REPORTS AND COMMENTS UPGRADING AN ESTABLISHED PROCESS N o process is so well established
that study of one of its constituent steps may not lead to improvements University professors are frequently accused of neglecting industrially relevant problems and I&EC has done its share of accusing (not without prompting spirited rebuttals, of course). T h e main obstacle in the path of a professor who would like to put his knowledge and fervor to work on a real industrial process has always been industry’s sturdy insistence on absolute secrecy about most of its
money-making technical activities. T o a large extent this preference for silence is understandable; a competitive edge often depends on a tight-lipped policy. The need for secrecy relaxes somewhat, however, when the process is a well-established one, especially if it bas been or is being supplanted by a more modern process. The Staff-Industry Collaborative Reports, a regular feature of I&EC in the nineteen fifties, were virtually all based on well-established processes. Before writing one, the I&ECeditor had free run of the plant for a day or two and prac-
I
I
RAW MATERIAL
MILL
Schematic vim of experimental xonthotion drum
COOLING WATER
Cs? AND LKALl CELLULOSE CRUMBS1
DRIVE
COOLING WATER BATH
Portio1 flow shcel of viscose rayon rnontcfncture
INDUSTRIAL A N D ENGINEERING CHEMISTRY
,
II
tically nothing about it was withheld from publication. Though the I&EC Collaborative Reports are no longer being prepared (very few established processes remain available for coverage), there are still many processes that are running commercially but from around which the tight securi t y guard has long been relaxed. Viscose rayon manufacture i- one such process. First produced commercially in the U. S. in 1910, viscose rayon has, of course, peaked as a major product, having been overtaken by synthetics like nylon and polyester. But even in the US., viscose production is still considerable (almost 1000 million Ib may be made in 1969, according to C&EN computer estimates) and in less advanced parts of the world i t is a highly important product. Here indeed is a process that, while certainly well established, can yet benefit from improvements, It is therefore very encouraging to read [in Chem. Eng. Sci., 23, 1347 (1968)] that three professorone Dutch, one Italian. and one American-have been able to study an important stage in the viscose rayon process. T h e study was performed at Delft University in Holland by W. J. Beek, Giuseppe Marrucci, and S. H. Davis, who enlisted the valuable cooperation of the Dutch firm A.K.U., a producer of viscose rayon in Arnhem. The production of viscose involves a number of steps, shown schematically below. In the first step, the cellulosic raw material. usually sheets of sulfite pulp, is treated with caustic soda i n a steeping press:
(C,H,O,
-
OH). (C,H,O,
+ nNaOH ONa). + nH,O
-
+
The resulting soft sheets of alkali cellulose are shredded to yield small crumbs in the second step.
“Aging” of the crumbs in large steel cans follows. Precisely what happens during aging is not understood (though it is known that some oxidation and degradation occur) but aging is needed to ensure a spinnable solution viscosity later in the process. T h e next step is xanthation of the alkali cellulose-Le., treatment with carbon disulfide:
+
(CGH,O, ONa) ,, nCS, -+ (CGHoO4-O-CS-SNa), T h e cellulose xanthate is dissolved in caustic soda, filtered, and ripened (a chemical change in which coagulation tendency is increased) in subsequent steps before the cellulose is regenerated in the form of a fiber by extrusion in a sulfuric acid bath. From all these steps, the men at Delft chose the xanthation operation for close study. Xanthation is customarily carried out batchwise in a continuously rotating cylindrical drum (see sketch) in which the
alkali cellulose crumbs react with CS,. Although the CS, is added as a liquid, the heat of reaction vaporizes it, and the actual reaction is between the solid crumbs and gaseous CS,. Since the heat of reaction per unit mass of CS, is greater than the heat needed to evaporate the CS,, the drum has to be cooled during the reaction. This is usually accomplished by running water over its outside surface. T h e temperature of the reaction mixture must also be maintained below 38°C. T h e Delft experimenters made studies on several types of apparatus: an operational xanthation drum in the plant, a pilot-plant drum having about one fourth the volume of the plant drum, a simple laboratory bomb in which purely kinetic studies were carried out, and small model drums having volumes as small as 1/200th of the volume of the smallest pilot-plant drum.
Their results are too detailed to repeat here, but some of their conclusions are interesting. Important among these is the conclusion that the laboratory kinetic studies and small-scale heat transfer studies on model drums were together sufficient to enable accurate prediction to be made of large-scale plant performance. I n other words, the fullscale production xanthation drum could have been designed on the basis of quite simple experiments, without any need for work at the pilot-plant scale. Evidence regarding the optimum size of drum and the need for control of CS2 vapor pressure was also obtained. T h e over-all study gave the investigator an excellent feel for the rate-controlling steps in the xanthation reaction and served both to upgrade this vital step in an established process and to broaden the investigators’ appreciation of industrial problems.
I&EC DIVISION SUMMER SYMPOSIUM ON FLOW THROUGH POROUS MEDIA WASHINGTON, D.C., JUNE 9-1 1, 1969 Registration Information If you intend to attend the symposium, please use the preregistration form below and return it as soon as possible. It i s not essential to preregister-there will
be a registration desk at the symposium site-but note that it i s possible to save money by preregistering.
HOTELS Hotel reservations must b e made b y the Individuals attending the symposium. I n the vicinity of The Carnegie Institution are several good hotels and motels, such as: The Mayflower (Connecticut Ave. at De Sales St.), The Madison (15th and M Sts.), the Statler Hilton and Sheraton Carlton (16th and K Sts.), the Executive House Motor
Inn (16th St. and Rhode Island Ave.), two Holiday Inns (17th St. and Rhode Island Ave. and 15th St. and Rhode Island Ave.), and the Gramercy Inn (across from the 17th St. Holiday Inn). I n view of the large influx OF visitors i n the late spring and early summer, hotel space should be booked as far i n advance as possible.
...................................................... PREREGISTRATION FORM
Name
Symposium on Flow Through Porous MediaACS Division of Industrial and Engineering Chemistry Carnegie Institution. Washington, D.C., June 9-1 1, 1969
Business or Professional Affiliation
ACS Member,
Division Member
Nonmember of I&EC Division
Other
Student
$20.00
$25.00
$30.00
$ 5.00
l&EC
Registration
Address
Symposium Manuscripts (each)
3.00
3.00
3.00
3.00
luncheon
3.75
3.75
3.75
3.75
$25.00
$30.00
$38.00
$10.00
SPECIAL PACKAGE *
*
Includes: Registration Fee, Choice of 2 Manuscripts, and luncheon. ‘AVAILABLE ONLY THROUGH ADVANCE REGISTRATION
Mail this farm and check for item(s) circled to: Editor, Industrial and Engineering Chemistry (make check payable to Industrial & Engineering Chemistry), 1155 16th Street, N.W., Washington, D. C. 20036.
All Preregistrants will receive their badae and proaram, also . luncheon ;icket---(lF ORDERED)-by June 5- provided this form i s received i n the l&EC Editorial O f i c e at the address above no later than M a y 26. Manuscripts will be available at the meeting site.
AUTHORS AND TITLES of papers to be presented were published in our March 1969 issue Abstracts will appear in our May 1969 issue.
[I&EC, 61 (3), 1 1 ( 1 9 6 9 ) ] .
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NO. 4
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