Polymerization processes costs

Over the last decade, the utility of layered silicate nanoparticles as additives to enhance polymer performance has been established (5-17). These nanoscale fillers result in physical behavior that is dramatically different from that observed for conventional microscale counterparts. For instance, increased modulus (7,8), decreased permeability (9-11), reduced coefficient of thermal expansion (CTE) (12,13) and impact strength retention (7,14) are observed with only a few volume percent addition of exfoliated layered silicate thus maintaining polymeric processability, cost and clarity. 

Other than fuel, the largest volume appHcation for hexane is in extraction of oil from seeds, eg, soybeans, cottonseed, safflower seed, peanuts, rapeseed, etc. Hexane has been found ideal for these appHcations because of its high solvency for oil, low boiling point, and low cost. Its narrow boiling range minimises losses, and its low benzene content minimises toxicity. These same properties also make hexane a desirable solvent and reaction medium in the manufacture of polyolefins, synthetic mbbers, and some pharmaceuticals. The solvent serves as catalyst carrier and, in some systems, assists in molecular weight regulation by precipitation of the polymer as it reaches a certain molecular size. However, most solution polymerization processes are fairly old it is likely that those processes will be replaced by more efficient nonsolvent processes in time. 

The ionic liquid process has a number of advantages over traditional cationic polymerization processes such as the Cosden process, which employs a liquid-phase aluminium(III) chloride catalyst to polymerize butene feedstocks [30]. The separation and removal of the product from the ionic liquid phase as the reaction proceeds allows the polymer to be obtained simply and in a highly pure state. Indeed, the polymer contains so little of the ionic liquid that an aqueous wash step can be dispensed with. This separation also means that further reaction (e.g., isomerization) of the polymer s unsaturated ot-terminus is minimized. In addition to the ease of isolation of the desired product, the ionic liquid is not destroyed by any aqueous washing procedure and so can be reused in subsequent polymerization reactions, resulting in a reduction of operating costs. The ionic liquid technology does not require massive capital investment and is reported to be easily retrofitted to existing Cosden process plants. 

Polyethylene terephthalate also has the tendency, because it is produced by a condensation polymerization process, to depolymerize under high pressure and temperatures in the presence of water. Although this is usually a negative attribute, it can be utilized to regenerate pure monomers which can be repolymerized to make fresh polymer. This avoids the issues experienced by reprocessing resins, as the new resin has not experienced a previous heat history. A major drawback to this process is the requirement that the monomers used in polymerization processes must be highly pure, Unfortunately, this process is extremely costly and not performed on a commercial scale. 

It is clear from this discussion that the dose requirement and unit cost will be lower if the material has a higher molar mass M and the reaction has a high G value. Thus, the best candidates will be a polymeric material and a chain reaction. Quite often, a free-radical irradiation is used. The radiation source of choice is usually a 60Co - y facility, although electron beam irradiation is also used. Since most radiation-chemical reactions used in industry can also be brought about by other conventional means such as thermal, or photochemical processes, the processing cost must be below 10irradiation cost one has to include the cost of operation, maintenance, and the like. (Danno, 1960). 

The expected contribution of catalysis in this area will derive both from the availability, at low processing costs, of new monomers obtained from biomasses and from the development of an optimized combination of biotechnology processes with classical and new biocatalytic processes. Research priorities for catalysis in the area of polymers from renewable materials for packaging, furniture, domestic water purification and recycling include the need to develop novel catalysts, e.g., for functionalization of polymeric and dendrimeric materials, with side-chain photoactive molecular switches (to be used as smart materials), or the development of multifunctional materials, combining, for example, nanofiltration with catalytic reactivity. 

Polymeric materials are intrinsically expensive, but their use becomes appealing if one takes into account the processing costs, the new technical possibilities that they permit and the total cost at the end of their lifetime. 

The question of choosing a PFTR or a CSTR will occur throughout this book. From the preceding arguments it is clear that the PFTR usuaUy requires a smaller reactor volume for a given conversion, but even here the CSTR may be preferred because it may have lower material cost (pipe is more expensive than a pot). We will later see other situations where a CSTR is clearly preferred, for example, in some situations to maximize reaction selectivity, in most nonisothermal reactors, and in polymerization processes where plugging a tube with overpolymerized solid polymer could be disastrous. 

From the results presented in this chapter we can conclude that it is feasible to prepare sugar-based polymers analogous to the more qualified technological polymers - polyamides, polyesters, polyurethanes - with an enhanced hydrophilicity and degradability. However, in most cases, the high costs associated with the preparation of the monomers restrict the application of these polymers to biomedical applications and other specialized fields. More readily available monomers and simpler polymerization processes have to be found if sugar-derived polymers should compete with petrochemical-based polymers that are used in domestic applications. 

For polymerizing monomers into commodity resins, cost of irradiation would have to be reduced to the cost of catalyst in order to compete economically with the present commercial polymerization processes. For engrafting monomers to finished articles, the cost can be higher, especially when solvents are eliminated. 

Although inclusion in motor gasolines is the most obvious alternative use for alkylate, this process would have to be economically competitive with processes such as polymerization, which also convert gaseous hydrocarbons to gasoline. Since the chief obstacle to the use of alkylate in motor gasolines is its high processing cost, it would appear that future research should be directed toward improvements in the process which will reduce these costs. 

The already low cost of converting VCM to PVC probably precludes any revolutionary new process replacing the current suspension and emulsion processes. The Pechiney-St. Gobain bulk polymerization process is being tested thoroughly within the next year it will be evident if the process offers advantages, either in product quality or conversion cost. 

The first three benefits are a direct consequence from the extremely low tendency of the Nd-catalyst to form branches and gel. Because of this remarkable feature, Nd-catalysts allow monomer conversions up to 100%. Therefore, the polymerization reaction does not have to be shortstopped below a critical monomer conversion in order to avoid gel. In addition, polymerization temperature does not have to be controlled within a well-defined temperature range. As the maximum polymerization temperature (at complete monomer conversion) can be as high as 120 °C the polymerization process can be performed in a fully adiabatic manner. In this case energy costs for cooling and for the removal of low molar mass residuals can be very low. Another benefit of the Nd-catalyst is the low tendency to catalyze the Diels-Alder dimerization of BD to vinyl cyclohexene. 

The similar, older slurry process uses a less active catalyst. The monomer is dissolved in isooctane, the titanium catalyst and aluminium cocatalyst are added and this mixture is fed to the reactor which is maintained at 70°C. The inorganic corrosive (Cl) residues are removed in a washing step with alcohols. The atactic material is removed by extraction. A third process employs propene as the liquid in combination with a high activity catalyst. The Himont Spheripol process, which uses spherical catalyst particles, gives spherical polymer beads of millimetre size that need no extrusion for certain purposes. A more recent development is the gas-phase polymerization using an agitated bed. All processes are continuous processes, where the product is continuously removed from the reactor. Over the years we have seen a reduction of the number of process steps. The process costs are very low nowadays, propene feed costs amounting to more than 60% of the total cost. 

Styrene-containing block copolymers are commercially very important materials. Over a billion pounds of these resins are produced annually. They have found many uses, including reinforcement of plastics and asphalt, adhesives, and compatibilizers for polymer blends, and they are directly fabricated into articles. Most styrene-containing block copolymers are manufactured using anionic polymerization chemistry. However, anionic polymerization is one of the more costly polymerization chemistries because of the stringent requirements for monomer and solvent purity. It would be preferred, from an economic cost perspective, to have the capability to utilize free radical chemistry to make block polymers because it is the lowest cost mode of polymerization. The main reasons for the low cost of FR chemistry are that minimal monomer purification is required and it can be carried out in continuous bulk polymerization processes. 

In step-growth polymerizations, overall costs of monomers, solvent recovery, and preparing the polymer for further processing usually dictate a preference for reactions that are slow at room temperature. (The reasons behind this generalization are summarized in Section 5.3.1.) The ratio of rates of macromolecular growth reactions in typical chain and step-growth polymerizations is often of the order of 10 . ... 

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