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Catalysis in Modern Petroleum Refining
A. Crucq and .\. Frennet (Editors), Catalysis and Automotive Pollution Control 1987 Elsevier Science Publishers B.V., Amsterdam - Printed in The Ne therl ands
CATALYSIS IN MODERN PETROLEUM REFINING by J. GROOTJANS
LABOFINA SA, Feluy, Belgium.
ABSTRACT The progressive lead phase out in motorspirits, deeper conversion schemes on crudes of poorer quality and more stringent regulations on polluant emissions determine to a large extent the ongoing research in catalysis related to petroleum refining. From the inspection of the gasoline pool of a conversion type refinery, it is clear that major contributions with respect to octane optimization, may be expected from the fluid catalytic cracker and the downstream upgrading of its products. The development of zeolites contributes very substantially to these goals, both by their introduction into FCC catalysts and their use in the upgrading of some of the side streams. The latter is illustrated by a new process developed at Labofina : low value C3-C4 olefinic streams are converted on a zeolitic catalyst to a light olefinic gasoline, particularly suited to be etherified with methanol. This combination process offers many advantages over the present commercial processes. INTRODUCTION The oil refining industry is obviously not the trendsetter with respect to regulations on polluant emissions. These regulations, whether they are related to automotive or heating applications are translated into some of the finished product specifications. Other specifications are dictated by the end use and the marketplace. The task of the oil refining industry is to use in the most profitable way the available resources (crude oil and refining processes) in order to satisfy the demands of finished specification products. During the last 15 years, the oil industry has been facing many challenging problems that are well known by the public. Many refineries extended and adapted their processing units in order to produce from less expensive heavy crude oils, more valuable and cleaner white products. However, the white products obtained by conversion processes generally require further upgrading in order to meet the final specifications. The progressive lead phase out in motorspirits makes it far more complicated. The refiner has to produce more octane barrils from components which are much poorer and more difficult to upgrade. In this paper we aim to illustrate how
:31
32
catalysis, and zeolitic catalysis in particular, allows for some major breakthroughs. FLUID CATALYTIC CRACKING
In a conversion type refining, the fluid catalytic cracker (FCC) produces directly and through downstream upgrading some 30 to 50% of the gasoline pool components. The normal feedstock of the FCC is straight run vacuum gasoil. Deeper conversion routes, metal passivators and the development of more performing hydrotreating catalysts, allow for the production of additional feedstocks: - atmospheric residues, - visbroken and coker vacuum gasoils - solvent deasphalted oils - hydrometallized residues FCC catalyst manufacturers are facing the challenge of developing materials that convert these more refractory feedstocks, while yielding cracked gasoline of improved octane numbers. Two concepts are being used in the design of an octane analyst: - Shape selective zeolite: A shape selective zeolite cracks the low octane paraffinic components out of the gasoline boiling range, and therefore enhances the octane numbers at the expense of decreased gasoline yield. The LPG olefinic fragments can however be converted to premium gasoline components in downstream upgrading units. - Zeolites with reduced hydrogen transfer activity: These zeolites of the faujasite type have as well good hydrogenation as dehydrogenation activity. Slowing down the hydrogen transfer versus the cracking activity is established via controlling the Si/Al ratio during their synthesis and the natural dealuminating process which takes place during the hydrothermal equilibration. The equilibrated unit cell size is well related to the Si/AI ratio, and is a convenient tool in selecting and controlling these octane catalysts. Slowing down the hydrogen transfer favors the production of olefins. Heavy naphtenic compounds are converted into aromatic gas oil components under fast hydrogen transfer, but into aromatic gasoline components when the hydrogen transfer is slowed down relative to the rate of cracking. These catalysts therefore contribute in two ways to increased gasoline octane. On the commercial scale we see effectively a gain of a few RON points when using these catalysts. The gain on the motor octane MaN is in general much less pronounced.
33
DOWNSTREAM UPGRADING More octane enhancement can be achieved through further processing of some of the FCC products. The traditional ones are : - iso-butane/butenes alkylation (HF and H2S04 catalyzed) - catalytic oligomerization of propylene and butenes (H 3P04 on Kieselghur) - dimerization of propylene and butenes (lFP's DIMERSOL) Alkylation is a mature process, and we see little incentive for new catalytic systems, unless they would allow to carry out the reaction without isobutane excess. The olefins condensation processes produce blending stocks of good RON's but somewhat low MaN's:
r - - - - - - - - - · - - - · - - · - - - - - - - - - - - - ---
,
RON
MON
(RON + MONh
93-95 96-97
92-94 81-82
93.5 89
97
79-82
89
---I
f-- -.--.-------.-.---- ---- . . !
C4 alkylate Oligomerisate (C4) Dimerisate cq)
More recently, new options have been made available: -MTBE: The FCC produces about 1.5 wt% on feed of isobutylene. Isobutylene is easily etherified with methanol into MTBE. MTBE has excellent octane numbers (RON == 117, MaN = 101), but obviously, even if all i-C 4 could be recovered from the FCC, the total MTBE product would be less than 2.5% of the gasoline blend. -TAME: The FCC produces roughly 2.5 wt% on feed of tertiary amylenes. They are also readily etherified on cationic resins into TAME. The octane numbers for TAME are somewhat lower than for MTBE : RON = 112, MaN = 99. In blends one finds that part of the MTBE may be substituted by TAME without penalty on the blend octane numbers. Again, full recovery and etherification of the tertiary amylenes would yield a total TAME product representing less than 3.5% of the gasoline pool. - Heavy ethers: Processes are being proposed that aim to etherify the total light catalytic gasoline. The tertiary olefins become however rapidly more difficult to convert with increasing carbon number.
,I
:34
Still other techniques are gaining interest in optimizing the octane barril from FCC derived products such as : - butene-1 to butene-2 isomerization for better alkylate - reforming of the low octane heart cut of the cat cracked gasoline. If the European gasoline demand for high MaN remains steady, esthers will increasingly contribute when lead anti-knocks progressively disappear.
A NEW COMBINAnON PROCESS Refineries that have access to isobutylene streams from steam cracking may face the problem that the existing alkylation and possibly catalytic condensation units cannot take the normal butenes which are contained in the pyrolysis stream. Skeletal isomerization of normal butenes is an active research domain, but has not yet found an industrial realization. Also in a conversion type refinery, there are several streams containing substantial amounts of olefins which are not upgraded: for instance, the propylene splitter bottom. Labofina developed a combination process that very effectively contributes to the octane barril : In the first step of the process, propylene and/or n-butenes are converted to species boiling in the gasoline range. The catalyst is a special shape selective zeolite, operating conditions are mild and the space velocity is exceptionally high. On a propylene feedstock, very substantial amounts of isobutylene are found in the reactor effluent. On a n-butene feedstock, attractive yields of polypropylene are obtained as well as iso-butylene. Material balances and product distributions are presented in Table 1. For comparison, the same analyses are given for the oligomerization on phosphoric acid. At a conversion of 90% on n-butenes, the differences in selectivity between both systems are striking. The ranges reflect the influences of the operating conditions. It is stressed that the shape selective zeolite is very slowly deactivated by coke lay-down. Cycle times of several months are readily obtained, regeneration is carried out by simple coke burning. On an octane basis, it is clear that the gasoline obtained on phosphoric acid is superior. The zeolite however produces essentially gasoline species boiling in the C4-C7 range, a substantial part being tertiary olefins. The phosphoric acid produces dominantly dimers and trimers.
35
Table 1 : Step 1
Material balances at 90% conversion
Feed Type:
C4 Effluent from a MTBE process n-C 4content: 50 wt%
Catalyst:
Shape Selective Zeolite
Typical range
Yield on feed (wt%) Propylene Iso-butylene Gasoline Gasoline analysis (Vol % distillation) 36-98°C 98-150°C 150 - 195°C ,> 195°C !
Phosphoric Acid on Kieselguhr
3.7 - 15.3 3.0 - 6.3 38.3 - 23.4
o o
45.0
36
In a second processing step, the depropanized effluent of the zcolitic conversion is etherified with methanol on a cationic resin. Table 2 summarizes the global material balances, and again gives the comparison with the phosphoric acid process.
r----.---._-I
-----._----_.-
Table 2: Overall material balances after etherification
Labofina cornbination process wt%
-r
vol%
f - - - - - . - - - - - - - - - - - - - - - + - - - - - _.----------
Phosphoric acid on Kieselguhr wt%
~.~_.
--------_... .._,.--,---
vol%
'"
IN: I +N-Butane N-Butenes Methanol Total
50.0 50.0 4.3
50.0 50.0 3.2
50.0 50.0
50.0 50.0
104.3
103.2
100.0
100.0
0.9 8.3 50.0 5.0 5.5 2.0 2.3 30.3
9.6 50.0 5.0 4.4 1.6 1.9 24.4
50.0 5.0
50.0 5.0
45.0
36.1
104.3
96.9
100.0
91.1
OUT: Light ends Propylene I +N-Butane N-Butenes MTBE TAME Heavy ethers Olefinic gasoline Total
Table 3 gives the analysis of the final etherified gasoline. Emphasis is given on the blend octane numbers since these reflect how this component will perform in the gasoline pool. For a complex refinery with alkylation and a phosphoric acid oligomerization process, the linear programming simulation selects the combination process while shutting down the phosphoric acid oligomerization unit. The alkylation remains at full capacity.
;17
Table 3: Analysis of the gasoline obtained by the Labofina combination process
Specific Gravity d1J WT%of ETHERS: MTBE TAME HEAVY ETHERS Total Reid Vapor Pressure, KPA (PSI) Vol % distilled at 100°C RON MON Blend RON - Base at RON - Base at RON
=94.8 unleaded =90.9 (0.15g/l TEL)
BlendMON - Base at MON - Base at MON
=83.5 unleaded =84.0 (0.15 gil TEL)
0.7515 17.6 6.3 7.3 31.2 35.9 (5.2) 49.0 98 83
100 85
96 96
100 100
85 86
90 90
CONCLUSION
The fluid catalytic cracker plays a key role in the increased octane demand resulting from the progressive lead phase out. Zeolites contribute substantially, both in the main cracking process and the downstream upgrading of cracked products. As an example, a new combination process has been discussed that compares very favorably to the traditional condensation processes.
CATALYSIS IN MODERN PETROLEUM REFINING by J. GROOTJANS
LABOFINA SA, Feluy, Belgium.
ABSTRACT The progressive lead phase out in motorspirits, deeper conversion schemes on crudes of poorer quality and more stringent regulations on polluant emissions determine to a large extent the ongoing research in catalysis related to petroleum refining. From the inspection of the gasoline pool of a conversion type refinery, it is clear that major contributions with respect to octane optimization, may be expected from the fluid catalytic cracker and the downstream upgrading of its products. The development of zeolites contributes very substantially to these goals, both by their introduction into FCC catalysts and their use in the upgrading of some of the side streams. The latter is illustrated by a new process developed at Labofina : low value C3-C4 olefinic streams are converted on a zeolitic catalyst to a light olefinic gasoline, particularly suited to be etherified with methanol. This combination process offers many advantages over the present commercial processes. INTRODUCTION The oil refining industry is obviously not the trendsetter with respect to regulations on polluant emissions. These regulations, whether they are related to automotive or heating applications are translated into some of the finished product specifications. Other specifications are dictated by the end use and the marketplace. The task of the oil refining industry is to use in the most profitable way the available resources (crude oil and refining processes) in order to satisfy the demands of finished specification products. During the last 15 years, the oil industry has been facing many challenging problems that are well known by the public. Many refineries extended and adapted their processing units in order to produce from less expensive heavy crude oils, more valuable and cleaner white products. However, the white products obtained by conversion processes generally require further upgrading in order to meet the final specifications. The progressive lead phase out in motorspirits makes it far more complicated. The refiner has to produce more octane barrils from components which are much poorer and more difficult to upgrade. In this paper we aim to illustrate how
:31
32
catalysis, and zeolitic catalysis in particular, allows for some major breakthroughs. FLUID CATALYTIC CRACKING
In a conversion type refining, the fluid catalytic cracker (FCC) produces directly and through downstream upgrading some 30 to 50% of the gasoline pool components. The normal feedstock of the FCC is straight run vacuum gasoil. Deeper conversion routes, metal passivators and the development of more performing hydrotreating catalysts, allow for the production of additional feedstocks: - atmospheric residues, - visbroken and coker vacuum gasoils - solvent deasphalted oils - hydrometallized residues FCC catalyst manufacturers are facing the challenge of developing materials that convert these more refractory feedstocks, while yielding cracked gasoline of improved octane numbers. Two concepts are being used in the design of an octane analyst: - Shape selective zeolite: A shape selective zeolite cracks the low octane paraffinic components out of the gasoline boiling range, and therefore enhances the octane numbers at the expense of decreased gasoline yield. The LPG olefinic fragments can however be converted to premium gasoline components in downstream upgrading units. - Zeolites with reduced hydrogen transfer activity: These zeolites of the faujasite type have as well good hydrogenation as dehydrogenation activity. Slowing down the hydrogen transfer versus the cracking activity is established via controlling the Si/Al ratio during their synthesis and the natural dealuminating process which takes place during the hydrothermal equilibration. The equilibrated unit cell size is well related to the Si/AI ratio, and is a convenient tool in selecting and controlling these octane catalysts. Slowing down the hydrogen transfer favors the production of olefins. Heavy naphtenic compounds are converted into aromatic gas oil components under fast hydrogen transfer, but into aromatic gasoline components when the hydrogen transfer is slowed down relative to the rate of cracking. These catalysts therefore contribute in two ways to increased gasoline octane. On the commercial scale we see effectively a gain of a few RON points when using these catalysts. The gain on the motor octane MaN is in general much less pronounced.
33
DOWNSTREAM UPGRADING More octane enhancement can be achieved through further processing of some of the FCC products. The traditional ones are : - iso-butane/butenes alkylation (HF and H2S04 catalyzed) - catalytic oligomerization of propylene and butenes (H 3P04 on Kieselghur) - dimerization of propylene and butenes (lFP's DIMERSOL) Alkylation is a mature process, and we see little incentive for new catalytic systems, unless they would allow to carry out the reaction without isobutane excess. The olefins condensation processes produce blending stocks of good RON's but somewhat low MaN's:
r - - - - - - - - - · - - - · - - · - - - - - - - - - - - - ---
,
RON
MON
(RON + MONh
93-95 96-97
92-94 81-82
93.5 89
97
79-82
89
---I
f-- -.--.-------.-.---- ---- . . !
C4 alkylate Oligomerisate (C4) Dimerisate cq)
More recently, new options have been made available: -MTBE: The FCC produces about 1.5 wt% on feed of isobutylene. Isobutylene is easily etherified with methanol into MTBE. MTBE has excellent octane numbers (RON == 117, MaN = 101), but obviously, even if all i-C 4 could be recovered from the FCC, the total MTBE product would be less than 2.5% of the gasoline blend. -TAME: The FCC produces roughly 2.5 wt% on feed of tertiary amylenes. They are also readily etherified on cationic resins into TAME. The octane numbers for TAME are somewhat lower than for MTBE : RON = 112, MaN = 99. In blends one finds that part of the MTBE may be substituted by TAME without penalty on the blend octane numbers. Again, full recovery and etherification of the tertiary amylenes would yield a total TAME product representing less than 3.5% of the gasoline pool. - Heavy ethers: Processes are being proposed that aim to etherify the total light catalytic gasoline. The tertiary olefins become however rapidly more difficult to convert with increasing carbon number.
,I
:34
Still other techniques are gaining interest in optimizing the octane barril from FCC derived products such as : - butene-1 to butene-2 isomerization for better alkylate - reforming of the low octane heart cut of the cat cracked gasoline. If the European gasoline demand for high MaN remains steady, esthers will increasingly contribute when lead anti-knocks progressively disappear.
A NEW COMBINAnON PROCESS Refineries that have access to isobutylene streams from steam cracking may face the problem that the existing alkylation and possibly catalytic condensation units cannot take the normal butenes which are contained in the pyrolysis stream. Skeletal isomerization of normal butenes is an active research domain, but has not yet found an industrial realization. Also in a conversion type refinery, there are several streams containing substantial amounts of olefins which are not upgraded: for instance, the propylene splitter bottom. Labofina developed a combination process that very effectively contributes to the octane barril : In the first step of the process, propylene and/or n-butenes are converted to species boiling in the gasoline range. The catalyst is a special shape selective zeolite, operating conditions are mild and the space velocity is exceptionally high. On a propylene feedstock, very substantial amounts of isobutylene are found in the reactor effluent. On a n-butene feedstock, attractive yields of polypropylene are obtained as well as iso-butylene. Material balances and product distributions are presented in Table 1. For comparison, the same analyses are given for the oligomerization on phosphoric acid. At a conversion of 90% on n-butenes, the differences in selectivity between both systems are striking. The ranges reflect the influences of the operating conditions. It is stressed that the shape selective zeolite is very slowly deactivated by coke lay-down. Cycle times of several months are readily obtained, regeneration is carried out by simple coke burning. On an octane basis, it is clear that the gasoline obtained on phosphoric acid is superior. The zeolite however produces essentially gasoline species boiling in the C4-C7 range, a substantial part being tertiary olefins. The phosphoric acid produces dominantly dimers and trimers.
35
Table 1 : Step 1
Material balances at 90% conversion
Feed Type:
C4 Effluent from a MTBE process n-C 4content: 50 wt%
Catalyst:
Shape Selective Zeolite
Typical range
Yield on feed (wt%) Propylene Iso-butylene Gasoline Gasoline analysis (Vol % distillation) 36-98°C 98-150°C 150 - 195°C ,> 195°C !
Phosphoric Acid on Kieselguhr
3.7 - 15.3 3.0 - 6.3 38.3 - 23.4
o o
45.0
36
In a second processing step, the depropanized effluent of the zcolitic conversion is etherified with methanol on a cationic resin. Table 2 summarizes the global material balances, and again gives the comparison with the phosphoric acid process.
r----.---._-I
-----._----_.-
Table 2: Overall material balances after etherification
Labofina cornbination process wt%
-r
vol%
f - - - - - . - - - - - - - - - - - - - - - + - - - - - _.----------
Phosphoric acid on Kieselguhr wt%
~.~_.
--------_... .._,.--,---
vol%
'"
IN: I +N-Butane N-Butenes Methanol Total
50.0 50.0 4.3
50.0 50.0 3.2
50.0 50.0
50.0 50.0
104.3
103.2
100.0
100.0
0.9 8.3 50.0 5.0 5.5 2.0 2.3 30.3
9.6 50.0 5.0 4.4 1.6 1.9 24.4
50.0 5.0
50.0 5.0
45.0
36.1
104.3
96.9
100.0
91.1
OUT: Light ends Propylene I +N-Butane N-Butenes MTBE TAME Heavy ethers Olefinic gasoline Total
Table 3 gives the analysis of the final etherified gasoline. Emphasis is given on the blend octane numbers since these reflect how this component will perform in the gasoline pool. For a complex refinery with alkylation and a phosphoric acid oligomerization process, the linear programming simulation selects the combination process while shutting down the phosphoric acid oligomerization unit. The alkylation remains at full capacity.
;17
Table 3: Analysis of the gasoline obtained by the Labofina combination process
Specific Gravity d1J WT%of ETHERS: MTBE TAME HEAVY ETHERS Total Reid Vapor Pressure, KPA (PSI) Vol % distilled at 100°C RON MON Blend RON - Base at RON - Base at RON
=94.8 unleaded =90.9 (0.15g/l TEL)
BlendMON - Base at MON - Base at MON
=83.5 unleaded =84.0 (0.15 gil TEL)
0.7515 17.6 6.3 7.3 31.2 35.9 (5.2) 49.0 98 83
100 85
96 96
100 100
85 86
90 90
CONCLUSION
The fluid catalytic cracker plays a key role in the increased octane demand resulting from the progressive lead phase out. Zeolites contribute substantially, both in the main cracking process and the downstream upgrading of cracked products. As an example, a new combination process has been discussed that compares very favorably to the traditional condensation processes.