Depolymerization process

The stmctural architecture of siUcone polymers, such as the number of D, T, and Q sites and the number and type of cross-link sites, can be deterrnined by a degradative analysis technique in which the polymer is allowed to react with a large excess of a capping agent, such as hexamethyidisiloxane, in the presence of a suitable equiUbration catalyst (eq. 38). Triflic acid is often used as a catalyst because it promotes the depolymerization process at ambient temperature (444). A related process employs the KOH- or KOC2H -catalyzed reaction of siUcones with excess Si(OC2H )4 (eq. 39) to produce ethoxylated methylsiUcon species, which are quantitatively deterrnined by gc (445). 

Figure 10.4 Four major polyester depolymerization processes (hydrolysis, alcoholysis, acidolysis, and aminolysis).

A two-step methanolysis-hydrolysis process37 has been developed which involves reaction of PET with superheated methanol vapors at 240-260°C and atmospheric pressure to produce dimethyl terephthalate, monomethyl terephthalate, ethylene glycol, and oligomeric products in the first step. The methanolysis products are fractionally distilled and the remaining residue (oligomers) is subjected to hydrolysis after being fed into the hydrolysis reactor operating at a temperature of ca. 270°C. The TPA precipitates from the aqueous phase while impurities are left behind in the mother liquor. Methanolysis-hydrolysis leads to decreases in the time required for the depolymerization process compared to neutral hydrolysis for example, a neutral hydrolysis process that requires 45 min to produce the monomers is reduced... 

Polylactic acid (PLA) has been produced for many years as a high-value material for use in medical applications such as dissolvable stitches and controlled release devices, because of the high production costs. The very low toxicity and biodegradability within the body made PLA the polymer of choice for such applications. In theory PLA should be relatively simple to produce by simple condensation polymerization of lactic acid. Unfortunately, in practice, a competing depolymerization process takes place to produce the cyclic lactide (Scheme 6.10). As the degree of polymerization increases the rate slows down until the rates of depolymerization and polymerization are the same. This equilibrium is achieved before commercially useful molecular weights of PLA have been formed. 

Since the depolymerization process is the opposite of the polymerization process, the kinetic treatment of the degradation process is, in general, the opposite of that for polymerization. Additional considerations result from the way in which radicals interact with a polymer chain. In addition to the previously described initiation, propagation, branching and termination steps, and their associated rate constants, the kinetic treatment requires that chain transfer processes be included. To do this, a term is added to the mathematical rate function. This term describes the probability of a transfer event as a function of how likely initiation is. Also, since a polymer s chain length will affect the kinetics of its degradation, a kinetic chain length is also included in the model. 

Because all depolymerization processes will generate waste that may be classified as hazardous waste or at least chemical waste, it will always be economically preferable to separate as much non-PET material from the PET material as is practical. Traditional bottle washing procedures can produce used bottle flake that is clean enough to be used to make more bottles or somewhat less clean and less expensive material. Technologies have been proposed to dissolve the polyester scrap in appropriate solvents to separate PET from other materials such as cotton fiber or magnetic tape components [19]. 

Depolymerization processes have been proposed for poly(butylene terephtha-late) by the glycolysis of PBT with 1,4-butanediol and a titanium catalyst [65]. Methanolysis of poly(ethylene naphthalate) to dimethyl naphthalate and ethylene glycol has also been proposed [66, 67], but not implemented. The lack of commercial depolymerization of PEN is probably due not to technical limitations, but to insufficient supplies of PEN polymer feedstock to meet the minimum quantities needed for economical operations. 

Kinetic Analysis of the Lyase Catalyzed Depolymerization Process... 

The taking apart or separation of a single substance or molecular entity into two or more other substances or different molecular entities. Dissociation includes het-erolytic and homolytic reactions, the release of free ions from ion pairs, the depolymerization process of a polymer consisting of smaller subunits, etc. 

Continued polymerization/depolymerization, PROCESSIVITY Continuous variation method,... 

DIETHYL PYROCARBONATE DEPHOSPHO-CoA KINASE Dephospho-CoA pyrophosphorylase, PANTETHEINE-RHOSRHATE ADENYLYL-TRANSFERASE DEPOLARIZATION ACTION ROTENTIAL HYPERROLARIZATION DEPOLYMERIZATION PROCESSIVITY... 

Some microorganisms degrading condensed tannins have been isolated and described, but no reports on the mechanism of the depolymerization process, or the enzymes involved in biodegradation, have appeared. It must be stressed that condensed tannin degradation may be associated with other... 

Barix process Barium is fust added to the resin in the form of a liquid hydroxide. Subsequently, the resin is heated in the absence of oxygen and broken into its original components. Barium plays the role of catalyst in this depolymerization process and reacts with the sulfur in the cationic functional groups to form barium sulfate, which in turn acts as a binder for the metallic species in the waste. Moreover, the barium hydroxide adjusts the pH so that the metals contained in the resins stay in the residue after the steps of drying and destruction (IAEA, 2002). 

Available methods for the synthesis of macrolides involve the cyclization of long-chain bifunctional precursors,3 depolymerization processes,4 ring-enlargement reactions,5 and special methods... 

Fluorescein-labeled proteins are also used to measure the translational mobility of proteins and lipids by the Fluorescence Recovery After Photo-bleaching technique [54-59]. The uniformly labeled fluorescent sample is flashed with an intense light source to bleach a spot, thus producing a concentration gradient. The rate of recovery of fluorescence in that bleached area is measured and used to calculate the diffusion coefficient of the probe dye into the bleached zone. Such diffusion coefficient measurements have been used to determine the association constants of proteins in cells [60], to measure the exchange of tubulin between the cytoplasm and the microtubules [61,62], to study the polymerization-depolymerization process of actin [63-65] and to monitor the changes that occur upon cell maturation [66,67]. 

In aqueous solutions, polymerization and depolymerization processes are slow under normal conditions. This, in addition to the analytical difficulties in discriminating between different degrees of polymerization,... 

Viscosity of dissolved polymers drops irreversibly under acoustic treatment65 A8). The depolymerization process us rather fast during the first minutes of the treatment and then it becomes slow and ceases completely when the equilibrium molecular mass (MM) M is reached. The higher the polymer s initial molecular mass N0, the higher the rate of destruction. The majority of authors associate polymer destruction in solution with cavitation effects occurring under acoustic treatment. 

Thermal Conversion Process Resource Recovery Corporation, Inc. Thermo-Depolymerization Process, LLC Renewable Energy solutions, LLC... 

Thermo-Depolymerization Process, LLC CHANGING WORLD TECHNOLOGIES INC Think Green WASTE MANAGEMENT INC Thomas H. Lee Partners L.P. HAWKE YE HOLDINGS INC... 

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