 olefins with carbon
monoxide and a BF
3,ROH acid composition to form a product composition;
(b) adding ROH to the product composition of (a); and
(c) separating a BF
3ROH maid product from the ester, wherein ROH is
selected from methanol; n-propanol; 2-propanol; u-butanol 2-ethyl hexanol; isohexanol;
isoheptanol; isooctanol; isononanol; 3,5,5-trimethyl hexanol; isodecanol; isotridecanol;
1-octanol; 1-decanol; 1-dodecanol; 1-tetradecanol mid mixtures thereof and wherein
the molar equivalents of ROH in the BF
3ROH, ranges from about 2 to about
4.
32. A method of making an ester comprising:
(a) contacting an ether with carbon monoxide and a BF
32ROH acid composition
to form a product composition;
(b) adding ROH to the product composition of (a); and
(c) separating a BF
32ROH acid product from the ester, wherein ROH
is selected from methanol; n-propanol; n-butanol; 2-propanol 2-ethyl hexanol; isohexanol;
isoheptanol; isooctanol; isononanol; 3,5, 5-trimethyl hexanol; isodecanol; isotridecanol
1-octanol; 1-decanol; 1-dodecanol; 1-tetradecanol and mixtures thereof.
33. The method of claim 32 further comprising recycling a portion of the separated
acid product to contact the ether.
34. The method of claim 32 wherein the other is represented by the formula R′—O—R",
wherein R′= saturated C
1-C
13 alkyl and R"=saturated
C
1-C
13 alkyl, and R′ and R" can be the same or different.
35. The method of claim 32 wherein the ether is methyl-t-butylether.
36. The method of claim 32 wherein the ether is contacted with carbon monoxide
and a BF
32ROH acid composition at a temperature from about 60°
C. to about 200° C.
37. The method of claim 36 wherein said temperature is from about 110° C.
to about 160° C.
38. The method of claim 32 wherein the ether is contacted with carbon monoxide
and a BF
32OH acid composition at a pressure from about 30 atm to about
200 atm.
39. The method of claim 38 wherein said pressure is from about 110 atm to about
160 atm.
40. The method of claim 32 wherein ROH is methanol.
41. The method of claim 32 wherein the ether is methyl-t-butyl ether.
42. The method of claim 32 wherein the ether is diisopropyl ether and ROH is 2-propanol.
43. The method of claim 32 further comprising contacting the ether with a saturated
linear or branched hydrocarbon having at least six carbons.
44. The method of claim 32 further comprising adding to the product composition
a saturated linear or branched hydrocarbon having at least six carbons.
45. The method of claim 44 further comprising separating the hydrocarbon and
ROH from BF
32ROH and directing a portion of the separated hydrocarbon
and the separated ROH to a unit selected from the group consisting of separation
unit, a reaction unit, and a combination thereof.
46. The method of claim 32 further comprising contacting the ether with phosphoric acid.
47. The method of claim 32 wherein die acid product is separated by concentrating
the acid product such that the molar ratio ROH:BF
3 in the concentrated
acid product is from about 2:1 to about 4:1.
48. The method of claim 47 wherein said molar ratio of ROH:BF
3 is
about 2:1 to about 3:1.
49. The method of claim 32 wherein the acid composition has a molar ratio of
ROH:BF
3 from about 1.6:1 to about 3:1.
50. The method of claim 49 wherein said molar ratio of ROH:BF
3 is
from about 1.9:1 to about 3:1.
51. The method of claim 32 wherein the product composition contains less than
3% by weight carboxylic acid.
52. A method of making an ester comprising:
(a) contacting an ether with carbon monoxide and a BF
3 ROH acid composition
to form a product composition;
(b) adding ROH to the product composition of (a); and
(c) separating a BF
3ROH acid product from the ester, wherein ROH is
selected from methanol; n-propanol; n-butanol; 2-butanol 2-ethyl hexanol; isohexanol;
isoheptanol; isooctanol; isononanol; 3,5,5-trimethyl hexanol; isodecanol; isotridecanol;
1-octanol; 1-decanol; 1-dodecanol; 1-tetradecanol and mixtures thereof and wherein
the molar equivalents of ROH in the BF
3ROH, ranges from about 2 to about 4.
Description
FIELD OF THE INVENTION
This invention relates to a process for the production of esters from olefins
and ethers.
BACKGROUND OF THE INVENTION
Esters are compounds which currently find use in such areas as pesticides
and herbicides, metal extraction agents, synthetic lubricants, polymerization aids
for acrylic acid esters, insect attractants and repellants, industrial fragrances,
odorants and cosmetic components, pharmaceutical applications, and photographic
applications. Esters are typically made from a two step process. First, the corresponding
carboxylic acid is produced. The acid is then reacted with an alcohol to produce
the desired ester via a condensation process.
High volume production of dialkyl esters (two alkyl groups at the α-carbon)
and trialkyl esters (three alkyl groups at the α-carbon) can be very difficult
to prepare from the corresponding acid because of the hydrolytic instability of
the product esters. Koch and Moller (U.S. Pat. No. 2,967,873) describe a synthesis
of trialkyl esters from olefins using a catalyst system of BF
3.H
2O.ROH
where ROH is an aliphatic alcohol of low molecular weight and an olefin having
six or more carbons. However, this process always produces some carboxylic acid
along with the desired ester and requires continual adjustment of the water to
alcohol ratio in the recycled BF
3 catalyst.
Commercial use of this technology is currently employed by Exxon Chemical
Company (Baton Rouge, La.) and Shell (Pernes, Holland). ExxonMobil's products are
known as "neo acids" while Shell's products are called Versatic™ acids.
ExxonMobil Chemical employs BF
3.2H
2O as catalyst and Shell
employs H
3PO
4.BF
3.H
2O in a 1:1:1 ratio
(J. Falbe, "New Synthesis with Carbon Monoxide", Springer-Verlag, 1980, p. 406).
Olefins used in these processes include isobutylene, propylene oligomers and C
8-C
11
fractions. The major commercial products are 1,1,1-trimethyl acetic acid (pivalic
acid or neopentanoic acid) and neodecanoic acid or Versatic™10. The major
disadvantage of these processes is the difficulty, relatively high cost, and process
inefficiencies in recycling the acid catalyst in the process.
Gelbein (Re. 31,010) discloses a one step process for the preparation of
esters from olefins in the presence of BF
3.CH
3OH. This process
requires that uncomplexed BF
3 be distilled from the reaction products.
This distillation is very inefficient and requires the use of corrosion resistant
processing equipment. Following the distillation of uncomplexed BF
3,
methanol is added to form an azeotrope with the desired ester and a BF
3.2CH
3OH
adduct. The distilled BF
3 or fresh BF
3 is added to BF
3.2CH
3OH
to form BF
3.CH
3OH, which is recycled to the reaction unit.
The BF
3.CH
3OH is a preferred because it is stronger acid
than BF
3.2CH
3OH, and the esterfication of propylene or ethylene
can occur at temperatures below 100° C., preferably below 60° C.
Jung and Peress (U.S. Pat. No. 4,311,851) also disclose the preparation of esters
from a BF
3.ROH complex catalyst. This process also requires that uncomplexed
BF
3 be distilled from the reaction products and then recycled to form
the active BF
3.ROH catalyst.
Large volume, commercial scale production of dialkyl and trialkyl esters remains
a problem in the chemical industry. Presently, the production of these esters,
particularly trialkyl esters (neo acid esters), are limited by having to use a
relatively large amount of purified acid catalyst and/or by having to distill off
a corrosive strong acid (HF or BF
3) from the reaction products so the
acid can be recycled in the process. Distillation of this acid requires special
operational handling and specialized process units which results in a highly inefficient process.
BRIEF SUMMARY OF THE INVENTION
The invention provides a selective process to dialkyl and trialkyl esters from
olefins and ethers. The invention provides a method to recover and recycle the
acid catalyst without the need to distill BF
3 from the reaction products.
The process comprises contacting an olefin or ether with carbon monoxide and an
acid composition containing BF
3.2ROH to form a product composition,
adding ROH to the product composition, and separating an acid product comprising
BF
3.2ROH from the ester. The acid composition will have a molar ratio
of ROH:BF
3 from about 1.6:1 to about 3:1, preferably from about 1.9:1
to about 3:1. The process may further include recycling a portion of the separated
acid product to contact the olefin or ether. It may also be desirable to contact
the olefin or ether with phosphoric acid.
The separation of the acid product from the product esters may take place in
multiple separation units. The separation process may include concentrating the
acid product such that the molar ratio ROH:BF
3 of the concentrated acid
product is from about 2:1 to about 4:1, preferably from about 2:1 to about 3:1.
The separation of the acid product from the product esters may be facilitated
by the presence of a hydrocarbon, wherein the hydrocarbon is selected from a saturated
linear or branched hydrocarbon having at least six carbons. The hydrocarbon can
be added to the reaction unit as a co-solvent in the carbonylation reaction, and/or
one or more separation units as an extracting solvent.
The carbonylation reaction in the process includes contacting the olefin or ether
with the carbon monoxide and acid composition at a temperature from about 60°
C. to about 200° C., preferably from about 110° C. to about 160°
C. The pressure of the carbonylation reaction includes contacting the olefin or
ether at a pressure from about 30 atm to about 200 atm, preferably from about 110
atm to about 160 atm.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention will be better understood by reference to the Detailed Description
of the Invention when taken together with the attached drawings, wherein:
FIG. 1 is a schematic diagram of one embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In this invention, a variety of dialkyl and trialkyl acid esters are produced
from olefin or ether feedstocks, carbon monoxide, and an acid composition containing
BF
3.2ROH, wherein ROH is an alcohol and BF
3 is boron trifluoride.
The olefin feedstock may be obtained from a variety of sources, including a dilute
olefin feedstock from the steam cracking of hydrocarbons. The carbon monoxide (CO)
can be used in a relatively pure form, or the CO can be mixed with an inert gas,
e.g., hydrogen, nitrogen, carbon dioxide, or mixtures thereof. If a gas mixture
is used, the CO concentration should be at least about 40% by volume. Preferably,
the CO concentration in the gas mixture is at least about 90% by volume. The alcohol
is selected from methanol, n-propanol, n-butanol, 2-propanol, 2-ethyl hexanol,
isohexanol, isoheptanol, isooctanol, isononanol, 3,5,5-trimethyl hexanol, isodecanol,
isotridecanol, 1-octanol, 1-decanol, 1-dodecanol, 1-tetradecanol and the mixtures
thereof. Preferably, the alcohol is methanol. If MTBE is used as the feed ether,
methanol is preferably used as the alcohol.
In contrast to prior olefin carbonylations, the molar concentration of the alcohol
should be greater than the molar concentration of the BF
3 in the acid
composition. Typically, the molar concentration of alcohol to the molar concentration
of BF
3 is from about 1.6:1 to about 4:1, preferably from about 1.9:1
to about 3:1, most preferably from about 2:1 to about 2.5:1. Because the acid composition
contains primarily BF
3.2ROH, rather than BF
3.ROH, the invention
utilizes a relatively weaker acid to convert olefin or ethers to the desired ester
products. The strength of the acid depends upon the relative molar concentration
ratio of alcohol:BF
3. The greater the molar concentration ratio the
weaker the acid.
After the olefin or ether contacts the CO and the acid composition for the
desired amount of time, the product composition is cooled and the excess CO vented.
An alcohol is added to the product composition to quench the reaction. Preferably,
the alcohol used is the same alcohol that is contained in the acid composition.
The addition of the alcohol results in the formation of an azeotrope containing
the desired ester products and alcohol, and an acid product. The acid product contains
BF
3.2ROH, as well as the azeotrope, which contains alcohol and the product esters.
The azeotrope and the acid product are then separated. Complete or near complete
separation of the azeotrope from the acid product may require one or more separation
steps. The desired product esters are distilled from the azeotrope to give the
alcohol and any remaining acid product that may remain after the separation. The
alcohol can be recycled to the reactor, to one or more separation units, or to
any combination thereof. A portion of the separated acid product, preferably with
little or no purification step, is recycled to the reactor. Distillation of BF
3
from the product composition or the acid product is not carried out in the process.
Instead, the acid product is concentrated by removal of alcohol and the remaining
azeotrope that may remain in the acid product following one or more separations.
In the preferred embodiment, the acid product is concentrated by removing the
alcohol and azeotrope under vacuum at elevated temperatures. The pressure during
the acid concentration process is from about 0.01 mmHg to 200 mmHg, preferably
from 0.1 mmHg to 100 mmHg, most preferably from 1 mmHg to 50 mmHg. The temperature
during the acid concentration process is from about 30° C. to about 110°
C., preferably from about 50° C. to about 90° C.
The concentrated acid product, which comprises primarily BF
3.2ROH,
is recycled to the reactor. In some cases an acid purge stream is used to control
and maintain the quality of the acid catalyst in the process. The molar ratio of
alcohol:BF
3 in the concentrated acid product is from about 2 to 5, preferably
from about 2 to 3, most preferably, the molar ratio of alcohol:BF
3 is
about 2 before the acid product is recycled to the reactor.
In the carbonylation reaction, which is catalyzed by the acid composition, the
respective molar concentrations of the acid and the alcohol should be greater than
the molar concentration of the olefin or ether in the reaction mixture. Typically,
the molar concentration of the alcohol to the molar concentration of the olefin
or ether is from about 2:1 to about 20:1, preferably from about 2:1 to about 10:1,
most preferably from about 2:1 to about 6:1. Typically, the molar concentration
of BF
3 to the molar concentration of the olefin or ether is from about
0.5:1 to about 15:1, preferably from about 1:1 to about 8:1, most preferably from
about 1:1 to about 6:1.
In the process of the invention, the olefin or ether is carbonylated in the presence
of the acid catalyst at an effective carbonylation temperature and pressure, which
minimizes undesirable side reactions to oligomers and other products. The catalytic
reaction of olefin or ethers to dialkyl and trialkyl esters may be performed at
temperatures from about 30° C. to about 200° C., preferably from about
110° C. to about 170° C., more preferably from about 120° C. to
about 150° C. The specific temperature requirement is a function of the olefin
or ether used in the process as well as the reaction pressure.
To minimize undesirable side reactions (typically olefin oligomerization reactions)
it is desirable to maintain a large excess of CO in the reaction. This ratio is
controlled by a number of parameters including: the reaction pressure, the rate
of olefin feed, and the extent and effectiveness of mixing of the reactants and
catalyst in the reaction vessel. The reaction pressure is not critical so long
as a stochiometric excess of carbon monoxide is maintained in the reactor. The
total pressure in the reactor is from about 30 atm to 200 atm, preferably from
about 70 atm to about 160 atm, more preferably from about 110 atm to about 160
atm. These pressures are within current commercial unit capabilities for such carbon
monoxide containing processes as hydroformylation and neoacid production.
In a batch process a large excess of the carbon monoxide is available to react
with the olefin. In a continuous process the reaction process begins with an excess
of acid catalyst, alcohol, and CO, however, once steady state conditions are achieved,
the feed rate of CO can be maintained such that about one mole of CO is fed to
the reactor for every mole of olefin or ether fed to the reactor.
Following the addition of the alcohol a phase separation between the acid
product and the azeotrope may not occur. This phase separation will depend upon
the olefin or ether as well as the alcohol used in the process. Generally, the
greater number of carbons in the olefin, ether, and/or alcohol the greater likelihood
of a phase separation.
Separation of the azeotrope and the acid product can be facilitated by
the addition of a hydrocarbon. The hydrocarbon can be added to a separation unit
as an extracting solvent, or added to the reactor as a co-solvent in the carbonylation
reaction. In certain instances it may be desirable to add the hydrocarbon to the
separation unit as well as the reactor. The hydrocarbon is a saturated, linear
and/or branched hydrocarbon having at least six carbons. Preferably, the hydrocarbon
is selected from the hexanes, heptanes, octanes, nonanes, or any combination thereof.
The separation units that may be used in the invention are known to those of
ordinary skill in the art. Such separation units include a liquid-liquid extraction
unit including a counter-flow extraction unit with mixing wells or plates.
Following the separation of the azetrope containing the ester products
from the acid product, the ester products are separated from the azeotrope, hydrocarbon
and alcohol. This separation can be carried out in a distillation column under
conditions required to obtain the desired product specifications. The hydrocarbon
or alcohol from the distillation can be recycled to the reactor or one or more
separation units.
In one embodiment, phosphoric acid may be used as a co-catalyst in the reaction
without adversely effecting product separation, catalyst recovery, and reaction
selectivity. In some instances the addition of about 0.25 mol of H
3PO
4
per mole of BF
3 may result in a small improvement in product selectivity
and/or product yield of the desired ester product.
FIG. 1 describes one embodiment of the invention. Fresh feed streams into the
reactor
10 include CO
11, olefin or ether,
12, and BF
3
13. An acid recycle stream
14 and an alcohol/hydrocarbon recycle
stream
15 is also directed to the reactor
10. Fresh alcohol
16
can be added to the process in any number of ways, including to the reactor
10,
the separation unit
20, or the alcohol/hydrocarbon recycle stream
15.
A portion of the reaction product
18 is directed to a separation unit
20.
Alcohol is added to the reaction product
18 in the separation unit
20.
A portion of the acid product
21 is separated from the product containing
the esters
22 in separation unit
20. In most embodiments additional
separation units are required to maximize the separation of the acid product from
the product containing the esters. As a result, the acid product
21 from
separation unit
20 is directed to separation unit
24. The concentrated
acid product
25 from the separation unit
24 is directed to the reactor
10. In many instances an acid purge stream
26 is required to maintain
and control the quality of the acid catalyst in the reactor
10. Additional
ester and alcohol is recovered from separation unit
24.
Stream
28 is combined with product stream
22 which is directed
to a separation unit
30. Preferably, separation unit
30 contains
one or more distillation columns to separate the desired ester products from the
alcohol, any remaining acid product, and hydrocarbon. The desired ester products
exit the separation zone
30 as ester product streams
32 and
32′.
Acid product
34 from separation unit
30 is directed to concentrated
acid product stream
25. A portion of the alcohol from separation unit
30
may be directed to the reactor via stream
35 or directed to separation unit
20 via stream
36. Because the concentrated acid product
25
is primarily BF
3.2ROH, that is, the alcohol:BF
3 molar ratio
in the recycled acid product
14 is about or greater than 2, most of the
alcohol from the separation zone
30 is directed to separation unit
20.
An alcohol purge stream
40 may be used to maintain and control the quality
of the alcohol used to quench the reaction and separate the reaction products in
separation unit
20. The hydrocarbon from separation unit
30 may be
directed to the reactor via stream
37 or directed to separation unit
20
via stream
38. Fresh hydrocarbon
42 can be added to the process in
any number of ways. As shown, fresh hydrocarbon
42 is added to stream
38
which is directed to separation unit
20. A hydrocarbon purge stream
41
may also be necessary.
The esters produced from this invention can find use in a variety of applications
including, but not limited to: as a chemical intermediate in the areas of pesticides
and herbicides; metal extraction agents; synthetic lubricants; polymerization aid
for acrylic acid esters; insect attractants and repellants; industrial fragrances,
odorants and cosmetic components; pharmaceutical applications; photographic applications;
as a solvent for paints, inks, and the like; as a carrier for agricultural chemicals;
and as a octane enhancing fuel component. In all of these end use areas, a very
useful feature is that these products will be low or very low or negligible generators
of low level atmospheric ozone formed via photochemical reactions.
Motor gasoline, solvents and the like contain various volatile organic compounds
(VOC's), which are involved in complex photochemical atmospheric reactions, along
with oxygen and nitrogen oxides (NO
X) in the atmosphere under the influence
of sunlight, to produce ozone. Ozone formation is a problem in the troposphere
(low atmospheric or "ground-based"), particularly in an urban environment, since
it leads to the phenomenon of smog. Since VOC emissions are a source of ozone formation,
motor gasoline manufacture and formulation and solvents for use in paints, inks,
etc. are regulated to attain ozone compliance. Historically, governmental regulation
of motor gasoline has focused on limiting the volatility of motor gasoline sold
in the United States. Currently, motor gasoline volatility is regulated through
seasonally limiting motor gasoline Reid Vapor Pressure. A listing of EPA's regulatory
motor gasoline RVP limits is found at 40 C. F. R. 80.27,
Controls and Prohibitions
on Gasoline Volatility.
The United States Environmental Protection Agency (EPA) has developed National
Ambient Air Quality Standards (NAAQS) for six pollutants: ozone, nitrogen oxides
(NO
x), lead, carbon monoxide, sulfur dioxide and particulates. Ground-level
ozone, a primary component of smog, exceeds target levels in many areas of the
United States. The CAA90, for example, includes provisions to reduce urban ozone
levels. Reformulated gasoline is targeted to reduce ozone forming hydrocarbon emissions
in the United States worst ozone non-attainment areas by 15 percent in 1995 and
by 20 percent by 2000. The CAA90 includes several programs to reduce urban ozone
including stricter automobile tailpipe emissions limits of 0.25 grams per mile
non-methane hydrocarbons and stricter gasoline Reid Vapor Pressure limits. Therefore,
ozone non-attainment has an impact on motor gasoline formulation through regulatory
seasonal Reid Vapor Pressure limitations and gasoline reformulation.
According to current VOC emission regulations in the U.S.A., some gasoline
components belong to one of two groups depending on their reactivity toward atmospheric
photochemical ozone formation:
(a) Negligible reactivity organic compounds which generate about the same or
less quantity of ozone as would be produced by the same weight % as ethane. These
organic compounds are exempt from the definition of a VOC and are not considered
to be a VOC in any fluid composition. There are numerous such compounds exempted
by the EPA from the definition of VOC. Other such organic compounds, such as tertiary
butyl acetate which is under exemption consideration by the EPA, while having a
significantly improved flammability level and evaporation rate, may be too chemically
and thermally unstable for motor gasoline applications.
(b) Other oxygenated and hydrocarbon compounds are considered to be VOC's and
treated by the EPA as equally (on a weight basis) polluting.
Current regulations based on VOC emissions do not take into consideration
the wide difference in ozone formation among non-exempt VOC compounds. For example,
two non-exempt VOC compounds can have dramatically different ozone formation characteristics.
Accordingly, current regulations do not encourage end users to minimize ozone formation
by using low reactivity hydrocarbon compositions.
Hydrocarbon compounds currently viewed as essentially non-ozone producing
are those which have reactivity rates in the range of ethane. Ethane has a measured
reactivity based on the MIR method of 0.35. In fact, the EPA has granted a VOC
exemption to certain solvents with reactivity values in this range including acetone
(MIR=0.48) and methyl acetate (MIR=0.12).
However, the number of known materials having reactivities of 0.50 or less
based on the MIR scale is relatively small. Moreover, it is a discovery of the
present inventors that many if not most of the known fluids having acceptable reactivities
with respect to ozone formation have other unfavorable performance characteristics.
For example, ethane is a gas under ambient conditions and hence is a poor choice
as an industrial solvent. Methyl acetate has an excellent MIR=0.12, but a low flash
point of about -12° C.; acetone has an acceptable MIR=0.48, but is extremely
flammable. As a further example, tertiary butyl acetate (t-butyl acetate) has an
excellent MIR=0.21, but has limited thermal stability.
Among the most preferred fluids according to the present invention are dimethyl
carbonate and methyl pivalate. Table 1 demonstrates the extremely low relative
reactivities—significantly lower than both acetone and ethane—of methyl
pivalate. This data shows that the EPA requirements for exempt solvents in accordance
with current VOC regulations and demonstrating extremely low reactivity for the
possible future reactivity based rules.
| TABLE 1 |
|
| Summary of calculated incremental reactivities (gram basis) for |
| ethane, acetone, and methyl pivalate, relative to the average |
| of all VOC emissions. |
| |
Ozone Yield |
Max. 8 Hour |
| |
Relative Reactivities |
Avg. Relative Reactivities |
| Scenario |
Ethane |
Acetone |
Me-Pvat |
Ethane |
Acetone |
Me-Pvat |
|
| Max |
0.09 |
0.12 |
0.06 |
0.08 |
0.15 |
0.07 |
| React |
| Max |
0.16 |
0.14 |
0.11 |
0.10 |
0.15 |
0.09 |
| Ozone |
| Equal |
0.21 |
0.15 |
0.12 |
0.12 |
0.15 |
0.09 |
| Benefit |
|
Table 2a shows the conversion of a portion of the data in Table 1 into Absolute
Maximum Incremental Reactivities (MIRs) for methyl pivalate. As seen from Table
2a, Absolute Ozone Formation for different levels of NO
x in ROG is highest
for highest level of NO
x scenario (MIR) and lowest for lowest level
of NO
x scenario (EBIR). As a result, Absolute Reactivity in atmospheric
photochemical ozone formation for tested compounds is highest for MIR scenario
and lowest for EBIR scenario.
| TABLE 2a |
|
| Absolute Reactivity Conversion Ratios |
| Ozone Yield Relative |
MIR |
1 |
0.09 |
0.12 |
0.06 |
| Reactivities |
MOIR |
1 |
0.16 |
0.14 |
0.11 |
| |
EBIR |
1 |
0.21 |
0.15 |
0.12 |
| Ozone Yield |
MIR |
3.93 |
0.354 |
0.472 |
0.236 |
| Absolute Reactivities |
MOIR |
1.41 |
0.226 |
0.197 |
0.155 |
| |
EBIR |
0.82 |
0.172 |
0.123 |
0.098 |
|
Table 2b shows methyl pivalate as having acceptable flash points, boiling temperature,
evaporation rate, low toxicity, good solvency and overall outstanding performance
as a versatile environmentally preferred exempt, extremely low ozone formation
fluid (solvent) for a very wide range of applications.
The compounds presented in Tables 3-4 show calculated Absolute MIR reactivities
for compounds useful as Very Low Polluting Potential Fluids (VLPPF) and Negligibly
Polluting Potential Fluids (NPPF). These fluids provide favorable MIR reactivities,
a very wide range of evaporation rates, and a wide range of solvency and compatibility
with other solvents, polymers, pigments, catalysts, additives, etc., necessary
for actual applications. All the compounds listed in the present invention, especially
in Tables 2a -4, are very useful as substitute conventional solvents having an
Absolute MIR between 1.5 and 3.0 and especially in solvents having high reactivity
Absolute MIR greater than 3.0 in atmospheric photochemical ozone formation.
| TABLE 2b |
|
| Fluid Solvent Properties |
| Boiling Temperature, ° C. |
56 |
|
| Viscosity (cps, 20° C.) |
0.33 |
0.74 |
| Specific Gravity |
0.792 |
0.873 |
| Surface Tension |
22.3 |
23.8 |
| Flash Point (° C.) |
-20* |
7 |
| Evaporation Ratio to Butyl Acetate |
18 |
2.2 |
| Hansen Solubility Parameter |
| Total |
9.2 |
8.1 |
| Nonpolar |
7.6 |
7.2 |
| Polar |
5.1 |
1.8 |
| H-Bonding |
3.4 |
3.1 |
| Toxicity (LD-50, mg/kg) |
5800 |
|
| *Reflects Varied Reported Literature Data |
| TABLE 3 |
|
| Calculated Absolute MIR Reactivities For Negligibly Polluting |
| Potential Fluids |
| |
|
Absolute MIR |
| |
Compound |
(gram ozone produced/gram fluid) |
| |
|
| |
Methyl Pivalate |
0.236 (Actual measured value) |
| |
Tertiary Butyl Pivalate |
0.324 |
| |
|
| TABLE 4 |
|
| Calculated Absolute MIR Reactivities For Very Low Polluting |
| Potential Fluids |
| |
|
Absolute MIR |
| |
Compound |
(gram ozone produced/gram fluid) |
| |
|
| |
Ethyl Pivalate |
0.657 |
| |
Neopentyl Pivalate |
0.700 |
| |
Isopropyl Isobutyrate |
0.930 |
| |
Isopropyl Pivalate |
0.971 |
| |
|
The invention includes a method of reducing atmospheric ozone formation. There
currently are two approaches to evaluation of the factors influencing ground level
ozone formation. One is based on the total amount of organics emitted into the
atmosphere which ultimately combine with nitrogen oxides in a photochemical reaction
to form ozone. Based upon this, all organics are treated equivalently and all contribute
equally to ozone formation, and for gasoline, RVP is used as the parameter correlating
with the amount of total organics released into the air through evaporative pathways.
The second approach recognizes that in fact there are significant differences (as
much as about two orders of magnitude) in ozone formation for different compounds.
Thus, the first approach is not scientifically as useful as the second approach.
To measure specific ozone formation for individual compounds, Maximum Incremental
Reactivity (MIR) method is employed. MIR is defined as grams ozone formed under
atmospheric photochemical reaction conditions per gram of test substance (compound).
Thus, the preferred oxygenated compositions of the instant invention are products
whose absolute maximum incremental reactivity (absolute MIR) is below 1.5 g ozone/gram
of compound (low), preferably below 1.0 g ozone/gram of compound (very low) or
most preferably below 0.5 g ozone/gram compound (negligible).
The invention also includes producing a gasoline fuel containing an ester for
use in internal combustion engines, wherein the ester has a Reid Vapor Pressure
less than about 4 pounds per square inch. An important factor in determining a
compound's ozone formation potential includes the compound's vapor pressure. Compounds
with relatively high vapor pressures are more likely to volatilize into the atmosphere
from open sources. Potential open sources include, for example, sources from production,
distribution, storage and/or combustion of fuels containing oxygenates. The C
7
to C
14 esters according to the invention are expected to have low vapor
pressures in comparison to MTBE and some other oxygenates. Preferably, the esters
have a RVP less than about 3.5 psi. More preferably, less than about 3.0 or 2.0
psi. For example, Methyl Pivalate has a Reid Vapor Pressure of about 1.6 psi.
The invention further includes a method for reducing atmospheric ozone formation.
The method comprising producing a gasoline fuel containing an ester for use in
spark-ignition engines, wherein the ester has an absolute MIR <0.5, thereby
reducing atmospheric ozone formation caused at least in part by production, distribution,
storage and/or combustion of oxygenated fuels as compared to oxygenated fuels containing
oxygenates that are photochemically reactive. Certain hydrocarbon compounds have
little or no potential to participate in photochemical reactions that result in
ozone formation. Well known examples include methane and ethane, which are not
considered as photochemically reactive compounds. When a reactivity scale for ozone
formation is employed to estimate ozone formation, the contribution to ozone formation
derived from the esters of this invention are very small, significantly below that
of currently employed oxygenates such as MTBE, TAME, and ethanol. Because of this
advantage this enables the gasoline blender to have a wide range for oxygen content
based on the esters of this invention, meet RVP requirements and still substantially
reduce ozone formation through evaporative emissions. It is even possible to formulate
a gasoline using the esters of this invention having essentially no ozone forming
potential as based on absolute MIR values.
An important feature of MIR based ozone formation is that compounds which have
MIR values equal to or lower than that of ethane (acetone) are considered to be
non-polluting in terms of ozone formation. These compounds are under current regulations
considered as not contributing to ozone formation. Ethane has an absolute MIR of
0.35 gram ozone/gram ethane. Acetone has been defined by the EPA as exempt under
this definition and therefore is also excluded from consideration as an ozone forming
compound. Acetone has an absolute MIR of 0.48 (W. P. L. Carter, Preliminary Report
to California Air Resources Board under Contract No. 95-308, Aug. 6, 1998). For
example, among the esters of this invention, methyl pivalate has an absolute MIR
of 0.24 and methyl isobutyrate has an absolute MIR of 0.42.
Many of the esters according to the invention, particularly the esters of lower
neoacids, more particularly MP, provide very low reactivity toward ozone formation.
The esters are expected to not participate appreciably in photochemical atmospheric
reactions. Therefore, many of the esters according to the invention can be considered
environmentally preferred components of gasoline fuels.
The present invention is also directed to environmentally preferred fluids and
fluid blends, their use as industrial solvents, and to a method of reducing ozone
formation in a process wherein at least a portion of a fluid eventually evaporates.
The fluids and fluid blends of this invention have been selected by the present
inventors for their actual or potential low reactivity in the complex photochemical
atmospheric reaction with molecular oxygen (O
2) and nitrogen oxides
(NO
X) to create ozone.
The present invention provides a means to reduce ozone formation by photochemical
atmospheric reactions from a fluid solvent composition which is intended at application
conditions to at least partially evaporate into the atmosphere. By properly selecting
low reactive components for a fluid solvent composition, ozone formation can be reduced.
For the purposes of the present invention three groups of reduced ozone reactivity
fluids and their uses are described: (a) Low Polluting Potential Fluid (LPPF),
(b) Very Low Polluting Potential Fluid (VLPPF), and (c) Negligibly Polluting Potential
Fluid (NPPF), according to the Absolute MIR numbers as follows:
|
| |
Absolute MIR |
| Fluid Solvent Designation |
(gm ozone produced/gm fluid) |
|
| Low Polluting Potential Fluid |
1.0-1.5 |
| Very Low Polluting Potential Fluid |
0.5-1.0 |
| Negligibly Polluting Potential Fluid |
<0.5 |
|
Where a composition is a blend of fluids, a weight average MIR (WAMIR) can
be calculated as
WAMIR=ΣWi*MIRi
Where Wi is a weight fraction of solvent fluid component i, and MIRi is the
absolute MIR value of solvent fluid component i. For the purposes of the present
invention, WAMIR will be the preferred method of measuring "ozone formation potential"
or OFP.
It is preferred that the fluids and fluid blends also provide at least one other
desirable performance property such as high flash point, low particulate formation,
suitable evaporation rates, suitable solvency, low toxicity, high thermal stability,
and chemical inertness with respect to non-ozone producing reactions, particularly
with respect to acids which may be present in coating formulations.
In a particularly preferred embodiment, the fluids are used in a blend with known
industrial solvents or other fluids which present an environmental problem with
respect to MIR or lack one or more of the aforementioned desirable performance
properties, so that the new fluid blends will have lower MIR than they would without
the substituted low ozone formation reactivity fluid or have at least one of the
aforementioned other desirable performance properties.
The present invention also includes a method of reducing ozone formation from
atmospheric photochemical reactions in an application wherein a fluid eventually
evaporates, at least partially, into the atmosphere, comprising replacing at least
a portion of a fluid having a relatively higher MIR with a fluid having a relatively
lower MIR. In the case where a blend results, it is preferred that the weighted
average MIR of the blend be similar to or less than the MIR of a Low Polluting
Potential Fluid, and most preferably similar to the MIR of a Negligibly Polluting
Potential Fluid.
A fluid or fluid blend according to the present invention may be used as a carrier,
diluent, dispersant, solvent, or the like. It is preferred that the fluid or fluid
blend be used in a stationary industrial process and it is preferred that the process
is a non-combustion process. The present invention offers its greatest benefit
from the standpoint of safety and health in large-scale industrial or commercial
processes, particularly in large scale coating processes or in formulations used
in large quantities overall.
The fluids used in accordance with this invention have been selected for their
low or reduced ozone formation potential (as reflected in their low or reduced
MIR). The ozone formation potential of a composition or fluid solvent may be determined
by any scientifically recognized or peer reviewed method including but not limited
to, the MIR scale, the K
OH scale, smog chamber studies, and modeling
studies such as those performed by Dr. William P. L. Carter. Most references in
the description of the present invention will be to the Absolute MIR scale measured
in grams ozone produced/gram of fluid solvent. By "low MIR" is meant that the fluids
have an MIR similar to or less than 1.5 gram of ozone per gram of the solvent fluid.
By "reduced MIR" is meant that, in a process according to the present invention,
a first fluid is replaced, in whole or in part, by a second fluid, the second fluid
having an MIR lower than the first fluid. One of ordinary skill in the art can
determine ozone reactivity of a material according to methods in numerous literature
sources and tabulated data published in the open literature. It is mentioned that
the terms "replace", "replacement", "replacing" and the like used herein are not
to be taken as implying only the act of substituting a second fluid (having acceptable
MIR as described herein) in a formulation for a first fluid that may have been
previously used in that and similar formulation(s), with such first fluid has undesirable
MIR as described herein. Rather, the terms are intended to include the formulations
themselves comprising a mixture of the first and second fluids, or one or more
such second fluid(s) without any of said first fluid(s), as the fluid system of
the formulation. In the case where no such first fluid(s) are present, the concept
of "replacement" is intended to refer to corresponding formulations that have only
such first fluid(s) present instead of such second fluid(s) and therefore have
a lower OFP.
The MIR is preferably determined by smog chamber studies, modeling studies, or
a combination thereof, but is more preferably determined by "incremental reactivity",
and still more preferably by the Absolute MIR.
The MIR of a fluid used in this invention is preferably less than or equal to
1.5 gram of ozone per gram of solvent fluid, more preferably less than or equal
to 1.0 gram of ozone per gram of solvent fluid, and most preferably less than or
equal to 0.5 gram of ozone per gram of solvent fluid, but the benefits of the present
invention are realized if ozone formation is reduced by replacing a first fluid
with a second fluid, in whole or in part, wherein the MIR of the second fluid is
reduced from that of the first fluid, even if the second fluid has an MIR greater
than 1.5 gram of ozone per gram of solvent fluid.
Therefore, it is preferred that the fluid according to the present invention
have an MIR less than or equal to 1.50 and more preferably less than or equal to
1.00, still more preferably less than or equal to 0.50. In an even more preferred
embodiment, the reactivity in ozone formation is preferably equal to or less than
that of acetone and even more preferably equal to or less than that of ethane,
by whatever scale or method is used, but most preferably by the MIR scale. Thus,
in a more preferred embodiment, the fluid used in a composition according to the
present invention will have an MIR less than or equal to 0.50, even more preferably
less than or equal to 0.35.
Specifically preferred fluids according to the present invention include:
pivalates such as methyl pivalate (methyl 1,1,1-trimethyl acetate), ethyl
pivalate, isopropyl pivalate, t-butyl pivalate (TBP), neopentyl pivalate (NPP),
and neopentyl glycol mono pivalate;
isobutyrate compounds such as methyl isobutyrate, isopropyl isobutyrate,
neopentyl isobutyrate, and neopentyl glycol mono isobutyrate; and
isopropyl neononanoate; pivalonitrile; and methyl 2,2,4,4-tetramethyl pentanoate
(methyl neononanoate). Other preferred fluids are oxygenated (oxygen containing)
organic compounds substantially free of moieties containing unsaturated carbon-carbon
bonds or aromatic groups.
In the case of a blend, the weighted average MIR of the fluids in a composition
according to the present invention will also have the preferred, more preferred,
and most preferred MIR levels as discussed herein.
In another preferred embodiment, wherein the blend results from replacing part
of a first fluid with a second fluid and thereby reducing the weight average MIR,
it is preferred that the weight average MIR be reduced 10%, more preferably 25%,
still more preferably 50%, from the MIR calculated prior to the fluid replacement.
In yet another preferred embodiment, the Low Polluting Potential Fluids (LPPF),
Very Low Polluting Potential Fluids (VLPPF), and Negligibly Polluting Potential
Fluids (NPPF), as described herein will provide at least one other desirable performance
property such as high flash point low particulate formation, suitable evaporation
rates, suitable solvency, low toxicity, high thermal stability, and chemical inertness.
Of course, it is more preferable that the fluid or blends have two or more of these
performance attributes, and so on, so that the most preferred fluid or fluid blend
has all of these performance attributes.
In the case of a process of reducing ozone formation, wherein a fluid according
to the present invention replaces a fluid, at least in part, having a higher MIR,
described in more detail below, it is preferred that this fluid replacement process,
in addition to reducing ozone formation does not negatively impact any other desirable
performance attributes of the composition as described above.
The flash point of a fluid according to the present invention is preferably at
least -6.1° C. or higher, more preferably greater than +6.0° C., even
more preferably greater than 15° C., still more preferably greater than 25°
C., yet even more preferably greater than 37.8° C., and most preferably greater
than 60° C. One of ordinary skill in the
