Arkenol Process
In 1989 an American company related to ARK Energy called Arkenol began researching several technologies with the aim of developing thermal hosts sitting in conjunction with ARK Energy power plant projects that were were being bid into local utilities. Arkenol determined that the concentrated acid hydrolysis process could be made economically viable through the development and use of new technology. During these efforts, they developed the two-stage concentrated acid hydrolysis technology. A simplified schematic flow diagram of the Arkenol process is shown in Figure 7.1. In the first stage of the Arkenol process, decrystallization is carried out by adding 70-77% concentrated sulfuric acid to biomass that has been dried to 10% moisture. Acid is added at a ratio of 1.25:1 (acid:cellulose + hemicellulose) and temperature is controlled at less than 50°C. In the second stage, water is added to dilute the acid to 20-30% and heating at 100°C for an hour resulting in the release of sugars. The gel from this reactor is pressed to remove an acid/sugar product stream. Arkenol owns several key patents related to acid-sugar separation and recovery and the development of this process. The sugar separation and recovery is based on a chromatographic method called pseudo moving bed column. This technology utilizes a unique patented resin as the chromatography column material to separate the acid and sugars. Using the ion exchange separation technology first introduced by TVA and researchers at the University of Southern Mississippi [7], Arkenol has been able to take acid/sugar feed streams containing 12-15% sugar concentrations and produce a sugar stream with 98% purity. The recovered sulfuric acid is concentrated to the 90% level required for the decrystallization of cellulose and was reused. The small quantity of acid remaining in the sugar is neutralized with lime to form hydrated gypsum, an insoluble precipitate that can be used in agriculture as a soil conditioner. Separated sugar contained
a mixture of C5 and C6 sugars, which could be fermented after separation of gypsum. The fermentation could convert both the xylose and the glucose to ethanol at theoretical yields of 85% and 92%, respectively. A triple effect evaporator was used to concentrate the acid to 90% concentration [8-10]. Arkenol claims that sugar recovery in the acid/sugar separation column is at least 98%, and acid lost in the sugar stream is not more than 3% [9, 10].