Balanced process

Although a small fraction of the world s vinyl chloride capacity is stiU based on acetylene or mixed actylene—ethylene feedstocks, nearly all production is conducted by the balanced process based on ethylene and chlorine (75). The reactions for each of the component processes are shown in equations 1—3 and the overall reaction is given by equation 4 ... 

In a typical balanced plant producing vinyl chloride from EDC, all the HCl produced in EDC pyrolysis is used as the feed for oxychlorination. On this basis, EDC production is about evenly spHt between direct chlorination and oxychlorination, and there is no net production or consumption of HCl. The three principal operating steps used in the balanced process for ethylene-based vinyl chloride production are shown in the block flow diagram in Eigure 1, and a schematic of the overall process for a conventional plant is shown in Eigure 2 (76). A typical material balance for this process is given in Table 2. 

If the production of vinyl chloride could be reduced to a single step, such as dkect chlorine substitution for hydrogen in ethylene or oxychlorination/cracking of ethylene to vinyl chloride, a major improvement over the traditional balanced process would be realized. The Hterature is filled with a variety of catalysts and processes for single-step manufacture of vinyl chloride (136—138). None has been commercialized because of the high temperatures, corrosive environments, and insufficient reaction selectivities so far encountered. Substitution of lower cost ethane or methane for ethylene in the manufacture of vinyl chloride has also been investigated. The Lummus-Transcat process (139), for instance, proposes a molten oxychlorination catalyst at 450—500°C to react ethane with chlorine to make vinyl chloride dkecfly. However, ethane conversion and selectivity to vinyl chloride are too low (30% and less than 40%, respectively) to make this process competitive. Numerous other catalysts and processes have been patented as weU, but none has been commercialized owing to problems with temperature, corrosion, and/or product selectivity (140—144). Because of the potential payback, however, this is a very active area of research. 

In all of these oxide phases it is possible that departures from the simple stoichiometric composition occur dirough variation of the charges of some of the cationic species. Furthermore, if a cation is raised to a higher oxidation state, by the addition of oxygen to tire lattice, a conesponding number of vacant cation sites must be formed to compensate tire structure. Thus in nickel oxide NiO, which at stoichiomen ic composition has only Ni + cations, oxidation leads to Ni + ion formation to counterbalance the addition of extra oxide ions. At the same time vacant sites must be added to the cation lattice to retain dre NaCl sUmcture. This balanced process can be described by a normal chemical equation thus... 

The balancing process must be in accord with the rotor dynamics, as specified by the operating environment. Unfortunately, the dynamic characteristics are often not properly recognized when the balancing procedure is specified. As a result, the unbalance distribution problem may not be identified not enough planes may be provided sensors may be located at nonoptimum positions, or critical speeds may be overlooked entirely. It is the responsibility of the machinery end user to satisfy himself that the manufacturer has considered ... 

The major method for preparing the monomer commercially since the early 1960s has been the so-called balanced process from ethylene. In the first stage of the reaction, 1,2-dichloroethane is prepared by reacting ethylene with chlorine in either the vapour or the liquid phase Figure 12.2). In a typical liquid phase... 

Figure 1-11. Typical material balance process flowsheet.

The need for and use of multiple inlets/oudets for centrifugal compressors becomes apparent when balancing process flow and pressure requirements. See the later discussion, and also refer to Figures 12-40B and 12-40D. 

With a keyed-shaft rotor, the balancing process can introduce machine vibration if the assumed key length is different from the length of the one used during operation. Such an imbalance usually results in a mediocre or good running machine as opposed to a very smooth running machine. 

This is the final balanced equation for the reaction of hydrazine with dinitrogen tetraoxide. Three points concerning the balancing process are worth noting. 

O2 + A > ( i=180-240 nm) 0 + 0 Second, an oxygen molecule captures one of these oxygen atoms to form an ozone molecule 02+0 03+ Heat The second step occurs twice for each O2 fragmentation, giving the overall balanced process for ozone formation 3 O2 + h V( =l30-240 nm) Heat... 

Exampie iiiustrates the entire balancing process, and Example illustrates the balancing procedure in basic soiution. 

The block diagram shows the main steps in the balanced process for the production of vinyl chloride from ethylene. Each block represents a reactor and several other processing units. The main reactions are ... 

The relationship between the quality concept and human or animal health needs to be established from a holistic health perspective. The Louis Bolk Instituut has already started animal feeding experiments. Such research can only be done if foodstuffs are available which have been produced using well-balanced processes, in the sense described above, and which have thus achieved an optimum level of quality (defined hereunder). 

Predesign (Conceptual design) flow sheet preliminary pid feasibility study preliminary operation instructions material balance energy balance process concept operating conditions sketch of layout isi, pns (coarse Dow F E Index, Mond Index, Hazop)... 

The balancing process described above does not require a formal benefit-cost analysis under which a monetary value is assigned to the risks associated with a substance and to the cost to society of proposed regulatory action on the availability of such benefits. Because a monetary value often cannot be assigned to a benefit or cost, such an analysis would not be very useful. 

For analytical studies involving the interplay of flow processes and chemical reactions, we require a set of chemically balanced equations that lead from the known reactants to the measured reaction products. For the complete oxidation of CH4, this last statement implies that we need a reaction scheme producing only H20 and C02. This requirement is incompatible with Equations 1-1 to 1-10. To achieve consistency, we first replace Equation I—1 by the balanced process... 

The third most crucial stage in the balanced process is the oxychlorination step.188-190,272,273 In this reaction ethylene and HC1 are converted to 1,2-dichloroethane in an oxidative, catalytic process. The reaction proceeds at temperatures of 225-325°C and pressures 1-15 atm. Pure oxygen or air is used as oxidant.276-278 Numerous, somewhat different industrial processes were developed independently.272-274 However, the reaction is generally carried out in the vapor phase, in fixed-bed or fluidized-bed reactors. 

Because the performance of a particular piece of equipment depends on its input, recycling of streams in a process introduces temporarily unknown, intermediate streams whose amounts, compositions, and properties must be found by calculation. For a plant with dozens or hundreds of streams the resulting mathematical problem is formidable and has led to the development of many computer algorithms for its solution, some of them making quite rough approximations, others more nearly exact. Usually the problem is solved more easily if the performance of the equipment is specified in advance and its size is found after the balances are completed. If the equipment is existing or must be limited in size, the balancing process will require simultaneous evaluation of its performance and consequently is a much more involved operation, but one which can be handled by computer when necessary. 

Water balance processes are best developed in species inhabiting deserts, where little drinking water is available and climatic conditions accentuate evaporation. 

Anodes. There are two types of anodes soluble and insoluble. Most electroplating baths use one or the other specifically however, a few baths use either or both. Chromic acid plating baths use insoluble anodes alkaline zinc cyanide baths use both noncyanide alkaline zincs may use either. Soluble anodes are designed to dissolve efficiendy with current flow and preferably, not to dissolve when the system is idle. A plating solution having the anode efficiency close to the cathode efficiency provides a balanced process that has fewer control problems and is less cosdy. If the anode efficiency is much greater than the cathode efficiency and there are only small solution losses, the dissolved metal concentration rises until at some time the bath has to be diluted back or the excess metal has to be reduced by some other means. If the anode efficiency is less than the cathode efficiency, the dissolved metal decreases, pH decreases, and eventually metal salt additions and other solution corrections are required. Based on the cost of metal, it is usually considerably more economical to plate from the anode rather than add metal salt. Copper cyanide, for example, costs about twice as much to add than to dissolve a comparable amount of copper anode. Additionally, the anion added with the metal salt may build up in the plating solution. 

We would expect the radical balance reactions (6) through (16) to be equilibrated at all points in these flames. Tests of the equilibration have been made, as for example in Figure 6, by evaluating the equilibrium concentration ratios using experimentally measured concentration values. Since O, H, S, and H2S concentrations were not measured directly we can indirectly evaluate the equilibration of the radical balance process by using reactions that are sums of the above listed processes. Four such reactions are listed below with an indication of a combination of reactions (6) through (16) that is chemically equivalent. 

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