Modeling and Scale up of CO2-Water Pretreatment of Guayule Biomass

A carbon dioxide – water pretreatment process was developed for guayule biomass. The guayule biomass was mixed with water and then loaded to a reactor where it was exposed to a biphasic environment consisting of CO2 rich vapor phase and water rich liquid phase. Then, the biomass was enzymatically hydrolyzed and the sugar content was measured at the end. The effects of temperature, pressure, moisture content, accessible volume and holding time in the pretreatment step were investigated. One hundred and twenty (120) experimental runs were carried out in the temperature range of 145 C to 210 C, pressure was between 3.4 MPa to 34 MPa, the moisture content ratio was between 0.6 to 6, the accessible volume was between 0.2 to 0.1 L and the holding time was between 20 to 50 minutes. A model was fit to the experimental data based on dissolved CO2 in the liquid phase using CO2-H2O phase envelop and a temperature dependant constant. The model fits to one hundred and twenty (120) data points with an average absolute percent deviation(AAD%) of 13. Then, the same process was implemented to a pilot scale vessel with a 1 liter volume. The process was carried out in batch and semi-continuous methods and twenty (20) data points were produced to confirm the model. The model predicted the pilot plant runs with a 15% average absolute percent deviation (AAD%). In the lab scale of 190 C, 26 MPa, moisture ratio of 1.5, accessible volume of 0.22L, biomass load of 15 grams and 35 minutes in holding time resulted in 78% glucose yield and 66% hemicelluloses yield. In the pilot scale of 200 C, 10MPa, moisture ratio of 2, accessible volume of 0.88, biomass load of 60 grams and 35 minutes in holding time resulted in 78% total sugar yield.