Wood in Chemical Engineering Construction

The important role of wood in chemical engineering construction and the need for further research aimed toward its most effective use are discussed. Data are given showing the loss in bending strength of thin cross sections of cypress, Douglas-fir, southern pine, redwood, maple, and white oak exposed to 3 acids and 2 alkalies. Data are also given on redwood cross sections exposed to dilute solutions of eight chemicals that are commonly present in water passed over cooling towers. The results of table 1 show that even at moderate to low concentrations and at temperatures well below the boiling point, the common acids and alkalies show marked differences in their attack on wood. The softwoods showed consistently better resistance to the two mineral acids than did the hardwoods. There was much less difference between the hardwoods and softwoods in resistance to alkalies. The definitely greater effect of 2 percent nitric acid than 2 percent sulfuric is surprising in view of the fact that nitric acid tends to lose its oxidizing power at low concentrations. The superior acid resistance of conifers compared with hardwoods has been attributed to higher lignin and lower hemicellulose content. In view of the nature of these tests, the resistance of hardwood and softwood lignin to dilute acids, and the manner in which lignin is distributed in wood, one is led to suspect that the difference in lignin content is less important than the difference in the amount and nature of hemicellulose. Of the chemicals that may be present in cooling towers, chlorine is shown to be the most harmful. Sodium carbonate at 0.1 percent was also definitely harmful. Sodium chloride, sodium sulfate, and calcium sulfate showed no effect within the probable experimental error. On the other hand, sodium bisulfite ferrous sulfate should be regarded with suspicion; whenever conditions lead to abnormally high concentrations of these chemicals, corrective measures should be taken.

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