Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
1999-10-14
2001-10-23
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S210000, C208S212000, C208S25100H
Reexamination Certificate
active
06306287
ABSTRACT:
The present invention relates to refining and converting heavy hydrocarbon fractions containing, inter alia, asphaltenes, and sulphur-containing and metallic impurities, such as atmospheric residues, vacuum residues, deasphalted oils, pitches, asphalts mixed with an aromatic distillate, coal hydrogenates, heavy oils of any origin and in particular those from bituminous schists or sands. In particular, it relates to treating liquid feeds.
Feeds which can be treated in accordance with the invention normally comprise at least 100 ppm by weight of metals (nickel and/or vanadium), at least 1% by weight of sulphur, and at least 2% by weight of asphaltenes.
The aim of catalytic hydrotreatment of such feeds is both to refine, i.e., to substantially reduce their asphaltene, metal, sulphur and other impurity contents while increasing the hydrogen-to-carbon ratio (H/C) while transforming them to a greater or lesser extent to lighter cuts, the different effluents obtained possibly serving as bases for the production of high quality fuel, gas oil and gasoline, or feeds for other units such as residue cracking.
The problem with catalytic hydrotreatment of such feeds originates from the fact that such impurities gradually deposit themselves on the catalyst in the form of metals and coke, and tend to rapidly deactivate and clog the catalytic system, which necessitates a stoppage to replace it.
Processes for hydrotreating that type of feed must therefore be designed to allow as long as possible a cycle of operation without stopping the unit, the aim being to attain a minimum one year cycle of operation, namely a minimum of eleven months of continuous operation plus one month stoppage maximum to replace the entire catalytic system.
A variety of treatments for this type of feed exist. Such treatments have until now been carried out:
either in processes using fixed catalyst beds (for example the HYVAHL-F process from the Institute Français du Pétrole);
or in processes comprising at least one reactor enabling the catalyst to be replaced quasi-continuously (for example the HYVAHL-M moving bed process from the Institut Français du Pétrole).
The process of the present invention is an improvement over fixed catalyst bed processes. In such processes, the feed circulates through a plurality of fixed bed reactors disposed in series, the first reactor or reactors being used to carry out hydrodemetallisation (HDM) of the feed in particular and part of the hydrodesulphurisation, the final reactor or reactors being used to carry out deep refining of the feed, and in particular hydrodesulphurisation (HDS step). The effluents are withdrawn from the last HDS reactor.
In such processes, specific catalysts adapted to each step are usually used, under average operating conditions of about 150 to 200 bars pressure and a temperature of about 370° C. to 420° C.
For the HDM step, the ideal catalyst must be suitable for treating feeds which are rich in asphaltenes, while having a high demetallisation capacity associated with a high metal retention capacity and a high resistance to coking. The Assignee of the present invention, Institut Francais du Petrole has developed such a catalyst on a particular macroporous support (the “sea urchin” structure) which endows it with precisely the desired qualities for this step (European patents EP-B-0 113 297 and EP-B-0 113 284):
a degree of demetallisation of at least 80% to 90% in the HDM step;
a metal retention capacity of more than 60% with respect to the weight of new catalyst, which results in longer cycles of operation;
high resistance to coking even at temperatures of more than 400° C. which contributes to extending the cycle period which is often limited by increasing the pressure drop and the activity loss due to coke production, and which means that the majority of the thermal conversion can be carried out in this step.
For the HDS step, the ideal catalyst must have a high hydrogenating power so as to carry out deep refining of the products: desulphurisation, continuation of demetallisation, reducing the Conradson carbon and the amount of asphaltenes. The Assignee has developed such a catalyst (EP-B-0 113 297 and EP-B-0 113 284) which is particularly suitable for treating that type of feed.
The disadvantage of that type of high hydrogenating capacity catalyst is that it rapidly deactivates in the presence of metals or coke. For this reason, combining a suitable HDM catalyst, which can function at a relatively high temperature to carry out most of the conversion and demetallisation, with a suitable HDS catalyst, which can be operated at a relatively low temperatures as it is protected from metals and other impurities by the HDM catalyst which encourages deep hydrogenation and limits coking, then in the end overall refining performances are obtained which are higher than those obtained with a single catalytic system or with those obtained with a similar HDM/HDS arrangement using an increasing temperature profile which leads to rapid coking of the HDS catalyst.
The importance of fixed bed processes is that high refining performances are obtained because of the high catalytic efficacy of fixed beds. In contrast, above a certain quantity of metals in the feed (for example 100 to 150 ppm), even though better catalytic systems are used, the performance and especially the operating period for such processes becomes insufficient: the reactors (in particular the first HDM reactor) rapidly become charged with metals and thus deactivate; to compensate for that deactivation, the temperatures are increased, which encourages coke formation and increases pressure drops; further, it is known that the first catalytic bed is susceptible to becoming clogged quite rapidly because of the asphaltenes and sediments contained in the feed or as a result of operating problems.
The result is that the unit has to be stopped a minimum of every 3 to 6 months to replace the first deactivated or clogged catalytic beds, that operation possibly lasting up to three weeks and which further reduces the service factor of the unit.
Different attempts have been made to overcome the disadvantages of fixed bed arrangements.
Thus, one or more moving bed reactors have been proposed, installed at the head of the HDM step (U.S. Pat. No. 3,910,834 or British patent GB-B-2 124 252). Such moving beds can operate in co-current mode (the HYCON process from SHELL, for example) or in counter-current mode (the Applicant's HYVAHL-M process, for example). This protects the fixed bed reactors by carrying out part of the demetallisation and filtering the particles contained in the feed which could lead to clogging. Further, quasi-continuous replacement of the catalyst in that or those moving bed reactors avoids the need to stop the unit every 3 to 6 months.
The disadvantage of such moving bed techniques is that in the end, their performances and efficiency are rather inferior to those for fixed beds of the same size, that they cause attrition of the circulating catalyst which can lead to obstruction of the fixed beds located downstream, and which above all, under the operating conditions used, the risks of coking and thus the formation of agglomerates of catalyst are far from negligible with such heavy feeds, in particular in the event of problems, which can prevent the catalyst from circulating either in the reactor or in the used catalyst withdrawal lines, and finally cause stoppage of the unit to clean the reactor and the withdrawal lines.
In order to retain the excellent performance of fixed beds while maintaining an acceptable service factor, the addition of a fixed bed guard reactor (space velocity HSV=2 to 4) in front of the HDM reactors has been considered (U.S. Pat. No. 4,118,310 and U.S. Pat. No. 3,968,026). Usually, this guard reactor can be short-circuited by using an isolation valve in particular. Thus the principal reactors are temporarily protected against clogging. When the guard reactor is clogged it is short-circuited, but then the following principal reactor can become clogged in its turn and lead
Billon Alain
Ha Sung Ki
Heor Haen
Kim Sun Dong
Kressmann Stephane
Griffin Walter D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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