Melting, pressure filters

The slime is recovered and heated in a brick-lined tank to melt the sulfur. The molten sulfur is filtered in a heated stainless-steel pressure filter to separate remaining nickel sulfide pieces and insoluble precious metals, and cast into moulds. The residue is remelted and cast into anodes, the resulting anode slime is now a relatively concentrated precious metal residue and is treated for the extraction of individual metals. 

N-Benzylmaleimide (500 g, 2.67 mole), 90% bromonitromethane (831 g, 5.34 mole), powdered molecular sieves 200 mesh (2020 g) and toluene (12 dm3) were stirred under nitrogen at -10°C. 1,2-Dimethyl-l,4,5,6-tetrahydropyrimidine (616 g, 5.49 mole) was added slowly over about 3 h maintaining the reaction temperature at <-8°C throughout the addition. After completion of the addition, the reaction mixture was stirred for 1.5 h at 25°C, filtered under a nitrogen atmosphere in a sealed pressure filter to remove sieves and resulting tar, and the sieves were washed with toluene (2 L). The combined filtrates were washed with 2 N dilute hydrochloric acid (3 times 750 cm3), treated with carbon (50 g) at 70°C, 1 h filtered, concentrated, and triturated with 2-propanol (about 4 dm3) to obtain crystals of the (la,5a,6a)-3-N-benzyl-6-nitro-2,4-dioxo-3-azabicyclo[3.1.0]hexane (223 g, 34%) melting point 116°-118°C. 

The most common form of melt filtering is the use of screen packs. The screen pack is held in the breaker plate by melt pressure as the polymer exits the barrel. The breaker plate often contains a pocket to hold screens that are nominally the same diameter as the screw. 

A melt filter (Figure 4.83d) is used with small gates which are easily blocked as a result of mechanical impurities in the melt. A filter must be used when recycled material is being injected. The filter may be located in an open sprue bushing (see also Figure 4.60) or in the injection machine nozzle. A drawback to the filter is the substantial pressure loss, as much as 30%, depending on the type of filter. For this reason, filters with a filter area of at least 125 mm are recommended. 

Propane deoiling is accomplished using high pressure filters that are required to handle die higher temperatures that must be used to melt the softwax. The finished wax produced from deoiling is a valuable by-product and margins may at times exceed dewaxed oil margins. 

A disadvantage is that the increasing melt pressures may give an improved result. To eliminate this problem, DIN-EN 13900-5 [10] was issued in which a gear pump was introduced between the extruder and screen pack to provide a consistent back pressure for the extruder. This filter-pressure value test starts and finishes with extrusion of the matrix polymer without masterbatch [7]. 

In a 1-litre three-necked flask, fitted with a mechanical stirrer, reflux condenser and a thermometer, place 200 g. of iodoform and half of a sodium arsenite solution, prepared from 54-5 g. of A.R. arsenious oxide, 107 g. of A.R. sodium hydroxide and 520 ml. of water. Start the stirrer and heat the flask until the thermometer reads 60-65° maintain the mixture at this temperature during the whole reaction (1). Run in the remainder of the sodium arsenite solution during the course of 15 minutes, and keep the reaction mixture at 60-65° for 1 hour in order to complete the reaction. AUow to cool to about 40-45° (2) and filter with suction from the small amount of solid impurities. Separate the lower layer from the filtrate, dry it with anhydrous calcium chloride, and distil the crude methylene iodide (131 g. this crude product is satisfactory for most purposes) under diminished pressure. Practically all passes over as a light straw-coloured (sometimes brown) liquid at 80°/25 mm. it melts at 6°. Some of the colour may be removed by shaking with silver powder. The small dark residue in the flask solidifies on cooling. 

Pour the resulting dark reddish-brown liquid into 500 ml. of water to which 17 ml. of saturated sodium bisulphite solution has been added (the latter to remove the excess of bromine). Steam distil the resulting mixture (Fig. II, 41,1) , collect the first portion of the distillate, which contains a little unchanged nitrobenzene, separately. Collect about 4 litres of distillate. Filter the yellow crystalline solid at the pump, and press well to remove the adhering liquid. The resulting crude m-bromonitrobenzene, m.p. 51-52°, weighs 110 g. If required pure, distil under reduced pressure (Fig. II, 19, 1) and collect the fraction of b.p. 117-118°/9 mm. it then melts at 56° and the recovery is about 85 per cent. 

Add 40 ml. of ethyl alcohol to 21 -5 g. of 70 per cent, ethylenediamine solution (0 -25 mol) dissolve 36 -5 g. of adipic acid (0 -25 mol) in 50 ml. of a 6 1 mixture of ethyl alcohol and water. Mix the two solutions, stir and cool. Filter off the resulting salt and recrystalliae it from 60 ml. of a 6 1 ethyl alcohol - water mixture, and dry the salt in the air. Heat the salt in an atmosphere of oxygen-free nitrogen or of carbon dioxide in an oil bath until it melts (ca. 160°) the product will sohdify after a short time. Reduce the pressure to 15 mm. of mercury or less and raise the temperature of the oil bath until the product remelts (about 290°) and continue the heating for 4r-5 hours. Upon coohng, a nylon type polymer is obtained. 

The residue is cooled and dissolved in 171 ml. of nitric acid (sp. gr. 1.4) (Note 3), and the solution is warmed for 30 minutes on the steam bath. It is immediately concentrated to complete dryness under reduced pressure (Note 4). The flask is cooled, 300 ml. of benzene is added, and the mixture is refluxed for a short time to render the cake friable. The benzene is removed by decantation, and the cake is pulverized and extracted six times by refluxing it briefly with 300-ml. portions of ether. The combined benzene and ether extracts are filtered and concentrated to a volume of about 225 ml. In the meantime the residual salts are extracted twice by refluxing them vigorously for a short time with 300-ml. portions of benzene. The benzene solutions are separated by decantation and added to the ether concentrate. The distillation is then continued untO about two-thirds of the benzene has been removed, when the benzene solution is poured into a beaker and allowed to cool. The methylsuccinic acid is collected on a filter and is washed by shaking a suspension of it in 150 ml. of chloroform (Note 5). The yield of air-dried product, melting at 110-111 , amounts to 87-93 g. (66-70%) (Note 6). 

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