Heterogeneous degradation modelling

Kenji O, Kazuya I, Yoshihiro Y, Hiroshi B, Rokuro N, Yasuaki M (2005) Sonochemical degradation of azo dyes in aqueous solution a new heterogeneous kinetics model taking into account the local concentration of OH radicals and azo dyes. Ultrason Sonochem... 

Schematic representation of the diffusion-reaction phenomena that occur during the hydrolytic degradation of implants according to the model of heterogeneous degradation (modified from Grizzi 6t simf 1995 ). 

Using low-crystallinity (7% crystallinity) and biaxially oriented PET films (35% crystallinity), the T. insolens lipase showed maximum hydrolysis activity on low-crystallinity PET film between 70 and 80°C [91]. With a Tg value of 75°C, the increased chain mobility of the low-crystallinity film at this reaction temperature strongly facilitated its hydrolysis by the thermostable T. insolens PET hydrolase. The low-crystallinity PET film was almost completely hydrolyzed after 96 h at 70°C, while tenfold lower activity was detected with the semi-crystalline PET film. Degradation of the low-crystallinity PET film followed a heterogenous kinetic model considering substrate-limited conditions with a limited surface area available to the enzyme [94]. 

Modelling heterogeneous degradation of polymeric devices due to short chain diffusion... 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

The overall degradation of (103) assisted by the cluster [(Cp )2 M o2Co2S3(CO)4] (Cp = CH3C5H4) is the model reaction that best resembles the heterogeneous counterparts, particularly those classified as Co/Mo/S phase,158 in terms of both structural motif and HDS activity.229 Morever, the Co/Mo/S cluster has successfully been employed to show that the C—S bond scission in the desulfurization of aromatic and aliphatic thiols occurs in homolytic fashion at 35 °C and that thiolate and sulfido groups can move over the face of the cluster as they are supposed to do over the surface of heterogeneous catalysts.230... 

An accurate evaluation of kxa is complicated by the heterogeneous nature and poor definition of contaminant/soil systems. Some success has been achieved in modeling mass transfer from a separate contaminant phase. During degradation these nonaqueous phase liquids (NAPLs) often dissolve under conditions where phase equilibrium is not achieved and dissolution is proportional to k a. Experimental determinations and correlations for k-p depend on interfacial area of the NAPL and liquid velocity at the interface (Geller Hunt, 1993). For adsorbed contaminants, kxa varies with soil composition and structure, concentration and age of contamination, and therefore with time. For example, slurry reactor tests indicate that the rate of naphthalene mass transfer decreases with time, with media size, and with aging of the tar prior to testing (Luthy et al., 1994). 

Stafford, U., Gray, K., and Prashat, K., Photocatalytic degradation of organic contaminants halophenols and related model compounds, Heterogeneous Chem. Rev., 3, 77, 1996. 

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