Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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INTEGRATED PROCESS FOR MAKING HIGH-OCTANE GASOLINE AND HIGH-CETANE DIESEL
BACKGROUND
[0001] The present invention relates to an integrated process to upgrade
relatively low-value
paraffinic materials to high-octane gasoline and high-cetane diesel. The
process is particularly
.. applicable to the upgrading of low-value paraffinic feeds, such as iso-
butane and heavy virgin
naphtha to make high-octane alkylate and high-cetane diesel via oxidation.
[0002] Alkylate is composed of a mixture of high-octane, branched-chain
paraffinic
hydrocarbons (mostly iso-heptane and iso-octane). Alkylate is a premium
gasoline blending stock
because it has exceptional antiknock properties, relatively low Reid Vapor
Pressure (RVP), and is
1() clean burning. The octane number of an alkylate depends mainly upon the
kind of feeds used and
upon operating conditions. For example, iso-octane results from combining C4
olefins with iso-
butane and has an octane rating of 100 by definition. There are other products
in the alkylate, so
the octane rating will vary accordingly. Current technologies for producing
high octane alkylate
require C4 olefins, particularly iso-butylene, which are alkylated with iso-
butane using an acid
catalyst, such as H2SO4, HF, or solid acids as zeolites. When C4 olefins are
constrained, expensive
on-purpose C4 olefin generation is utilized to provide feedstock, and requires
high temperatures,
low pressures, and frequent catalyst regeneration. There remains a need to
develop a new process
for utilizing abundant paraffins, specifically iso-butane, to produce high-
octane alkylate without
expensive C4 olefin as a feedstock.
[0003] High-cetane diesel (diesel with a cetane number in the range of
about 40-110, preferably
about 45-90, and more preferably about 50-80) is typically obtained from crude
distillation, or from
Fischer-Tropsch synthesis. These diesel molecules, particularly those from
Fischer-Tropsch
synthesis, require an additional hydro-isomerization (i.e. dewaxing) step to
meet the cloud point
specification for diesel. Low octane naphtha, such as heavy virgin naphtha, is
typically converted
to aromatics, a high octane gasoline blend, using catalytic reforming. There
remains a need to
utilize abundant naphthas, such as heavy virgin naphtha, heavy cat naphtha,
and coker naphtha, to
produce high-cetane diesel, a more carbon-efficient disposition for heavy
virgin naphtha than
gasoline.
[0004] Demand for high-octane gasoline and high-cetane diesel is
expected to grow.
Additionally, the increased supply of light paraffins in North America and the
abundance of heavy
virgin naptha creates a need and opportunities for upgrading to high-octane
gasoline and high-
cetane diesel. Disclosed herein is an integrated process for achieving both.
SUMMARY
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100051 We have now found a novel integrated process for upgrading low-
value paraffinic
materials to high octane gasoline and high-cetane diesel. In a first
embodiment of the present
invention, the process involves: (1) oxidation of an iso-paraffin to alkyl
hydroperoxide and alcohol;
(2) converting the alkyl hydroperoxide and alcohol to dialkyl peroxide; (3)
converting low-octane,
-- paraffinic gasoline molecules using the dialkyl peroxides as radical
initiators, thereby forming
high-cetane diesel, while the dialkyl peroxide is converted to an alcohol; (4)
converting the alcohol
to an olefin; and (5) alkylating the olefin with iso-butane to form high-
octane alkylate. An
alternative embodiment to Step 5 is dimerization of the olefin giving another
type of high octane
fuel. The net reaction is thus conversion of iso-paraffin to high-octane
gasoline alkylate, and
conversion of low-octane paraffinic gasoline to high-cetane diesel.
[0006] In another embodiment of the present invention, the process
involves (1) oxidation of
iso-butane to t-butyl hydroperoxide and t-butyl alcohol; (2) converting the t-
butyl hydroperoxide
and the t-butyl alcohol to di-t-butyl peroxide; (3) converting heavy naphtha,
such as heavy virgin
naphtha, heavy cat naphtha, or coker naphtha, using the di-t-butyl peroxide as
radical initiators,
thereby forming high-cetane diesel, while the di-t-butyl peroxide is converted
to t-butyl alcohol;
(4) converting the t-butyl alcohol to iso-butylene; and (5) alkylating the iso-
butylene with iso-
butane to form high-octane alkylate. An alternative to Step 5 is dimerization
of the olefin giving
another type of high octane fuel. The net reaction is thus conversion of iso-
butane to high-octane
gasoline alkylate, and conversion of heavy virgin naphtha to high-cetane
diesel.
DETAILED DESCRIPTION
[0007] The present invention relates to an integrated process for
upgrading low-value
paraffinic materials to high octane gasoline and high-cetane diesel. The
process of the present
invention involves three primary steps: (1) oxidation of an iso-paraffin to
alkyl hydroperoxide and
alcohol; (2) converting the alkyl hydroperoxide and alcohol to dialkyl
peroxide; (3) converting
low-octane, paraffinic gasoline molecules using the dialkyl peroxides as
radical initiators, thereby
forming high-cetane diesel, while the dialkyl peroxide is converted to an
alcohol; (4) converting
the alcohol to an olefin; and (5) alkylating the olefin with iso-butane to
form high-octane alkylate.
The net reaction is thus conversion of iso-paraffin to high-octane gasoline
alkylate, and conversion
of low-octane paraffinic gasoline to high-cetane diesel.
[0008] In a preferred embodiment of the present invention, the iso-paraffin
feedstock is iso-
butane. The process proceeds as described generally above: (1) oxidation of
iso-butane to t-butyl
hydroperoxide and t-butyl alcohol; (2) converting the t-butyl hydroperoxide
and the t-butyl alcohol
to di-t-butyl peroxide; (3) converting heavy naphtha, such as heavy virgin
naphtha, heavy cat
naphtha, or coker naphtha, using the di-t-butyl peroxide as radical
initiators, thereby forming high-
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cetane diesel, while the di-t-butyl peroxide is converted to t-butyl alcohol;
(4) converting the t-
butyl alcohol to iso-butylene; and (5) alkylating the iso-butylene with iso-
butane to form high-
octane alkylate. An alternative to Step 5 is dimerization of the olefin giving
another type of high
octane fuel. The net reaction is thus conversion of iso-butane to high-octane
gasoline alkylate, and
conversion of heavy virgin naphtha to high-cetane diesel.
[0009] The chemistry of Steps 1-5 with respect to iso-butane feed is
shown below in
corresponding Equations 1-5:
Equation 1: y YOCH roH
H-)0
Equation 2: Yoogi y)H >r-oek
0
-0
Equation 3:
YOH
Equation 4 YoH + H20
[0010] Steps 1 and 2 have been previously described with respect to
mixed paraffinic
feedstocks in applicant's co-pending application, U.S. Publ. App. No.
2016/0168048, incorporated
by reference herein in its entirety. U.S. Publ. App. No. 2016/0168048
describes a process to
convert light paraffins to heavier hydrocarbons generally, for example,
distillates and lubricant
base stocks, using coupling chemistry analogous to Steps 1 and 2 described
above. Whereas U.S.
Publ. App. No. 2016/0168048 is directed to mixed paraffinic feed to create
distillates and lubricant
base stocks, the present invention utilizes analogous coupling chemistry to
create high-cetane
diesel utilizing iso-paraffins such as iso-butane and iso-paraffinic gasoline
as feedstock.
[0011] Iso-butane oxidation in Step 1/Equation 1 is well-established
commercially for making
t-butyl hydroperoxide (TBHP) for propylene oxide manufacture, with variants of
the process also
described, for example, in U.S. Pat. No. 2,845,461; U.S. Pat. No. 3,478,108;
U.S. Pat. No.
4,408,081 and U.S. Pat. No. 5,149,885. EP 0567336 and U.S. Pat. No. 5,162,593
disclose co-
production of TBHP and t-butyl alcohol (TBA). As TBA is another reactant used
in Step 2 of the
present invention, the present inventive process scheme utilizes Step 1 as a
practical source of these
two reactants. Air (¨ 21% oxygen), a mixture of nitrogen and oxygen containing
2-20 vol% oxygen,
or pure oxygen, can be used for the oxidation, as long as the oxygen-to-
hydrocarbon vapor ratio is
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kept outside the explosive regime. Preferably air is used as the source of
oxygen. Typical oxidation
conditions for Step 1 of the present invention are: 110-150 C (preferably 130
to 140 C, at a
pressure of about 300-800 psig (preferably about 450-550 psig), with a
residence time of 2-24
hours (preferably 6-8 h), to give a targeted conversion of 15%-70% (preferably
30-50%).
Selectivity to TBHP of 50-80% and to TBA of 20-50% is typical.
[0012] In Step 2/Equation 2, the conversion of the TBHP and TBA to di-t-
butyl peroxide
(DTBP) is performed using an acid catalyst. For example, U.S. Pat. No.
5,288,919 describes the
use of an inorganic heteropoly and/or isopoly acid catalyst (such as for the
reaction of TBA with
TBHP. The conjoint production of DTBP and TBA from TBHP is also described in
U.S. Pat. No.
5,345,009. A preferred configuration for the present invention uses reactive
distillation where
product water is continuously removed as overhead by-product. Typical reaction
temperature is in
the range of 50 ¨ 200 C, preferably 60¨ 150 C, more preferably 80-120 C.
The TBHP to TBA
mole ratio is in the range of 0.5 ¨2, preferably 0.8 ¨ 1.5, more preferably
0.9¨ 1.1. The reaction
can be performed with or without a solvent. Suitable solvents comprise
hydrocarbons having a
carbon number greater than 3, such as paraffins, naphthenes, or aromatics.
Conveniently, the
unreated iso-butane from Step 1 can be used as solvent for Step 2. Pressure
for the reaction is held
at appropriate ranges to ensure the reaction occurs substantially in the
liquid phase, for example, 0
¨ 300 psig, preferably 5 ¨ 100 psig, more preferably 15 ¨ 50 psig. An acid
catalyst such as
AmberlystTM resin, NafionTM resin, aluminosilicates, acidic clay, zeolites
(natural or synthetic),
silicoaluminophosphates (SAPO), heteropolyacids, acidic oxides such as
tungsten oxide on
zirconia, molybdenum oxide on zirconia, sulfunated zirconia, liquid acids such
sulfuric acid, or
acidic ionic liquids may be used in Step 2/Equation 2 to promote the
conversion of TBHP and TBA
into DTBP.
[0013] In Step 3/Equation 3, DTBP is introduced to a coupling reactor to
initiate free radical
coupling of heavy virgin naphtha (HVN). Typical reaction conditions for Step 3
of the present
invention are: 100-170 C (preferably about 145-155 C), with pressure
maintained to ensure that
paraffins stay in the liquid or supercritical phase, typically 300-1500 psig
(preferably about 500-
1200 psig). Residence time is normally in the range of 2-24 hours (preferably
4-16 hours). The
molar ratio of DTBP to HVN to be coupled is in the range of about 0.01-100,
preferably in the
range of about 0.05-10, and more preferably in the range of 0.1-2. By
controlling the reaction
severity for radical coupling (Equation 3), higher molecular weight products
can also be obtained.
Complete conversion of DTBP is normally achieved in this step. Following Step
3, the mixed
product stream is fractionated, with unreacted HVN being recycled to the
coupling reactor, TBA
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being sent to Step 4, and byproduct acetone being removed. Due to the nature
of the coupling
chemistry, the diesel fraction (C14-C28) are branched with short chain alkyl
groups such as methyl
and ethyl, yielding a resulting product having a high cetane value. It is
envisioned that other heavy
naphtha feeds, such as heavy cat naphtha (i.e. the heavy naphtha fraction from
a catalytic cracker)
or coker naphtha, are acceptable feedstock for Step 3 of this invention.
[0014] In Step 4/Equation 4, TBA is sent to a dehydration reactor, where
it is dehydrated over
an acid catalyst to yield iso-butylene and water. An acid catalyst such as
AmberlystTM resin,
NafionTM resin, aluminosilicates, acidic clay, alumina, zeolites (natural or
synthetic),
silicoaluminophosphates (SAPO), heteropolyacids, acidic oxides such as
tungsten oxide on
.. zirconia, molybdenum oxide on zirconia, sulfunated zirconia, liquid acids
such sulfuric acid, or
acidic ionic liquids may be used. Typical reaction temperature is in the range
of 150 ¨ 400 C,
preferably 200 ¨ 350 C, more preferably 250 ¨ 350 C. Typical pressure for
the reaction is 50 ¨
500 psig, preferably 100 ¨ 400 psig, more preferably 200 ¨ 300 psig. The
reaction can be performed
in fixed-bed or batch reactor. A preferred embodiment of this step utilizes
reactive distillation to
continuously remove co-product water.
[0015] In Step 5/Equation 5, iso-butylene (from Step 4) is sent to an
alkylation reactor, where
it is alkylated with iso-butane to yield high-octane alkylate. The alkylation
reaction can be
conducted in a wide range of reactor configurations including fixed bed
(single or in series), slurry
reactors, and/or catalytic distillation towers. In addition, the alkylation
reaction can be conducted
in a single reaction zone or in a plurality of reaction zones, preferably in a
plurality of reaction
zones. The mole ratio of iso-butane to iso-butylene may be in the range of 1 ¨
100, preferably 5 ¨
80, more preferably 10 ¨ 50. The alkylation is conducted in the presence of an
acid catalyst. Any
catalyst suitable for isoparaffin alkylation, whether homogeneous or
heterogeneous, may be used.
Examples of suitable acidic homogeneous catalysts include hydrofluoric acid,
sulfuric acid, and
mixtures thereof. Examples of suitable acidic heterogeneous catalysts include
chlorided alumina,
fluorided alumina, zeolites, acidic metal oxides and mixed metal oxides, and
mixtures thereof
Non-limiting examples of such zeolites include those of the MOR, BEA, FAU,
MTW, and MWW
families, preferably the FAU, MWW, and MOR families. Non-limiting examples of
acidic metal
oxides or mixed metal oxides include tungsten oxides (W0x), molybdenum oxide
(Mo0x), mixed
oxides such as W0x/Zr02, W0x/Ce02, Mo0x/Zr02, Mo0x/Ce02, and sulfated
zirconia. When
a homogenous acid catalyst is used, such as hydrofluoric acid or sulfuric
acid, suitable reaction
temperatures range from about 0 C and about 50 C, such as from about 5 C and
about 40 C, or
from about 10 C and about 25 C. When a heterogeneous acid catalyst is used,
such as a zeolite,
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suitable reaction temperatures range from about 100 C to about 400 C,
preferably from about
125 C to about 300 C, more preferably from about 150 C to about 250 C.
Irrespective of the
catalyst employed, the reaction pressure is preferably maintained so that the
C4 olefinic feed
remains in liquid form within the reactor. For instance, suitable reaction
pressures are from about
100 kPa to about 7000 kPa absolute (e.g., atmospheric to about 1000 psia),
such as from about 500
kPa to about 5000 kPa absolute.
EXAMPLE
[0016] In order to provide a better understanding of the foregoing
disclosure, the following
non-limiting example is offered. Although the example may be directed to
specific embodiments,
they are not to be viewed as limiting the invention in any specific respect.
[0017] This example illustrates the general procedure for coupling n-
heptane (to demonstrate
HVN) using DTBP to form high-cetane diesel. In a 300 cc autoclave the
following were loaded:
60 g of n-heptane and 30 g of DTBP (trade name Luperox DI from Aldrich
Chemicals, 98%). The
autoclave was sealed, connected to a gas manifold, and pressurized with 600
psig nitrogen. The
reactor content heated under stirring (500 rpm) at a rate of 2 C/min to 150
C and held for 4 hours.
The heat was turned off and the autoclave allowed to cool down to room
temperature. A sample
was taken and analyzed by GC analysis, showing complete conversion of DTBP and
30%
conversion of n-heptane. The autoclave was opened and the reactor content
collected at the end of
the run, recovering 88% of the materials loaded. The products are shown in
Table 1 below:
Reaction temperature (oC) 150
Time (h) 4
n-heptane loading, g 60
DTBP loading, g 30
HC wt, sel. (%)
C14 38
C14+ 60
Oxygenates wt. sel. (%)
Acetone 13
t-Butanol 87
Table 1
[0018] As demonstrated in Table 1, a high-cetane diesel composition can
be produced
according to certain teachings of the present invention. Due to the nature of
the coupling chemistry,
the diesel fraction (C14-C28) are branched with short chain alkyl groups such
as methyl and ethyl,
yielding a resulting product having a high cetane value. One of ordinary skill
in the art will
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appreciate that by controlling the reaction severity for radical coupling
(Equation 3), higher
molecular weight products can also be obtained. The TBA co-product can be
further upgraded to
high-octane alkylate using known dehydration and alkylation technologies, as
described in Steps
4-5 above.
ADDITIONAL EMBODIMENTS
[0019] Embodiment 1. A process for upgrading substantially paraffinic
feed to high-cetane
diesel, comprising oxidizing a first feed stream comprising one or more iso-
paraffins to form
alkyl hydroperoxides and first alcohols, catalytically converting the alkyl
hydroperoxides and
first alcohols to dialkyl peroxides, and coupling a second feed stream
substantially comprising
paraffins using the dialkyl peroxides as a radical initiator to create high-
cetane diesel and second
alcohols.
[0020] Embodiment 2. A process according to embodiment 1, further
comprising converting
the second alcohols to olefins.
[0021] Embodiment 3. A process according to embodiment 2, further
comprising alkylating
the olefins with iso-paraffins to form high-octane gasoline.
[0022] Embodiment 4. A process according to embodiment 2, further
comprising dimerizing
the olefins to form high octane gasoline.
[0023] Embodiment 5. An integrated process for upgrading low-value
paraffinic materials to
high octane gasoline and high-cetane diesel, comprising oxidizing a first feed
stream comprising
one or more iso-paraffins to form alkyl hydroperoxides and first alcohols,
catalytically
converting the alkyl hydroperoxides and first alcohols to dialkyl peroxides,
coupling a second
feed stream substantially comprising paraffins using the dialkyl peroxides as
a radical initiator to
create high-cetane diesel and second alcohols, converting the second alcohols
to olefins, and
alkylating the olefins with iso-butane to form high-octane gasoline.
[0024] Embodiment 6. A process according to any of the previous
embodiments, wherein the
first feed stream comprises iso-butane.
[0025] Embodiment 7. A process according to any of the previous
embodiments, wherein the
second feed stream comprises heavy virgin naphtha.
[0026] Embodiment 8. A process according to any of the previous
embodiments, wherein the
second feed stream comprises coker naphtha.
[0027] Embodiment 9. A process according to any of the previous
embodiments, wherein the
second feed stream comprises heavy cat naphtha.
[0028] Embodiment 10. A process according to any of the previous
embodiments, wherein
the second feed stream comprises paraffins in the carbon number range of 7-12.
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100291 Embodiment 11. An integrated process for upgrading low-value
paraffinic materials
to high octane gasoline and high-cetane diesel, comprising, oxidizing iso-
butane to form t-butyl
hydroperoxide and t-butyl alcohol, catalytically converting the t-butyl
hydroperoxide and the t-
butyl alcohol to di-t-butyl peroxide, coupling heavy naphtha using di-t-butyl
peroxide as a radical
initiator to create high-cetane diesel and t-butyl alcohol, converting the t-
butyl alcohol to iso-
butylene, and alkylating the iso-butylene with iso-butane to form high-octane
gasoline.
[0030] Embodiment 12. A process according to embodiment 11, wherein the
heavy naphtha
comprises heavy virgin naphtha.
[0031] Embodiment 13. A process according to embodiment 11, wherein the
heavy naphtha
comprises coker naphtha.
[0032] Embodiment 14. A process according to embodiment 11, wherein the
heavy naphtha
comprises heavy cat naphtha.
[0033] Embodiment 15. A process according to embodiment 11, wherein the
second feed
stream comprises paraffins in the carbon number range of 7-12.
[0034] Embodiment 16. An integrated process for upgrading low-value
paraffinic materials
to high octane gasoline and high-cetane diesel, comprising, oxidizing iso-
butane to form t-butyl
hydroperoxide and t-butyl alcohol, catalytically converting the t-butyl
hydroperoxide and the t-
butyl alcohol to di-t-butyl peroxide, coupling heavy naphtha using di-t-butyl
peroxide as a radical
initiator to create high-cetane diesel and t-butyl alcohol, converting the t-
butyl alcohol to iso-
butylene, and dimerizing the iso-butylene to form high-octane gasoline.
[0035] Embodiment 17. A process according to any of the previous
embodiments, wherein
the high-cetane diesel has a cetane number greater than 40.
[0036] Embodiment 18. A process according to any of the previous
embodiments, wherein
the high-cetane diesel has a cetane number greater than 45.
[0037] Embodiment 19. A process according to any of the previous
embodiments, wherein
the high-cetane diesel has a cetane number greater than 50.
[0038] Therefore, the present invention is well adapted to attain the
ends and advantages
mentioned as well as those that are inherent therein. The particular
embodiments disclosed above
are illustrative only, as the present invention may be modified and practiced
in different but
equivalent manners apparent to those skilled in the art having the benefit of
the teachings therein.
It is therefore evident that the particular embodiments disclosed above may be
altered or modified
and all such variations are considered within the scope and sprit of the
present invention. Unless
otherwise indicated, all numbers expressing quantities of ingredients,
properties, reaction
conditions, and so forth, used in the specification and claims are to be
understood as
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approximations based on the desired properties sought to be obtained by the
present invention.
Whenever a numerical range with a lower limit and an upper limit is disclosed,
a number falling
within the range is specifically disclosed. Moreover, the indefinite articles
"a" or "an", as used in
the claims, are defined herein to mean one or more than one of the element
that it introduces.
