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Issue 31/2014 - Utilization scheme study of isobutane in carbon tetrafractions

 Last Update: 2022-11-13
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Study on the utilization scheme of isobutane in carbon four fractions

□ Li Tao, Nanjing Research Institute, Sinopec Yangzi Petrochemical Co.
, Ltd

Li Tao

At present, domestic refining and chemical enterprises generally separate n-paraffins and isoparaffins through adsorption and separation processes for saturated carbon four fractions of atmospheric decompression, medium-pressure hydrogenation and aromatic reforming devices, n-butane is usually used as cracking material for ethylene plants, and isobutane is mostly used
as fuel.
For the carbon four fraction derived from the catalytic cracking unit, usually first with methanol etherification to synthesize MTBE, the isobutylene component is used, the etherified carbon four fraction contains a higher concentration of n-butylene component, can produce methyl ethyl ketone, the remaining butane component as fuel, and some enterprises directly use
the catalytic cracking carbon four fraction as liquefied gas.

MTBE, the isobutylene component is utilized, the etherified carbon four fraction contains a higher concentration of n-butene components, can produce methyl ethyl ketone, the remaining butane components as fuel, and some enterprises directly use
catalytic cracking carbon four fractions as liquefied gas.

From the current utilization of isobutane at home and abroad, it mainly includes three ways: (1) isobutane and butene, pentene and other olefins react to synthesize alkylated oil
.
Isobutane alkylation technology is relatively mature, the current production route of the world's large equipment is basically still based on sulfuric acid method and hydrofluoric acid method, liquid acid alkylation process has problems such as
large waste acid emissions and serious corrosion of production equipment.
In recent years, alkylation processes with solid acids and ionic liquids as catalysts have also become the focus
of attention.
Compared with the liquid acid alkylation process, the solid acid alkylation process has shown a certain degree of economy, but whether it can operate stably on large industrial plants remains to be tested
.
(2) Isobutane/propylene co-oxidation to produce propylene oxide (PO) and co-produced tert-butanol (TBA).

Currently industrialized isobutane/propylene co-oxidation processes include Lyondell technology and Huntsman technology, which differ mainly in the use of catalysts, product separation and PO purification units
.
In the typical isobutane co-oxidation production PO/TBA process, the mass ratio of raw propylene to isobutane is about 1:2.
4, and the mass ratio of product PO to TBA is 1:(2.
4~2.
7), and the co-produced TBA can be further processed into MTBE; (3) Isobutane dehydrogenation to isobutylene
.
At present, the industrialized isobutane dehydrogenation process includes the FBD-4 process jointly developed by Snamprogetti of Italy and Yarintez of Russia, the Catofin process of Lummus, the Oleflex process of UOP, the Star process of Phillips and the Linde process of Linde AG
.

/propylene co-oxidation to propylene oxide (PO) and co-production of tert-butanol (TBA).

Currently industrialized isobutane/propylene co-oxidation processes include Lyondell technology and Huntsman technology, which differ mainly in the use of catalysts, product separation and PO purification units
.
In the typical isobutane co-oxidation production PO/TBA process, the mass ratio of raw propylene to isobutane is about 1:2.
4, and the mass ratio of product PO to TBA is 1:(2.
4~2.
7), and the co-produced TBA can be further processed into MTBE; (3) Isobutane dehydrogenation to isobutylene
.
At present, the industrialized isobutane dehydrogenation process includes the FBD-4 process jointly developed by Snamprogetti of Italy and Yarintez of Russia, the Catofin process of Lummus, the Oleflex process of UOP, the Star process of Phillips and the Linde process of Linde AG
.

1.
Co-oxidation of isobutane and propylene

Propylene oxide

This scheme is to co-oxidize isobutane and propylene to produce propylene oxide, and the co-produced tert-butanol can react with methanol to synthesize MTBE, and MTBE can also be further dehydrated to produce high-purity isobutene
.
Raw materials come from isobutane from refineries or aromatic reformers, and propylene from refinery catalytic crackers or ethylene
crackers.

MTBE, MTBE can also be further dehydrated to produce high-purity isobutylene
.
Raw materials come from isobutane from refineries or aromatic reformers, and propylene from refinery catalytic crackers or ethylene
crackers.

This process route is more suitable for the current development status of domestic petrochemical enterprises, and can convert isobutane resources of petrochemical enterprises into products
with higher added value.
At present, MTBE has not been banned in China, and the market demand is still growing, MTBE has almost become a component necessary for most domestic refineries to adjust octane number, even if MTBE is banned in China in the future, it can also be converted to high-purity isobutylene through the construction of tert-butanol dehydration isobutylene
equipment.
As shown in Figure 1, a variety of organic chemical raw materials and fine chemicals such as methacrylate (MMA), polyisobutylene and butyl rubber can be further prepared through high-purity isobutylene, and in recent years, there has been a huge potential demand
for polymeric-grade isobutylene at home and abroad.
So far, there are two main production methods of high-purity isobutylene in the industry: MTBE cleavage method and tert-butanol dehydration method
.
The tert-butanol dehydration method has a simple process, less side reactions, easy separation and refining, high product quality, and low investment (3O%
less than MTBE pyrolysis method).
In addition, the circulating logistics of the TBA dehydration process to produce isobutylene is water, while the circulating logistics of MTBE pyrolysis is methanol, which is more environmentally friendly
.

MTBE, and the market demand is still growing, MTBE has almost become a component necessary for most domestic refineries to adjust the octane number, even if MTBE is banned in China in the future, it can also be converted to high-purity isobutylene through the construction of tertiary butanol dehydration isobutylene
equipment.
As shown in Figure 1, a variety of organic chemical raw materials and fine chemicals such as methacrylate (MMA), polyisobutylene and butyl rubber can be further prepared through high-purity isobutylene, and in recent years, there has been a huge potential demand
for polymeric-grade isobutylene at home and abroad.
So far, there are two main production methods of high-purity isobutylene in the industry: MTBE cleavage method and tert-butanol dehydration method
.
The tert-butanol dehydration method has a simple process, less side reactions, easy separation and refining, high product quality, and low investment (3O%
less than MTBE pyrolysis method).
In addition, the circulating logistics of the TBA dehydration process to produce isobutylene is water, while the circulating logistics of MTBE pyrolysis is methanol, which is more environmentally friendly
.

2.
Isobutane synthesis direct alkylated oil

In the long run, domestic MTBE may be limited due to environmental protection issues, while domestic refineries produce high-grade clean gasoline, which requires a large amount of high-octane gasoline blending components
.
Alkylated oil not only has good anti-explosion performance, but also the vapor pressure is much lower than MTBE
.
In addition, alkylated oils do not contain benzene and olefins, and have a low sulfur content, so they have ideal volatility and clean combustibility, and are ideal blending components of aviation gasoline and motor gasoline
.
With the improvement of environmental protection requirements, alkylated oil will be the main blending component of gasoline in the future
.

MTBE may be limited by environmental concerns, while domestic refineries produce high-grade clean gasoline, which requires a large amount of high-octane gasoline to blend components
.
Alkylated oil not only has good anti-explosion performance, but also the vapor pressure is much lower than MTBE
.
In addition, alkylated oils do not contain benzene and olefins, and have a low sulfur content, so they have ideal volatility and clean combustibility, and are ideal blending components of aviation gasoline and motor gasoline
.
With the improvement of environmental protection requirements, alkylated oil will be the main blending component of gasoline in the future
.

Direct alkylation refers to the process of alkylation of isobutane and C3~5 olefins under the action of
strong acid catalyst to generate alkylated oil.
Theoretically, the alkylation process has certain requirements for the ratio of raw material isobutane and olefin (alkanene molar ratio), and appropriately increasing the alkane ratio can reduce the occurrence
of side reactions such as alkene superposition and oxidation.
In the catalytic cracking carbon four fractions from the refinery, the butene content is more than the isobutane content, which is not suitable for direct alkylation of the raw material, you can use the etherization-alkylation combination route, the isobutylene component in it is etherified
first.
In addition, the 1-butene component can be separated by rectification to ensure a more suitable alkyne ratio
.

C3~5 olefins undergo alkylation reaction under the action of strong acid catalyst to generate alkylated oil
.
Theoretically, the alkylation process has certain requirements for the ratio of raw material isobutane and olefin (alkanene molar ratio), and appropriately increasing the alkane ratio can reduce the occurrence
of side reactions such as alkene superposition and oxidation.
In the catalytic cracking carbon four fractions from the refinery, the butene content is more than the isobutane content, which is not suitable for direct alkylation of the raw material, you can use the etherization-alkylation combination route, the isobutylene component in it is etherified
first.
In addition, the 1-butene component can be separated by rectification to ensure a more suitable alkyne ratio
.

This scheme uses catalytic cracking mixed carbon four fractions as raw materials, hydrogenation of butene and isobutane-based components (diolefin selective hydrogenation into monoolefins), isomerization (isomerization of 1-butene to 2-olefins), and then alkylation reaction to produce high-octane alkylated gasoline
.
Figure 2
is shown for a schematic flow diagram.

1-butene isomerization to 2-olefin), followed by alkylation reactions to produce high-octane alkylated gasoline
.
Figure 2
is shown for a schematic flow diagram.

UOP of the United States has developed the Alkylene heterogeneous solid acid alkylation process, which is about to enter the stage
of industrial application after several years of pilot research.
The catalyst is spherical, easy to circulate in the reactor, and the optimal molar ratio of isobutane to olefin is about 5:1~15:1
.
According to reports, CB&I announced in April 2013 that the world's first solid acid alkylation plant will start construction at a refinery in China, using AlkyClean technology, with a production capacity of 100,000 tons of alkylated oil, which is expected to be put into operation
in 2014.

UOP has developed the Alkylene heterogeneous solid acid alkylation process, which is about to enter the industrial application stage
after several years of pilot research.
The catalyst is spherical, easy to circulate in the reactor, and the optimal molar ratio of isobutane to olefin is about 5:1~15:1
.
According to reports, CB&I announced in April 2013 that the world's first solid acid alkylation plant will start construction at a refinery in China, using AlkyClean technology, with a production capacity of 100,000 tons of alkylated oil, which is expected to be put into operation
in 2014.

3.
Isobutane dehydrogenation to isobutylene

At present, the fine chemical industry with isobutylene as a resource is developing rapidly, and with the rapid development of isobutylene downstream industries such as methyl methacrylate, butyl rubber and MTBE, the domestic demand for isobutylene has grown rapidly
in recent years.
In this solution, isobutane is converted into high value-added isobutylene using a dehydrogenation unit, which is then used as a feedstock for the MTBE plant (see Figure 3 for details).

China can design and build large-scale MTBE production plants of any scale, and Yanshan Petrochemical Company Research Institute has developed a complete set of technologies
for chemical MTBE synthesis and MTBE cracking to isobutylene.

With the rapid development of downstream industries such as MTBE, domestic demand for isobutylene has grown rapidly
in recent years.
In this solution, isobutane is converted into high value-added isobutylene using a dehydrogenation unit, which is then used as a feedstock for the MTBE plant (see Figure 3 for details).

China can design and build large-scale MTBE production plants of any scale, and Yanshan Petrochemical Company Research Institute has developed a complete set of technologies
for chemical MTBE synthesis and MTBE cracking to isobutylene.

At present, foreign MTBE plants have transformed the original MTBE devices into production, using indirect alkylation process to produce isooctane, which is used
as a high-octane gasoline blending component.
The advantage of this solution is that the investment is small, most of the MTBE production equipment can be used, as long as the hydrogenation part is added, and even the catalyst can still use the original ion exchange resin
.
Of course, if you change to a solid phosphoric acid catalyst, because n-butylene can participate in the dimerization reaction, the product yield is higher
.

MTBE plants have converted the original MTBE plants to produce isooctane using an indirect alkylation process, and isooctane is used
as a blending component of high-octane gasoline.
The advantage of this solution is that the investment is small, most of the MTBE production equipment can be used, as long as the hydrogenation part is added, and even the catalyst can still use the original ion exchange resin
.
Of course, if you change to a solid phosphoric acid catalyst, because n-butylene can participate in the dimerization reaction, the product yield is higher
.

The original MTBE device is modified to use isobutylene and ethanol as raw materials to synthesize ethyl tert-butyl ether (ETBE).

Although ETBE belongs to the same class as MTBE, it has a higher octane number, lower Ray's vapor pressure, and is much less soluble than MTBE, and can also be decomposed
by aerobic microorganisms.
The main attraction is that the use of bio-ETBE blends does not require the modification of the car and can be used directly as a substitute for gasoline, which can be blended in the refinery
.
Many problems
such as increased gasoline volatility caused by the use of ethanol, phase separation due to water mixing, and blending at the point of sale can be avoided.
At present, Europe and the United States are rapidly switching to ethanol-type ethers, and many sets of MTBE plants have been converted to produce ETBE, and the first bioether plant for the production of ETBE was put into operation in 2004, and the output of ETBE in Europe reached 5.
2 million tons
in 2010.

MTBE plant modification, using isobutylene and ethanol as raw materials, can also synthesize ethyl tert-butyl ether (ETBE).

Although ETBE belongs to the same class as MTBE, it has a higher octane number, lower Ray's vapor pressure, and is much less soluble than MTBE, and can also be decomposed
by aerobic microorganisms.
The main attraction is that the use of bio-ETBE blends does not require the modification of the car and can be used directly as a substitute for gasoline, which can be blended in the refinery
.
Many problems
such as increased gasoline volatility caused by the use of ethanol, phase separation due to water mixing, and blending at the point of sale can be avoided.
At present, Europe and the United States are rapidly switching to ethanol-type ethers, and many sets of MTBE plants have been converted to produce ETBE, and the first bioether plant for the production of ETBE was put into operation in 2004, and the output of ETBE in Europe reached 5.
2 million tons
in 2010.

4.
Conclusion

Isobutane in carbon four fraction is an important basic organic chemical raw material, which has high utilization value and should attract sufficient attention
from domestic refining and chemical enterprises and related research.
It is suggested that domestic refining and chemical enterprises can consider using isobutane in three ways according to their actual conditions, combined with market demand and technical sources: First, isobutane and propylene are co-oxidized to produce propylene oxide, and the co-produced tert-butanol can be synthesized by reaction with methanol MTBE, tert-butanol can also be dehydrated to produce high-purity isobutylene; The second is to synthesize alkylated oil from isobutane and butene, pentene, etc.
through direct alkylation reaction; The third is to dehydrogenate isobutane to isobutylene, and then use it as a raw material for MTBE device, if the domestic MTBE market is saturated or MTBE is banned, it can also be converted to high-purity isobutylene by MTBE cracking to produce high-purity isobutylene, or the original MTBE device is transformed, and the indirect alkylation process is used to produce isooctane or isobutylene and ethanol are used to synthesize ETBE
.

MTBE, tert-butanol can also be dehydrated to produce high-purity isobutylene; The second is to synthesize alkylated oil from isobutane and butene, pentene, etc.
through direct alkylation reaction; The third is to dehydrogenate isobutane to isobutylene, and then use it as a raw material for MTBE device, if the domestic MTBE market is saturated or MTBE is banned, it can also be converted to high-purity isobutylene by MTBE cracking to produce high-purity isobutylene, or the original MTBE device is transformed, and the indirect alkylation process is used to produce isooctane or isobutylene and ethanol are used to synthesize ETBE
.

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