Processes for converting wood into molasses have been known for more than a century.
To change cellulose into glucose, high temperatures and pressures are required when dilute acids are used. With concentrated acids the process can be carried out at room temperature, but the percentage of unrecovered acid makes the cost very high. Hemicellulose is more easily converted into sugars. The hemicellulose from hardwood (e.g., maple and beech) yields a high percentage of 5-carbon sugars, while hemicellulose from softwood (e.g., pine and fir) yields a fifty-fifty mixture of 5-carbon sugars and 6-carbon sugars. Ruminants can assimilate both types of sugars, whereas the 5-carbon sugars are less available to monogastric animals.
The Madison wood-sugar process, which consists in hydrolysing cellulose into simple sugars, is one of the more economical of the many methods developed for this purpose. It involves continuous pumping of a spray of hot 0.5-0.6% sulphuric acid on chips or sawdust heated in a digester to 150 C at the start and gradually increased to 185 C. After removal from the digester the sugar solution is cooled to 138 C and neutralized with lime. The resulting sugar solution contains 5-6% simple sugars and is concentrated to a syrup for feeding. One ton of wood will yield about 0.5 ton of sugars.
A newer related procedure is the solubilization of hemicellulose from wood by steam during the manufacture of hardboard. This process is economical as it does not require chemicals. The hemicellulose sugars are concentrated or spray-dried and sold as animal feed under the name wood molasses.
