May, 1930
INDUSTRIAL AND ENGINEERING CHEMISTRY
turing company is either directly or indirectly interested in the manufacture of yarn by the acetate process and the Celanese companies are practically the only independent group of synthetic-fiber manufacturers in the world today. Another trend in the industry in the past has been the gradual elimination of the nitrate process in favor of cheaper methods of manufacture. While the present nitro yarn is very satisfactory, the cost of manufacture is undoubtedly higher than that of any other type. I n 1928 by far the largest part of the profits of the Fabrique de soie artificielle de Tubize of Belgium, which manufactures nitro, viscose, and acetate yarns, was derived from the acetate process, and this company has recently announced that it will discontinue the manufacture of nitro yarns. I n the cuprammonium field the tendency is towards fine and malti-filament yarns, and remarkable progress has been made along this line. Although the cost of manufacture by this process is probably higher than that of either the viscose or acetate methods, Bemberg yarn has a higher elasticity than viscose rayon and the fine-filament cupra yrirns are in big demand, especially by the knit-goods trade. I t is possible that the stretch-spinning processes now in development by the Celanese companies may rival these very fine cupra yarns in the near future. Hollow-filament acetate yarns are also a possibility of the very near future. I n the viscose field the tendencies are towards finer and more filaments, as well as stronger yarns with a greater elasticity and more even dyeing properties. The hollow-filament rayon yarns seern to be gaining ground, although they are not yet manufactured in America commercially. Of course, the matter of costs is always in the foreground in
467
every process and, with the increased competition of the acetate yarns, this problem will probably become more acute in the viscose industry in the near future. At present very little effort is made to recover the chemicals or by-products of the viscose industry and developments in this field may be expected in the near future. The so-called artificial wools also come under the classification of the synthetic fibers and a number of synthetic products of this type have been on the market since shortly before or during the war. Large quantities were manufactured in Germany during the war and it has been stated that they can now be produced in England a t less than 40 cents a pound. Most of these products are of the viscose type and some develop ments in this line are possible. Novelty yarns of every type are, and will be in the future, in great demand by all branches of the textile industry. I n spite of all the enormous increases in the production of the synthetic fibers within recent years and all that we have heard regarding the “saturation point,” the real and permanent saturation point is just as far off today as it was ten years ago, if the research and developments of the past are continued a t the same rate. It is true that the sales competition will be more keen in the future and that certain unprogressive plants may pass into the discard, but this very competition will be the greatest stimulus to research and further advancements that the industry has ever experienced. Probably no other branch of the chemical industry offers any greater o p portunity to the chemist and chemical engineer today. Literature Cited (1) Woolf, Tezlile World, 77, 645 (1930).
Manufacture of Chemical Cotton’ W. Donald Munson SOCTHERN CliEMICAL COTTON CO., CHATTANOOGA, TENN.
N
0 ARTICLE of commerce has contributed more t o
the industrial and economic development of the South than cotton. Investments of recent years in cotton industries have been of vast proportions and of great significance. History.of Development The use of cotton as a textile fiber is of prehistoric origin; and today, as a raw material for the textile industry, it is regarded as the universal fiber. The importance of cotton as a chemical raw material is of more recent development. For years it has been regarded a s the standard for cellulose, since from cotton is obtained the purest cellulose known in nature. With the outbreak of hostilities in 1917 and the increased demand for cellulose for the manufacture of munitions, the War Industries Board ordered the leading cotton-oil mills to install additional delinting machinery and commandeered every pound of residual fiber that could be removed from the cottonseed. While formerly the larger part of this byproduct mas used in mattresses and bedding, practically all of the increased production during the war mas con’ Received February 17, 1930. Presented a t t h e General Meeting under t h e auspices of t h e Division of Industrial and Engineering Chemistry, a t t h e 79th Meeting of t h e American Chemical Society, Atlanta, Ga
April 7 t o 11 1930
,
sumed in the manufacture of guncotton and nitrocellulose powder. With the signing of the armistice a paramount problem was presented in the utilization of this now surplus war material. Several of the large producing interests undertook the development of a cotton-pulp for paper manufacture, the paper industry being the largest potential consumer of cellulose. With the consumption of the surplus mar material and the increase in cost of the cotton fiber other cheaper competitive pulps largely displaced cotton in the paper mills. Cotton, of the long staple variety, on account of its higher cost than wood pulp and other cellulose, could not be considered as a raw material for the various cellulose-base chemical products. It has been through the utilization of a by-product from the cottonseed, known as cotton linters, that this economic problem has been solved. Cotton linters, although a by-product of the oil mill in the process of crushing and extracting the oil from the cottonseed, have now become a very important source of cellulose. Since the war those industries employing cotton cellulose as a base have experienced phenomenal growth. The estimate of linters purified in the United States in 1929 for chemical purposes is 300,000 bales, 35 per cent of the total linter consumption. With the increased demand it is expected that within a few years cheaper methods of production will
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INDUSTRIAL AND ENGINEERIh’G CHEMISTRY
be developed and the shorter fibers, now left on the seed, utilized. Production of Linters
Vol. 22, No. 5
U. S. Department of Agriculture to undertake the study of linters with a view of establishing standard grades. As a result seven standard grades of linters were prepared and the production and purchase of linters against these grades became effective several years ago. The setting up of these standards has been a great forward step in the development of the industry. With the increased demand each year for cotton cellulose, attention has been focused on the improvement in the quality of the linters and through education and cooperation on the part of the producers and consumers p r o g r e s s h a s been made. Most of the mills have installed improved seed-cleaning facilities and machinery, realizing that in cotton linters they have a valuable by-product.
Cottonseed after ginning retain an appreciable quantity of relatively short residual fiber, which, principally for economic reasons due to oil absorption and improper separation of the hulls and meats, must be removed. A brief description of this delinting process is as follows: The seed coming from the cotton gins are received in storage warehouses or tanks a t the oil mill. As they are contaminated with s a n d , pieces of cotton stalks, and other foreign material, it is necessary to clean them mechanically prior to delinting. Of recent years a great deal of stress has been put upon Types of Linters this cleaning Used operation on acM o s t of t h e count of the more c h e m i c a l cotton exacting demands now produced is for clean linters. f r o m second-cut F o r e i g n matter, linters, correparticularly of the sponding to U. S. leafy, shaley type, will remain in the Standard G r a d e Figure 1-General View of Plant of Southern Chemical Cotton Company linters if the seed Nos. 6 and 7. To are not cleaned obtain certain beforehand. The machine for removing this residual chemical characteristics, longer fiber length, and freedom from cotton fiber is known as a linter, as is ilso its product. dust, and where a mild chemical treatment is necessary, a The cottonseed passing through the delinting machine first-cut or high-grade mill run linter is required. These come in contact with saws, revolving a t high speed, which types grade U. S. Standard Nos. 3 , 4 , and 5. remove the fiber. The adjustment of this machine with Apart from the above, the selection of the type of raw respect to the pressure of the seed against the teeth of material is one of economics. The increased depth of cut the delinting saws varies the percentage of fiber removed. and corresponding shorter fiber are unavoidably accompanied This adjustment is generally known as the “setting” of by an increase in particles of hulls which are pulled off by the machine and the quantity of fiber removed as the the delinting saws and projected into the linters. A drastic “cut.” We thus speak of a 50-pound cut of linters as a chemical treatment is required to eliminate these hulls measure of the quantity of linters produced per ton of seed and other woody matter, with the consequent lowering of yield and increased expense of conversion. For this reason, put through. From the viewpoint of the manufacturers of chemical irrespective of the resultant quality, the yield of cellulose and cost of processing must be. taken into consideration cotton three types of linters are regularly produced-a low f i s t cut, mill run, and second cut. To make the last with the cost of the linters when comparing two different type of linter, the seed are again delinted, after removal of types. The measure of the value of linters for production the longer fiber in the first cut. I n case of the mill run of chemical cotton is, therefore, the percentage of pure type the total quantity of fiber is removed in one operation. cellulose, as well as the quantity and character of foreign The linters as produced are conveyed to a baling press and matter, contained in the linters. To produce a cotton packed for storage and shipment. A bale the size of the cellulose of the highest quality great care and experience standard cotton bale is generally used and weighs about must be exercised in the selection of linters. 600 pounds. Purification Need of Standardization of Raw Materials
When it is realized that the average oil mill operates from fifteen to twenty-five linter machines, each machine contributing its product to a bale, the problem of maintaining a uniform product will be appreciated. Moreover, the quantity of seed put through the linters is often governed by the demands of the press room for seed meats, which also affects the uniformity of the linters. Realizing the need for standardization of grades of linters, the Cottonseed Crusher’s Association in 1924 requested the
The following typical analysis shows that there is a considerable percentage of inert non-cellulose material which must be removed by purification: PER CEHT
Chemical yield of cellulose (by digestion with NaOH) Ash lmll
Ether extract Lignin (H?SOd-insoluble) Moisture
80 t o 85 1 to 1 . 5 0.06 31 6
I n plant practice the yield of cellulose is approximately 5 per cent lower than this, owing to mechanical losses.
May, 1930
IaVDUS1'RIAL A N D ENGINEERING CHEMISTRY
Figure 2-Ixpesfers
Tlie purificatiun of the lint,ers and conversion to cottoii cellulose is accornplislied iii the followiiig main steps: (1) blending the raw materials, (2) digestion or cooking, (3) washing:, (4) l~leaching,arid (5) drying. Inasmncli as tlie purification is carried ont iii a hatch system, the raw inaterial progresses through the various parts of the process in oliarges. T o a s u r e qeater uniformity it is necessary to blend the raw linters in soincwliat the same proportions as received, for it rriay hc readily appreciated that the products of no two oil inills are identical, regardless of intelligent type grading. The weighed quantity of linters (7000 pounds) is opened into the digester (Figure Z), intG which is pumped a solution of caustic soda of winst.ant volunie and percentage NaOH (2.5 to 3.5 per cent). The digester is then rotatcd and steam introduced ttirougli each end below the solutioii level. The pressnre is then raised to that required for cooking----from40 to 80 poiincis, dciiending upon tho required
Figure 4- E x t r a c f e r ~and Snrgenf Pickers
clieinical clinracteristies of the product.. Tirrougl~oiit the cooking period (3 to 5 hours) the digester is rotated tu assure agitation and constant mixing of the solution and linters, a primary requisite for uniformity of product. At tlie end of the cooking period tlie pressure is released froin the digester and water is introduced through the ends to dilute the caustic concentration and serve as a first wash. The reaction of tlie hot caustic liquor in contact with the air produces an inferior quality of cellulose. The treatment
469
Figure 3 --Blenching Tubs
tinder ateain pressure with caustic soda solirt,ioir disirrtegrates and dissolves the non-cellulose constitnents, sue11 as the hulls and other ligneous materials, present in tlie raw linters. After completion of the 1:ooking, the charge is droppcd through iiianholcs in the side of the digester into a steel wasli tanlr. wliere washing completely removes all caustic and black liqnor. The cooked unbleached cellulose is then pimped tu tlie bleaching tub. (Fignre 3) This tub is of wood stave cuiistruction, equipped with vertical agitators and a perforated false bottom to permit drainage of the spent bleach solutioii and washing of the cellulose. Calcium hypochlorite is usually used as a bleaching reagent. When the cottoii celliilosc is at a definite temperature the measured quantity of available chlorine (0.75 to 1.25 per cent) is introdaced into the bleach tub. The batch is agitated throughout the hleacliing process. After drainage of tlie discolored solution,
Figure J
-view of Drier Room Showing Product
Baling and Wrvlpping of
a nicasured quantity of diluted sulfuric acid is added tu
accelerate tho bleaching and reduce the ash content. Many modifications of this bleaching operation are necessary, depending upon the cliernioal characteristics of the cellulose required. Sodium bisulfite or some other reducing agent is generally used &s an antichlor. An oxalic acid solution is sometimes used after bleaching to reduce the iron content.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 22, No. 5
Final purification of the linters is accomplished by washing with complete removal of the by-products of the bleaching reaction.
in cuprammonium solution, the relationship of the viscosity of the cellulose to its solutions or esters has been established. I n recent years major emphasis has been placed on the viscosity of cellulose, so the purification treatment, parDrying ticularly the caustic soda digestion, is carried out m t h The cotton is now ready for drying. I n a concentration special regard to the viscosity of the product. The deterof less than 0.5 per cent cotton in water, the purified bleached mination of viscosity of the raw linters is very difficult owing cellulose is pumped through the riffling system, where re- to the presence of ether-extractive matter and contamination moval of foreign mat- oi hull particles. For this reason there is not always a ter, of higher density definite relationship between the viscosity of the linters and than water,iseffected. the cotton cellulose produced therefrom. The results It is posaible by this obtained indicate that in different linters of the same type method to deposit in the cellulose molecular aggregate is not the same. It is traps such m i n e r a l therefore impossible to obtain identical viscosities from linters m a t t e r as sand and of different sources, all conditions of treatment being concinders and even very stant. To overcome this variance, blending of the raw fine siltlike organic linters, as consumed a t the plant, is essential to assure unimatter not removed formity. Reduction of viscosity is obtained by reduction b y t h e purification of the cellulose molecular aggregate and modification of the process. The drying cellulose. operation is continuIn practice this reous, e a c h d i g e s t e r d u c t i o n i s accomc h a r g e retaining its plished by a more id e n t i t y throughout d r a s t i c chemical Figure 6-Estimated Distribution of Chemical Cotton by Industries in 1929 the process. The cot- treatment. Temperaton cellulose is then ture of digestion is conveyed through rubber-covered squeeze rolls (Figure 4) t h e m o s t important for extraction of water to less than 50 per cent bone dry, factor in reducing the into a Sargent wet picker which blows the opened cotton viscosity, while time onto the traveling apron of the continuous air drier. The of treatment in the material on the apron progresses at comparatively slow speed digester and concento the dry end of the drier, air being continuously circulated tration of alkali have over steam coils through the cotton. With the cotton picked correspondingly 1e s s and fluffed up by agitation during the drying it is possible to effects. To produce employ comparatively low drying temperature (150-160' F.). cotton cellulose of the Figure 7-Estimated Distribution in Cotton cellulose is generally dried in sheet form for the lower viscosity types 1929 of Principal Products of Chemical Manufactured in t h e United viscose process for rayon manufacture. Equipment of the economically and t o Cotton States same general type for making paper is used. For drying assure uniformity, it in this form the purified cotton is beaten and dried in a con- has proved best to adopt high-pressure cooks of 80 pounds tinuous sheet like blotting paper. The sheet is then cut to or more. The medium and higher viscosity types are prothe required size. duced by modification of the time of treatment within practical limitations. Bleaching also tends to reduce the visBaling cosity, the percentage of reduction depending upon the inThe dried cotton is baled and wrapped with kraft paper tensity of the process. Chemical cotton is now sold on specifications which limit preparatory to storage and shipment. (Figure 5 ) For domestic use a standard bale, which measures about 17 X 22 X the viscosity variations. I n practice the relative reduction 36 inches and weighs from 100 to 150 pounds, has been in the viscosity of the cotton in each step of the purification process is established for each viscosity type of cellulose adopted. During the baling samples from each lot are drawn at produced. Tests made on samples after digestion permit frequent intervals. A portion of each sample is sent to the modification of the subsequent processing and control of laboratory for chemical analysis. A typical analysis of the viscosity of the finished product within specifications. chemical cotton follows: Technical control of the plant operations is difficult and results are not infallible. PER CENT Alpha-cellulose Ash
Eiher extract Lignin (HtSO4-insoluble) Iron Moisture
99
0.10 0.20 0.20 0.002 5
The other portion of the sample is used for testing the color, cleanliness, moisture, and other physical characteristics. By comparing nrith a set of standards under a glass the sample is given a numerical value for color. To determine the cleanliness, a weighed sample is formed into a pressed mat and, after wetting, all the visible particles of foreign matter are counted over a strong light box. Reduction and Control of Viscosity
With the development of a satisfactory and accurate method (1) for the determination of viscosity of cellulose
Principal Chemical Products
The fact that chemical cotton has a uniform viscosity, a very high alpha-cellulose content, and is highly absorbent and reactive makes it particularly suitable for manufacture of nitrocellulose, cellulose acetate, and cuprammonium products. It is estimated that 28,000 tons of chemical cotton were produced in the United States in 1929 for nitrocellulose products. The cotton cellulose is treated with a mixture of nitric and sulfuric acids. After removal of the spent acids the nitrated cellulose is drenched with water, washed, and neutralized. It is then boiled to remove the last traces of free acid and to stabilize the product. Water in the nitrated cotton is removed by dehydration with alcohol. Nitrocellu-
IND VSTRIAL A S D EA'GIXEERING CHEMISTRY
May, 1930
lose (soluble cotton) is the base for such important products as pyroxylin plastics (celluloid), photographic films, lacquers, nitro-rayon, artificial leather, and explosives. Lacquers and safety glass, involving the use of transparent sheet pyroxylin, have been recent outstanding factors in the growth of the nitrocellulose industry. The making of cellulose acetate is a very complicated process and requires a cellulose of high purity and reactivity. Cotton cellulose is treated with acetic anhydride and acetic acid in the presence of a catalyst, usually sulfuric acid. During the acetylation the temperature is carefully controlled. When the reaction is completed the cellulose acetate is precipitated by addition of water into the form of white flakes. It is washed to remove free acid and carefully dried. The principal product of cellulose acetate is acetate rayon although it is also gaining recognition for molded articles and lacquers. In the preparation of the solution by the acetate process for rayon manufacture the dried cellulose acetate is dissolved in a suitable volatile solvent, usually acetone. After filtering, the spinning solution is forced through fine openings into warm air. Coming in contact with the air, the volatile solvent evaporates and coagulates the solution, forming a filament. The filaments are wound upon a cone or spool. The estimate of chemical cotton
47 1
produced in 1929 for manufacture of cellulose acetate rayon is 6000 tons. Approximately 60 per cent of this quantity was exported. The use of chemical cotton in products of viscose and cuprammonium solution is also closely affiliated with the rayon industry. Since the leading producer of rayon by the viscose process is the largest consumer of chemical cotton and also owing to the increasing demand by other large viscose rayon manufacturers, this division of the industry is outstanding in the consumption of cotton cellulose. Searly 40,000 tons of chemical cotton are estimated to have been produced in the United States during 1929 for the manufacture of rayon. The use of rayon fibers in articles of wearing apparel is now generally known. The fact that chemical cotton, made from linters, is the base for various other outstanding products, such as toilet and other celluloid articles, photographic and moving-picture films, non-shatterable glass, automobile lacquer finishes, and artificial leather, indicates the diversity of its uses and its importance as a chemical raw material. Literature Cited (1) Committee on Viscosity of Celliiloqe 1 , 4 9 (1929)
ISD
EXG CHFM indl Ed
,
Vanadium Compounds as Catalysts for the Oxidation of Sulfur Dioxide' Harry N. Holmes and A. L. Elder SEVERAXCE CHEMICAL
I
3 A previous publication
H o l m e s , Ramsay, and Elder (3) studied t h e conversion of sulfur dioxide to sulfur trioxide using platinized silica gel as the catalyst. In that article they stated that the study of the oxidation of sulfur dioxide was to be continued using vanadium cornpounds as the contact masses.
LABORATORY, OBERLIN
COLLEGE, OBERLIN, OHIO
A new method for preparing extremely intimate mixtures of catalysts containing vanadium compounds, promoters, and supports is described in detail. The best of these shows a 98 per cent conversion of sulfur dioxide to sulfur trioxide without any decrease in efficiency even after 60 hours of continuous use. Intimate mixtures of vanadates with silicates, hydrated silica, and promoters such as compounds of iron, calcium, copper, cobalt, and nickel were made and tested.
Previous Work
Several attempts have been made to use vanadium compounds as catalysts for increasing the conversion of sulfur dioxide to sulfur trioxide. The early experiments were cited by Alexander (1) and Nickel1 (9). Recently Jaeger and his associates claimed remarkable advantages, in the catalytic oxidation of sulfur dioxide, for the use of vanadium compounds associated with certain promoters as effective catalytic mixtures. Using vanadium in the non-exchangeable nucleus of non-siliceous base-exchange bodies, Jaeger (4) claims to have an excellent catalyst which is immune to the common poisons of platinum catalysts. Spangler (IO) predicts that the contact mass developed by Jaeger will replace to a large extent other active masses used in sulfuric acid manufacture. I n fact, it is now in considerable use in this country. It is of interest to note that 35 per cent of the 8 million tons of sulfuric acid produced in 1929 in this country was manufactured by contact processes. 1 Received iMarch 7, 1930. Presented before the Division of Industrial and Engineering Chemistry at the 79th Meeting of the American Chemical Society, Atlanta, Ga , April 7 to 11, 1930.
The patent literature relating t o the use of vanadium compounds as catalysts has been reviewed by Waeser ( I d ) . Another survey is to be found in a journal published by the V a n a d i u m Corporation of America (11). The most important patents of recent date p e r t a i n i n g to the use of vanadium compounds in the contact process for making sulfuric acid are those by Jaeger and his associates (5,6). It would appear from these patents that many of the known elements in some form are promoters for vanadium catalysts. Few figures are available in the patents on actual rates of conversion. Jaeger does state that with one catalyst 135 liters of 7 per cent burner gas may be passed per hour over 200 cc. of the contact mass. This is equivalent to 0.067 gram of sulfur per hour per cubic centimeter of catalyst on the basis of perfect conversion, which was, of course, not attained. In one patent he claims a conversion efficiency of 98 per cent on a 6 to 9 per cent sulfur dioxide mixture, but he fails to disclose the actual weight of vanadium in the catalyst used. Neumann (8) and his associates have published some very valuable data on the use of vanadium catalysts and have included curves showing the effect of temperature variation on the per cent conversion when using different catalysts. Comparisons were made of the catalytic value of silver vanadate, vanadium pentoxide, copper vanadate, tungstic oxide, silver, ferric oxide, ferric oxide and bismuth oxide, strontium oxide and ferric oxide, tin oxide, chromium oxide, and titantium oxide. One of the best catalysts prepared
