Paper's Tiger
September 1997

Today's paper industry is the principal, perhaps surprising beneficiary of the secret boron hydride fuel research program which dates from the early years of the Cold War. Certain boron-hydrogen combinations, also known as boranes, had been found to possess tigerish energy - up to four times as much, weight for weight, as conventional hydrocarbon fuels such as the high octane used in military aircraft.

Unlike other boron compounds, boranes were difficult and dangerous to make, hazardous to handle or use - and extremely expensive. Accordingly the chemistry, technology, and super-fuel potential of at least four complex boron hydrides were locked away by the Pentagon, and the huge research effort behind them was suspended in the early 1960s. One borane, however, was much less expensive and problematical.

Discovered in 1943 by H.C. Brown, one of boron chemistry's Nobel prizewinners, and H.I. Schlesinger, sodium borohydride (NaBH4) proved not only to have strong possibilities as a missile propellant, but also as a reducing agent. 'Reduction' is a term used for any process which produces chemical change by the addition of electrons - for example, the liberation of a metal from its compounds. The peaceful commercialization of sodium borohydride was taken over in the early 1960s by Ventron Corporation, now integrated into Morton International Inc. Long famous for table salt, Morton is also a major manufacturer of specialty chemicals.

By far the world's leading sodium borohydride producer, Morton makes it at sites in the northwest United States (Elma, Washington) and northeast Netherlands (Delfzijl). The process involves reacting boric acid with methanol to produce tri-methyl borate which is then reacted with sodium hydride at elevated temperatures. This yields sodium borohydride and sodium hydroxide (caustic soda) together with methyl products which can be re-used in the process as methanol, plus some impurities and oils which are removed in a purification process.

Although considerable care and technical skill are required for the potentially explosive methyl borate-sodium hydride reaction, the overall process is straightforward and non-hazardous compared with the distillation of boron hydride fuels. Similarly this borohydride when made is both air- and moisture-stable, and is non-sensitive to shock - user-friendliness personified compared to some of the other boranes. It is mostly produced as Borol Solution, a 12 percent solution, with caustic soda and water, but is also made in solid forms - caplets, granules, and powder.

Commercial quantities of sodium borohydride are also made by Finnish Chemicals (Nokia) in Finland, Eagle-Picher in USA, and Bayer in Germany.

In paper bleaching, borohydride acts as a reducing agent to generate hydrosulphite within the mechanical pulping process. Hydrosulphite decolorizes the wood's lignin, most of which is retained in mechanical pulping (as opposed to chemical pulping in which most of the lignin is removed). Lignin is largely responsible for the brownish color of unbleached pulp. Borol Solution yields twice its own weight in hydrosulphite, and this modifies the color components of the lignin.

Borol Solution is used for most of the North American and European newsprint production and for a large range of other papers. Compared with most alternative bleaching agents, sodium borohydride leads to paper with higher finished strength characteristics and better brightness levels. It gives paper with excellent printing and ink-absorbing qualities, high bulk, high opacity, and high yield - at lower cost than other methods of bleaching. A more expensive process which employs hydrogen peroxide as the main bleaching agent can, in fact, yield up to ten percent extra brightness, and this is used for very high quality, 'whiter than white' papers.

Recycling

Borol Solution can also be employed as a bleaching agent for the pulp made from recycled paper, and an active area of research for Morton International is the additional use of sodium borohydride as a de-inking agent, further to improve the quality and brightness of recycled paper.

In the paper industry's perennial quest for better and whiter paper at lower cost, Morton and sodium borohydride are dedicated partners.

Organic chemicals synthesis

Sodium borohydride is used in the chemicals processing industry to reduce impurities. It can effectively control color, odor, and stability problems in basic, intermediate, and finished organic chemicals. In particular, it deals effectively with carbonyls, peroxides, and metal compounds, the three major impurities which cause quality problems in the production of alcohols, glycols, amines and amides, and ethers.

Morton's Venpure Solution borohydride is specially formulated for process stream purification, for example in the production of plasticizers, surfactants, and detergents. It is also used to reduce impurities in natural oils and fats such as sunflower and linseed.

Pollution control

As an extremely powerful reducing agent, sodium borohydride facilitates the removal of metals from industrial waste streams and effluents. Metal finishing operations, such as the photographic and electronics industries, inevitably produce waste water which requires purifying treatment.

Sodium borohydride enables manufacturers to meet the most stringent effluent limits, and to precipitate metals in their elemental form (rather than metal complexes) for recovery and subsequent industrial re-use. At the same time it reduces sludge volumes by as much as 90 percent compared with alternative treatments such as ferrous sulphate.

Morton's Venmet Solution treats both precious and heavy metal streams, and is particularly effective - and cost-effective - at recovering the copper from printed circuit board wastewater. Gold, silver, and platinum group metals are recovered equally efficiently from electrolytic plating and other industrial effluents - to reduce processing costs while helping to safeguard the environment.

It is strangely appropriate that a boron hydride originally developed for military defense should now be helping to defend the natural world from industrial pollution.