Residual water polyamides

Serkiz and Perdue (1990) were the first to report the successful use of RO to isolate NOM from river water. Polyamide (PA) membranes on a polysulphone (PS) support were used. Freshwatcrs were pretreated with a cation exchange resin and, due to a low salt content, no further desalination was required. Concentrates were then freeze dried. Recoveries of about 90% were achieved. The method appears to be well suited for NOM removal with the possibility of subsequent use of XAD for separation of FA and HA from the NOM. The method can be applied to freshwatcrs containing DOC in the range of 3 to 40 mgL h Problems of the method include the presence of residual inorganics such as H2SO4 and Si(OH)4. 

The desired final viscosity is obtained passing the flow of the melt polymer through a finisher where, at a temperature of 285 °C, the residual water is lost and the correct average molecular weight of the polyamide is reached. 

The detailed setting is Two input streams feed an initial mixer. The substances Caprolactam (monomer) and water are fed through the streams into a mixing device, then into a reactor modeled by a CSTR. The result is the Polyamide-6 product and the residual non-reacted monomer. These substances have to be separated, as the monomer has to be fed back into the reactor. Now the task of the chemical engineer is to find a useful model for the separation unit. 

Sodium bisulfite is added to the effluent from the polishing filters to remove residual chlorine which would be harmful to the polyamide reverse osmosis membrane. Sulfuric acid is then added to the filter effluent to adjust the pH to about 6.5 and the pretreated water is routed to the primary reverse osmosis system. 

Polyamides can be readily identified by the acids formed on acid hydrolysis of the respective polyamides. For this purpose, heat 5 g of the sample with 50 ml concentrated hydrochloric acid using a reflux condenser (Figure 6.2). Continue reflux until the major part of the sample has dissolved. Then boil the solution with charcoal until the color disappears and filter it while it is hot. After cooling, filter off the precipitated acids and recrystallize them from a small amount of water. If no acids precipitate, extract the filtrate with ether. Evaporate the ether and recrystallize the residue from water. The acids have the following melting points ... 

Chemical treatment consists of three weU-known treatment processes for ensuring rehable operation of RO membranes. First, a 20% sodium bisulphite (SBS) solution is injected by the chemical dosing pump (one pump is on standby). The iiyection rate is proportional to the RO feed water flow rate and is controlled by the PLC based on the chlorine concentration monitored by a chlorine analyser downstream of the in-line mixer. SBS like sodium sulphite and sodium metabisulphite is a reducing agent commonly used to dechlorinate RO feed or lower the chlorine concentration to less than 0.05 mg/1 in RO plants that use polyamide aromatic membranes. It takes 7.33 mg/1 of 20% NaHS03 solution to remove 1 ppm of residual chlorine in water on a stoichiometric basis. 

Iq the case of pyrolysis under vacuum at 400°C of the mixed polyamide produced by polycondensation of caprolactam and hexamethylene-adipamide, as well as the mixed polyamide obtained from hexamethylene-adipamide, e-caprolactam, and hexamethylenesebacamide [15, 16], the following products were detected in the gas phase by mass spectroscopic analysis carbon monoxide, carbon dioxide, cyclopentanone, water, various hydrocarbons (methane, ethane, propane, butane, ethylene, butenes). Ammonia and other nitrogen compounds were not detected in the gas phase. All the nitrogen remains in the solid residue [15-18]. The... 

Protease was used as catalyst for polymer modification. Phenylalanine residues at the side chain of methacrylamide polymers were coupled with alanine (-butyl ester by Q -ch3nnotrypsin catalyst in water-chloroform solvent (71). Up to 35% peptide-bond formation was achieved for 7 days at room temperature. Polyamide synthesis was performed by cellulase-assisted polycondensation of chiral fiuorinated compoimd having carboxylic acid and amino groups (72). 

Presence of a deep yellow color, or oils, is indicative of residual amines and requires repurification. Polyamides are stable at RT, but 0.1 mg aliquots should be prepared in microcentrifuge tubes and stored at -20°C. The best way to make the aliquots is by dissolving a larger amount of polyamide into water, measuring the absorbance, determining the concentration, and pipetting an appropriate amount into the tubes. The solutions are then re-lyophilized to produce solids. 

---