1.GBH Enterprises, Ltd.Process Engineering Guide: GBHE-PEG-RXT-800How to use the GBHE Reactor Technology GuidesInformation contained in this publication or as otherwise supplied to Users is believed to be accurate and correct at time of going to press, and is given in good faith, but it is for the User to satisfy itself of the suitability of the information for its own particular purpose. GBHE gives no warranty as to the fitness of this information for any particular purpose and any implied warranty or condition (statutory or otherwise) is excluded except to the extent that exclusion is prevented by law. GBHE will accept no liability resulting from reliance on this information. Freedom under Patent, Copyright and Designs cannot be assumed.Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com

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Process Engineering Guide:How to Use the GBHE Reactor Technology GuidesCONTENTS 0 1 2 3 4 5 6INTRODUCTION / PURPOSE SCOPE FIELD OF APPLICATION DEFINITIONS BACKGROUND THE DECISION TREE GBHE REACTION ENGINEERING2 2 2 2 3 3 37GENERAL ASPECTS OF REACTOR TECHGNOLOGY77.1 Criteria of Reactor Performance 7.2 Factors of Economic Importance 7.3 Physicochemical Mechanisms 8GENERAL GUIDE TO SELECTION OF REACTOR TYPE AND OPERATION 8.1 Choice of Reactor Type 8.2 Reaction Mechanism and Kinetics 8.3 Thermodynamics 8.4 Other Factors9GENERAL REFERENCES AND SOURCES OF INFORMATION7 7 813 13 13 14 1622Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 3. APPENDICES ARELATIONSHIP BEWTEEN DEFINED TERMS23FIGURES 1 2 3DECISION TREE RELATIVE YIELDS OF B FOR BATCH (OR PLUG FLOW) AND CST REACTORS REACTOR SURVEY FORMDOCUMENTS REFERRED TO IN THIS PROCESS ENGINEERING GUIDE4 10 1824Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 4. 0INTRODUCTION/PURPOSEThis Guide is one in a series on Reactor Technology produced GBH Enterprises. The guides are intended to assist in the qualitative and quantitative understanding of the behavior of chemical and biochemical reactors. They are generally aimed at the formulation of a mathematical model of the physical and chemical phenomena occurring in a reactor. More often than not, the solution will require the use of a computer. It is not intended that the guides should substitute for the many excellent textbooks in Reaction Engineering, but rather to provide a collection of information which people in GBH Enterprises have found to be helpful in practice. It should be useful when: (a)modifying the performance of an existing reactor within its process, or(b)designing a new reactor.The series of guides on Reactor Technology do not claim to be comprehensive. There are gaps because no one within GBH Enterprises was found to have experience which would add to, or select key aspects from, information available in the open literature. The Guides assume that the user is familiar with the general text book material and with the fundamentals of model formulation.1SCOPEThis Guide provides an overview of the guides available in the area of Reactor Technology and directs the user to the individual guides appropriate to his/her problem. A decision tree is presented to aid the user in identifying the most appropriate guides. The general aspects of reactor technology are described. None of the guides covers the detailed mechanical design of reactors.Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 5. 2FIELD OF APPLICATIONThis Guide applies to the process engineering community in the GBH Enterprises world-wide.3DEFINITIONSFor the purposes of this Guide, the following definitions apply: ConversionThe number of moles of a key reactant which have reacted divided by the total number of moles of the key reactant fed to the reactor.Operational YieldThe number of moles of a key reactant transformed into a desired product divided by the total number of moles of the key component fed to the reactor.SelectivityThe number of moles of a key reactant transformed into desired product divided by the number of moles of the key reactant transformed into unwanted products.YieldThe number of moles of a key reactant transformed into desired product divided by the total moles of the key reactant which have reacted.The relationships between the above terms and a diagrammatic representation are given in Appendix A. With the exception of terms used as proper nouns or titles, those terms with initial capital letters which appear in this document and are not defined above are defined in the Glossary of Engineering Terms.Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 6. 4BACKGROUNDReaction Engineering is unique in the discipline of process engineering in that it displays an immense variety of controlling mechanisms which may act on their own or in combination. In the simpler cases a single mechanism dominates; e.g. heat or mass transfer or homogeneous reaction kinetics. In the more intractable situations, transport phenomena and kinetics combine to produce systems of considerable mathematical complexity. The aim of the guides is to help the user identify and then formulate the problem so that a solution can be obtained. Since the majority of industrial reactors are operated without detailed physicochemical understanding of the processes involved, the reactor analyst or designer has to identify these before he/she can start to formulate a suitable model. The stage has not yet been reached where there are general purpose computer programs available, into which data can be fed to obtain a rating calculation as, for instance, in heat transfer. Nor can reactor analysis or design be reduced to a series of simple steps which any inexperienced person can safely follow. Often a specific simulation program will have to be written and this series of guides will hopefully provide some of the building blocks and tools for this task.5THE DECISION TREEA logic diagram in the form of a decision tree is shown in Figure 1 to direct the user to the individual Guides in this series and in some cases to specific clauses within these Guides. Particular attention is drawn to the contents of a general nature in the following Guides: GBH EnterprisesReactor Dynamics, Control and Safety which includes a collection of case histories describing dangerous incidents;GBHE-PEG-RXT-816Case Studies in Reactor Technology which contains reactor development case studies;GBHE-PEG-RXT-811New Reactor Technology which draws attention to new types of reactor.Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 7. Users should also consult the relevant Process SHE Guides, especially No. 8, Part A Section 3 on inherent safety and alternatives to pressure relief, Part B on causes of relief situations and Part E on discharge and disposal system design. Safety and environmental considerations can have a very significant effect on both reactor design and process economics. Users should therefore take these into account at an early stage in the reactor selection and design phases. An add-on solution is usually much more expensive and may not get authorization under the Environmental Protection Act 1990 as the best environmental option.Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 8. FIGURE 1DECISION TREERefinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 9. FIGURE 1DECISION TREE (Continued)Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 10. FIGURE 1DECISION TREE (Continued)Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 11. 7GENERAL ASPECTS OF REACTOR TECHNOLOGY7.1Criteria of Reactor PerformanceYield, Conversion and (in polymerization reactions) degree of polymerization constitute the most common criteria for judging the performance of chemical reactors. Definitions of these criteria (and associated quantities such as Selectivity and Operational Yield) are frequently technology dependent. It is therefore imperative that the reactor analyst familiarize himself with the meaning of such terms in the technological context and does not assume text book or Clause 3 definitions. Ambiguities arise not only from day to day sloppy usage but also out of genuine semantic difficulties. An example of the former category is the term conversion which may refer either to conversion to a desired product or conversion of reactants (to both products and side reactions). Semantic difficulties arise when reactants yield products which are not single well defined substances but mixtures whose constituents may not be analyzed separately and whose uses are determined by the aggregate properties of the mixture. Often in such cases, chemists will (for convenience) calculate "yields" based on an analysis which is referred to the molecular weight of a notional simple (predominant) compound. For example in reactions aimed at substitution in aromatics, isomers and/or multiple substituted products can be formed; analyses picking up the total of substituted groups may be adequate for the product characterization (particularly where all groups are reactive) but totally inadequate for a characterization of the reaction mechanisms and kinetics. It is all too easy for such analytic conveniences to become assumed knowledge which is not immediately made privy to workers new to the technology; this can result in considerable wasted effort and frustration. In the case of polymerization reactions, limitations of chemical analysis often preclude molecular weight distribution measurements, consequently performance must be judged on some mean molecular weight / degree of polymerization criterion determined from an overall property measurement (e.g. viscosity of melt/solution). Where both Yield and Conversion data are available the reactor designer/analyst is in a good position to quantify kinetic and Selectivity effects. In real life situations such data are rarely obtainable. Batch reactions are frequently set up to convert substantially 100% of the "important" precursor and here product Yield is optimized. Where such high Conversions are not possible both Yield and Conversion may be open to optimization. Conversely in many continuous reactors Yield estimation (on an instantaneous basis) is difficult due to inadequate precision in flow measurement and chemical analyses. In these Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 12. situations Conversion is monitored as an hour-to-hour measure of reactor performance. In such circumstances Yield estimates result from periodic stock analyses which are insensitive to short term changes in operating conditions. The inability to quantify fully reaction problems is largely responsible for the substantial lag between established reaction engineering theory and its application to industrial situations. Gathering of data, even with the sophisticated tools now available, consumes valuable time and effort, commodities rarely available within the time allocated to solve industrial problems. A methodology is presented which ensures efficient data gathering by prompting the correct questions and thereby revealing the minimum amount of data necessary for solution of a specific problem. The terms Yield and Conversion will be assumed to refer to the definitions in Clause 3. As discussed above, the user should establish for himself any departures from this terminology which might apply in his problem. Where a product of the reaction is a solid, physical form may be an important criterion of performance.72Factors of Economic ImportanceChemical reactor design and engineering attempts the successful exploitation of chemical reactions on a commercial scale. It is very rare that only the capital and variable costs associated with the reactor are the dominant feature of a process plant economic evaluation. Usually the operating conditions of the reactor have considerable influence on the surrounding process plant and product specification, and the process designer needs to consider the influence of varying the reaction conditions and reactor type and design on the rest of the plant. Successful design of the chemical reactor requires understanding of what a reactor can produce and which of the design options is the most favorable. Close co-operation is required between the process engineer and chemist or biochemist in order to obtain an adequate understanding and description of the reaction scheme and how products vary with conditions, and hence can be controlled to meet needs. While the time constants of reactions remain virtually independent of reactor size, most chemical engineering parameters change with vessel size, and control of the reaction environment becomes a function of bulk flow, mixing and turbulence. Knowledge of the reactor system and its constraints allows performance to be assessed in real (i.e. less than ideal) reactor systems. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 13. It is usually found that when a process involves chemical conversion or synthesis the optimum conversion is not 100%. Varying reactor conditions will permit a design optimization of reactant preparation and presentation, product separation and purification and recycle of unconverted reactants. A strong intuitive sense of reactor choice and good process design guided by and reinforced by formal optimization methods, will help in putting together a viable and economic process. The reaction scheme will almost certainly permit a conversion anywhere in the range 0-100% by varying reaction conditions. Testing the whole plant design over that range is recommended. In particular, the assumptions about reactor design should be tested when repeating existing processes. A radically improved whole plant design concept can often be found by moving away from historic design points in the reactor systems. Further information is given in GBHE-PEG-RXT-801. 7.3Physicochemical MechanismsThe probability that a molecule is changed chemically is determined by its state and usually also by its environment. For gases, it is possible to calculate the number of collisions a molecule has in a given time with other molecules and with the walls of the container. Only a tiny fraction of such collisions result in a chemical change. The sort of molecules with which it collides is determined by molecular diffusion and convection, and so these factors have a profound effect on reaction. Collectively, these factors are termed DISPERSION. In continuous reactor theory, two idealized reactors are postulated. In the "plug flow" reactor the assumption is made that the reactants enter in a fully mixed state and go through the reactor in such a way that there is zero mixing in the direction of flow and infinite mixing at right angles to the direction of flow. The reacting fluid goes through the reactor in rod-like flow. Velocity profile is flat. Axial dispersion is zero, radial dispersion is infinite. Ideal batch and plug flow reactors have identical mathematics. In both plug flow and batch reactors, reactant can be added part way along the length/time, though full mixing occurs at the point of addition. At the other extreme the "fully back-mixed" reactor (ideal continuous stirred tank reactor CSTR) assumes that the reaction space is totally mixed. Some molecules leave the reactor an instant after entry, while some others, having got in, never leave. The environment of the molecules is constant with time but molecules are exposed to it for a distribution of time. Dispersion is infinite.Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 14. Neither ideal reactor is exactly realized in practice. The degree of departure is a function of the relative rates of dispersion and reaction, and of the hydrodynamic conditions. If reaction is fast, it is extremely difficult to approach a CSTR. On the other hand, if the reaction is slow, it is more difficult to produce a plug flow reactor, although this difficulty disappears with batch reactors. Generally, the reaction mechanism indicates the sort of ideal reactor suited to achieving the best result in terms of material efficiencies. The reactor design problem is to specify to hardware which sufficiently approximates to one or other of the ideals, within the constraints of practicable ways of producing the dispersion required. Heat transfer requirements also affect the design. As a simple example, consider the reaction scheme:where the two reactions are first order. For a batch reaction, reaction rates are given by:where:CA, CB and CC are concentrations of materials A, B and C; CA0 is concentration of A at time zero; t is time; k1 and k2 are reaction rate constantsRefinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 15. When k 1 = k 2 , the reaction path for isothermal plug (or batch) and fully backmixed reactors can be illustrated as in Figure 2. This shows the value of CB at any value of CA. The reaction starts on the right at CA/CA0 =1 and moves to the left towards CA/CA0 =0. It can be seen that for any given value of CA/CA0 (i.e. 1conversion) the yield of B would be greater in a plug flow reactor than in a CSTR. Conversely, the yield of C would be lower. For a reaction scheme:where again the two reactions are first order; i.e.the yields of B and C for a given conversion of A in an isothermal reactor are not affected by reactor type. This qualitative picture would be true whether or not k1 = k 2 which was assumed merely for the purpose of illustration.Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 16. FIGURE 2RELATIVE YIELDS OF B FOR BATCH (OR PLUG FLOW) AND CST REACTORSRefinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 17. where n1 and n2 are the orders of reactions 1 and 2 with respect to component B. If n1 > n2 then yield of C is enhanced by high concentrations of B and vice versa. Yield of C is clearly a function of the mixing of A and B. An illuminating discussion of these matters may be found in Levenspiel (1974) Chapter 7. Remarks so far have been aimed at single phase reactors. When a second or third phase is present, interphase mass and heat transfer are superimposed on the effects already discussed, further complicating the picture. The chemical reaction generally increases the departure of the phases from physical equilibrium in comparison with the departure which would exist in the absence of reaction. The difference can vary from negligible for relatively slow reactions, to dominating when reactions are very fast. In the latter case, the physical rate processes are said to be controlling, since they control the environment surrounding the sites where the reactions take place. The general effect would be to denude the site of primary reactant molecules and flood it with product molecules. This environment is of course different to the bulk phase conditions, which may affect conversion and yield. If reliable technical calculations are to be done, it is important to be in a position to judge the magnitude of the contribution of dispersion, hydrodynamics, chemical kinetics and interphase mass and heat transfer to the reactor performance. Considerable work is reported in the literature which allows estimates of the physical processes to be made. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 18. However, at the present time, there is no way of calculating a priori the rate constants of chemical reactions to anywhere near the same degree of reliability, and these have to be evaluated from laboratory or plant measurements. Plant data are usually of limited value for a number of reasons. Absolute accuracy is not a requirement for plant instrumentation and upgrading is often required before even an acceptable mass and heat balance has been obtained. The range that experimental variables can be allowed to take is also limited. However, very useful results have been achieved by fitting model equations of the right general shape to plant data and then using the model for relatively small extrapolations. Laboratory experimentation must be aimed at producing data when dispersion and physical and chemical mechanisms are separately quantifiable. Chemical kinetic information should be obtained from an apparatus which approximates closely to one of the two ideal reactors, i.e. plug flow/batch, or CSTR. A CSTR has the advantage that rate data can be measured directly as a function of composition temperature and pressure. Such results may themselves give a clue as to the most suitable form of kinetic expression. Data from a plug flow or batch reactor can only be analyzed by comparing with the mathematical integration of some possible kinetic expressions. However, if measurements along the profile of the reaction are taken, more data can be obtained per run from a plug flow or batch reactor than from a CSTR. In achieving approach to an ideal reactor and/or in eliminating other physical processes from control the general principle is to adjust reaction fluid convection or mass/heat transfer path length until they no longer have an effect on the measured reaction rates. The following table indicates the steps which can be taken:Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 19. If experiment showed a significant difference in reaction rate by varying those conditions indicated while keeping temperature, residence time etc. constant, then this would indicate control by physical processes to a significant degree, and the conditions at the reaction site would not correspond to the local bulk conditions observed in the reactor. True chemical kinetics can only be measured either when all physical control is eliminated, or when the physical processes are accurately modeled. It was mentioned earlier that physical process rate constants can often be calculated with reasonable confidence. This means that in multiphase reactors, maximum possible rates and gradients can be calculated. For instance fluidparticle mass and heat transfer coefficients and effective thermal conductivities can be estimated for packed beds. Clearly, maximum consumption rate of reactant would occur for "zero back pressure"; i.e. for infinitely fast reaction. From the mass and heat convection transfer analogy, the maximum difference between particle surface temperature and fluid temperature can be calculated. Knowing particle thermal conductivity, the temperature gradient at the surface can be calculated, which is a maximum for the particle. Knowing bed conductivity, maximum temperature variation in the bed can be estimated. So, much can be done on paper to identify possible physical control mechanisms. The reader is now referred to GBHE-PEG-RXT-801 for a more detailed quantitative discussion of these effects.Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 20. 8GENERAL GUIDE TO SELECTION OF REACTOR TYPE AND OPERATION8.1Choice of Reactor TypeMany factors arise in the choice between batch, semi-batch and continuous operation. The decision trees embody a number of heuristics and it is appropriate to expand some of the reasoning. Much of the fine chemicals manufacturing area involves low tonnage (less than a few thousand tonnes per annum, frequently very much less), limited life products made in general purpose plant. Typically many synthesis steps are involved (e.g. giving rise to 6-8 intermediates). Some of these synthesis steps may be classified as "unit processes of organic synthesis" (e.g. nitration, sulfonation, amination, reduction, etc.), and are accommodated in plant which is purpose-built for such operations. The various chemical substrates involved in these unit processes, give rise to widely disparate reactivities, to such an extent that continuous operation designs are not possible. Furthermore, the work-up processes for isolation, purification and (where appropriate) recycle are also product specific. In such circumstances it is inappropriate to apply the batch versus continuous criteria of improved productivity, lower capital and intensive operation to products in isolation. Even in circumstances where continuous operation is indicated, process development time versus product life, the problems of online measurement and control, feed, product and intermediate storage requirements must be fully assessed. Conversely there will be special applications where process inventory hazard assessments point the way towards small, intensive continuous processing in circumstances which would not be otherwise indicated.8.2Reaction Mechanism and KineticsIf the reaction mechanism for production of desired product B is simplythen Yield of B at any Conversion of A will be equal to unity and will not be affected by reactor type. It is very rare for this simple mechanism to apply. If the mechanism is complicated by even a single further step, Yield of B per unit Conversion of A (YB) will be less than unity. This is because either parallel competing reactions are consuming feed reactant, or consecutive competing reactions are consuming product, or both. Schematically this can be shown: Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 21. The general rule is that reactions having higher orders are favored by higher reactant concentrations, and reactions having higher activation energies are favored by higher temperature. In terms of Yield, if the desired reaction has the highest order, then a PFR would be best; if it has the lowest order then a CSTR may be best. If both reactions of mechanism 2 shown above are of the same order (except zero) then YB will be higher in a PFR than in a CSTR. If both reactions are the same order in mechanism 1, then YB is not affected by reactor type. If activation energy for reaction 1 is greater than for reaction 2, then YB for mechanism 1 will increase with temperature for all Conversions of A. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 22. In the case of mechanism 2, and with E2 greater than E1, YB would be favored by a temperature falling as A is converted. Special techniques are available for calculating optimum temperature profiles. In the absence of chemical kinetic information, the effect of changing temperature over the reaction path may be difficult to predict but at least the trends with a rising or falling profile are easily identifiable by doing the two experiments in the laboratory. It is often the case that the reaction mechanism will consist of several parallel (mechanism 1) and consecutive (mechanism 2) reactions of various orders and activation energies and the picture can rapidly become unclear which of the two basic reactor types best favors yield. But given the kinetics, the situation can be examined easily either by using commercially available programs or by writing a simple computer program to simulate the kinetics in ideal reactors. Of course, Yield is not the sole criterion for selection of reactor type. Except for zero order reactions, the volume of an isothermal PFR is always less than that of a CSTR operating at the same temperature and to the same conversion, from considerations of reactant concentrations. It may be that when overall process costs are compared for PFR and CSTR, the PFR will win even when it is at a Yield disadvantage. Temperature has already been indicated to be a key and possibly overriding parameter and this is further considered in the next section.8.3ThermodynamicsThe approximate adiabatic temperature change can be calculated from:Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 23. See GBHE-PEG-RXT-801 for acquisition of data. If T is not too large, then an adiabatic reactor is feasible. If it is too large it may be possible to reduce it by feeding inert fluid to the reactor, thus proportionately reducing the concentration terms in equation 1 and possibly modifying other terms. Alternatively the overall T could be reduced by operating several adiabatic reactors in series with interstage heat exchange. In PFR, the feed temperature must be high enough for the reaction to start; for exothermic reactions the obvious danger is that the reaction could run away. This danger increases as the activation energy increases. There is no way of predicting, in the absence of kinetic information, whether this will occur, but the maximum possible temperature should be calculated from the above equation, setting CA and C'A to zero or to the values for chemical equilibrium, and a judgment made as to whether this can be tolerated or dealt with in some way. If the reaction is endothermic in PFR the less dramatic danger is that the reaction would die. Again it is impossible to predict if kinetic data are unavailable. The CSTR has the advantage that the whole reactor operates at one temperature so that the adiabatic reactor feed temperature can be calculated from:For particularly sensitive reactions it may be possible to operate a CSTR for the initial and dangerous part of the reaction, and follow it with a PFR to complete the more easily controllable part. Reaction temperature can only be selected in the light of kinetic information, except when it is known that the reactions are so fast that chemical equilibrium is achieved.Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 24. Chemical equilibrium constants and their variations with temperature, can be calculated from thermodynamic data (see GBHE-PEG-RXT-801). Equilibrium adiabatic temperature change information can be shown very conveniently in graphical form:If it is judged that adiabatic operation is not feasible, then the reactor design must incorporate heat transfer through some surface in the reactor. The PFR is usually in the form of a long thin tube and it is convenient to pass heat through the tube wall to or from some heat transfer medium. The CSTR may be in the form of an agitated tank, and in this case, internal coils, jacket, or external heat exchanger with pump circulation or condensing vapor and refluxing condensate are the norm. Reaction heat should be used to adjust the temperature of feed streams. This is essentially what happens in a CSTR. It may be possible to use the feed stream of a PFR to do at least part of the heat exchange for the reactor, but supplementary exchange may be necessary for dealing with emergencies. Before leaving the consideration of the thermal requirements, it is essential to say that attention must be paid to dealing with dynamics of the reactor; i.e. startup, shutdown and control. It may also be necessary to consider how the reaction is to be stopped, i.e. quenched, at the reactor exit. In the foregoing, no mention of pressure has been made. This is because concentration has been defined in units of kmol/m3 which for gases is pressure dependent. Where there is a change of phase, then the temperature is a direct function of pressure, and of course would be incorporated in this way. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 25. The implied need for vapor pressure data could be extended to the other physical properties which the process engineer commonly needs for his work. The need for consistent physical and thermodynamic data (including standard states and datum temperatures) is emphasized.8.4Other FactorsIt was stated at the beginning that factors other than reaction mechanism, kinetics and thermodynamics may be overriding in choosing reactor type. This is particularly the case in multiphase reactors. Batch, semi-batch and recirculating loop reactors can be used for most reacting systems. When a continuous reactor is required, the choice of equipment is much wider. The following table indicates the sort of equipment which is practicable for various cases.Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 26. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 27. 9GENERAL REFERENCES AND SOURCES OF INFORMATIONCarberry J J (1976) Chemical and Catalytic Reaction Engineering (McGraw-Hill). Coulson, J M and Richardson, J F (1979) Chemical Engineering Vol 3 2nd Ed. (Pergamon Press). Cox, J d and Pilcher, G (1970) Thermochemistry of Organic and Organometallic Compounds (Academic Press). Dankwerts, P V (1970) Gas-Liquid Reactions (McGraw-Hill). Denbigh, K G (1981) The Principles of Chemical Equilibrium 4th Ed. (Cambridge University Press). Harris, M L (1977) Kinpak Kinetics Package User Guide CL/R/77/1202/A. Westerkerp, K R van Swaaij; W P M and Beenackers, A A C M (1984) Chemical Reactor Design and Operation (John Wiley). Lapidus, L and Amundson, N R (1977) Chemical Reactor Theory, A Review (Prentice-Hall). Levenspiel, O (1974) Chemical Reaction Engineering 2nd Ed. (John Wiley). Rase, H F (1977) Chemical Reactor Design for Process Plants Vols. 1 and 2 (John Wiley). Reid, R C; Prausnitz, J M and Poling, B E (1987) The Properties of Gases and Liquids 4th Ed. (McGraw-Hill). Rose, L M (1981) Chemical Reactor Design in Practice (Elsevier Scientific Publishing Company). Satterfield, C N (1970) Mass Transfer in Heterogeneous Catalysis (MIT Press). Shah, Y T (1979) Gas-Liquid-Solid Reactor Design (McGraw-Hill). Smith, J M (1981) Chemical Engineering Kinetics 3rd Ed. (McGraw-Hill).Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 28. APPENDIX A LetRELATIONSHIPS BETWEEN DEFINED TERMSFbe number of moles of key reactant fed to reactor;Abe number of moles of key reactant converted to desired product(s);Bbe number of moles of key reactant converted to unwanted product(s);Cbe number of moles of key reactant not reactedRefinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 29. DOCUMENTS REFERRED TO IN THIS PROCESS ENGINEERING GUIDE This Process Engineering Guide makes reference to the following documents: GBHE ENGINEERING GUIDES Glossary of Engineering Terms(referred to in Clause 3)GBHE-PEG-RXT-801Chemical Process Conception (referred to in Figure 1 and 7.3)GBHE-PEG-RXT-803Reaction Rates and Equilibria (referred to in Figure 1 and 8.3)GBHE-PEG-RXT-804Physical Properties and Thermochemistry for Reactor Technology (referred to in Figure 1)GBHE-PEG-RXT-810Homogeneous Reaction Gas Solid System (referred to in Figure 1)GBHE-PEG-RXT-810Gas Liquid Reactors (referred to in Figure 1)GBHE-PEG-RXT-810Liquid - Liquid Reactors (referred to in Figure 1)GBHE-PEG-RXT-811Biochemical Reactors (referred to in Figure 1)GBHE-PEG-RXT-811New Reactor Technology (referred to in Clause 5)GBHE-PEG-RXT-813Case Studies in Reactor Technology (referred to in Clause 5)GBHE-PEG-RXT-817Reactor Dynamics, Control and Safety (referred to in Clause 5 and Figure 1)Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 30. OTHER DOCUMENTS The Environmental Protection Act 1990 (referred to in Clause 5 and Figure 1).Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com 31. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts / Process Technology Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology Petrochemicals Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries Web Site: www.GBHEnterprises.com