Recycle Cleaning Solutions

At Desoto, in Greensboro, N.C., wash solvent from each solvent-based paint batch is separately collected and stored. When the same type of paint is going to be produced, waste solvent from the previous batch is used in place of virgin solvent, reducing the volume of the wastestreams which can contain metals as well as other paint wastes and solvent. In 1981, Desoto produced 25,000 gallons of waste mineral spirits. In 1982, when the system was implemented, waste solvent production amounted to 400 gallons. This same technique is currently being applied to their latex paint production operation (Kohl 1984). 

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Fritsch, J. and Zimmermann, B., Recycling of caustic cleaning solution with nanofiltration, Filtr. Sep., 12, 248, 1998. 

Many different compormds are able to act as catalysts. The most powerful catalysts are those foimd in nature. They are needed to speed up the reactions necessary for a cell to function efficiently. These biological catalysts are called enzymes. Enzymes help your body use food for fuel, build up your bones and muscles, and store extra energy as fat. Enzymes are involved in almost every process in a cell. For example, proteases are enzymes that break down proteins, as shown in Figure 6.22. These enzymes occur naturally in cells to help with recycling proteins so their parts can be used over and over. Proteases are also used in many common products, including contact lens-cleaning solution and meat tenderizer. 

Novalic S, Dabrowski A, Kulbe K D (1998), NanofUtration of caustic and acidic cleaning solutions with high COD, Part 1. Recycling of sodium hydroxide , J. Food Eng., 38,125-132. 

Lime Soda. Process. Lime (CaO) reacts with a dilute (10—14%), hot (100°C) soda ash solution in a series of agitated tanks producing caustic and calcium carbonate. Although dilute alkaH solutions increase the conversion, the reaction does not go to completion and, in practice, only about 90% of the stoichiometric amount of lime is added. In this manner the lime is all converted to calcium carbonate and about 10% of the feed alkaH remains. The resulting slurry is sent to a clarifier where the calcium carbonate is removed, then washed to recover the residual alkaH. The clean calcium carbonate is then calcined to lime and recycled while the dilute caustic—soda ash solution is sent to evaporators and concentrated. The concentration process forces precipitation of the residual sodium carbonate from the caustic solution the ash is then removed by centrifugation and recycled. Caustic soda made by this process is comparable to the current electrolytic diaphragm ceU product. 

The commercial recovery of iodine on an industrial scale depends on the particular source of the element.Erom natural brines, such as those at Midland (Michigan) or in Russia or Japan, chlorine oxidation followed by air blowout as for bromine (above) is much used, the final purification being by resublimation. Alternatively the brine, after clarification, can be treated with just sufficient AgNOs to precipitate the Agl which is then treated with clean scrap iron or steel to form metallic Ag and a solution of EeU the Ag is redissolved in HNO3 for recycling and the solution is treated with CI2 to liberate the h ... 

Spills of endosulfan, according to FAOAVHO (1975a), should be cleaned up by first washing with 5% sodium hydroxide solution and then rinsing with large quantities of water. In addition, empty containers that held endosulfan residues should be rinsed two or three times with water while the sides are scrubbed, and once with 5% sodium hydroxide solution. Thus decontaminated, the empty containers can be recycled and used by pesticide manufacturers to package a chemical similar to endosulfan if the containers remain in good condition and if such reuse is not prohibited by federal, state, or local laws. 

Figure 5.8 shows such a system we call it a Soxhlet apparatus. Solvent is passed continually through a porous cup holding the ground coffee. The solvent removes the caffeine and trickles through the holes at the bottom of the cup, i.e. as a solution of caffeine. The solvent is then recycled solvent at the bottom of the flask evaporates to form a gas, which condenses at the top of the column. This pure, clean solvent then irrigates the coffee a second time, and a third time, etc., until all the caffeine has been removed. 

The unreacted propylene is taken off the top of the reactor and cleaned up for recycling. By bubbling this stream through a dilute caustic solution (like sodium hydroxide, NaOH), the chlorine and HCl carried along with the propylene are removed by converting them to sodium chloride, NaCl, and water. The scrubbed propylene is then taken overhead (from the top of the fractionation column) and is ready as fresh feed or use elsewhere in the plant. 

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