Jones D.S.J., Pujado P.R. Handbook of Petroleum Processing
Подождите немного. Документ загружается.
382 CHAPTER 9
Table 9.2.4. Blending octanes of polygasolines
Polymer type
C3 poly C3/C4 poly C4 poly
Measured clear octanes
RON 93 96 98
MON 83 83 83
Blending octanes
10 vol% blend
RON 94 103 126
MON 83 95–99 112.5
20 vol% blend
RON 103
MON ∼92
Note: Base stock was a mixture of about 60% FCC gasoline
and 40% reformate with MON/RON of about 93/81.
Based on these studies, and for these particular base stocks, it was determined that
propylene-derived polymer gasoline had blending octanes of 94 RON and 83 MON;
these values are almost identical to the clear values measured on the blend stock so
that there is no synergism between the propylene condensation product and the base
stock. The situation with the propylene–butenes polymer gasoline is quite different.
Here, the blend stock had RON and MON of 96 and 83, respectively, but it blended
with the base stock at the 10% level as though the octane numbers of the blend stock
were 103 RON and 95 MON, a clear display of synergism with the base stock. Slightly
different but still very high blending values are obtained when blended at the 20 vol%
level. Naturally, the blending values decline progressively when the blend stock is
added in higher and higher proportions, until they reach the clear measured values on
the blend stock at a 100% blend stock proportion.
The impact of synergism is even higher for the butene-derived polymer gasoline.
Here, instead of the measured octanes, 98 RON and 83 MON, we calculate blending
octanes of 126 and 99, respectively, a synergism of 28 numbers for RON and 17
numbers for MON.
The above observations are for the olefinic catalytic condensation products. Similar
observations can be made with the hydrogenated products. In general, however, the
paraffinic product does not exhibit significant synergism with this type of base stock.
A corollary from these observations is that propylene polymer gasoline is fairly poor
for most motor fuel applications. Propylene–butene feeds can make reasonably good
gasolines, and the gasoline products from the Catalytic Condensation process based
on butenes can be best characterized as superb.
GASOLINE COMPONENTS 383
Selective and nonselective gasoline production with the
catalytic condensation process
Most Catalytic Condensation operations with SPA catalysts are conducted in a non-
selective mode in which the main objective is to maximize conversion and the yield of
useful products. Nonselective units tend to be operated at higher temperatures, typi-
cally between 160
◦
C inlet and 200
◦
C outlet temperatures for propylene or propylene–
butene feeds. The objective is to maximize the yield in the gasoline fraction at a target
octane number with little regard for the occurrence of side reactions that may modify
the skeletal structure of the isomers.
For butenes, however, there can be significant differences between selective and nons-
elective operations. Nonselective operations at higher temperatures typically will pro-
duce some C
6
’s and C
7
’s, a lot of C
8
’s , C
9
’s , C
10
’s, and C
11
’s, and significant amounts of
C
12
’s. Selective operations are carried out at lower temperatures and usually at a lower
space velocity. The butenes react selectively with each other to form virtually noth-
ing but the product dimers, C
8
, and trimers, C
12
. Most of the dimers are the so-called
“codimers,” or selective condensation products of one molecule of isobutene with one
molecule of n-butene. The resulting codimers are trimethylpentenes. Typical proper-
ties of the codimers and of their hydrogenated counterparts (the “hydrocodimers”) are
illustrated in Table 9.2.5 (note that this material is slightly different from those shown
in Table 9.2.3 or Table 9.2.4, always as a function of the precise feed composition
and the range of operating conditions). The total codimer product comprises the C
8
and C
12
fractions, and has a very flat boiling range even when expressed in terms
of an Engler or ASTM distillation, which is a less precise fractionation than a TBP
distillation. The total product had a 99 RON and a 82 MON. The hydrogenated total
Table 9.2.5. Properties of codimer products
Total product Dimer product
Olefinic Hydrogenated Olefinic Hydrogenated
Specific gravity 0.744 0.728 0.737 0.717
Engler distillation (
◦
C)
IBP 104 104 102 102
10 109 109 107 107
30 113 112 109 109
50 117 117 110 109
70 124 124 111 110
90 174 170 112 111
EP 210 213 134 132
Octane numbers
RON 99 98 96.8 99
MON 82 93 82.4 93
384 CHAPTER 9
70
80
90
100
110
0 0.2
0.3
0.4 0.5 0.6
iC4= / C4= ratio
octane number
RON clear
MON clear
0.1
Figure 9.2.4. Octane numbers of 90% hydrogenated dimmer versus iC
4
=/nC
4
= ratio in feed.
product, including C
12
’s, had 98 RON and 93 MON. As expected, the specific gravity
of the paraffinic product is slightly lower than the gravity of the olefinic material, but
the boiling range remains virtually unchanged. If one considers the C
8
’s only, after
fractionating out the C
12
’s, we obtain about 97 RON and 82 MON for the olefinic
product, and about 99 and 93, respectively, for the saturated material. Not shown in
here but worth noting is that the lead response of the paraffinic product is always
much higher than for the olefinic material.
The C
12
materials thus made are quite unusual. They are relatively high boiling, and
thus hardly qualify as favored gasoline fractions, but the hydrogenated C
12
’s h a v e
RONs in the 95–97 range, which is indicative of a highly branched structure. Many
different isomers are made and a precise characterization of the product is difficult.
The operation can be conducted in the “dimer” mode with n-butenes only (1-butene
or 2-butene) reacting among themselves, but the end product is not as attractive as
the “codimer” that is obtained by reacting isobutene with n-butenes, or essentially
by reacting isobutene with 2-butene since 1-butene rapidly isomerizes to 2-butene
as the reaction proceeds. Figure 9.2.4 plots the octane number of the hydrogenated
dimer product (in this case after only 90% hydrogenation), versus the weight ratio
of isobutene reacted relative to the total weight of butenes reacted. The reciprocal
of this value is sometimes called the “reaction ratio.” It was soon learned during
World War II that a low reaction ratio is desirable in order to obtain a high octane
product.
The reason that Figure 9.2.4 is based on only 90% hydrogenation is that, as shown in
Figure 9.2.5, a maximum RON is obtained when butylene dimers are hydrogenated to
the corresponding paraffins. This slight optimum is a function of the relative synergism
GASOLINE COMPONENTS 385
80
85
90
95
100
105
110
020406080100
wt% olefin in the product
octane number
MON clear
MON + 0.5% TEL
RON clear
RON + 0.5% TEL
Figure 9.2.5. Heptene yields effect of olefin composition.
between olefins and paraffins and, although no longer used, is especially significant
for the leaded material. Thus, for leaded material, partial hydrogenation of about
85–90% leads to a maximum octane value. For clear, unleaded material, a maximum
octane value is obtained at around 60–70% hydrogenation. Because it is difficult to
control the degree of hydrogenation, it is easier to simply bypass some of the material
around the hydrogenation reactor.
Catalytic condensation process as a source of diesel fuels
The catalytic condensation process can also produce fuels in the diesel boiling range,
although because of their relatively high degree of branching, they all have fairly poor
cetane characteristics, even after hydrogenation.
Table 9.2.6 illustrates a typical range of products in the diesel range obtained by the
Catalytic Condensation process with SPA catalyst followed by hydrogenation. The
worst product is the heavy polymer from a C
3
–C
4
gasoline operation. The other three
materials are products derived from propylene feeds: propylene tetramer (dodecene),
heavy polymer from a tetramer operation, and the entire feed to the tetramer rerun
distillation column.
A commercial operation for the production of synthetic diesel fuel from propylene
was built in South Africa. The commercial results agree reasonably well with the
numbers in Table 9.2.6.
386 CHAPTER 9
Table 9.2.6. Comparison of hydrogenated polymer products in the diesel range
Heavy polymer
Propylene Heavy propylene Tetramer plus from C
3
/C
4
tetramer polymer heavies gasoline
API gravity 54.2 44.4 51.8 49.3
Engler distillation (
◦
C)
10 184 262 188 154
30 187 266 192 206
50 189 271 198 215
70 193 279 208 229
90 198 300 238 271
EP 213 329 277 304
Cetane numbers 32.8 37.0 36.9 28.7
It is possible to improve the quality of the diesel range products by operating in the
selective mode at lower temperatures and lower per-pass conversions with a higher
recycle rate of unconverted material. This approach, however, has not been commer-
cialized.
Petrochemical operations
Petrochemical applications of catalytic olefin condensation center on the production of
heptenes, nonenes, and dodecene (or propylene tetramer). Though initially recovered
by fractionating olefins out of the olefinic product from the Catalytic Condensation
process for the production of polymer gasoline, modern units are specifically designed
and operated to maximize the yield of the desired olefin fractions. The by-products
are still blended into the gasoline pool.
Heptenes and nonenes are the main products used for the production of octyl and decyl
alcohols via the “oxo” or hydroformylation process. Both these alcohols find end use
as esters in plasticizer applications, principally for PVC. Dodecene at one time was a
major product for the manufacture of dodecylbenzene sulfonates as active detergent
ingredients; however, their relatively poor biodegradability led to the discontinuance
of this operation. Dodecenes are still used in the production of tridecyl alcohols via the
oxo process. Some nonenes are also used in the production of nonyl phenols. Because
this chapter is confined to olefin condensation, mostly for motor fuel applications,
only heptenes and nonenes will be discussed briefly.
Heptenes
Table 9.2.7 illustrates a wide range of specifications for heptenes. Though fairly com-
mon to all producers, the values can vary depending on the desired end-use application.
GASOLINE COMPONENTS 387
Table 9.2.7. Typical heptene specifications
Parameter Specification Typical values
Specific gravity 0.705 min 0.711
0.715 max
Boiling range (
◦
C)
IBP 85 min 85
50% 88 min 89
90.5 max
95% 95 max 93
Bromine number 150 min 154
Sulfur 0.02 wt% –
Peroxide number 40 mg/L –
Color +20 Saybolt min –
Ratio of dimethyl-pentenes to
methyl-hexenes
2/1 to 3/1 2.6
Thus, for example, the boiling range and the desired ratio of dimethylpentenes to
methylhexenes may determine the operating conditions in a catalytic condensation
unit and the net recovery and yield of the useful fraction. The product heptenes consist
of a fairly complex mixture of heptene isomers. Table 9.2.8 shows a typical composi-
tion and approximate boiling points for individual major isomer components; many
Table 9.2.8. Major isomers in the heptene fraction (> 0.1 wt% approx.)
No. Component Wt% Boiling point (
◦
C)
1 4,4-Dimethyl-1-pentene 0.8 72.5
2 4,4-Dimethyl-trans-2-pentene 4.4 76.8
3 3,3-Dimethyl-1-pentene 0.2 77.6
4 4,4-Dimethyl-cis-2-pentene 0.1 80.4
5 3,4-Dimethyl-1-pentene 0.2 81.1
6 2,4-Dimethyl-1-pentene 6.2 81.7
7 2,4-Dimethyl-2-pentene 16.5 83.4
8 2,3-Dimethyl-1-pentene 7.8 84.3
9 5-Methyl-trans-2-hexene 1.0 86.1
10 2-Methyl-trans-3-hexene 0.2 86.1
11 3,4-Dimethyl-trans-2-pentene 16.3 87.2
12 3,4-Dimethyl-cis-2-pentene 4.4 87.2
13 3-Methyl-1-ethyl-1-butene 3.1 88.9
14 3-Methyl-trans-3-hexene 0.5 93.6
15 3-Methyl-trans-2-hexene 1.5 93.9
16 3-Methyl-cis-2-hexene 2.9 93.9
17 3-methyl-cis-3-hexene 2.2 95.3
18 2-methyl-2-hexene 2.2 95.4
19 3-Ethyl-2-pentene 1.2 96.0
20 2,3-Dimethyl-2-pentene 27.5 97.4
21 Trans-2-heptene 0.6 97.9
22 Cis-2-heptene 0.1 98.5
388 CHAPTER 9
0 20 40 60 80 100
% propylene in olefins
heptene yield
isobutene
mixed butenes
n-butene
Figure 9.2.6. Hydrogenation of butane dimer.
other isomers can be present at lower concentrations. As a rule, dimethylpentenes
are produced mainly from isobutene, while methylhexenes tend to originate from
n-butenes.
The relative yield of heptenes is illustrated in Figure 9.2.6 as a function of the olefinic
feed composition; as expected, higher yields of heptenes are obtained when the feed
mixture consists of equal proportions of propylene and butenes. Isobutene tends
to produce significantly higher yields of heptenes than n-butene. However, because
isobutene produces more dimethylpentenes, the final yield can only be calculated on
the end product after fractionation that meets the required specifications.
Nonenes
Typical nonene specifications are shown in Table 9.2.9. Actually, there are several
different specifications that could be called “typical,” a main characteristic being the
breadth or narrowness of the cut.
A minimum olefin concentration of 95% or higher is usually required. An olefin con-
centration of 95% can be easily obtained for nonene units that process only propylene
in the feed. However, in units that may also process olefinic recycle streams, as for
example from a tetramer operation, there may be a reduction in the olefin content of
the product owing to hydrogen transfer mechanisms in which hydrogen is transferred
from the heavier species to the lighter olefins. Units with a high gasoline recycle
may experience increased paraffin concentrations in the nonene fraction as high as
30–40%, which render the nonenes unsuitable as oxo plant feed. Most nonene units
GASOLINE COMPONENTS 389
Table 9.2.9. Typical nonene specifications
Specification Typical values
Parameter Narrow range Wide range Narrow range Wide range
Specific gravity 0.738 min 0.740 min
0.745 max 0.745
Boiling range (
◦
C)
IBP 134 min 134 min 134 134
50% – – 135 138
EP 143 max 155 max 142 150
Bromine number 125 min – 127
Sulfur 0.005 wt% max – –
C
8
olefins, wt% 0.5 max –
C
9
olefins, wt% 90.0 min 97.3
C
10
olefins, wt% 3.5 max 2.7
Olefin content (wt%) 95 min
today are disassociated from tetramer production and therefore this problem is seldom
encountered.
Dimersol
™
process
While the Catalytic Condensation process described above makes use of a supported
phosphoric acid catalyst, the Institut Fran¸cais du P´etrole (IFP) developed and com-
mercialized a different approach based on Ziegler-Natta catalyzed oligomerization
using organometallic catalysts. Because of the nature of the catalyst, this process can
be tailored to specific highly selective applications that have been identified by various
names (2):
Dimerization of ethylene to 1-butene
This version is known as Alphabutol
™
and is intended for the selective production of
1-butene for use as a comonomer in the production of linear low-density polyethylene
(LLDPE). Though not in the motor fuel range for refinery applications, its mention
is included here for the sake of completeness and continuity with the other Dimersol
process schemes. The reaction takes place under mild conditions at about 50–60
◦
C,
under sufficient pressure to maintain the reaction medium in the liquid phase, and
in the presence of a homogeneous titanium-based catalyst. Under these conditions,
the n-butene equilibrium favors an almost total conversion of 1-butene to 2-butene;
therefore, it is critical that the catalyst have a total lack of isomerization activity. Some
C
6
+ oligomers are also formed which are used to maintain the catalyst in solution.
390 CHAPTER 9
Molar yields in excess of 93% can be achieved in this operation. This type of operation
is best suited for locations where LLDPE is being produced and in which there is no
other local source of 1-butene. Alphabutol units have been reportedly built in Saudi
Arabia and Thailand.
Dimerization of ethylene to n-butenes
Whereas the IFP Alphabutol process is selective for the production of 1-butene, the
IFP Dimersol E process produces n-butenes and heavier oligomers. The Dimersol E
process also operates at about 50
◦
C in the liquid phase with a Ziegler-type catalyst
that can be a nickel derivative activated by an organometallic reducing agent. Whereas
the Alphabutol process avoids isomerization, the Dimersol E features both dimeriza-
tion and isomerization, and it produces a blend of n-butenes and heavier oligomers,
depending on the feed composition, the actual type of catalyst, and the operating con-
ditions. For polymer-grade ethylene, the Dimersol E process yields 30–70% n-butenes
with a once-through conversion of 90–100%, with the rest being in the C
6
+ gasoline
fraction. Gasoline production can be further enhanced by adding propylene to the
feed. It is worth noting though that in the Dimersol E process the ratio of 1-butene to
2-butene in the product is about 1/1, still well above the equilibrium ratio at 50
◦
C.
Dimerization of propylene and butenes, separately or combined
The Dimersol process (Figure 9.2.7) uses an organometallic catalyst consisting of a
nickel salt in combination with an alkylaluminum compound. Various modalities are
available:
r
Dimersol G—for the dimerization of propylene to isohexenes used in gasoline
blending
r
Dimersol E—for the oligomerization of ethylene and propylene olefins contained
in FCC gases and already described above for the nonselective dimerization and
oligomerization of ethylene
r
Dimersol X—for the selective dimerization of propylene and butenes for the produc-
tion of heptenes or for the dimerization of n-butenes for the production of octenes.
These octenes are fairly linear, have a poor octane number, and are unsuited for
gasoline applications. Heptenes and octenes obtained from the Dimersol X process
are feedstocks for the production of plasticizer alcohols.
In all these Dimersol processes, the olefinic feedstock and the liquid catalyst are
introduced into the reactor in a fashion compatible with the heat removal requirements
in the reaction system. The level of conversion and the distribution of dimers and
oligomers depend on the number of reactors used in series, the residence time, and
the concentration of catalyst. The effluent from the reactor is circulated through a
catalyst neutralization and elimination section and a water wash before fractionation
for the desired cuts.
GASOLINE COMPONENTS 391
catalyst
feed olefins
cooling
water
process
water
NH
3
reactor
scrubbing
waste water
treatment
debutanizer
LPG
olefin oligomers to
fractionation
steam
cooling
water
Figure 9.2.7. Dimersol process (IFP).
Other dimerization or oligomerization processes
No other dimerization or oligomerization processes are used commercially for the
catalytic condensation of light olefins into gasoline range products, but Chevron in
Richmond, California, and NPRC in Japan, use or have used liquid phosphoric acid
to produce propylene tetramers. There are also a few highly selective processes that
are used for the production of specific dimers in petrochemical applications. Some of
the most notable are:
r
Sulfuric acid dimerization of isobutene for the production of trimethylpentenes, in
particular a mixture of 2,2,4-trimethyl-1-pentene and 2,2,4-trimethyl-2-pentene.
These are excellent gasoline blending components (once hydrogenated, 2,2,4-
trimethylpentane is the reference 100 octane hydrocarbon for both RON and MON),
but the technology is fairly messy and not used commercially. Liquid acid catal-
ysis with either sulfuric acid or hydrofluoric acid is extensively used in refining
applications for the alkylation of isobutane with n-butenes or other olefins.
r
Selective dimerization of propylene to 2-methyl-1-pentene over triethylaluminum
in a process developed by Scientific Design and Goodyear. This dimer can be used
as an intermediate for the synthesis of isoprene.
r
Selective dimerization of propylene to 4-methyl-1-pentene over organopotassium
compounds or, in general, strong alkaline catalysts, in the liquid phase. 4-Methyl-
1-pentene is a monomer used in the preparation of transparent plastics with a
high melting point used in microwable cookware, labware, and medical products,
and manufactured commercially by Mitsui Plastics under the name “TPX” and by
Phillips 66 under the name “Crystalor.”