Optimization of the Liquefaction Process in Bioethanol Production & Development of Method for Quantification of Nonsolubilized Starch in Mash

Sammanfattning: Ethanol production at Lantmännen Agroetanol AB in Norrköping began in December 2000. The objective of this master's thesis is to find and optimize factors affecting the yield of the liquefaction, a part of the upstream process. To measure successfulness of liquefaction it is desired that amount of non-solubilized starch is quantified, and hence a method for determination of non-solubilized starch in mash has to be developed. Starch is a carbon reserve in plants. Starch granules are polymers of amylose and amylopectin which are polysaccharides of glucose. When a starch/water solution is heated the starch granules start to absorb water and swell, a process termed gelatinization. The swelling makes the granules susceptible to hydrolysis by enzymes such as alpha-amylase, this is called liquefaction. Eventually the granular structure is broken and the slurry contains solubilized starch which can be saccharified to glucose by glucoamylase. In the bioethanol production process, the milled grain is mixed with water and enzymes. The slurry is heated, gelatinization and liquefaction occurs. Saccharification occurs simultaneously to fermentation. Ethanol is purified from the fermented mash during downstream processing. Starch in the form of starch granules cannot be quantified. The adopted principle for determination of non-solubilized starch in liquefied mash is to wash away the solubilized starch, then quantitatively hydrolyze non-solubilized starch to glucose and quantify glucose. To find and optimize factors significant for yield of liquefaction multiple factor experiments were conducted where eight factors were studied. pH, temperature in mixtank and temperature in liquefaction tank 1 were the most significant factors. The temperature in liquefaction tank 1 should be kept as is is at 74°C. A small rise in pH should shorten the mean length of dextrins which is preferable. An increase of pH from 5.2 to 5.4 is therefore proposed. The temperature in mixtank should also be increased by a few degrees. The yield of the process should be carefully evaluated during the modifications.