Cellulose polymers for the future 168TH rfO I f J O f i rh€€TIMG Even if coal, gas, and oil reserves last longer than expected, they may become too expensive to permit continued growth of the synthetic polymer industries. Dr. Clayton D. Callihan of Louisiana State University's department of chemical engineering believes that the obvious replacement for the organic base for these synthetic polymers is cellulose. However, a lot of engineering is necessary to use renewable cellulose supplies profitably, though the chemistry for such polymer production is already well known. Dr. Callihan told a Cellulose, Paper, and Textile Division symposium on new developments in cellulose technology that the lack of large-scale production facilities for cellulose-derived polymers is a reflection of unfavorable economics in the past. But he also says that the economics of cellulose polymers aren't off all that badly anymore. In fact they are already competing in some areas. And with the expected rise in petroleum prices, only slight improvements in cellulose technology will make cellulose even more competitive. Probably the biggest problem in cellulose conversion is eliminating the lignin from natural wood pulps. Lignin prevents the otherwise easy substitution of modifying agents on the cellulose chain. During conventional removal of lignin with caustic and bleaches, cellulose crystallinity is completely destroyed, only to be re-established when the cellulose is dried for shipment to chemical plants. In the plants, the crystallinity is destroyed again. It is here that Dr. Callihan believes that a simple change would be of great economic benefit to the cellulose business. He suggests simply shipping the cellulose pulp with 15 to 20% moisture, instead of destroying the cellulose crystallinity again after receipt. An example of the benefits that would accrue by this procedure is in the manufacture of carboxymethylcellulose (CMC), an important raw material in paint. CMC is water soluble at a degree of substitution of about 0.3. However, commercial CMC invariably has three to four times this degree of substitution just to remove minute traces of unsolvated fibers. The use of "wet" cellulose would save greatly on the required degree of substitution. Another area in which better engineering would enhance the profitability of cellulose polymers is the design of the reactor used for substitution on the cellulose chain. Substitution of ether or ester groups for the normal hydroxyl groups is very exothermic and requires close temperature control of the reac-
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Sept. 16, 1974 C&EN
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GLYCINE
tion. In old reactors the necessary con trol was achieved by using extreme dilutions of carrier solvents to control heat transfer in the reactors. Better re sults are obtained, says Dr. Callihan, with "third generation" reactors, which use no carrier solvents or integral rib bon mixers. Though the newer reactors may be more costly in themselves, they compensate economically by permitting use of cheaper ancillary equipment. It is time to reverse the trend of phasing out research on cellulose deriv atives, says Dr. Callihan. Cellulose is a quickly renewable resource, he stresses, whose chemistry isn't nearly as formi dable as it was once thought to be.
Fast way to measure protein in cereals
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168TfMG iwioNN. meaiNG Among the growing number of coal
FOOD · COSMETICS PHARMACEUTICALS INDUSTRIAL USES G-V PROCESS
chattem
Catalysts are key to direct methanation
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Paulis and his coworker, Dr. Joseph S. Wall. Glutelin appears to further re duce the already low lysine content of corns high in zein. Thus, to get a bet ter total protein-lysine correlation, βmercaptoethanol is added to the basic alcohol solvent (0.1M) to yield glutelin as well as zein. β-Mercaptoethanol cleaves the disulfide bonds linking polypeptide chains (due to the amino acid cystine), Dr. Paulis explains. The result is a greater turbidity.
An aid to development of high-protein cereal grains comes from the U.S. De partment of Agriculture's Northern Re gional Research Laboratory in the form of a simpler and quicker method to screen cereals for protein quality. Basi cally, the method involves extraction of zein (a protein low in lysine) and sub sequent precipitation and measure ment of zein by turbidity. Lysine in cereals is important to pro tein quality because it is a nutritionlimiting amino acid in cereals. Thus, the proportion of lysine-deficient pro tein to total protein provides an index of a cereal's nutritional value. Lysine content varies among the dif ferent solubility classes of cereal pro teins. In normal and high-lysine corns, an inverse ratio (-0.87) between total lysine content and the amount of zein has been established, USDA's Jerrold W. Paulis told a symposium on chemi cal and biological methods for protein quality determination sponsored by the Division of Agricultural and Food Chemistry. Other methods for deter mining lysine content in cereals— amino acid analysis, gas chromatogra phy, colorimetry, and enzymic and mi crobiological methods—have been de veloped. But high cost and the necessi ty for special technical skills are drawbacks. In the USDA method, ground corn is shaken with a 70% solution of ethanol containing 0.5% sodium acetate. A por tion of the supernatant liquor is sepa rated and a 1.0% solution of sodium chloride added to precipitate the zein. Turbidity is measured in a colorimeter at590nm. Some corn genotypes exhibit varia tions in the amino acid composition of the protein glutelin, as well as in the amounts of glutelin and zein, thereby causing accuracy of the lysine estima tion to be reduced, according to Dr.
chief processes have employed multistep gasification procedures in which the methanation (upgrading) of the low-B.t.u. product gas is accomplished separately from primary gasification. The ideal process would accomplish pri mary gasification and upgrading in a single step. Technical problems have frustrated a single-step design, but Babcock & Wilcox Co. hasn't given up. B&W's Gordon D. Woolbert told the Division of Fuel Chemistry that the company has been looking into direct production of methane for some time because of the economic advantages in single-step conversion. The attractive ness of single-step conversion centers on higher efficiency, which can ap proach 90%, compared to a 69% limit for multistep processes. B&W is using a single-step process first conceived at the University of Wyoming several years ago. Though the single-step process is preferable on economic grounds, problems of catalyst maintenance have yet to be overcome. Mr. Woolbert says that most methana tion catalysts are forms of nickel and sell for about $3.00 per pound. Unless the catalysts can be maintained for pe riods exceeding 15 months, they are too expensive to justify a one-step process. So far all the tests that B&W has run with 55 catalysts indicate that the ac tive lifetime of the catalysts is much less than 15 months. The environment around the nickel catalysts is very harsh. In addition to temperatures of 1200° F, there is the presence of many contaminants, the worst ones being sulfur and sulfur com pounds. There also are problems with coking of the catalyst and high-temper ature sintering. Despite discouraging results with the tests so far, B&W still believes that the one-step methanation process is a good idea and it is continu ing the search for a catalyst rugged enough for the process environment.
