Catalyst preparation unit operations

In 1989, the NDF Company opened a facility in Georgetown, South Carolina to produce low density polyethylene. Manufacturing of the polyethylene is done in two 50-ton reactors that are encased individually within their own 8-story-high process unit. The main raw materials for the manufacturing operations include ethylene, hexane, and hutene. The polymerization is completed in the presence of a catalyst. The hase chemicals for the catalyst are aluminum alkyl and isopentane. The reactor and catalyst preparation areas are on a distributed control system (DCS). A simplihed process flow diagram is attached. 

In the catalyst preparation area where the fire occurred, aluminum alkyl and isopentane are mixed in a batch blending operation in three 8000-gallon kettles. The flow rates of components are regulated by an operator at the control room. Temperature, pressure, and liquid level within the kettles are monitored by the control room operator. The formulated catalyst is stored in four 12,000-gallon vertical storage tanks within this process unit. Aluminum alkyl is a pyrophoric material and isopentane is extremely flammable. Each vessel was insulated and equipped with a relief valve sized for external fire. 

The catalyst preparation area is positioned between the two polyethylene production units with 60 feet separating each one. The aluminum alkyls storage canopy and isopentane horizontal storage tank are located at a remote area at an approximate distance of 250 feet away from the production and utility areas. The isopentane is transported to the catalyst preparation area through a 3-inch pipeline. A remote actuated isolation valve on this supply line that fails closed is located at the isopentane storage tank. This control valve and an associated isopentane feed pump are managed by the operator in the control room. 

In the United States, approximately one-third of all processed crude oil, amounting to about 5 x 10° bbl/day, is catalytically converted over fluidized catalysts. Over 500 tons of catalyst are required daily, yielding sales that in 1987 were estimated at -250 million dollars (1). Thus, in terms of catalyst usage and product value, catalytic cracking is still the most important unit operation of the petroleumrefining industry. This year, the worldwide sales of catalysts to the petroleum, petrochemical, and chemical industry are expected to exceed 2.4 billion dollars, and catalyst producers are preparing themselves for the turn of the century when catalysts are projected to become a 5 billion dollars per year global business (2). 

Catalyst scale-up is a process in which a catalyst previously made in small quantities in a laboratory is manufactured in quantities of more than 100 lb with equipment that performs the same operations as larger commercial equipment. If possible, this should involve equipment that simulates the series of unit operations that will be used in commercial catalyst preparation. 

Che, M., From unit operations to elementary processes A molecular and multidisciplinary approach to catalyst preparation. Stud. Surf. Sci Catal. 130,115 (2000). 

Although catalyst preparations are usually composed of several successive unit operations (e.g. ion exchange, washing and drying) which are clearly separated, the identification of the elementary steps taking place at the molecular level are far more difficult to detect and to separate. There seems, however, to be some hope, using experimental key parameters, to achieve a better identification and separation so that new sequences can be proposed, making catalyst architecture possible. 

Filtration is a necessary unit operation when a catalyst is prepared by precipitation. Careful washing has to be performed when the counterions cannot be decomposed by the subsequent calcination. Therefore, carbonate ions or ammonium ions are preferred counterions. In case of nitrates, the evolution of nitrous gases during calcination and the formation of nitrate-containing wastewater has to be taken into consideration. 

It is well-known that a new generation of hydrotreating catalysts prepared with a silica promoted alumina support has been developed and are in use in a number of commercial hydrotreating units. Improved and more flexible operation should be possible especially in thermally cracked feedstocks with these catalysts having a higher HDS activity and resistance to carbon deposition than conventional CoMo or NiMo catalysts. 

The preparation of heterogeneous catalysts is a series of unit operations, particularly involving the processing of solids, to produce a catalyst with specific chemical and physical properties that are important in the performance of the material in the chemical process that it is being used. The type and order of imit operations involved in the preparation vary greatly from catalyst to catalyst. There are numerous possibilities of manufacturing processes for particular catalyst formulations with each affecting the chemical and physical properties of the final product. 

The preparation of a heterogeneous catalyst consists of a series of unit operations that mostly deal with solids... 

The preparation of heterogeneous catalysts is a complex operation that can incorporate many unit operations. The operation involves the formation of the catalyst precursor, separation, and purification, posttreatment, and forming. These operations can be carried out in many ways. All of these operations affect the physical and chemical properties of the final catalysts, which affect the performance in industrial use. Last, the economics of the process that uses the catalyst will be affected and is the ultimate driving force. 

This chapter is concerned with green reactions, products and methodological advances facilitating them. To those ends, our work has attempted to simplify processes by combining as many tasks as possible into unit operations. Aspects include selection of media, reactants, catalysts, conditions and product isolation. Examples are presented along with details of some specific classes of relatively complex molecules that may be prepared. These include novel macro-cycles, ligands and phenol/formaldehyde oligomers. 

When the unit operation processes and equipment have such a major influence on the final catalyst properties and performance, it would be logical and desirable to perform the catalyst test preparations in the catalyst plant process equipment or in a pilot production plant in order to avoid using development time on "wrongly prepared samples. However, there must be at least some selection of recipes. 

The topic of this series of symposia, which was initiated in 1975 and organized at four-year intervals, has invariably been the discussion of the fundamentals behind the unit operations in the preparation of industrially relevant solid catalysts. 

Heterogeneous catalyst materials are often employed in fixed-bed reactors and mm-sized catalyst bodies of various shapes and sizes are used in order to minimize pressure drop across the reactor (Chapter 9). Since the efficiency of the final catalytic system depends on both the nature and distribution of the active phase sufficient control over the preparation process is crucial. The classical unit operations of industrial catalyst preparation include impregnation and drying followed by calcination. In the steps of impregnation and drying the chemical processes taking place in the impregnation solution and at the solid/liquid interface are important, whereas gas/solid interface and solid-solid reactions are key in the calcination step [1-6]. 

The main difference from academic catalyst preparation is that in industry only a limited number of unit operations are used and therefore, several highly sophisticated lab preparation techniques, unless they result in extraordinary catalysts, cannot be applied in industry. Moreover, economic factors (costs of precursor materials) and ecological demands (avoid toxic and environmentally harmful waste) have to be considered. In fact, most catalysts in industry are manufactured by impregnation, precipitation, or ion-exchange techniques. Recently, Degussa has published some features of their high-throughput synthesis equipment illustrated by preparation of an advanced Pd-based vinyl acetate catalysts [109,118). 

Catalyst preparation by high-throughput technologies has become well adapted over the last decade. All unit operation with the exception of some solid handling operations can now be carried out on robotic platforms. Nevertheless, increasing the speed and throughput of preparation will remain an important... 

Solid catalysts are used in modem energy, chemical and environmental processes. Catalyst performance - activity, selectivity and stability-is largely determined by their preparation. In this respect, catalyst synthesis may be considered as one of the most influential unit operations in industry. This book provides an introduction to basic concepts and research tools relevant to catalyst synthesis followed by a number of case studies. In this way it is an introduction to the field of catalyst synthesis for students and newcomers as well as a reference book for experienced scientists and practitioners. I hope that this book will stimulate the research field of catalyst synthesis and that it will support research and applications of solid catalysts by facilitating reliable and reproducible synthesis of materials. 

Presently, 90% of the large and middle-size production processes in the chemical industry are based on catalysis. In the comprehensive effort aiming at the development of new catalytic processes, catalyst preparation constitutes just one part amid other contributions. But this part led to conspicuous innovation, and this because the chemical engineering aspect of catalyst industrial development was considered simultaneously with the basic science aspects and the development of the whole process. This remark fully justifies the ambition of the special symposium The Science and Engineering of Catalyst Preparation. It also justifies the fact that the selection of topics in the present contribution was essentially not influenced by fashion. In our opinion, the word engineering, when catalyst preparation is considered, should certainly apply to the unit operations of catalyst manufacture. But it should also point to the comprehensive approach that includes the first steps in the discovery of an interesting catalytic reaction as well as the industrial process development. With that in mind, one must conclude that the most promising avenue is to... 

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