Filtration efficiency over time

The objective of the present study is to develop a cross-flow filtration module operated under low transmembrane pressure drop that can result in high permeate flux, and also to demonstrate the efficient use of such a module to continuously separate wax from ultrafine iron catalyst particles from simulated FTS catalyst/ wax slurry products from an SBCR pilot plant unit. An important goal of this research was to monitor and record cross-flow flux measurements over a longterm time-on-stream (TOS) period (500+ h). Two types (active and passive) of permeate flux maintenance procedures were developed and tested during this study. Depending on the efficiency of different flux maintenance or filter media cleaning procedures employed over the long-term test to stabilize the flux over time, the most efficient procedure can be selected for further development and cost optimization. The effect of mono-olefins and aliphatic alcohols on permeate flux and on the efficiency of the filter membrane for catalyst/wax separation was also studied. 

Pilot-scale particle collection efficiency has been found to be similar to the cold and dry experiments over 300 hours filtration time, Figure 12 presents a relatively constant pressure drop over time for the hot and dry experiments conducted on the pilot-scale filter under a gas flowrate of 20 Nm /h (80 Nm /hr/m ), with a particle load of 3000 mg/Nm and using Ottawa sand as the filtering media. Deep holes on Figure 12 are air pulses to back-flush the solids plugging the exits. 

From Figure 6.32a and b, several observations can be made. First, the filtration efficiency to charged particles is higher than the filtration efficiency to reneutralized particles. Second, the filtration efficiency of charged particles is observed to decrease over time (data trend not observable in Figure 6.32a due to y-axis scale selection), whereas with the reneutralized particles, the filtration efficiency is often observed to increase over time. 

Filter stmcture greatly determines the pressure drop required in filtration. While high filter efficiency requires thinner fibres for more crossing points of fibres, thinner fibres in a filter fabric also lead to an increase in flow resistance and thus require relatively higher pressure drop and higher consumption." The filter efficiency also decreases over time as the filter becomes saturated with cells and debris."" " ... 

The overall efficiency of ozone is difficult to predict due to the complex nature of natural organic materials, water characteristics, temperature, and pH. Ozone dosage is based on two factors first, the amount of ozone needed (mg) to stoichiometrically consume the contaminants present, and second, the amount needed for disinfection in mg/1 based on a concentration over time. Both steps require correct injection and mixing time. Ozone must physically come into contact with the contaminants to be effective. Filtration is almost always required to remove particulates. Any excess ozone will create off gas, which must be destroyed. " Most water system conditions are variable in nature. In practice, dosage is based on the creation of a barely measurable residual. ... 

For alkaline electrolytes, the oxidizer reduction reaction (ORR) kinetics are more efficient than acid-based electrolytes (e.g., PEFC, PAFC). Many space appUcations utiUze pure oxygen and hydrogen for chemical propulsion, so the AFC was well suited as an APU. However, the alkaline electrolyte suffers an intolerance to even small fractions of carbon dioxide (CO2) found in air which react to form potassium carbonate (K2CO3) in the electrolyte, gravely reducing performance over time. For terrestrial applications, CO2 poisoning has limited lifetime of AFC systems to well below that required for commercial application, and filtration of CO2 has proven too expensive for practical use. Due to this limitation, relatively little commercial development of the AFC beyond space applications has been realized. Some recent development of alkaline-based solid polymer electrolytes is underway, however. The AFC is discussed in greater detail in Chapter 7. 

The idealized TMP cycle is depicted in Figure 10.2b for a cycle that is limited by AP ax rather than a specified cycle time. In reality the backwash efficiency will be < 100% so that APnjin (the cleaned membrane TMP) may slowly rise over time, eventually requiring chemical cleaning (see Section 10.5.2). During a filtration cycle the deposit resistance grows so that at time t it is given by... 

Water Treatment. The source of water for this experiment was a pilot plant located on the Seine River upstream from Paris, France (Figure 1). The pilot plant uses an upflow solids contact clarifier (Pulsator, Degremont, Rueil Malmaison, France) followed by rapid sand filtration (RSF). The filtered water is then distributed over four treatment lines to evaluate the efficiency of various ozone-GAC combinations (ozonation rates of 1 or 5 ppm O3 and 10-30 min of contact time). The GAC used in this study was Calgon F-400 (Calgon Corp.). Disinfection by chlorine or chlorine dioxide completed the process. In this chapter, line 3 treatment was not considered a complete treatment for the water supply. This line was studied to evaluate the efficiency of a high ozonation rate. 

C. 2-Phenylcycloheptanone. In a 2-1. three-necked flask fitted with a 500-ml. addition funnel, a sealed Hershberg stirrer, and a reflux condenser (Note 8) are placed 392 g. (4.0 moles) of freshly distilled cyclohexanone, 30 g. of finely powdered potassium carbonate, and 400 ml. of absolute methanol. To the stirred mixture is added 415 g. (2.0 moles) of ethyl N-nitroso-N-benzyl-carbamate over a period of 1.5 hours during which time the reaction temperature is maintained at 25° by means of an ice-water bath. The dark red reaction mixture is then allowed to stand at room temperature until the evolution of nitrogen has ceased (24-28 hours) (Note 9). The solid material is removed by filtration, the lower-boiling materials are removed by evaporation under reduced pressure on the steam bath (Note 10), and the residue is distilled through an efficient column. A fore-run consisting of 30-60 g. of material is discarded or refractionated (Note 10), and the fraction with b.p. 94-96°/0.4 mm. (124-126°/2 mm., 136-138°/4 mm.) is collected. It amounts to 155-177 g. (40-47%) of 2-phenylcycloheptanone, 1.5395-1.5398, which is... 

In a 5-I. three-necked, round-bottomed flask fitted with an efficient stirrer (Note 1), a separatory funnel, and a thermometer in a well, is placed a solution of 500 g. (9.7 moles) of powdered 95 per cent sodium cyanide in 1200 cc. of water and 900 cc. (713 g., 12.3 moles) of acetone. The flask is surrounded by an ice bath and the solution is stirred vigorously. When the temperature falls to 150, 2100 cc. (8.5 moles) of 40 per cent sulfuric acid (Note 2) is added over a period of three hours, keeping the temperature between io° and 20°. After all the acid has been added the stirring is continued for fifteen minutes and then the flask is set aside for the salt to settle. Usually a layer of acetone cyanohydrin forms and is decanted and separated from the aqueous layer. The sodium bisulfate is removed by filtration and washed with three 50-cc. portions of acetone. The combined filtrate and acetone washings is added to the aqueous solution which is then extracted three times with 2 50-cc. portions of ether (Note 3). The extracts are combined with the cyanohydrin previously separated and dried with anhydrous sodium sulfate. The ether and acetone are removed by distillation from a water bath, and the residue is distilled under reduced pressure. The low-boiling portion is discarded and the acetone cyanohydrin is collected at 78-82°/i5 mm. The yield is 640-650 g. (77-78 per cent of the theoretical amount). 

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