Recycle operations

Mujtaba and Macchietto (1988) used the measure, q, the degree of difficulty of separation (section 3.5.1) to correlate the extent of benefit of production and recycling of off-cuts for binary mixtures. It is reported that for some separations more than 70% batch time savings were possible when compared to no off-cut production and no recycle cases. Using the measure, q, the authors were also able to explain whether and when an initial total reflux operation was required in batch distillation. Further details are presented in Chapter 8. 

Initial Charge ( Mixed Charge Inteimediate Bottom Residue 

Bonny et al. (1996) developed a further strategy for off-cut recycling. Further details are discussed in Chapter 8. 

Boston, J.F., Britt, H.I., Jirapongphan, S. and Shah, V.B.,1980, In Foundation of Computer Aided Chemical Process Design, (Engineering Foundation, New York), II (1980), 203. 

Greaves, M. A., Hybrid Modelling, Simulation and Optimisation of Batch Distillation Using Neural Network Techniques. Ph.D. Thesis, (University of Bradford, Bradford, UK, 2003). 

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Chlorination can be carried out at 25°C or below. However, the reaction is exothermic and, as mills have used filtrate recycle, operating temperatures have unavoidably risen. Retention times are 30—60 minutes but decrease as temperature increases. In most mills the retention time cannot be changed because the tower is upflow in design. The normal pulp consistency is 3—4%, but the trend is toward higher (ca 10%) consistency or gas-phase chlorination. Target pH in the chlorination stage (also (7 ) is about 1.8. 

Recycling is not the total answer to the soUd waste problem. However, efficiently operated recycling programs can easily divert 35% or more of municipal soUd waste away from disposal. Curbside coUection systems offer the opportunity to coUect the greatest amount of recyclables in the most cost-efficient manner. It is imperative that communities and recyclers operate programs that are glass-friendly and which result in color-separated, contaminant-free material. 

Paper recycling has greatly iacreased in Canada, from one mill making recycled-content newspriat in 1989 to 60 paper recycling operations in 1995... 

Exxon was the first to investigate the suitabiUty of a wide range of different U.S. coals for conversion. Operation of the EDS process was demonstrated in a 230 t/d unit in Baytown, Texas that had a start-up in May of 1980. Data on the response of a variety of coals to once-through and bottoms recycle operations are shown in Eigure 4. Eigure 5 presents typical Hquefaction product distributions for the system operated both with and without the Elexicoking (fluidized-bed coking) option. 

Any type of sohds conveyor may be suitable for recycle mixing however, the most universally applicable is the double-shaft pug-miU-type paddle mixer. This conveyor or mixer should be insulated to prevent excessive heat losses from the hot, dry recycle product. To ensure uniformity in the recycle operation, a surge storage reserve of recycle sohds should be installed for startup purposes and in the event of interruption of product discharge from the cyhnder. In recycle operations, 50 to 60 percent product recirculation is found economical in many instances. 

Only one melamine molecule is formed from six urea molecules, whilst three molecules of ammonia carbamate are formed. Whilst this can be recycled to urea the conversion from urea to melamine per cycle is at most 35%. Both the main route and the recycling operation involve high pressures and the low process efficiency offsets some of the apparent economic attractions of the route compared to those from dicy . 

Because most plastic bottles are recycled, it is necessary to separate the label and adhesive from the bottle. The label is contaminated with ink and not recyclable. The adhesive is also not recycled. Ideally the adhesive will stick tenaciously to the film, but release cleanly from the bottle during the recycling operation. Adhesives designed to aid in recycling have been developed for this market. They incorporate conventional surfactants in place of some or all of the oil in PSA compositions [69] or use ingredients such as rosin which when neutralized by base can function as surfactants. A goal of the recycling industry is to eliminate the need to use base in the process. 

The choice of recycling to materials or energy has to be decided by an economic audit. Recycling is preferable to landfill practice, the costs of which are increasing and where the favorable properties of plastics are not used. Municipal authorities have to consider the economics of recycling operations, tak-... 

One such process was developed by the Outokumpu Company in Finland and used in the company s zinc smelter at Kokkola. The gases are scrubbed with concentrated sulfuric acid, whereby mercury is dissolved as mercuric sulfate. After several recycling operations, the mercury concentration reaches saturation level such that crystals of mercuric sulfate form and can be removed. 

Two other problems that fit this category are calculating the number of stages in a multicomponent distillation problem, and obtaining the material balance when complicated recycle operations occur. 

Certain specified waste shall cease to be waste. .. when it has undergone a recovery, including recycling, operation and complies with specific criteria to be developed in accordance with the following conditions ... 

PBDEs are a group of chemicals widely used as fire retardants in various commercial products. They have also been found in almost all environmental media around e-waste recycling sites, presumably due to unintended releases during primitive recycling operations. Herein a summary of the levels of PBDEs around e-waste recycling and reference sites is presented. 

In tree bark from Luqiao of Taizhou (Fig. 1), the mean concentrations of PCDD/ Fs (List 4 of Appendix) and PCBs (List 8 of Appendix) were 0.1 and 6.5 pg/g lipid weight, respectively. Among all the target analytes, 2,3,4,7,8-PeCDF and PCB-126 were the dominant contributors to toxic equivalency (TEQ). The high levels of PCDD/Fs and PCBs in tree bark suggested the impact of e-waste recycling operations on the local environment [50]. 

In summary, improper e-waste recycling operations are the major contributors of dioxin and dioxin-like compounds to the terrestrial environment in China [7]. The lower concentrations of dioxin and dioxin-like compounds at reference sites than at e-waste recycling sites suggest the likelihood for these chemicals to transport atmospherically from where they are generated to distant areas. We can also infer that dioxin and dioxin-like compounds initially derived from burning of e-waste can enter ambient air and dust and finally deposit into soil. This notion is supported by the significant positive correlation between the levels of PCDD/Fs in dust and soil samples from Taizhou. 

Heavies formation is accelerated by a variety of materials.[8] Successful Gas Recycle operation depends on keeping the catalyst solution as pristine as possible to limit heavies formation since in Gas Recycle there is no independent way to remove heavies. There are a single set of conditions for product formation, product removal and byproduct (heavies) removal. A key to successful operation is identifying conditions under which the heavies can be removed essentially at their rate of formation. A downside of Gas Recycle is that it may be difficult to recover from upsets in operation, which result in the catalyst solution containing a disproportionate amount of heavies. 

Notation and material balances for recycle operation are stated in problems P4.06.01 and P4.06.02. An adiabatic operation is studied in P4.06.08. 

With reversible reactions, sufficient improvement in conversion sometimes can be realized from removing the product to warrant a recycle operation. This can be done by sending the product to a separator and returning only unconverted material. Some systems, moreover, lend themselves to continuous removal of product in equipment integrated with the reactor. Extraction is thus employed in problem P4.06.13 and azeotropic distillation in problems P4.06.14 and P4.06.15. The gasoline additive, methyl-tert-butyl ether, is made in a distillation column where reaction and simultaneous separation take place. 

In order to study the repression of ethylene formation when the ethane is cracked along with other hydrocarbons, a test is proposed in which 20 mols of ethylene is to be charged along with 100 mols of ethane. If Vr/V is to be kept the same in both cases, find how much less ethylene is formed in the recycle operation. 

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