Rejecting data

GL 19] [R 9] [P 20] Experimental data were fitted to several empirical models from a mechanistic model [64]. By an iterative fitting process, a statistical model with first-order kinetics with respect to hydrogen was derived. With this model, a parity diagram was given, showing that 29 (17%) experiments of 170 had to be rejected the others were adequately described by the model. AU rejected data had higher conversion than theoretically predicted. 

The DIFFE program (Blessing and Smith, 1999) rejects data pairs ( Ei, IE2I) [i.e. SIR pairs ( Ep, EphI)/ sad pairs ( E- -, E— ), and pseudo-SlR dispersive pairs ( E). 11, x2l)] or difference E magnitudes ( EaD that are not significantly different from zero or deviate markedly from the expected distribution. The following tests are applied where the default values for the cut-off parameters (T jaXa XmiN/ ZmiN/ and Zmax), are shown in... 

Figure 2.9 Flux and rejection data for a model seawater solution (3.5 % sodium chloride) in a good quality reverse osmosis membrane (FilmTec Corp. FT 30 membrane) as a function of pressure [10]. The salt flux, in accordance with Equation (2.44), is essentially constant and independent of pressure. The water flux, in accordance with Equation (2.43), increases with pressure, and, at zero flux, meets the pressure axis at the osmotic pressure of seawater 350 psi...

Figure 5.14 Salt rejection with neutral, anionic and cationic nanofiltration membranes showing the effect of Donnan exclusion and solute size on relative rejections. Data of Peters et al. [36]...

Figure 5.17 Organic rejection data for the PEC-1000 membrane compared to FT-30, anisotropic aramide and anisotropic cellulose membranes [28]...

Unqualified data and estimated values are considered valid and can be used for project decisions, whereas the data points, which were rejected due to serious deficiencies in representativeness, accuracy, or precision, cannot. In an attempt to obtain data of better quality, the chemist may ask the laboratory to reanalyze some of the samples or extracts, if they are still available and have not exceeded the holding time. Depending on the number of the rejected data points and their importance for project decision, the chemist may recommend resampling and reanalysis. 

Figure 4.1 Flux and rejection data for a seawater FilmTec FT-30 membranes operating on 35,000 ppm (350 psi osmotic pressure) sodium chloride solution.2...

Table 11.1 lists primary data points that should be monitored to determine how an RO system is basically functioning.1 The parameters listed in Table 11.1 all affect the product flow rate and/or product quality, as described in Chapter 9. Of all the data points identified in Table 11.1, feed, product, and reject data are most commonly measured, and most RO skids are constructed with required instrumentation for measuring these variables. 

A summary of the properties of some of these materials is presented in Tables 8 and 9. Diffusion coefficients and NaCl partition coefficients are presented in Table 8 for cellulose triacetate and for Nomex K>lyamide. In most cases, however, intrinsic transport properties are not known, and what is reported in the literature is the water flux and salt rejection of RO membranes under given test conditions. Under comparable test conditions (0.5-1% NaCl, 27—68 atm) the water fluxes of these newer membranes are comparable (0.4-0.8 m /m -day). Salt rejection data are presented in Table 9. To put these data in perspective, the salt rejection of cellulose 2.5-acetate membranes is typically <99%. However, for various reasons none of these new membranes has yet become commercially important. 

Use extreme caution when rejecting data for any reason. 

Rejection data for NaCl were explained according to a low-capacity ion exchange mechanism. The ion exchange mechanism put forward in this work is not consistent with the porous structure of the membrcines and the high transmembrane pressure used in the filtration experiments. Ion exchange... 

Values of dR/dr were calculated from smoothed rejection data in Figure 1 for membranes A, B and C. b) Derivatives of theoretical rejection curves. Log-normal pore size distributions from SEM (Figure 2) and equations of the steric rejection theory (19) were used. 

Figure 2. The derivative of transmitted current in 1,3-butadiene. The curve marked "low rejection" is obtained by rejecting only those elastically scattered electrons which return to the monochromator. The "high rejection" data is derived by rejection of all scattered electrons (from Ref. 24).

Figure 3.2317 presents rejection data for three different dextrans on the same UF membrane as a function of pressure. Figure 3.2418 shows the effect of pressure on the rejection of 0.1 M NaCI by a cellulose acetate RO membrane. It is obvious that the mechanism for solute transport through the membrane is different for UF and RO. 

The rejection data of Table 3.655 indicate that more than 97% of the colorbearing material has an effective MW greater than 10,000. In these data, the pre-meate from the UM 10 membrane was fed to the UM 2 membrane and its permeate was fed to the UM05 membrane. Thus, the UM2 membrane can remove 99% of the color, 64% of the COD and 43% of the TDS. 

The sodium chloride rejection differs from that of other inorganic and organic dissolved solids, and membrane manufacturers will provide information and rejection data that are available for their specific membrane. Table 4.3... 

The thin film composite membrane exhibited superior overall rejection performance in these tests, with ammonia and nitrate rejection showing an outstanding improvement. It has also been reported that silica rejection by the thin film composite membranes is superior to that of cellulose acetate. While the above data indicates a marginal improvement in the rejection of chemical oxygen demand (COD), which is an indication of organic content, other tests conducted by membrane manufacturers show that the polyurea and polyamide membrane barrier layers exhibit an organic rejection that is clearly superior to that of cellulose acetate. Reverse osmosis element manufacturers should be contacted for rejection data on specific organic compounds. ... 

In other respects, it also shared the favorable characteristics of the NS-100 membrane. That is, it was resistant to pH 3 to 12, and showed far better compaction resistance than cellulose acetate. Also, it possessed the capability to operate at elevated temperatures, though some irreversible flux decline could still occur.34 Rejections of various organics were also good, as shown in Table 5.1 These were in sharp contrast to organic rejection data on cellulose acetate membranes. Initially, PA-300 was also postulated to possess good chlorine resistance.31 Subsequent experience showed it to be equally sensitive to chlorine as NS-100. 

The combination of piperazine with trimesoyl chloride in composite membrane form was named NS-300. Trimesoyl chloride leads to a crosslinked polyamide structure. Apparently, however, considerable formation of hydrolyzed carboxylate groups also occurs. This is evidenced by the anion selectivity of the membrane, demonstrated by the sequential salt rejection data in Table 5.4 for a series of salts on test with a single set of membrane specimens. 

A reverse osmosis membrane is commercially available, named NF-40 (FilmTec Corporation), which is closely based on the NS-300 membrane technology. Typical solute rejection data for this membrane are as follows sodium chloride, 45% calcium chloride, 70% magnesium sulfate, 93% sucrose, 98%. Water flux of the membrane averages about 23 gfd at 225 psi and 25°C. As already noted for NS-300, the sulfate anion is associated with high rejection the chloride anion, low rejection. Partial discrimination between monovalent and divalent cations (sodium versus calcium) has also been observed for NF-40. The membrane can be operated at temperatures to 45°C and in a pH range from 3 to 11. In this respect, it would find probable use in industrial separations where... 

In terms of organic rejections, PEC-1000 membrane shows the highest values among all commercial reverse osmosis membranes. Table 5.6 lists rejection data for a variety of organic compounds. In most cases, these were measured at solute concentrations of 4 to 5%, which represents a severe test protocol. Organic solute rejections determined for other commercial membranes were typi-... 

Should the outliers be rejected And by what criterion One should be conservative when rejecting data for three reasons ... 

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