Synthesis processes

Process synthesis may be defined as (Westerberg, 1987) the discrete decisionmaking activities of conjecturing (1) which of the many available component pjuts 

The result of process synthesis is a flowsheet which represents the configuration of the various pieces of equipment and their interconnection. Next, it is necessary to analyze the performance of this flowsheet. 

Process synthesis tries to find the flowsheet and equipment for specified feed and product streams. We define process synthesis as the activity allowing one to assume which process units should be used, how those units will be interconnected and what temperatures, pressures and flow rates will be required [2.15, 2.16[. 

Process flowsheet generation is an important part of process synthesis. The following tasks have been established for process flowsheet generation [2.17] (i) the generation of alternative processing routes, ii) the identification of the necessary unit operations, (iii) the sequencing of unit operations into an optimal flowsheet. 

A vital aim of process synthesis is to reduce the complexity of the problem in order to enable simple solutions to be recognized quickly. In order to systematically analyse processes involving reversible reactions, a comprehensive process synthesis strategy has 

To achieve this, various authors have developed transformation methods. These transformation methods enable reactive distillation to be described by a system of equations that is known from conventional distillation see Equation (9). The method is limited by the fact that it is possible only for equilibrium reactions and is more an estimation than a design. 

Some answers to this question will be offered from the viewpoint of an industrial user. The first question refers to the phase of the process synthesis, the second to process development by simulation and experimental validation, and the third to the choice and design of suitable equipment. 

The results presented here are not only internal research results but also from joint research in Europe. 

In view of the fact that, unlike conventional distillation, there was no integrated development strategy for progressing from the idea to a working process for RD, several European companies and universities joined forces in 1996 to work on a development strategy for RD processes under the umbrella of a Brite-Euram pro- 

This first Brite-Euram Project had a duration of 3 years and a budget of about 3.8 million dollars. The task of the Universities was to develop methods and software the task of the industrial partners was to run the experiments. The key subject areas for this project were process synthesis, process design, and experiments using industrially relevant reaction systems and catalyst systems. In the areas of process synthesis and design, computational tools were developed in accordance with the CAPE programming guidelines. 

Now a second European project has started. It is called Intelligent column internals for reactive distillation (INTINT) and deals specifically with the design of suitable column internals adapted to the requirements of reaction and distillation, not only of distillation, as is the case with normal packing. Again, experimental results and simulation tools are the key subjects. The project duration is 3 years, up to 2003, and the budget is comparable with that of the first EU project. 

After one has obtained the necessery data on physical properties, transport properties, phase equilibria, and reaction kinetics, sorted ont (he flow of material through the system, and exploited any particular charac- 

To illustrate the complexity that must be deslt with in developing an optimei process, Thompson and King1 made the following calculation. If a process stream containing N componeats is to be separated into N pare-componem products, using M different separation methods, the number of possible sequences R can be determined as follows  

The assumption made in this calculation is that each separator will yield two product streams from one feed stream and ench component can exit in only one of these streams. This ignores, for example, distillation columns wjlh sidestream removal. Nonetheless, (he combiextorial problem that arises can be monumental fbr even apparently simple synthesis problems  

It shonld be apparent thet as the numher of components and possible separation methods increase, the development of hd optimei design bacomes nearly impossible without some systematic method to discard alternatives that are not feasible. 

The wide variety of possible choices of separation processes bas been catalogued by King. Also, a detailed discussion of procedures for selecting a separation process is provided by Null in Chepter 22. Hare, some comments on separation process selection are included to provide some perspective for later discussion. 

The appropriate tools such as software, experimental equipment, and instruments for executing the task should be identified. The activities to meet the objective such as computer simulation, modeling and experimentation are defined. To meet the project deadline, it is also necessary to estimate the time needed to complete the tasks. Proper allocation of human and monetary resources to perform the activities is also essential [3]. 

Because of its high dimensionality, it is difficult - or even impossible - to view the phase diagram of a multicomponent system in its entirety. For example, an isobaric phase diagram for four components would involve a four-dimensional space. To 

Since it is desired to separate pure A and B from the mixture, two crystallizers are needed (Fig. 11.4(a)). To achieve the separation objective, one must visit compartments A and B. By inspection of the phase diagram, it is found that the feed (located in compartment AB2) can be brought to compartment A by adding S (Fig. 11.4(b)). This implies that A should be separated first, and B recovered next However, it is not possible to move from compartment A to B, because the two compartments are not adjacent to each other. One option to deal with this problem is to crystallize AS, which is an adduct that can be easily separated using distillation. Instead of A, the adduct AS is recovered in the first crystallizer (Fig. 11.4(c)). Solvent removal is then used to cross from compartment AS to B, followed by crystallization of B. The final mother liquor (point 4) is recycled (Fig. 11.4(d)). To complete the flowsheet, two units are added a dissolver to introduce solvent S to the feed, and a distillation column to recover A from the adduct (Fig. 11.4(e)). S is recycled back to the dissolver. Cooling-type crystallizers are used for both Cl and C2, since the boiling point of 

Before one can begin addresang the problem of sequencing separators, the dmce of a particular separation method or methods must be made. Of course, decisions are based on bodi technical and economic merits and it is not uncommon for conflicts to arise. For instance, although die technical feasibility of a given separation method might be attractive, it may not be compatible with the expected product value. 

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Thus the complexity of chemical process synthesis is twofold. First, can we identify all possible structures Second, can we optimize each structure for a valid comparison When optimizing the structure, there may be many ways in which each individual task can be performed and many ways in which the individual tasks can be interconnected. This means that we must simulate and optimize... 

Lott, D. H-, Simulation Software as an Aid to Process Synthesis, IChemE Symposium Series No. 109, IChemE, 1988. 

Douglas, J. M., A Hierarchical Decision Procedure for Process Synthesis, AIChEJ, 31 353, 1985. 

Papoulias, S. A., and Grossmann, I. E., A Structural Optimization Approach in Process Synthesis II. Heat Recovery Networks, Computers Chem. Eng., 7 707, 1983. 

Resources for Nitrogen Fertilizers. The production of more than 95% of all nitrogen fertilizer begins with the synthesis of ammonia, thus it is the raw materials for ammonia synthesis that are of prime interest. Required feed to the synthesis process (synthesis gas) consists of an approximately 3 1 mixture (by volume) of hydrogen and nitrogen. 

R. L. Motard and A. W. Westerberg, Process Synthesis, AIChE advanced seminar lecture notes. New York, 1988. 

See Extraction High pressure thchnology Separations process synthesis. 

Synthesis Gas Preparation Processes. Synthesis gas for ammonia production consists of hydrogen and nitrogen in about a three to one mole ratio, residual methane, argon introduced with the process air, and traces of carbon oxides. There are several processes available for synthesis gas generation and each is characterized by the specific feedstock used. A typical synthesis gas composition by volume is hydrogen, 73.65% nitrogen, 24.55% methane, <1 ppm-0.8% argon, 100 ppm—0.34% carbon oxides, 2—10 ppm and water vapor, 0.1 ppm. 

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