Chemistry: fischer-tropsch processes; or purification or recover – Group viii metal containing catalyst utilized for the...
Reexamination Certificate
2002-12-27
2004-09-07
Parsa, J. (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Group viii metal containing catalyst utilized for the...
C518S700000, C518S706000, C518S708000, C518S712000
Reexamination Certificate
active
06787576
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to producing linear alpha olefins from synthesis gas over a cobalt catalyst. More particularly the invention relates to producing C
4
-C
20
linear alpha olefins having low amounts of oxygenates, by reacting H
2
and CO in a synthesis gas produced from natural gas, over a non-shifting cobalt catalyst at reaction conditions of temperature, % CO conversion, H
2
:CO mole ratio and water vapor pressure effective for the mathematical expression of 200−0.6T+0.03P
H2O
−0.6X
CO
−8(H
2
:CO) to have a numerical value greater than or equal to 50. This can be integrated into a Fischer-Tropsch hydrocarbon synthesis process producing fuels and lubricant oils.
2. Background of the Invention
Linear alpha olefins in the C
4
-C
20
carbon atom range are large volume raw materials used in the production of, for example, polymers, detergents, lubricants and PVC plasticizers. The demand for these olefins is rapidly increasing, particularly for those that have from 6 to 12 carbon atoms, such as six and eight carbon atom linear alpha olefins desirable for making polyolefin plastics Most linear alpha olefins are produced by ethene oligomerization, for which the ethene feed cost can account for more than half the total cost of the alpha olefin production. It is known that alpha olefins can be produced from synthesis gas using iron, iron-cobalt, iron-cobalt spinel, copper-promoted cobalt and cobalt manganese spinel catalysts, most of which are shifting catalysts. Examples of linear alpha olefin production with such catalysts may be found, for example, in U.S. Pat. Nos. 4,544,674; 5,100,856; 5,118,715; 5,248,701; and 6,479,557. U.S. Pat. No. 6,479,557, for example, discloses a two-stage process to make paraffinic hydrocarbons in the first stage and olefinic hydrocarbons in the second stage. The paraffinic product is made by converting a substoichiometric synthesis gas feed (i.e., H
2
/CO feed ratio lower than about 2.1:1) over a non-shining catalyst in the first stage. Since the H
2
/CO usage ratio is stoichiometric, the effluent of the first stage is significantly depleted in CO. This effluent of the first stage is then used to make olefinic hydrocarbons in the second stage over a shifting Fischer-Tropsch catalyst.
Although iron-based shifting catalysts produce hydrocarbons from synthesis gas with high alpha olefin content even at high CO conversion levels, the undesirable water gas shift reaction associated with shifting catalysts wastes part (as much as 50%) of the CO feed by converting CO to CO
2
. Furthermore, in addition to high CO loss due to the water gas shift conversion of CO to CO
2
, iron-based catalysts produce linear alpha olefins containing more than 1 and even as much as 10 wt. % oxygenates. These oxygenates are poisons to catalysts used for producing polymers and lubricants from olefins. Hence, the concentration of oxygenates must be reduced to a level acceptable for polymer and lubricant production. The methods used for removing the oxygenates are costly, thus catalysts and processes yielding olefin products with low oxygenate content is highly desired.
It would be an improvement to the art if a way could be found to (i) produce linear alpha olefins with low oxygenates levels and particularly with (ii) non-shifting catalyst and preferably a non-shifting Fischer-Tropsch hydrocarbon synthesis catalyst that is also useful for synthesizing fuel and lubricant oil fractions. It would be a still further improvement if (a) linear alpha olefin production could be integrated into a Fischer-Tropsch hydrocarbon synthesis process and (b) if a hydrocarbon synthesis reactor employing a non-shifting Fischer-Tropsch hydrocarbon synthesis catalyst and producing fuel and lubricant oil fraction hydrocarbons could also be used for linear alpha olefin production, and vice-versa, without having to change the catalyst in the reactor.
SUMMARY OF THE INVENTION
The invention relates to a process for producing linear alpha olefins, and particularly linear alpha olefins having from four to twenty carbon atoms, having less than 3 and preferably less than 1 wt. % oxygenates, by reacting H
2
and CO, in the presence of a non-shifting Fischer-Tropsch hydrocarbon synthesis catalyst comprising a catalytic cobalt component, under reaction conditions defined by a Condition Factor (CF) greater than or equal to 50, which Condition Factor is defined as:
CF
=200−0.6
T
+0.03
P
H2O
−0.6
X
CO
−8(H
2
:CO)
where,
T=average reactor temperature in ° C.; the average reactor temperature is calculated by averaging the temperature readings from thermocouples measuring the temperatures of individual segments of the reactor. For example, if the temperature is measured in the middle of the first, second, and third equal-volume segments of a fixed bed reactor, the average temperature is equal to one third of the sum of the three readings.
P
H2O
=partial pressure of the water in the synthesis gas feed to the reactor, in kPa; the partial pressure of water in the feed is calculated by multiplying the mol fraction of water in the feed by the feed pressure measured in kPa. The mol fraction of feed components can be determined by, for example, using gas chromatographic methods.
X
CO
=CO conversion expressed as percent; the CO conversion can be determined from the CO balance. There are many methods available for establishing material balance. The method herein utilized measurements based on an internal standard such as a noble gas or nitrogen that is inert during Fischer-Tropsch synthesis. When using an inert internal standard, the conversion can be simply calculated by measuring the concentrations of CO and the internal standard in the feed and the effluent. This and other calculation methods are well known in the art of chemical engineering. The concentrations of CO and the inert internal standard in turn can be determined by gas chromatographic methods known in the art.
H
2
:CO=H
2
to CO molar ratio in the synthesis gas feed to the reactor; the concentrations of H
2
and CO in the feed can be determined by gas chromatographic methods.
By nonshifting is meant that under the reaction conditions the catalyst will convert less than 5 and preferably less than 1 mole % of the CO to CO
2
up to 90% CO conversion in Fischer-Tropsch synthesis. The wt. % of oxygenates is meant the wt. % of oxygenates in the total synthesized C
4
-C
20
hydrocarbon fraction, and by oxygenates is meant oxygen-containing hydrocarbon molecules, such as alcohols, aldehydes, acids, esters, ketones, and ethers. The process of the invention has been found to produce a C
4
-C
20
hydrocarbon fraction containing more than 50 wt. % linear alpha olefins and less than 3 wt. % preferably less than 1 wt. % oxygenates. This process can be achieved as a stand-alone process or it can be added to or integrated into a Fischer-Tropsch hydrocarbon synthesis process. The relatively low selectivity for alpha olefin production normally exhibited by a non-shifting Fischer-Tropsch cobalt catalyst, is at least partially overcome by operating the hydrocarbon synthesis reactor under reaction conditions in which the CF, according to the above expression, is greater than or equal to 50. By CO conversion is meant the amount of CO in the synthesis gas feed converted in a single pass through the reactor.
In another embodiment the invention relates to (a) producing a CO and H
2
containing synthesis gas from natural gas, (b) reacting the H
2
and CO containing synthesis gas in the presence of a non-shifting cobalt Fischer-Tropsch hydrocarbon synthesis catalyst, at reaction conditions effective to achieve a Condition Factor (CF) greater than or equal to 50, to synthesize linear alpha olefins, and particularly linear alpha olefins having from four to twenty carbon atoms having less than 3 wt. %, preferably less than 1 wt. % oxygenates. A process in which natural gas is converted to synthesis gas which, in turn, is converted to hydrocarbons, is referre
Fiato Rocco Anthony
Hershkowitz Frank
Kiss Gabor
Long David Chester
Bakun Estelle C.
ExxonMobil Research and Engineering Company
Parsa J.
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