1. Introduction

Sodium perborate, NaBO₃, exists in the tetrahydrate, trihydrate, monohydrate and anhydrous forms. Of these the tetrahydrate and the monohydrate are the most important commercially.

The tetrahydrate form was first prepared by Tanatar in 1898 and independently by Melikoff and Pissarjewski, by reacting hydrogen peroxide with an aqueous solution of sodium hydroxide and borax, Na₂B₄O₇.

For a long time, it was not known if the perborates were true peroxo salts or simply addition compounds with hydrogen peroxide. The problem was resolved in 1961 when Hansson showed by X-ray analysis of single crystals that they were true peroxo salts ¹ with constitutional formulae:

Sodium perborate tetrahydrate

Sodium perborate monohydrate

2. Uses of Sodium perborates

Both the tetrahydrate and the monohydrate of sodium perborate are used as oxidising and bleaching agents in cleaning, cosmetic and pharmaceutical preparations but their main application is in detergents. Typically a detergent will contain up to 15 wt% of the tetrahydrate and/or up to 10% of the monohydrate. The monohydrate is preferred if rapid solution is required.

3. Production process

The principal sources of boron for the production of sodium perborates are the minerals Kernite, Na₂B₄O₇.₄H₂O, and Tincal, Na₂B₄O₇.₁₀H₂O. Major deposits of both minerals are found in California, where they are mined, purified and converted in the pentahydrate. Commercially workable deposits of tincal are also found in Turkey. In Europe, mineral is obtained from both sources.

The tetrahydrate is produced in a two stage process. In the first stage, the boron-containing minerals are reacted with an aqueous solution of sodium hydroxide to produce a concentrated solution of sodium tetrahydroxyborate, NaB(OH)₄ . Any insoluble components are filtered out, the solution is diluted and the temperature is reduced to below 40°C.
In the second stage, the sodium tetrahydroxyborate is reacted with hydrogen peroxide and cooled to a temperature below 30°C. The sodium perborate tetrahydrate crystallises out of the solution.

The monohydrate is produced by dehydrating the tetrahydrate in either a warm air current or in a fluidised bed drier.

4. Data sources

The data used in the calculations leading to the results reported here were derived from four main sources.

1. Information on the production of sodium perborate was supplied by ten plants operating in Austria, Belgium, France, Germany, Italy, Spain and the United Kingdom (year 1995). Most of the plants supplying data produced both the tetrahydrate and the monohydrate.
2. Information on some chemical intermediates were derived from earlier work carried out for CEFIC and APME.
3. Information on the production of fuels and energy have been derived from the reports of the International Energy Agency. ^2,3,4
4. Data for supporting operations and transport have been obtained from other manufacturers and operators as part of an on-going exercise involved in maintaining a data-base for LCA calculations. No process data other than the fuel data noted above have been derived from the literature.

The reliability of the data tables in this report inevitably depends upon the quality of the information supplied by individual operators. It is possible to carry out a number of elementary checks on quality such as checking mass and energy balances and ensuring that the data do not violate any of the basic physical laws. However, beyond these checks, the data quality is dependent on the quality of the records maintained by individual companies. The detail of all calculations were referred back to individual companies before being incorporated into the final average to ensure that all information was transcribed correctly and that any anomalies were corrected.

¹ In Ullmann's Encyclopedia of Industrial Chemistry, Volume A19, p177ff. VCH Publishers.

² International Energy Agency. Coal Information 1994. ISBN 92-64-14530-3. OECD Paris 1995.

³ International Energy Agency. Oil and gas information 1994. ISBN 92-64-04494-9. OECD, Paris, 1995.

⁴ International Energy Agency. Electricity information 1994. ISBN 92-64-14547-8. OECD, Paris, 1995.