Volume 13, Number 5
Sep 1989

Diethyl Zinc Process Licensed

On July 28 the U.S. Department of Commerce granted Akzo Chemicals Inc., a Chicago-based specialty chemical firm, exclusive license to implement the diethyl zinc (DEZ) mass deacidification process, developed by the Library of Congress to stop deterioration of books and documents.

The Library of Congress estimated in 1984 that 97% of its collection was printed on acidic paper and either brittle or in danger of becoming brittle. Further evaluation determined that 16 million books and manuscripts in its collection required treatment. Faced with these figures, Congress voted in that same year to provide $11.5 million for a diethyl zinc deacidification facility.

The DEZ process was invented by John C. Williams and George B. Kelly of the Library of Congress in the 1970s and developed by them through the early 1980s. A pilot plant was built and operated by NASA through an aerospace contractor, and demonstrated that mass deacidification could be done with DEZ, but it was so accident-prone that it was closed down. In 1986, a new contractor was chosen: Texas Alkyls, Akzo' s joint venture with Hercules Incorporated. Texas Alkyls, which has considerable industrial expertise with this type of chemical, has worked in cooperation with the Library of Congress to develop the process further.

Each load of books is treated in a 50-hour sequence of steps in a low pressure ("vacuum") chamber. The books are dried to a certain moisture content, the air is replaced with nitrogen, and gaseous DEZ admitted. The DEZ diffuses between the pages of the closed hooks, neutralizing acids, and reacting with the moisture left in the paper to form zinc oxide, which serves as an alkaline reserve. Aluminum in the paper is converted to aluminum oxide, eliminating it as a potential future acid source. The treated paper has a pH between 7.0 and 7.5, and the alkaline reserve is between 1% and 2% The zinc oxide also inhibits future fungal growth. No visible difference can be detected between treated and untreated books or documents. Because the treatment has a minimal effect on pH, pH-sensitive colors change very little if at all.

Texas Alkyls, located in Deer Park, Texas, has operated a pilot plant for the past 18 months and demonstrated that books can be safely treated for as little as $6 to $10 each. This amount represents a substantial savings over the present $70 per volume cost for microfilming. As part of the license agreement with the federal government, Akzo has committed to make this technology economically available to major libraries, universities and colleges.

According to Akzo, the joint venture intends to build full-scale commercial plants in both the United States and Europe, each capable of treating one million books annually. The Texas Alkyls facility can currently handle 40,000 books per year.