This investigation was undertaken to find the best method of preparing oxalic acid from sawdust, either by one of the methods described in the
literature or a modification of it. The first work consisted in following the procedure recommended by a previous experimenter in order to become
acquainted with the methods which are now used and to discover their weak points. The procedures used commercially, and the experimental work of
Thorn, described in "Utilization of Wood Waste" by E. Hubbard form the basis of the work. No recent literature could be found on the subject, the work
of Thorn having been done nearly forty years before. Various commercial processes use slightly different methods; one uses KOH alone in the fusion and
precipitates MgC2O4 by adding MgCl2 to the K2C2O4 solution; in another a preliminary fusion is carried on in a vacuum at 180°, followed by the
regular fusion yielding a nearly colorless product. A process similar to that outlined by Thorn is also used.
The heating of sawdust with KOH results in the production of oxalic acid. Since NaOH is much cheaper, it is desirable to substitute it for KOH as far
as possible. Thorn found that a mixture containing 40% KOH and 60% NaOH by weight gave almost as good a yield, when heated in thin layers, as pure
KOH. The yield dropped off rapidly with a decreasing KOH percentage below 40%. He also found that the most satisfactory melt was made by using one
part of sawdust to two parts of lye, striking a balance between large percentage yield from lye with more sawdust, and more organic impurities which
are hard to remove if more sawdust is used. Soft wood gives a better yield than hardwood, and pure sawdust gives a better one than lignose left after
treating cellulose with HCl. |
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