The final objective of this investigation is to model the kinetic behaviour of cellulose during hydrolysis by means of stochastic simulation.
Part I of this study will thus report the experimental determination of kinetic parameters to be used in the simulation. These were established from kinetic experiments on cellobiose hydrolysis and glucose degradation. Furthermore, both cotton morphology and outer layer are analysed and the effects of cotton wax on cellulose depolymerization are studied. Finally, the effects of cotton milling on both cellulose depolymerization and glucose yield are investigated and presented in this first part.
Part II will deal more specifically with the stochastic modelling of these data. This simulation should be realistic enough to allow a representation of the effect of milling on the cellulose structure and its influence on acid hydrolysis kinetics.
Table of Contents
EXPERIMENTAL STUDY I : CELLULOSE PRETREATMENTS
INTRODUCTION TO CELLULOSE
EXPERIMENTAL APPARATUS
COTTON PREATREATMENTS
COTTON CHARACTERIZATION
EXPERIMENTAL RESULTS AND DISCUSSION
Cotton structure and morphology
Effects of cotton extraction on cellulose acid hydrolysis
Rolling up process of cotton wax
Effects of cotton boiling on cellulose depolymerization
Effects of milling on cotton morphology
Effects of milling on cellulose depolymerization
Effects of milling on the rate of glucose formation
CONCLUSION
EXPERIMENTAL STUDY II: KINETIC INVESTIGATION
INTRODUCTION TO CELLULOSE ACID HYDROLYSIS
EXPERIMENTAL RESULTS AND DISCUSSION
Glucose degradation
Cellobiose hydrolysis
Glucose build up during cellobiose hydrolysis
Cellulose sacharification
Effects of milling on cotton morphology
Effects of milling on cellulose depolymerization
Effects of milling on the yield of glucose
CONCLUSION
STOCHASTIC SIMULATION OF THE YIELD OF GLUCOSE
INTRODUCTION TO STOCHASTIC SIMULATION
CELLULOSE ACID HYDROLYSIS PROCESS
STOCHASTIC SIMULATION OF A POLYMER DEPOLYMERIZATION PROCESS
STOCHASTIC SIMULATION OF CELLULSOE ACID HYDROLYSIS
RESULTS AND DISCUSSION
CONCLUSION
Research Objectives and Core Themes
The primary objective of this thesis is to model the kinetic behavior of cellulose during acid hydrolysis using a stochastic simulation approach. By integrating experimental kinetic data—specifically from cellobiose hydrolysis and glucose degradation—with observations on cotton fiber morphology and the role of surface waxes, the study aims to clarify how mechanical and chemical pretreatments affect the accessibility of glycosidic bonds and, consequently, the rate of depolymerization and glucose production.
- Modeling cellulose depolymerization through Monte Carlo simulation and Markov chains.
- The impact of mechanical milling on cellulose crystallinity and structural accessibility.
- The influence of surface wax "rolling up" on cotton wettability and acid penetration.
- Kinetic analysis of cellobiose hydrolysis and the subsequent glucose degradation.
- Comparison of simulated outcomes against experimental yield data at various temperatures.
Excerpt from the Book
Effects of cotton extraction on cellulose acid hydrolysis
It is well known that, during cotton hydrolysis, the accessibility of the β (1,4) glycosidic bonds by the reactive ions depends on the wettability of cellulose. The hydrophilic surface character of cotton is confirmed by many authors but, as they are covered with wax materials, cotton fibers behave like a “low-energy surface”. Therefore, water forms droplets on the surface of fibers and the rate of cotton wetting is considerable lowered. In order to investigate the effects of cotton wax on cellulose depolymerization, the interface of the extracted cotton sample was first analyzed by ESCA technique and compared to the original cotton sample in Tables 1 and 2. The increase of the C/O ratio from 0.08 to 0.47 indicates that some of the cotton wax has been removed from the cotton outer layer. However, this value remains small compared to the theoretical value of pure cellulose (C/O=0.83). The relative small C2 and C3 values of the extracted cotton sample, compared to the values of pure cellulose (C2 = 83% and C3 = 17%) also indicate a poor extraction of the cotton wax. Moreover, in agreement with the ESCA analysis, Figure 3 shows clearly that the catalytic ions should first diffuse through the wax layer before reacting with the glycosidic bonds of cellulose located in the inner walls of cotton. Under these circumstances, the variation in time and space of the acid ions concentration in the cotton wax layer could be described by Fick’s second law of molecular diffusion.
Summary of Chapters
EXPERIMENTAL STUDY I : CELLULOSE PRETREATMENTS: This chapter analyzes how initial physical and chemical states of cotton, particularly the presence of surface wax and the effect of milling, influence the fiber's accessibility and subsequent acid hydrolysis rates.
EXPERIMENTAL STUDY II: KINETIC INVESTIGATION: This part focuses on the experimental determination of fundamental kinetic constants for cellobiose hydrolysis and glucose degradation, providing the necessary data for mathematical simulation.
STOCHASTIC SIMULATION OF THE YIELD OF GLUCOSE: This chapter presents a Monte Carlo-based approach using Markov chains to simulate cellulose depolymerization, successfully predicting experimental glucose yields by incorporating morphological factors.
Keywords
Cellulose, Acid Hydrolysis, Stochastic Simulation, Monte Carlo Method, Cotton Fiber, Depolymerization, Glucose, Milling, Crystallinity, Surface Wax, Kinetics, Markov Chain, Chemical Engineering, Glycosidic Bonds, Wettability
Frequently Asked Questions
What is the core focus of this research?
The research focuses on understanding and modeling the cellulose depolymerization process during acid hydrolysis, specifically investigating how fiber pretreatment and morphology affect reaction rates.
What are the central themes discussed?
The work covers the kinetics of cellobiose hydrolysis, the structural impact of mechanical milling, the inhibitory role of cotton surface waxes, and the implementation of stochastic modeling to predict glucose yields.
What is the primary goal of the simulation?
The primary goal is to create a realistic computer model capable of predicting experimental glucose concentrations during cellulose hydrolysis by accounting for both kinetic constants and the physical accessibility of cellulose chains.
Which scientific methodology is utilized?
The study employs an experimental approach involving acid hydrolysis in an autoclave, complemented by analytical techniques like ESCA, SEM, TEM, IR spectroscopy, and HPLC. This is followed by a stochastic simulation based on Monte Carlo techniques and Markov chain formulations.
What is covered in the main body of the work?
The main body details the experimental apparatus and methods, explores the influence of wax extraction and milling on fiber morphology, and provides the kinetic foundation for the subsequent stochastic simulations.
What defines the stochastic approach in this thesis?
The stochastic approach treats reaction rates as "probabilities per unit time" rather than deterministic rates, allowing for a simulation of bond rupture that reflects the inherent randomness and structural complexity of the cellulose fiber.
How does wax melting affect the hydrolysis process?
The study concludes that wax melting above certain temperatures leads to a "rolling up" effect, which significantly improves the wettability of the fiber and allows better access for catalytic ions to the inner cellulose layers.
What effect does mechanical milling have on cellulose?
Milling reduces the particle size and decreases the crystallinity of the cotton, which increases the accessibility of the glycosidic bonds, particularly those in the amorphous and semi-amorphous regions, thereby accelerating initial hydrolysis rates.
- Citation du texte
- Zin Eddine Dadach (Auteur), 1994, Mechanism of Depolymerization of Cellulose in Low Sulfuric Acid Medium. Kinetic Investigation and Stochastic Simulation, Munich, GRIN Verlag, https://www.grin.com/document/387594
