INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Vol. 15, No. f
Chemical Progress in Cane-Sugar Manufacture By Guilford L. Spencer THEICUBAN-AMERICAN SUGARCo.,NEWYORK, N. Y.
I
T MIGHT appear a t first glance that chemistry has
played a small part in the development of the cane-sugar industry. This is true as far as its applications in processes are concerned, but the chemist, in his control a t all stages from the materials of equipment to products and byproducts, has done much to advance the manufacture. Lime i s still the only chemical used in making raw sugar, as was true twelve centuries ago in Egypt. Lime and sulfurous acid, or lime, sulfurous and carbonic acids are used in making plantation-white and near-white sugars. These three reagents are the only ones that enter directly into the current processes. Sodium carbonate is occasionally, but not usually, used to assist in the elimination of the lime. Caustic soda and hydrochloric acid are employed in cleaning the heating and evaporating surfaces. Vegetable carbons are used to a limited and probably increasing extent, in the direct manufacture of white sugar. Animal charcoal is now used only in decolorizing refinery liquids. It is probable that more than 90 per cent of the world’s cane sugar is made with lime as the only chemical entering the process. The limited use of chemicals is not due to the lack of suitable reagents, but to the small possible margin of profit in changing existing methods. Unless some revolutionary process is developed that will eliminate much of the effort in the present juice treatment, evaporation, and purging of the sugar, present methods may be expected to persist. The French have long looked to alcohol to revolutionize the manufacture. More than sixty years ago they purified sorghum-cane juice with it, removing the gums by precipitation; and over thirty years ago the U. 5. Department of Agriculture used it similarly in treating sorghum sirup. The French later carried the process further, and, after a preliminary alcoholic precipitation of the gums, continued the ad-* dition of alcohol for the nearly complete precipitation of the sugar. Thus, a method was developed that eliminated several of the present operations and directly produced crystallized sugar. This is an example of a perfectly feasible process that so far has proved too expensive for its application, or is hedged in by too strict governmental restrictions. Other precipitation processes are possible, such as the calcium, strontium, barium, and lead saccharate methods, but none has yet been applied in regular manufacture. These processes are practicable from the commercial view only in their application to the molasses residue obtained in the present process. This residue is approximately 3l/2 per cent of the cane worked. The calcium saccharate process of Steffen is used by many of the American beet factories, but has only been tried experimentally with cane molasses. The molasses from the beet usually contains no reducing sugars or but traces of these, whereas that from the cane may contain as much as 25 per cent, or even more, dextrose and levulose. In a direct treatment of cane molasses, the reducing sugars would be largely precipitated with the sucrose and with no manufacturing advantage. Reducing sugars in solution made alkaline with lime may be destroyed by heating. After this treatment, the sucrose may be precipitated as a saccharate, and, after removing the metallic base by carbonation, be recovered by crystallization. The market value of molasses has been large enough to deter the use of precipitation processes, but recently the price has been so small that large
quantities of the by-product have been run to waste, and these processes may be considered. A precipitation process was developed and patented by Batelle,l in which the reducieg sugars are destroyed in the juice instead of the molasses. It seems like wilful waste to destroy the fermentable reducing sugars in order to recover the sucrose, which a t most is about 35 per cent of the material. Possibly some selective fermentation method may be found to utilize the reducing bsgars and make the sucrose available. Alcohol and ether are now produced at low cost in the tropics, and are used as motor spirit. Tropical countries can utilize very large quantities of alcohol and ether in the motors of tractors for plowing and general haulage. The conversion of the molasses into alcohol and ether would therefore apparently provide a profitable means of disposing of the by-product, and leave little opportunity for precipitation processes. The ash resulting from burning the bagasse for fuel is rich in potash, but in a combination that is insoluble in water and of little value as a fertilizer. A low-cost method of rendering the potash salt soluble would be valuable. No doubt considerable quantities of potash could be recovered from the flue gases by electrical precipitation. Von Lippmann,2 in 1909, published a list of 622 proposed processes for sugar manufacture. Several processes have since been reported, and he doubtless omitted many, but of this long list few have persisted, as is indicated at the opening of this article. Possibly the reason for failure in many cases is the small margin of profit, even if nearly all the sugar were recovered. The value as sugar of all the sucrose left in average molasses, a t present market price, is about 85 cents per ton of cane. The present market price is probably higher than may be expected when Europe again produces fully. It is easily conceivable that a fall in the price of sugar and a rise in that of molasses would leave little encouragement for a larger recovery of sugar, if a new process were involved. There has been considerable progress in the mechanical equipment of the cane factory, especially in the development of mills, the handling of cane, and the settling of juices. The experiments in diffusion nearly forty years ago under Dr. H. W. Wiley in Washington, Kansas, and Louisiana, spurred mill builders to better design and resulted in demonstrating the economic superiority of mills. These developments could hardly have been possible without the chemists’ control, from the foundry mixtures of mill rolls and other elements of the machinery to the bagasse from the last mill of the train. Boiling-house methods have progressed along such lines that laboratory control is imperative. The modern cane factory is chemically controlled a t every stage of the manufacture, and an increasing number of factories require the superintendent and, his principal assistants to have a good chemical training. Summarizing, there has been little chemical progress in the treatment of the juice of the cane, no chemicals are used a t other stages of the manufacture, but the reasons for present usages are much better understood. There has been great progress, however, in mechanical equipment a t all stages of the manufacture, and often with the assistance of the chemist. The construction of the mills, the grooving of their rolls, the delivery and feeding of the cane to the mills, the 1 Special
a
Report, Hawaiian Sugar Planters’ Assoc., 1913. Deut. Zuckerind., 84 (1909), 9.
January, 1923
INDUSTRIAL A N D ENGINEERING GHZMISTRY
settling devices for juices and parts of the evaporation have markedly improved in the past ten years. A grinding capacity of 2500 tons of cane per 24 hours per train of mills was thought to be near the maximum with high efficiency, in 1912. There are now single trains of mills that will grind 3600 tons of cane with even higher efficiency. There has been great
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progress in factory output. I n 1912 there was but one factory with an annual capacity of 85,000 tons of sugar; in the present year, several factories have largely exceeded this output and one has produced 170,000 tons of raw sugar. These increases are largely due to progress in mill design and construction.
The Manufacture of Sulfuric Acid By L. A. Pratt MERRIMAC CHEMICAL Co , BOSTON,MASS.
CHAMBER PROCESS URING the last ten years there has been a determined effort to intensify the production of acid by the chamber process, and to this end numerous improvements have been made in the methods of chemical control and in the design of “sets” and their accessories. During the war the production of chamber plants was greatly enlarged by increasing the proportion of nitrogen oxides to sulfur dioxide in circulation. This leads to higher niter losses and larger repair charges, and is therefore not applicable to these times. As a result, chemical engineers are devoting their efforts to changes in design which will afford a better mixing of the gases and a more efficient removal of the heat of reaction, with a view to minimum unit cost of investment, operation, and maintenance. The Faldingll* high chambers are built to utilize the mixing of gases by convection currents caused by the heat of the chamber reactions. The saving in cost of lead and ground space is, however, offset by the extra cost of construction of the high chambers. There is no adequate provision made for the condensation of the acid mist. Gaillard2 uses, in place of the usual chambers, lead towers built in a slightly conical form, truncated, and having the larger diameter at the top. A hollow shaft extending inside the tower through the closed top serves for the introduction of a small stream of cold, dilute sulfuric acid which falls onto a revolving channeled disk located on the lower end of the shaft. The cool acid is projected against the upper part of tower, down which it flows in a cooling and protective film. The speed of the disk is sufficiently great to cause some of the acid to rebound and fall in a fine, heavy rain to the bottom. It is claimed that this rain serves to thoroughly mix the gases and t o condense the acid formed in the tower. It is further claimed that the temperature. throughout the tower is readily controlled, thus increasing the efficiency as well as the life of the apparatus. The Mills-Packard3 system, which was developed in England, has as its object the water cooling of the lead surface of the reaction chambers. The chambers are built in the form of truncated cones down the outside of which runs a continuous stream of cooling water. Plants of this design have been erected by 23 companies, in England, France, Italy, and New Zealand. The first two chambers were erected in 1914 and the number has increased to 112 at the present time. The results of actual operation have shown that a set of this type can be successfully operated on 3.66 cu. ft. of chamber space per pound of sulfur burned per 24 hrs., with a niter consumption of 3.62 per cent. The cost of construction is materially lower than in old style sets, and the life o€ the lead should be longer because of the efficient
D
* T h e numbers in the text refer t o patent references a t end of the article.
water cooling. None of these chambers has been built in this country as yet, so far as the writer knows. According t o the published results, this system is one of the important developments in chamber acid manufacture. There is no special provision for thorough mixing of the gas in this design, but it is reported that modifications are being considered which may further increase the efficiency of this system. Several types of “intermediate” or “reaction” towers have been brought forth, the purpose of which is to both COOI and mix the reacting gases. These are inserted between the chambers and offer a large amount of contact surface. One of the most successful types is designed by the Chemical Construction Company and consists of a lead-lined tower packed with spiral rings. Results of careful tests in a set where the tower space is equal to 7 per cent of the total chamber space, have shown that 33.5 per cent of the “make” of the plant was produced in the intermediate towers. The efficiency of the chambers alone was 10.7 CU. ft. per lb. of sulfur, and of the chambers plus the tower capacity was 7.6 cu. ft. per lb. sulfur. Larger intermediate towers are now being designed with a view of cutting down the chamber space proportionately. A patent was recently taken out by C. H. MacDowell* which covers the spraying of a large amount of dilute sulfuric acid (in place of water) into a chamber set for cooling purposes. The necessary amount of sulfuric acid is continuously drawn from the chamber pans, diluted, cooled, and re-sprayed into the chambers. It is reported that the capacity of the plant where this process was tested over a period of 6 mo. was increased 46 per cent, making it possible to operate the set on 6’/2 cu. ft. of chamber space per pound of sulfur burned with a 3 per cent niter consumption. A radical departure frofn the use of large reaction chambers is embodied in a process patented by 0pl6in 1908, and in two processes vhich have recently been patented and are now being tested in this country. The Opl process is carried out in a series of six towers. I n the first three towers the sulfur dioxide gas comes in contact with a descending stream of nitrosylsulfuric acid dissdved in concentrated sulfuric acid. Denitration of the acid takes place just as in the ordinary Glover tower and simultaneously the sulfur dioxide is oxidized. The last three toivers are for the absorption of the oxides of nitrogen evolved in Towers 1, 2, and 3. By this arrangement it is claimed that 1 lb. of sulfur may be burned per 2.1 CU. ft. of tower space per 24 hrs. About of these systems are in operation in Europe. A recent British patent by P. Farrish0 and The Sou Metropolitan Gas Company claims to double the efficiency of the Opl process by passidg the ng gases through a 4-in. layer of nitrosylsulfurio acid,
