RESEARCH Acetone
Dried Sulfite Liquor Solids
H 2 SO.
DIACETONE SUGARS
+
Insoluble Ugnosulfonates
Diacetone Xylose
H-OH
Mixture of: *"" Xylose Mannose
HO
Glucose Galactose
H
OH
D—GALACTOSE
Sulphite Pulp Manufacturers' Research League's process for spent sulfite liquor sugars isolates a n d separates pentoses
and hexoses. But commercialization of the technique hinges on a market for the sugars and accompanying lignosulfonates
N e e d Some Sugar? Spent sulfite liquor's sugars can be freed, but block to commercialization is what to d o with them _1 HE PROBLEM of what to clo with spent sulfite liquor looks a little less ponderous now. Reason for the h a p pier outlook is the Sulphite Pulp Manu4 0
C&EN
JULY
14, 1 9 5 8
facturers' Research League's n e w method of isolating and separating the liquor's sugars, chief contributors to the biochemical oxygen demand of pulp
mill effluent. But commercialization of t h e technique is still far off and hinges on developing a market for the sugars as well as a market for t h e accompany-
ing lignosulfonates from the solids. Consisting primarily of hexoses and pentoses, the sugars make up only about 2 0 % of sulfite liquor's solids but can account for as much as two thirds of the BOD. Main six carbon sugars are D-mannose, D-galactose, and Dglucose; pentoses a r e D-xylose and Larabinose. These carbohydrates are formed by the hydrolytic reactions used in sulfite wood pulping, which cause wood's polysaccharides to break down to various degrees. How much of each sugar occurs in the liquor depends on the kind of wood used in pulping. A representative comparison of liquors from two main types of wood looks like this: Softwood Hardwood Hexoses 14.0% 4.0% Mannose 8.0 2.0 Galactose 4.0 0.5 Glucose 2.0 1.5 Pentoses 6.0 16.0 Xylose 5.0 15.5 Arabinose 1.0 0.5 Today, sulfite liquor sugars are used to produce ethanol and torula yeast. Other products that can be m a d e include lactic, fumaric, butyric, pro pionic and acetic acids, acetone, butanol, and methane. None of these, though, is now feasible on a large scale. By contrast, the league's new technique gets at the pure sugars themselves, doesn't use them t o get at other sub stances except after isolation of the sugars. • Diacetone Derivatives. The league's process, worked out in its labo ratory at the Institute of Paper Chem istry's campus in Appleton, Wis., is hased on the reaction of sugars with solvents and an acid catalyst. Accord ing to Averill J. Wiley, league tech nical director, the sugars in dried sul fite liquor are reacted with acetone and sulfuric acid to give di-O-isopropylidene derivatives—these are the diacetone sugars. These compounds are soluble in ace tone while t h e non-sugar fractions, mostly lignosulfonates, are not. After filtering off insolubles and stripping the acetone, the various sugars are sepa rated. In the first step, the solvent free residue, when taken up in water, yields crystalline diacetone mannose (di-Oisopropylidene-D-mannose) which is only slightly soluble in an aqueous solu tion. Acid hydrolysis of diacetone mannose gives the free sugar, D-man nose. Steam distilling the residue after mannose is filtered off separates the di acetone pentoses, the free sugars of
which are liberated by hydrolysis with ion exchange resin. With mannose and t h e pentoses gone, the left-over syrup contains diacetone galactose and glu cose with only small amounts of the other sugars. One of the remaining hexose com pounds is extracted with chloroform— a n alternative technique for separating pentoses, too—and the extract dried and hydrolyzed to get D-galactose. Hydrolyzing the C H C 1 8 extracted residue gives a mixture of all the sugars except arabinose. "Glucose separation hasn't been tried since supplies are more than plentiful. Catalytic reduction of the sugars gives their corresponding polyols. Or, reducing the diacetone mannose fol lowed by hydrolysis gives the same re sult. • Mannose Is Key. T h e mannose portion of the sugars has the best mar keting potential. And, Wiley stresses, any possibility of the method's commer cialization hinges on developing a mar ket for the sugar. But to make the price more attractive, t h e lignosulfo nates would have to be sold, too. Only b y recovering all possible value in the liquor's fractions can the process be eco nomical, he notes. The high cost of handling and processing t h e total waste can't be met with a single, specialty product. Meanwhile, though, league re searchers are evaluating mannose's properties in anticipation of future mar kets. Diacetone mannose differs from t h e other diacetone sugars in that it has a free reducing group. This structure enables it to undergo reactions similar t o those of free sugars—e.g., reduction t o the diol, oxidation to the aldonic acid o r its lactone, glycoside formation, and alkaline degradation. The compound's two, free hydroxyls (at C 1 and C 4 ) in dicate a possible use in making poly esters. And knocking off the acetone groups makes additional hydroxyls available for cross-linking. Another possible use is sodium mannonate as a sequestering agent for calcium in glass washing mixes. Sodium gluconate is used now, but league researchers think the mannose salt could be more effective. Xylose's use could be a s a sweeten ing agent in diabetic foods since it isn't metabolized by humans, but there is evidence of undesirable side effects. Industrially, pentoses can be another source of furfural, and hexoses for levulinic acid, both via acid treatment of the sugars. •
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JULY
14,
1958
C SEN
41
