Saccharification of concentrated biomass slurries in a resonating acoustic mixer. Samin Rezania

ISBN: 9781109299670

Published:

NOOKstudy eTextbook

266 pages


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Saccharification of concentrated biomass slurries in a resonating acoustic mixer.  by  Samin Rezania

Saccharification of concentrated biomass slurries in a resonating acoustic mixer. by Samin Rezania
| NOOKstudy eTextbook | PDF, EPUB, FB2, DjVu, audiobook, mp3, RTF | 266 pages | ISBN: 9781109299670 | 7.61 Mb

Biomass is converted to ethanol as the result of several processing steps of which enzymatic hydrolysis (saccharification) is a key rate and cost limiting step. It is desirable to begin with a high solids concentration in order to maximize theMoreBiomass is converted to ethanol as the result of several processing steps of which enzymatic hydrolysis (saccharification) is a key rate and cost limiting step. It is desirable to begin with a high solids concentration in order to maximize the product concentration in the sugar stream, minimize water and energy use, and minimize reactor volume.

However, when processing with concentrated slurries, the high viscosity leads to lower glucose release rates and yields. It is hypothesized that this is due to mass transfer limitations, specifically (1) inefficient contact between the enzyme and substrate, and (2) inefficient movement of product away from the reaction sites.

Both of these effects can hinder glucose release from the cellulose.-In the first part of this study, ultrasonic irradiation was employed to reduce the particle size of untreated sawdust slurries to less than 1 mum in an attempt to increase the enzymatic saccharification rate by increasing surface area for contact between the enzyme and substrate, and to lower the slurry viscosity.

Results showed that ultrasonic irradiation was effective in reducing the particle size of pretreated corn stover and untreated sawdust. Surprisingly, the amount and rates of sugar released in this study with ∼1 mum particles was comparable to, but no better than that seen for particle sizes in the range of 33 ≤ x ≤ 75 mum. Also surprisingly, the viscosity increased as the average particle sizes in the slurries decreased, which is opposite to the trend seen in a previous study at higher size ranges.-In the second part, a study was conducted to determine if overcoming mass transfer limitations in pretreated corn stover slurries can increase saccharification rates at high solids concentrations.

In order to achieve good dispersion of the liquid enzyme throughout high viscosity biomass slurries, a resonating acoustic mixer was employed for running saccharification tests with initial solids concentrations of 15 to 30%. Results showed that the mixer achieved higher glucose release rates and yields than in shake flasks, especially at higher viscosities.-In the last part, dispersion coefficients in the mixing vessel were determined as a function of viscosity in order to quantify the mass transfer improvements. Since conventional means of measuring dispersion could not be performed with these types of slurries, a computational fluid dynamics model was developed that simulated motion of the slunies in the resonating acoustic mixer.

The model was very well validated by comparing experimentally determined mixing times using an electrolytic tracer with mixing times from the simulations. Results showed that axial dispersion coefficients were higher than radial ones, with bigger differences at lower viscosities. Despite the very high viscosities studied here, dispersion values were still achieved on the order of values in other systems designed for much thinner fluids, which indicates the system was a valid choice for studying mass transfer limitations.



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