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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 15, No. 4
Causticization of Soda Ash’sa By J. Harrop and H. 0.Forrest MASSACHUSETTS INSTITUTE
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HIS PA4PERpresents the results of a study of the causticization of sodium carbonate with lime, followed the separation of the liquor from the by decantation. The variables studied were the amount and character of the lime and the time of causticization. The effects of the variables upon the “free settling”3 rate and percentage conversion of sodium carbonate to sodium hydroxide were determined. Throughout the runs the solution to be causticized was maintained constant in soda content at a value of 2.6 N , and in the study of the character of the lime and time of causticizatioii the amount of lime used was 10 per cent in excess of that theoretically necessary for the conversion. APPARATUS The apparatus consisted of a container 5 l / 4 in. in diameter by 71/4 in. deep, equipped with a closed steam coil for heating the solution and a motor-driven, propeller-shaped stirring device. A scale of l/s-in. graduations was fastened to the side of the beaker. This scale, used in determining the settling curves, had a zero mark at a volume of 2000 cc. and a mark of 44 at the bottom of the beaker. SLAKED LIMEUS. UNSLAKED LIME Two 225-g. samples of No. 2 lime, representing 10 per cent excess of the theoretical amount, were weighed out. One of the samples was slaked before being added to the sodaash solution and the other was added directly. Both samples were causticized a t boiling t)emperatures for 10 min. and the settling rates and percentage conversions determined. The settling curves 0 2 4 6 0 /O f2 f4 /6 f0 20 7ime - mmufcs are shown in Fig. 1. FIG. I-SETTLING CURVESAFTER CAUSTIThe free-settling C I l I N G WIT51 SLAKED AND UNSLAKED LIME rates for slaked lime and unslaked lime were, respectively, 0.11 and 0.53 in. per min. However, the percentage conversion for the slaked-lime run was 92.2 per cent against 91.7 per cent for unslaked lime, showing that slaking of lime before causticization increases the conversion but slightly, whereas it greatly reduces the rate of settling. 1 Presented before the Division of Industrial and Engineering Chemistry at the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 to 8, 1922. a Contribution No. 35 from the Department of Chemical Engineering, Massachusetts Institute of Technology. From a thesis submitted in partial fulfilment of requirements for the degree of Master of Science. a “Free settling” conditions are those in which the fall of particles through the solution is not interfered with by other paiticles.
TECHNOLOGY, CAMBRIDGE, MASS.
AMOUNT OF LIME samples of so.2 lime of 150, 175, 200, 225, and 250 g. wrere weighed out and each used to causticize 2 liters of solution, allowing min. for causticizing at boiling temperature, The /do
settling cur.,es ~~, 90 percentage conver- 3 Pion were determined 1.6 80 for each run, the ,.4 70 P results being shown .B 1 2 60 graphically in Fig. 2. fI i? 50 From this plot it & 1.0 is evident that in- $ 08 40 B crease in amount of 4 P Ob 30 Q lime increases the per- 4 B centage conversion 04 20 but decreases the rate oz IO of free settling, and 0 0 since, with a given SO 60 70 80 90 1UU //Q ,420 /30 fltnOUnf o f Lime -Per cent of Theoreficul decantation e q u i p merit available, proFIG.8-RELATION O F FREE-SETTLING RATE duction is propor- AND PERCENTAGE CONVERSION TO AMGUNT OF tional to the rate of free-settling, the choice of amount of lime must be determined from an economic balance of these factors.
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TIMEOF CAUSTICIZIXG Four samples of 225 g. of No. 4 lime were weighed out and causticized in 2 liters of soda-ash solution for periods of 5 , 10, 20, and 30 min. The results are shown graphically in Fig. 3, and it can be seen that with increasing time of causticization the percentage conversion is increased while the free-settling rate is decreased. Here again the economic aspect, as to the proper choice of time of causticizing, comes into play. CHARACTER OB LIME
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In the study of the effect of character of the lime on percentage conversion and free-settling rate, six limes of varying calcium and magnesium ol 1 1 1 l 1 1 1 l o content and varying 0 4 8 12 16 20 24 28 32 Time of Caustirizinq -Minutes degrees of air-slaking were used. The genFIG.3-RELATION OF FREE-SETTLING RATE PERCENTAGE CONVERSION T O TINE O F eral tendency, from a AND CAUSTICIZING study of the results, indiiates that the percentage conversion is unaffected by the character of the lime as long as there is present 10 per cent excess lime. On the other hand, the free-settling rate is markedly affected by the character of the lime. For instance, high-calcium limes give better settling rates than limes containing appreciable amounts of magnesium, and air-slaking produces lower settling rates.
April, 1923
IND UXTRIAL AND ENGINEERING CHEMISTRY
The physical properties of the lime, such as apparent density and size of particles, influence the free-settling rate-the more granular and compact the particles, the greater the settling rate. In the plant economics of causticieation, three problems frequently arise, namely: I-With a given equipment, what are the best operating conditions to yield a product of definite amount and concentra tion? 2-With a given equipment, what are the best operating conditions for maximum production?
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3-Por the design of a new plant what operating conditions should be chosen? The first two problems are of immediate importance, because a plant manager always desires to know how to operate his plant a t minimum cost and again how to obtain increased production without expending a “cent” for additional equipment. In all three problems, the final operating conditions are chosen after making an economic balance on the factors involved, such as cost data, time of causticization, and amount and character of the lime. This latter information can be obtained from runs made on the given lime, similar to thwe presented in this paper.
Detection of Sugar in Condensed Waters by Means of Cresol’ By G. E. Stevens THEGREATWESTERNSUGARCo., EATON,COLO.
URING the war several substitutes for alpha-naphthol as a reagent for the detecting of sugar in condensed waters were experimented with, but no satisfactory reagent was found that would give satisfactory results. The research had to do largely with the higher phenols, such as resorcinol, etc. It occurred to the writer that the lower phenols, such as creosote, cresol, etc., had possibilities. ,410ng with finding a suitable substitute was a desire to find also a cheap solvent which would eliminate the use of alcohol. With these ends in view several phenols mere experimented with, and after various comparisons and experiments cresol was found to give satisfactory results. The chief difficulty was in finding a solvent that in no wise hindered or affected the color reaction and a t the same time was a good solvent. Cresol has a solubility of only 0.3 in water; therefore, if water was to be used as a solvent or vehicle, some substance soluble in water and at the same time a solvent of cresol must be found. Castile soap was found to be a good solvent for cresol in the proportions of 6 g. of soap to 15 cc. of cresol, the soap previously being dissolved in 100 cc. of distilled water. This solution can be made up in liter quantities without apparent deterioration. If solution is not effected on warming and agitation, the addition of a little more soap will complete the solution. One objection to the use of a-naphthol has been that in most cases &naphthol is usually prfsent to some extent, which produces a green coloration on the addition of concentrated sulfuric acid, Iron and lime salts also produce various colorations which, if present in sufficient quantities, tend to mask the violet ring, especially in the detection of traces of sugar. By the use of the cresol solution the foreign color reactions are almost entirely eliminated and a decided color ring is obtained only in the p’resence of sugar. A solution containing 1 part sugar in 100,000 parts of water, and also a trace of oil, lime salts, iron (held in solution by means of ammonium oxalate), ammonia, and other mineral salts was tested, and the color reaction found to be unaffected to any extent with no foieign colors present sufficiently to mask the test. The castile soap in the presence of lime salts really acts as an aid, a3 the milky color produced serves as a good background in making the color reaction more prominent. PROCEDURE Put about an inch of the water to be examined in a 6 x 5 / ~in. test tube (a 6 x 1 in. test tube is recommended in detecting
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Presented before t h e Dlvislon of Sugar Chemistry a t the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 t o 8, 1922. 1
light traces) and add 5 to 10 drops of the cresol solution and contents thoroughly mixed. Cool the contents if warm and then add concentrated sulfuric acid from a dispensing buret, holding the tube in an inclined position so that the acid will run to the bottom and form a separate layer, and continue to add the acid until the acid layer is ‘/z to 3/4 in. deep. Then roll the tube between the hands and if sugar is present a reddish black to pink color ring will appear, the color depending upon the concentration of the sugar. It is recommended that white translucent screen be placed between the eye and the source of light, as this aids in recognizing more easily the color reaction, especially in faint traces. ADVANTAGES This solution can be cheaply prepared, the cost for a 100-day campaign would be approximately $1$00. It eliminates highpriced solvents, and is very sensitive, giving a color reaction on standing a half-hour of 1 part sugar in 500,000 to 1,000,000 parts of water. There are no serious foreign color reactions to interfere or mask the test, and the color rings are of such a nature that a rough estimate of parts of sugar present can be estimated. While this method has not been tried out during plant operations, various waters were tested and the writer believes it to be applicable in all respects and to serve the purpose as a possible substitute forthe a-naphthol method. The accompanying color chart shows the color reactions of various parts of sugar present in solution. This chart represents merely the colors observed by the writer while making the various tests, and to other individuals the color mould probably seem slightly different. COLOR REACTIONS WIITH KNOWN P A R T S Of SUGAR I N SOLUTIOh Parts Sugar in Solution COLORRBACTION 1100 Reddish black turning t o black 1500 Reddish brown t o black 11,000 Reddish brown 16,000 Deep red t o reddish brown 1 10,000 Red t o dark red 1 20,000 1,ight red t o deep red 140,000 Pink t o light red 60,000 Pink t o light red 1 180,000 Light t o heavy pink 1 100,000 Pink 1 180,000 Light pink in few sec. 1 200,000 Light pink in 20 sec. 1 250,000 Light pink in 30 sec. Light pink in 1 t o 2 min. 1 - 300,000 1 350,000 Light pink in 5 min. 1 - 400,000 Light pink i n 18 min. Light pink i n 1 t o 2 hrs. 1 1,000,000
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NOTE: Slight agitation of the contents of t h e tube hastens reaction in light traces. A very light brown color is t o be disregarded a n d will disappear upon agitation, and a pink color develop, if sugar is present.
