Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By dehydrogenation
Reexamination Certificate
2002-05-07
2004-03-02
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By dehydrogenation
C585S661000, C585S662000, C585S663000
Reexamination Certificate
active
06700028
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to catalysts useful in the dehydrogenation of paraffins, and to methods for using the catalysts. The catalysts of the invention provide a combination of selectivity, thermal stability, and initial catalyst bed activity per unit volume that is highly advantageous. In one preferred embodiment, the invention relates to the dehydrogenation of substantially linear paraffins having between about 9 and 15 carbon atoms per molecule, and monoolefins derived from such paraffins find particular use in the production of biodegradable detergents. Through the use of the catalysts and methods of the invention, it is possible to obtain excellent reaction selectivity in a process that includes regeneration of the catalyst.
BACKGROUND INFORMATION
Many chemical processes that are practiced on a commercial scale involve the use of one or more catalysts for the production of intermediate or finished products. This is particularly the case in the petroleum-dependent arts. Because of the large volumes commonly processed, it is often possible for even incremental improvements in the performance of catalytic processes to provide commercially significant benefits. Examples of important catalytic hydrocarbon conversion processes include alkylation processes, hydrogenation processes, dehydrogenation processes, and isomerization processes.
Although catalysts by definition are not directly consumed by the chemical reactions that they promote, in the aforesaid and other processes catalysts are frequently rendered progressively less active during their use by one or more mechanisms known to those skilled in the art. In some cases, it is possible by taking certain steps such as coke removal, acid washing, or calcining to restore much of the lost activity so that the useful life of the catalyst is extended. Such steps are often referred to as “regeneration” of the catalyst. In general terms, it is highly desirable to employ catalysts that respond well to regeneration, in order to reduce the costs associated with catalyst replacement. However, in many processes catalyst regeneration is not a viable option. For example, a catalyst that might otherwise be regenerable by burning off accumulated coke might not have sufficiently high thermal stability to adequately withstand the high local temperatures that are generated under effective coke burning conditions.
The present invention is concerned with catalytic materials useful in the dehydrogenation of paraffins (saturated hydrocarbons). Dehydrogenation of paraffins is often carried out with the goal of introducing one or more olefinic linkages, either to produce an olefin product useful in and of itself, or to provide an effective “handle” on a molecule for subsequent reaction with some other species. The present invention is particularly concerned with the heterogeneously catalyzed dehydrogenation of detergent range paraffins (paraffins with carbon numbers in the 9-15 range) to obtain products that contain a single unsaturated linkage per molecule (monoolefins). The resulting monoolefins (detergent range monoolefins) are useful for reaction with a second organic species that includes an aromatic nucleus to produce alkylbenzenes. Such alkylbenzenes having substantially linear alkyl substituents attached to benzene rings are useful for conversion to alkylbenzene sulfonates that are employed in detergent formulations in both the industrial and consumer products markets. Alkylbenzenes derived primarily from linear paraffins are particularly advantageous in the production of detergents, since their sulfonates possess a very high degree of biodegradability. The term “substantially linear” as used herein means that the type and degree of branching present in the paraffin that is to be dehydrogenated to obtain olefins for subsequent use in alkylbenzene sulfonate production are limited to those which provide an alkylbenzene sulfonate with a degree of biodegradability that is acceptable according to current standards promulgated by industry and regulatory agencies. Alkylbenzenes containing a single alkyl substituent attached to a benzene ring (monoalkylbenzenes) are advantageous, as is known in the art, since they tend to provide favorable detergent performance characteristics. Alkylbenzene mixtures consisting primarily of monoalkylbenzenes with linear alkyl substituents are also recognized as advantageous, and they are the types most widely used by the detergent industry. Such mixtures are commonly referred to as “linear alkylbenzene” or “LAB” by those skilled in the art.
Production of monoolefins in a dehydrogenation process typically involves the contacting of saturated hydrocarbons with a suitable catalyst under reaction conditions adjusted to favor monoolefin formation. However, the production of monoolefin is inevitably accompanied by some formation of undesirable by-products such as diolefins, aromatics, and cracking products. The amount of diolefin formed depends mainly upon the paraffin structure and the conversion level, and relatively little control of diolefin formation is possible by means of the other reaction conditions. The formation of cracking products can be minimized by using a nonacidic catalyst and by avoiding extremely high temperatures. Aromatics formation is significantly influenced by both the selectivity of the catalyst and the reaction conditions employed. It is well known in the art that great economic advantages can be realized by using a highly selective dehydrogenation catalyst that minimizes the formation of aromatics at a given level of paraffin conversion. Specific advantages associated with lower aromatics formation include lower paraffin consumption, lower consumption of monoolefin by side reactions with aromatics during alkylbenzene production, higher recycle paraffin purity, and less extensive catalyst inhibition and fouling.
Many catalysts useful for the dehydrogenation of paraffins to olefins are known in the art. Typically, known catalyst materials comprise one or more active metals or metal oxides in a finely divided form, deposited upon the surface of particles of a relatively inert carrier substance such as a silica or an alumina. Alternative means known in the art by which the primary catalytic component(s) or precursors thereof may be rendered into the required finely divided state upon the surface of a suitably pretreated support include such methods as precipitation, adsorption from an aqueous solution, and ion exchange techniques that make use of Zeolite® (molecular sieve) carrier materials. Typically, following the deposition of one or more species onto a selected support to provide a raw catalyst, the raw catalyst material is subjected to some sort of heat treatment at an elevated temperature for a suitable time, often in the presence of a controlled atmosphere, which may be inert, oxidizing, or reducing. The prior art is replete with examples of aluminas and silicas of various particle sizes, crystalline phases, pore structures, etc., combined with a very broad variety of other components deposited upon their surfaces. In many cases, the deposited components comprise at least one primary catalytic component and at least one additional component such as an activator, attenuator, or modifier.
In general terms, the performance of a catalyst is largely determined by three critical properties that are readily observable and known to those skilled in the art of catalysis. These properties are 1) selectivity, 2) activity, and 3) thermal stability.
In the case of paraffin dehydrogenation to produce monoolefin, the selectivity of a catalyst is a measure of its ability under appropriate reaction conditions to maximize the fraction of the total converted paraffin that is converted to monoolefin. Since higher formation of each unwanted by-product necessarily results in lower formation of monoolefin at a given paraffin conversion, selectivity is improved if by-product formation is reduced at a given paraffin conversion. Thus, comparisons of catalyst selectivity can be made in terms
Dang Thuan D.
Huntsman Petrochemical Corporation
Whewell Christopher J.
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