Process for maximizing 371° C.+ production in...

Details Process for maximizing 371° C.+ production in... Process for maximizing 371° C.+ production in...

2001-11-20

2002-10-01

Parsa, Jafar (Department: 1621)

Chemistry: fischer-tropsch processes; or purification or recover

Group viii metal containing catalyst utilized for the...

C518S700000, C518S705000, C518S712000, C518S715000

Reexamination Certificate

active

06458857

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the production of hydrocarbon products from a hydrocarbon synthesis (HCS) reaction. More particularly, the invention relates to a process for maximizing the production of hydrocarbons boiling above 371° C. in a Fischer-Tropsch synthesis process.
BACKGROUND OF THE INVENTION
The catalytic production of higher hydrocarbon materials from synthesis gas, i.e. carbon monoxide and hydrogen, represented by the equation 2H
2
+CO→—(CH
2
)—+H
2
O, commonly known as the Fischer-Tropsch process, has been in commercial use for many years. The hydrocarbon product of a typical Fischer-Tropsch process includes a wide variety of chemical components including oxygenates, olefins, esters, and paraffins, much of which can be gaseous or liquid at reaction conditions. These Fischer-Tropsch products have benefits over those obtained via traditional refining processes in that the material is essentially free of sulfur, metals, nitrogen-containing compounds and aromatics.
The Fischer-Tropsch process depends on specialized catalysts. The original catalysts for Fischer-Tropsch synthesis were typically Group VIII metals, particularly cobalt and iron, which have been adopted in the process throughout the years to produce higher hydrocarbons. As the technology developed, these catalysts became more refined and were augmented by other metals that function to promote their activity as catalysts. Such promoter metals include the Group VIII metals, such as platinum, palladium, ruthenium, and iridium, other transition metals such as rhenium and hafnium as well as alkali metals. Preferred Fischer-Tropsch catalysts are supported on an inorganic refractory oxide selected from Groups III, IV, V, VI, and VIII of the Periodic Chart. Preferred supports include silica, alumina, silica- alumina, the Group IVB oxides, most preferably titania, such as those disclosed, e.g. in U.S. Pat. No. 5,128,377.
The choice of a particular metal or alloy for fabricating a catalyst to be utilized in Fischer-Tropsch synthesis will depend in large measure on the desired product or products. The more valuable product fractions lie in the heavy paraffinic wax range, more specifically in those products boiling above 371° C. (typically referred to as 371° C.+ products). Generally, the wax obtained from the Fischer-Tropsch process is catalytically converted to lower boiling paraffinic hydrocarbons falling within the gasoline and middle distillate boiling ranges, primarily by hydrogen treatments, e.g. hydrotreating, hydroisomerization and hydrocracking. Additionally, as new markets for high quality waxes have expanded, the Fischer-Tropsch wax itself has increased in value as an end product.
Catalyst deactivation of Fischer-Tropsch catalyst is a long-standing problem known to have a deleterious effect on commercial productivity particularly in a high activity catalyst. Catalyst deactivation occurs for a variety of reasons, most notably sulfur poisoning due to small amounts of sulfur which may contaminate synthesis gas produced from natural gas, but can also occur due to sintering of the metal particles or coke formation as well as several other mechanisms. As catalyst activity declines, so does reactor productivity. Productivity is defined as the standard volume of carbon monoxide converted/volume catalyst/hour and can be expressed as %CO conversion. As catalyst activity declines, %CO conversion declines assuming all other reaction variables, e.g. temperature, gas hourly space velocity (GHSV) are held constant. This holds true for all reactor types.
To offset catalyst deactivation, production plants typically switch to a Temperature Increase Required (TIR) mode, whereby the synthesis gas feed rate is kept constant and reactor temperature is increased in order to maintain constant CO conversion at an optimal level. However, increasing reaction temperature to maintain productivity levels leads to a corresponding increase in methane selectivity and a decrease in the production of more valuable liquid hydrocarbons. Thus, in a TIR mode, as the rate of reaction is increased by operating at higher temperatures, methane formation is favored. This is an unfavorable result as methane is not a desired product. In addition, the production of methane is accompanied by a shift in the entire product slate to lower boiling materials, particularly C
1
-C
4
gases and naphtha, at the expense of higher boiling, more valuable liquid products, such as diesel and waxes.
Thus, while high productivities are desirable in commercial operations, it is essential that high productivity be achieved without high methane formation, because high methane production results in lower production of more valuable higher liquid hydrocarbons. Despite advancements in the development of selective high activity catalysts which are capable of high productivity combined with low methane selectivity, there remains a need for improved gas conversion processes that overcome catalyst deactivation and achieve still higher productivity while favoring the production higher value liquid hydrocarbon products, preferably C
10
+, more preferably those boiling above 371° C.
Accordingly, the present invention provides a process for the preferential conversion of synthesis gas to liquid hydrocarbon products that combines high productivity with low methane selectivity.
SUMMARY OF THE INVENTION
In one embodiment of this invention, a Fischer Tropsch reactor is operated under process conditions maximizing the production of valuable heavy wax products while minimizing the production of less valuable products such as light gases (C
1
-C
4
) and naphtha fractions. The process is characterized by high C
10
+ selectivity, preferably high C
19
+ selectivity, resulting in the preferential production of material boiling above 371° C.
Thus, a hydrocarbon synthesis process is provided which comprises the steps of a) reacting carbon monoxide with hydrogen in a Fischer-Tropsch reactor in the presence of active Fischer-Tropsch hydrocarbon synthesis catalyst to induce a hydrocarbon synthesis reaction with a predetermined methane selectivity under initial reaction conditions comprising an initial synthesis gas feed rate (F
i
) and an initial reaction temperature (T
i
) wherein the initial reaction conditions are selected to achieve a target %CO conversion; and, b) thereafter adjusting the synthesis gas feed rate over time to maintain the target %CO conversion at the initial reaction temperature (T
i
) by decreasing the synthesis gas feed rate from the initial synthesis gas feed rate to a predetermined minimum synthesis gas feed rate (F
min
). Optionally thereafter, the temperature may be adjusted as necessary to maintain the target %CO conversion at the minimum synthesis gas feed rate (F
min
) by increasing reaction temperature from the initial reaction temperature to a maximum final temperature T
max
. The maximum final temperature is the temperature at which methane selectivity reaches a predetermined maximum level.
In other embodiments, at any time during the hydrocarbon synthesis process, a portion of the catalyst which has been at least partially deactivated may optionally be removed from the reactor, treated to restore catalyst activity and re-introduced into the reactor as fresh catalyst.
In another embodiment, additional active catalyst may be introduced, up to a maximum catalyst loading, prior to decreasing the synthesis gas feed rate to prolong maintenance of the target %CO conversion at the initial reaction conditions.
DETAILED DESCRIPTION OF THE INVENTION
The Fischer-Tropsch hydrocarbon synthesis process can produce a wide variety of materials depending on catalyst and process conditions. Much research has focused on the development of selective catalysts which are capable of high liquid hydrocarbon selectivity combined with low methane selectivity. However, catalyst deactivation, particularly with a high activity catalyst, has a detrimental effect on commercial productivity. In the present invention, novel process mod

Affiliated with

Also associated with

Rating

Process for maximizing 371° C.+ production in... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for maximizing 371° C.+ production in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for maximizing 371° C.+ production in... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2946765