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TECHNOLOGY
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Descaling: Route to MAP Process removes scale-formers from sea water, gives high-analysis fertilizers
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C & E N
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At the W. R. Grace research laboratories in Clarksville, Md., research workers are developing a process intended for double duty. First, it removes from sea water the scale-forming materials that disrupt evaporator plants trying to convert it into fresh water. At the same time, it yields a valuable, high-analysis fertilizer, magnesium ammonium phosphates (MAP). The process, based on phosphate precipitation, is just about ready for the pilot plant. But the future of the pilot unit rests in the Office of Saline Water, which sponsored the Grace project. An OSW spokesman says that the agency is highly pleased with the results of Grace research, but won't plan the next step until it receives a final report from Grace sometime this summer. If OSW gives the go-ahead, it must also decide which of its own demonstration plants or pilot plants will get the process. OSW will also dictate ultimate design of the pilot plant, because it must determine just how much scale a conversion plant can tolerate. The fertilizer materials which Grace recovers as it pretreats sea water are metal ammonium phosphates, in particular magnesium ammonium phosphate. Grace has been working with them for more than three years, now produces them as specialty fertilizers on a semicommercial scale (C&EN, Sept. 11, 1961, page 83). But how it makes them and where they are produced are closely guarded secrets. MAP has passed agricultural tests \ ith flying colors. Besides the major plant nutrients, N and P 2 0 3 , it also contains magnesium, which is an important secondary plant food. It is nonburning, long-lasting, and is an excellent controlled-release fertilizer. To descale sea water, and get high analysis fertilizer at the same time, Grace continuously adds wet-process phosphoric acid and anhydrous ammonia to raw sea water. This precipitates the scale-forming elements—cal-
cium, magnesium, iron, and other metals—as metal ammonium phosphates and other phosphates. The precipitated solids are removed by settling, and the descaled sea water can be pumped to the saline water conversion plant. The descaled water holds only 1% of the original magnesium and 5% of the original calcium. The settled slurry is dewatered to about 35 to 40% solids by continuous centrifuges, then heated to 90° C. This converts MAP hexahydrate to the monohydrate. Then the slurry is filtered, washed, mixed with recycled fines, and granulated. MAP hexahydrate contains about 40% more water than MAP monohydrate, which means that the percentage of plant food in the fertilizer is increased by converting to the mono form. But it's impractical to dehydrate by heating the dry hexahydrate, because ammonia is lost during the process. Above 25% solids, only a small amount of nitrogen is lost, and, in addition, the P 2 0 5 : N ratio approaches that of the original slurry. The monohydrate also provides a more stable product. Actually, the fertilizer produced by the process is a mixture of MAP, calcium hydrogen phosphate, and trace metal phosphates of iron, zinc, copper, manganese, cobalt, and nickel. It contains approximately 7% nitrogen, 44% phosphoric acid ( P 2 O s ) , 2 1 % magnesium oxide, and 5% calcium oxide. A lot of question marks surround the economics of the process. For a plant descaling 1 million gal. of sea water per day (output: about 11,000 tons per year of fertilizer), Grace estimates that the fertilizer would have to command a price higher than that of conventional farm fertilizers. This estimate assumes current market prices for raw materials (phosphoric acid and ammonia) and takes no credit for the increased value of the descaled water. The cost is, incidentally, just about the same as that of Grace's present route to MAP.
This means that fertilizer-from-thesea would have to go to market as a specialty product, which it could do because of its premium quality. On the other hand, a larger plant, such as the contemplated 10 million gal.per-day units, may help lower costs, but the large volumes would dictate that it compete with conventional farm fertilizers. Larger plant sizes, surely, will not reduce costs that much. The place to chop costs, as Grace sees it, is in raw materials, which account for 85% of total expense. Phosphoric acid and ammonia take two thirds and one third, respectively, of the raw materials dollar. For plants descaling 10 million gal. or more per day of sea water, it may be practical to build a phosphoric acid plant on site. Building this plant without concentration facilities would reduce its capital cost. Or it may be possible to slash costs by using cheaper raw materials. Although phosphoric acid is best, chemically, to precipitate metal ammonium phosphates, it isn't necessarily the most economical. Using the acid route, it takes three moles of ammonia to neutralize the acid and two of these are lost to the descaled sea water as ammonium chloride. But sodium phosphates will also work and, if an inexpensive method could be developed to make either mono- or disodium phosphate, it would be more economical to make the fertilizer with these. There are many alternate m e t h o d s two appear best. One converts monocalcium phosphate (normal or triple superphosphate) to sodium phosphate by ion exchange. The other neutralizes phosphoric acid with dilute sodium hydroxide which, in turn, is produced electrolytically from waste brine of the sea water conversion process. Regardless of which process wins out, several questions remain. How far can you go, economically, in converting sea water to fresh water if scale isn't a problem? What fraction of the scale-forming elements really needs to be removed? What is the value of the descaled water to various desalination processes? What other value can be recovered from waste evaporator brines and phosphate precipitates, or the ocean itself? Perhaps the answer lies in an integrated operation which takes as much as possible out of the ocean. Grace is working on several extraction processes. Among them are processes for halogens and potassium chemicals.
Diphenolic Acid Finds Applications Acid derivatives for printing inks, can coatings, air-drying paints pave way for DPA commercialization Commercial stature for Diphenolic Acid (DPA) is just around the corner. After two years in pilot plant, S. C. Johnson & Son's intermediate has found a variety of promising applications, is poised for full scale production. Now ready for market are DPA polyamide resins for use in flexographic inks, alkyd-phenol formaldehyde derivatives for can coatings, and coesters for printing inks and air drying paints. Johnson has already made plans to build a 10 million lb.-per-year DPA plant at Waxdale, Wis. (C&EN, Jan. 1, page 7 ) , by early 1963. Flexographic inks are used to print on flexible packaging films. They are usually based on polyamides and polyester, last year consumed about 10 million lb. of resin. Johnson's new resin for this use is a polyamide derivative of DPA. It gives inks which dissolve in simple alcohols (many mixed solvents attack and deform rubber printing surfaces) and adhere better than conventional inks, the company says. It has good shelf life, and is compatible with a wide number of other ink resins, at competitive prices, Johnson adds. The growing can coating market will use a sizable portion of the new DPA plant's capacity. Of the 42 billion metal containers produced annually, 80% of them need linings. Johnson's entrant is an alkyd-phenol formaldehyde derivative of DPA for formulating can coatings. These coatings resist chemical attack better than do
epoxy, oleoresinous, phenolic, and butadiene-based coatings, are competitive with them in price. They offer potential as linings for cans to hold latex emulsion paint, motor oil, antifreeze, and food, beer, and beverages. DPA co-esters—chemical combinations of phenolic resins and drying oils —are aimed at the $250 million printing ink and overprint varnishes market. They give inks that have higher gloss and that dry two to three times faster than do conventional ink resins. Johnson has also developed co-ester derivatives for use in air-drying coatings. Called diphenolic acid co-esters, they are acetic anhydride-drying oil fatty acid derivatives and are slated for the $120 million premium paint market. They dry quickly, have high gloss and color retention, and are very durable to exposure. Potential uses include interior gloss paints, rapid dry floor finishes, and industrial enamels and varnishes. The coatings will be competitive in price with other high grade systems. DPA is currently being produced in Johnson's 250,000 lb.-per-yr. pilot plant, is selling for 75 cents per lb. The company's new plant will have an annual capacity of 16 million pounds of DPA and DPA derivatives. And most of its output has already been contracted for, Johnson says. Price of the acid when the plant goes on stream will be 52 to 55 cents a pound. As for DPA's future, Johnson predicts the acid's market will reach 50 million lb. by the end of the decade.
Johnson Has Developed DPA Derivatives for. . . • Printing inks • Can coatings • Air-drying paints
Is Working on DPA-Based . . . • • • • • • •
Corrosion inhibitors for oil well drilling Epoxy molding powders, casting resins, coatings High-compatibility vehicles for flushed color pigments Tackifying additives for acrylonitrile rubbers Plasticizers for synthetic rubbers, PVC Fire-retardant polyurethanes Nonwoven textile additives JAN.
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