Recyclate, analysis

Figure 8.9 shows the turbine exhaust gas temperatures for the cathode recycle and recuperated cases. The cathode recycle has a comparatively higher quality of heat. Systems with temperatures above 800 K are a good candidate for heat recovery steam generation. Thus, up to a PR of about 20 there is some potential for the addition of a steam cycle to the cathode recycle analysis, which would increase both system power and efficiency. 

To master the concepts of recycle analysis, it is recommended that the reader solve several of the exercises at the end of the chapter. Of these, the so-called flash with recycle problem (Exercise 4.1a) should be tackled first. Although it involves just one recycle loop, it demonstrates a very important principle. See if you can identify it ... 

The first form of aerosol modifier is a spray chamber. It is designed to produce turbulent flow in the argon carrier gas and to give time for the larger droplets to coalesce by collision. The result of coalescence, gravity, and turbulence is to deposit the larger droplets onto the walls of the spray chamber, from where the deposited liquid drains away. Since this liquid is all analyte solution, clearly some sample is wasted. Thus when sensitivity of analysis is an issue, it may be necessary to recycle this drained-off liquid back through the nebulizer. 

Table 17. Properties and Analysis of Liquid Fuel and No. 6 Fuel Oil Liquid fuel produced by flash pyrolysis using char recycle (Fig. 10).

The environmental appHcations of infrared spectrometry are many and varied. Many appHcations at industrial sites are analogous to those for on-line process analysis waste streams and recycling processes can be monitored in the same way. Commercial infrared stack-gas monitors are based on either an extractive probe attached to a long-path gas ceU or an open-path (across stack) configuration (69). Stack plume and flare monitoring can be done externally... 

Economic Analysis. The economic success of recycling programs is subject to the following inequaUty where X = the cost to recover recyclable materials, Y = the cost of disposal, and Z = the value of the resource recovered. 

Ethyltoluene is manufactured by aluminum chloride-cataly2ed alkylation similar to that used for ethylbenzene production. All three isomers are formed. A typical analysis of the reactor effluent is shown in Table 9. After the unconverted toluene and light by-products are removed, the mixture of ethyltoluene isomers and polyethyltoluenes is fractionated to recover the meta and para isomers (bp 161.3 and 162.0°C, respectively) as the overhead product, which typically contains 0.2% or less ortho isomer (bp 165.1°C). This isomer separation is difficult but essential because (9-ethyltoluene undergoes ring closure to form indan and indene in the subsequent dehydrogenation process. These compounds are even more difficult to remove from vinyltoluene, and their presence in the monomer results in inferior polymers. The o-ethyltoluene and polyethyltoluenes are recovered and recycled to the reactor for isomerization and transalkylation to produce more ethyltoluenes. Fina uses a zeoHte-catalyzed vapor-phase alkylation process to produce ethyltoluenes. 

Bosch and co-workers devised laboratory reactors to operate at high pressure and temperature in a recycle mode. These test reactors had the essential characteristics of potential industrial reactors and were used by Mittasch and co-workers to screen some 20,000 samples as candidate catalysts. The results led to the identification of an iron-containing mineral that is similar to today s industrial catalysts. The researchers recognized the need for porous catalytic materials and materials with more than one component, today identified as the support, the catalyticaHy active component, and the promoter. Today s technology for catalyst testing has become more efficient because much of the test equipment is automated, and the analysis of products and catalysts is much faster and more accurate. 

Most flow sheets have one or mote recycles, and trial-and-ettot becomes necessary for the calculation of material and energy balances. The calculations in a block sequential simulator ate repeated in this trial-and-ettot process. In the language of numerical analysis, this is known as convergence of the calculations. There ate mathematical techniques for speeding up this trial-and-ettot process, and special hypothetical calculation units called convergence, or recycle, units ate used in calculation flow diagrams that invoke special calculation routines. 

Accordingly, the change in concentration (or in temperature) across the reactor can be made as small as desired by upping the recycle ratio. Eventually, the reac tor can become a differential unit with substantially constant temperature, while substantial differences will concurrently arise between the fresh feed inlet and the produc t withdrawal outlet. Such an operation is useful for obtaining experimental data for analysis of rate equations. 

Time-Delay Compensation Time delays are a common occurrence in the process industries because of the presence of recycle loops, fluid-flow distance lags, and dead time in composition measurements resulting from use of chromatographic analysis. The presence of a time delay in a process severely hmits the performance of a conventional PID control system, reducing the stability margin of the closed-loop control system. Consequently, the controller gain must be reduced below that which could be used for a process without delay. Thus, the response of the closed-loop system will be sluggish compared to that of the system with no time delay. 

Calculate the annual operating costs for the existing process that needs waste treatment, and estimate how these costs would be altered by the introduction of waste-reduction options. Tabulate and compare the process and waste-treatment operating costs for both the existing and proposed waste-management options. If there are any monetary benefits (such as recycled or reused materials or wastes), then these should be subtracted from the total process or waste-treatment costs as appropriate. The expanded cost-analysis scheme discussed in Chapter 8 is appropriate to include at this point in the process. 

Figure 7.13 is structural representation of segregation, mixing, and direct recycle candidate strategies for the problem. Each source is split into several frac-tions that can be fed to a sink. The flowrate of the streams passed from source w to sink u is referred to as The terms F, Z", and represent the inlet flowrate, inlet composition, and outlet flowrate of the streams associated with unit u. Since mixing is embedded, there is no need to include the mixing tank (m = 4) or the source that it generates u> = 5) in the analysis. Unless recycle of biotreatment effluent is considered, there is no need to represent the biotreatment sink in Fig. 7.13. However, streams allocated to biotreatment should be represented and their flowrates are referred to as (m = 5 is the biotreatment sink). Finally, fresh water may be used in any unit at a flowrate of Fresh,.

FIGURE 9.27 Analysis of recycled polybutylene terephthalate. Columns PSS PFG 100 + 1000. Eluent HFIP. Temp 2S°C. Detection UV 254 nm, Rl. Calibration PSS PBT standards (broad). 

As a matter of fact, the main advantage in comparison with HPLC is the reduction of solvent consumption, which is limited to the organic modifiers, and that will be nonexistent when no modifier is used. Usually, one of the drawbacks of HPLC applied at large scale is that the product must be recovered from dilute solution and the solvent recycled in order to make the process less expensive. In that sense, SFC can be advantageous because it requires fewer manipulations of the sample after the chromatographic process. This facilitates recovery of the products after the separation. Although SFC is usually superior to HPLC with respect to enantioselectivity, efficiency and time of analysis [136], its use is limited to compounds which are soluble in nonpolar solvents (carbon dioxide, CO,). This represents a major drawback, as many of the chemical and pharmaceutical products of interest are relatively polar. 

Another important parameter is the eluent composition. Binary mixtures (and obviously pure solvents) should be preferred to complex mixtures, since new systems perform an on-line analysis of the composition of binary eluents. These eluent systems allow the automatic eluent recycling, with a reduced number of controls. 

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