Submitted to: Rice Chemistry and Technology
Publication Type: Book / Chapter
Publication Acceptance Date: September 3, 2003
Publication Date: January 20, 2004
Citation: Marshall, W.E. 2004. Utilization of rice hull and rice straw as adsorbents. Rice Chemistry and Technology. p. 611-630 Interpretive Summary: The utilization of the rice co-products, hull and straw, is an area of great importance to the rice industry. The large quantity of these co-products produced each year must be developed into value-added products, that would allow the rice industry to grow at an accelerated rate. This book chapter describes recent research on the utilization of rice hull and straw as adsorbents, which are value-added products. The production of adsorbents, such as activated carbons and ion exchange resins, is an area of hull and straw chemistry and technology that has undergone perhaps the greatest change over the last decade. This research area engenders technology and resultant adsorbent products which may be useful in a variety of environmental and industrial applications.
Technical Abstract: Total rice production in the United States for crop year 2002 was 21.1 billion lbs of rough rice. Therefore, approximately 4 billion lbs of rice hulls and 26 billion lbs of rice straw were potentially produced. A major issue then faces the rice processing industry with what to do with this prodigious quantity of co-products. A large quantity of hull is burned by the rice miller to produce steam for processing, particularly parboiling, or for production of electricity. Hull burning results in rice hull ash, a by-product that consists of varying amounts of silica and carbon and minor amounts of alkali oxides and alkali earth oxides, depending on the amount of air used to burn the hulls. However, the net result is now both unburned rice hull and rice hull ash for either disposal or utilization. The same picture emerges for rice straw. Since rice straw is a field residue found on individual rice farms, rather than a processing residue collected at a single location, as is rice hulls, its collection and transportation to a central incineration facility is more expensive. Most rice straw is burned in the field. There is a need to utilize rice hull, hull ash and straw, especially for the production of value-added products. With a bit of ingenuity on the part of scientists and technologists, a number of different uses have been developed for these co-products. Since the objective of this book chapter is to describe value-added products of rice hull and straw, preference will be given to their use as adsorbent material in the following forms: char, activated carbon, ash, and hull or straw, non-modified or modified by chemical treatment.