Eastman process

Now that we have laid the groundwork by looking at the control of individual unit operations, we are ready to return to the plantwide control problem. In the next four chapters we illustrate the application of the nine-step design procedure with four industrial process examples. 

We begin with a fairly simple process consisting of a reactor, condenser, separator, compressor, and stripper with a gas recycle stream (Fig. 8.1). This process was developed and published by Downs and Vogel (1993) as an industrial plantwide control test problem. A FORTRAN program is available from them that does the derivative evaluations for the process. The user must write a main program that initializes the simulation, does the controller calculations, performs the numerical integration, and plots the results. 

A detailed description of the process in this book is unnecessary since one was provided in the original paper. We summarize here only some of the essential and unusual dynamic features. A small amount of an inert noncondensible component B is introduced in a feed stream and must be purged from the process. There are four fresh gas feed streams F A, FoD, FoE, and FoC. The first three are mixed with the recycle gas and fed into the bottom of the reactor. The last fresh feed FoC is fed into the bottom of the stripper. 

There are two main reactions, both of which are irreversible and exothermic  

Two additional irreversible and exothermic side reactions produce by- 

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The chemical complex includes the methanol plant, methyl acetate plant, and acetic anhydride plant. The methanol plant uses the Lurgi process for hydrogenation of CO over a copper-based catalyst. The plant is capable of producing 165,000 t/yr of methanol. The methyl acetate plant converts this methanol, purchased methanol, and recovered acetic acid from other Eastman processes into approximately 440,000 t/yr of methyl acetate. 

The Eastman Chemical Company has pubHshed extensively in the patent Hterature (65—74) and the scientific Hterature (75—77) on processes for making poly(phenylene sulfide)- (9-(phenylene disulfide), and related copolymers. The Eastman process involves the reaction of elemental sulfur with Ndiiodobenzene to yield a phenylene sulfide polymer that also contains phenylene disulfide repeating units in the polymer. The fraction of repeating groups containing... 

SAMDANI Heat Transfer Technologies and Practices for Effective Energy Management SAWERS, EASTMAN Process Industry Procedures and Training Manual... 

The Eastman process breaks down the PET down into basic components that can be separated from dyes, additives and other impurities. At this stage the pilot plant is still a rather small operation that is designed primarily to produce data rather than the product (97). 

In the Eastman process for 2,5-dihydrofuran production, the situation is different and the problem of heavy products has been tackled in a highly original manner. [31] The oligomers formed in the process are highly polar and insoluble in alkanes. The ionic liquid, [P(oct)3C18H37]I and the Lewis acid catalyst, [Sn(oct)3]I, which are non toxic (LD50 > 2 g kg"1 for each), non-flammable (flammability 1) and non-corrosive (340 stainless steel is used for the reactor), have been designed to be soluble in... 

Water also causes a change in the reaction medium, which may be advantageous. A drawback of the reducing medium in the Eastman process is that in addition to acetic anhydride, the by-product ethylidene diacetate is formed, CH3CH(AcO)2. This can be thermally decomposed to vinyl acetate and acetic acid, or it can be reduced to ethyl acetate, which in the recycle would lead eventually to propionic acid. 

In addn to the above mentioned processes for the production of acetylene, several others were developed, of which the Tennessee Eastman process (Ref 22) and the Societe Beige de 1 Azote (SB A)-Kellogg process (Ref 27) are the most recent... 

The Genencor-Eastman process to ascorbic acid (vitamin C) ferments glucose in one step to 2-ketogulonic acid, with subsequent chemical conversion to ascorbic acid. It replaces the old Reichstein-Griissner process with its 55% overall yield, 3 d cycle time, five chemical steps, 17-20 different downstream processing steps, and at least seven different solvent systems. 

Figure 20.9 Genencor-Eastman process to ascorbic acid.

Acetic anhydride is also produced by the Rh-catalyzed carbonylation of methyl acetate. The method is called the Eastman process (Scheme 3.11). The Rh-catalysed production of acetic anhydride from methyl acetate can be understood by the formation of Mel and acetic acid by the reaction of methyl acetate with HI. Finally, attack of AcOH on the acetylrhodium affords the anhydride and HI, or acetyl iodide reacts with AcOH to give acetic anhydride and HI. 

The Eastman process for reacting methanol with acetic acid to produce methyl acetate and water in one column. Product separation (instead of increased feed concentration) is used to drive the equilibrium to the right. 

Larsson, T., Hestetun, K., Hovland, E., and Skogestad, S. (2001). Self-optimizing control of a large-scale plant the Tennessee Eastman process. Ind. Eng. Chem. Res., 40(22), 4889M901. 

In the new Eastman process, synthesis gas (carbon monoxide and hydrogen) is made from coal. Then, from the generated synthesis gas, methanol was prepared. (Prior to this time, methanol had been made from methane, i.e., natural gas.)... 

In recent years several commercial plants have been constructed for conversion of coal to synthesis gas for chemical manufacturing. These include the Eastman Chemical s acetic anhydride plant, the Ube (Japan) ammonia plant, the SAR (Germany) oxo chemicals plant, and several coal to ammonia plants in China (e.g., Weihe, Huainan, and Lunan). The Ube plant and the SAR plant have since converted to lower-cost opportunity fuels (petroleum coke and residues). The Eastman plant is still operating exclusively on coal. Feedstock changes at the other plants illustrate the vulnerability of coal conversion processes to a changing economic climate. The fact that the Eastman process remains competitive under changing conditions is due to a set of special circumstances that favor a coal-based process. The success of the Eastman chemicals from coal complex demonstrates that synthesis gas from coal is a viable feedstock for some industrial chemicals under certain conditions. 

A block diagram of the Monsanto process for acetic acid production is shown in Fig. 4.13. The process flow sheet is simple since the reaction conditions are mild (180°C/30-40 bar) when compared to the BASF process (250°C/700 bar). More than 40% of world s acetic acid is made by the Monsanto process. One of the problems with this process is the continuous loss of iodine. A block diagram of the Eastman process for acetic anhydride production is shown in Fig. 4.14. The process generates minimum waste, and all process tars are destroyed to recover iodine and rhodium. 

Very few unbiased publications have appeared in the literature comparing control effectiveness using MPC versus a well-designed conventional control system. Most of the MPC applications reported have considered fairly simple processes with a small number of manipulated variables. There are no published reports that discuss the application of MPC to an entire complex chemical plant, with one notable exception. That is the work of Ricker (1996), who compared MPC with conventional PI control for the Eastman process (TE problem). His conclusion was there appears to be little, if any, advantage to the use of nonlinear model predictive control (NMPC) in this application. In particular, the decentralized strategy does a better job of handling constraints—an area in which NMPC is reputed to excel.51... 

Figure 2.2 contrasts a typical column with a variable feed rate as set by an upstream unit to an on-demand column with bottoms flowrate set by a downstream operation. Further examples are given in later chapters when specific plants are considered (Chap. 8 for the Eastman process and Chap. 11 for the vinyl acetate process). 

Several different control structures have been published in the literature for the Eastman process Ricker (1993), McAvoy and Ye (1994), Price et al. (1994), Lyman and Georgakis (.1995), Ricker and Lee (1995), Baneijee and Arkun (1995), Kanadibhotla and Riggs (1995), McAvoy... 

Figure 8.2 Eastman process base steady-state conditions for Mode 1.

A word needs to be said about controller type and controller tuning. Controller algorithm selection and tuning are important to the success of any control system. Two features should be recognized about the Eastman process. First, it is an integrating process with little selfregulation in terms of pressure, liquid levels, and chemical components. Second, there are no tight specifications on any variables. 

A plantwide control design procedure was used to develop a simple but effective regulatory control system for the Eastman process with an on-demand product control objective. With this strategy, control of production rate is essentially instantaneous. Drastic upsets and disturbances are handled by simple proportional-only overrides. 

Developing a plantwide control system for the Eastman process is fairly straightforward. There are only five unit operations and one gas recycle stream. No energy7 integration is present. So the major feature of this process from a plantwide viewpoint is the problem of accounting for the multiple component inventories. 

In the previous chapter we studied a fairly simple process consisting basically of a boiling-liquid reactor and a simple separation section. Although the Eastman process has some plantwide control features, it is essentially just a nonlinear reactor control problem. The gas recycle loop acts like a big stirrer. The management of chemical components through fresh feed makeup streams and product streams is the principal aspect that illustrates plantvvide control considerations. 

In this section we illustrate how the control scheme is modified if a different control criterion is specified. Suppose business objectives dictate that the organic product from the decanter must be an on-demand stream, i.e., a downstream unit or customer sets the desired flowrate of this stream and the plant must immediately supply the requested flowrate of organic product. In this situation the organic product flow-rate will be flow controlled, with the setpoint of the flow controller coming from the downstream consumer. A similar case was considered in Chap. 8 with the Eastman process. 

Thermodynamically, the carbonylation of methyl acetate (AG298 -10 kJ/mol) is considerably less favourable than that of methanol (AG298 -74 kJ/mol). This means that the reaction does not reach completion but attains an equilibrium which is dependent on the temperature and the CO pressure. Two variants are currently practised commercially that developed by Tennessee Eastman, based on a Halcon process, and a BP process in which acetic acid and the anhydride are co-produced in proportions which can be varied according to demand. Syngas for the Eastman process is made from coal which is mined close to the plant in Tennessee and the acetic anhydride produced is used to make cellulose acetate for film production. The BP process uses syngas generated from North Sea gas which is piped directly to the BP plant in EIull. [Acetic anhydride manufacture M. J. Eloward, M. D. Jones, M. S. Roberts, S. A. Taylor, Catalysis Today, 1993, 18, 325]. 

The basic organometallic reaction cycle for the Rh/I catalyzed carbonylation of methyl acetate is the same as for methanol carbonylation. However some differences arise due to the absence of water in the anhydrous process. As described in Section 4.2.4, the Monsanto acetic acid process employs quite high water concentrations to maintain catalyst stability and activity, since at low water levels the catalyst tends to convert into an inactive Rh(III) form. An alternative strategy, employed in anhydrous methyl acetate carbonylation, is to use iodide salts as promoters/stabilizers. The Eastman process uses a substantial concentration of lithium iodide, whereas a quaternary ammonium iodide is used by BP in their combined acetic acid/anhydride process. The iodide salt is thought to aid catalysis by acting as an alternative source of iodide (in addition to HI) for activation of the methyl acetate substrate (Equation 17) ... 

Even with added iodide salt formation of the inactive [Rh(CO)2l4] can be a problem, since under anhydrous conditions this Rh(III) species cannot be reduced to the active [Rh(CO)2l2] by reaction with water. In the Eastman process, this problem is addressed by addition to the CO gas feed of some H2 which can reduce [Rh(CO)2l4] by the reverse of Equation 8. However, the added H2 does lead to some undesired by-products, particularly ethylidene diacetate (1,1-diacetoxyethane) which probably arises from the reaction of acetic anhydride with acetaldehyde (Equation 19 from hydrogenolysis of a rhodium acetyl) ... 

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