Cellulose acetate membranes estimates

The major chemical processes of membrane deteriorations are hydrolysis and oxidation. Cellulose acetate is most stable at the level of around pH 4.7, and at the pHs lower or higher than that value, membrane hydrolysis is accelerated. In practical applications of cellulose acetate membranes, feed water pH is usually controlled between 5 to 6. But it is Impossible to control the pH of demineralized pure water for electronic and pharmaceutical uses, i.e. for ultrapure water polishing. In such cases feed water pH 7 should be supplied to cellulose acetate material. Studies of membrane behaviour under such conditions will give good information for estimating the membrane life. 

Table VIII. Mass Balance Data and Estimates of Solute Recovery (Test Run 618-41) Cellulose Acetate Membrane Concentration without Humics...

Bacterial production was estimated by incorporation of 3H-thymidine (Fuhrman and Azam 1982). Duplicate 10 ml subsamples were incubated for 1 h in the dark at 2°C in the presence of 20 nM of 3H-thymidine (Amersham 40-50 Ci mol ), filtered on 0.2-pm cellulose acetate membrane filters (Sarto-rius) and extracted with ice-cold 5% Trichloroacetic acid (TCA) (Becquevort and Smith 2001). Thymidine incorporation was converted into bacterial production using conversion factors of Ducklow et al. (1999) established for the Ross Sea bacterial communities (i.e., 8.6 X 1017 bacteria produced per mole of thymidine incorporated in the cold TCA insoluble material). For bacterial production, the relative standard deviation was 9.3% (n = 20). The specific growth rate was estimated from bacterial production and bacterial biomass. 

Estimation of Interfacial Forces Governing the Reverse-Osmosis System Nonionized Polar Organic Solute-Water-Cellulose Acetate Membrane... 

The ideal separation factors and the mobility and solubility contributions comprising this parameter for the various polymers shown in Fig. 20.3-9 are presented in Table 20.3-1 for a case corresponding to a 600 psia total feed pressure with 3(X) psia of CO2 upstream and veiy low downstream pressures of both components. The data for preparation of Table 20.3-1 were estimated from a number of sources, and the absolute value of the entries for cellulose acetate may be in error up to 10-15%. - The data for selectivities reported in the table are higher than those normally report for asymmetric polysulfone and cellulose acetate membranes since the dense-film forms of the samples tend to eliminate flow through pores that are present in asymmetric membranes and decrease their selectivity (see Table 20.1-2). 

D-glucose and the three-enzyme system GOx, mutarotase and invertase for sucrose estimation. A common format was adopted to facihtate design and operation, in this case immobilization method, the fact that all enzymes used were oxidases and that a common detection principle, reoxidation of H2O2 generated product, was chosen (except for ascorbic acid which was estimated directly). Pectin, a natural polysaccharide present in plant cells, was used as a novel matrix to enhance enzyme entrapment and stabilization in the sensors. Interferences related to electrochemi-caUy active compounds present in fruits under study were significantly reduced by inclusion of a suitable cellulose acetate membrane diffusional barrier or by enzymatic inactivation with ascorbate oxidase. Enzyme sensors demonstrated expected response with respect to their substrates, on analyte average concentration of 5 mM. 

A third relevant factor is the chemical composition of the membranes, with cellulose acetate, polyamide and a number of composite membranes sharing the seawater installed capacity. It is my estimate that polyamide membranes have at least 90% of the market. 

The value of X found here appears to agree well with the values 5.0 and 2.3mequiv dm 3 absorbed water found by Oemisch and Pusch (4) by analytical and electro-chemical measurements respectively in cellulose acetate from a different manufacturer. The agreement is deceptive however because their value is based on the total water held in an asymmetric membrane. A value of M estimated from their data is almost ten times our M. It may be noted that their electrochemical method and their assumptions are quite different from ours. 

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