1999 Progress Report: Polymer-Based Aqueous Biphasic Extraction Technology for Reaction Engineering of the Alkaline Paper Pulping ProcessEPA Grant Number: R826732
Title: Polymer-Based Aqueous Biphasic Extraction Technology for Reaction Engineering of the Alkaline Paper Pulping Process
Investigators: Rogers, Robin D. , April, Gary C. , Huddleston, Jonathan G. , Wiest, John M.
Institution: University of Alabama - Tuscaloosa
EPA Project Officer: Richards, April
Project Period: October 1, 1998 through September 30, 2001 (Extended to December 30, 2002)
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $350,139
RFA: Technology for a Sustainable Environment (1998) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
The long-range goal of this project is to reduce waste and lower energy costs in the alkaline paper pulping process by understanding and improving the cellulose/lignin separation. This will be accomplished through a molecular level understanding of the polymer/polymer separations involved in removing lignins from cellulosic fibers. In the simplest case, a basic understanding of the cellulose/lignin system and its relationship to more commonly studied polymer/polymer aqueous biphasic systems will allow process control utilizing temperature or salt concentration. More elaborate biphasic separations of the sulfonated lignins also will be investigated utilizing environmentally benign polymers to promote or enhance phase separation. The intermediate objectives that will lead to the long-range goal may be broken down as follows:
- Determine the phase characteristics and parameters of interaction for polymer/polymer systems including cellulose/lignin, cellulose/polyethylene glycol (PEG), and lignin/PEG as a function of molecular weight, polymer modification, salt concentration, and temperature.
- Determine the relationship between polymer/polymer or PEG/salt aqueous biphasic system (ABS) and cellulose/PEG and cellulose/lignin ABS.
- Determine the transport and distribution of sulfonated lignins between cellulose/PEG ABS.
- Optimize the uptake and capacities of the PEG system for the target solutes.
- Process design.
- Determine the utility of separated lignins as environmentally benign polymers for separation of metal ions in the environment.
Progress Summary:Distribution of Lignins and Cellulosics in Simple Polymer Biphases. In efforts to apply a polymer-based ABS extraction to the paper pulping process, the study of the distribution of various lignin and cellulosic fractions in ABS and the effects of temperature on system composition and solute partitioning have been investigated. The partitioning of three lignin species (Indulin AT, Indulin C, and Reax 85A) has been studied in ABS prepared from stock solutions of 40 percent (w/w) PEG-2000 and increasing concentrations of K2CO3, (NH4)2SO4, and NaOH. The partitioning of these lignins is affected by the free energy of hydration of the salt forming the ABS, the tie line length, and the dissociation of the sulfonic acid and hydroxyl groups of the distributed solutes (see Figure 1).
The partitioning of fibrous cellulose and diethylaminoethyl cellulose has been studied in 40 percent (w/w) PEG-2000/(NH4)2SO4 ABS. The hydrophilic nature of these species is important in terms of their phase preference when designing a polymer-based aqueous biphasic extraction process for use in a paper pulping process. Both cellulosic samples do not dissolve, but rather report to the salt-rich phase of an ABS.
In both chemical pulping and Organosolv pulping, temperatures in excess of 120?C are needed to solubilize the lignin from the cellulose fraction of wood. To study the effects of temperature on the phase diagram and solute partitioning, phthalic acid and NH499TcO4 (as system probes) have been partitioned in 40 percent (w/w) PEG-2000/(NH4)2SO4 ABS at known tie line lengths as a function of temperature. Temperature does not appear to affect the partitioning results beyond the expected increase in phase divergence as temperature is increased (see Figure 2). The PEG-2000 polymer itself appears to be stable to chemical pulping conditions (size exclusion chromatography revealed no profound effect on the retention time and peak shape of PEG-2000).
Pulp Experiments. Three complete time-at-temperature batch cooking experiments (130, 150, and 160?C) have been conducted using a mock pulping solution (1.75 M NaOH, 0.38 M Na2S, 0.19 M Na2CO3). The purpose of these initial runs was to collect baseline data on Kraft-like solutions. The results for wood chips composed of a mixture of southern hardwoods are shown in Figure 3. The data for these runs show characteristic loss of pulp and lignin extraction curves as time-at-temperature increases. Lignin extraction increases with corresponding decreases in pulp yield. Figure 4 illustrates the initial separation of lignin (to the upper PEG-rich phase) from cellulose. Although this work is not yet complete, these results are encouraging as they indicate that successful lignin/cellulose separations are possible using an aqueous biphasic system based on PEG.
Simulation Efforts. We are working on two-dimensional, lattice-based simulations of polymer systems and off-lattice three-dimensional Monte Carlo simulations for a polyethylene glycol-water-salt model system. For both the lattice and off-lattice simulations, we have designed and created the basic simulation algorithms and models, and now we are exploring various options for determining the excess Gibbs free energy.
Future Activities:We propose to screen further wholly aqueous solvent extraction systems for their applicability to this separation problem. The stability of our initial choice of materials has been confirmed, and we have successfully operated these systems at temperatures commensurate with conventional alkaline paper pulping processes. Our immediate goals are concerned with demonstrating and characterizing these separations under realistic conditions using standardized wood samples in a high-temperature pressure vessel.
The experiment apparatus (a semibatch extraction/reaction system) is located in the Department of Chemical Engineering at The University of Alabama. The apparatus consists of a tubular reactor that can be rapidly heated using a three-zone tube furnace. Temperature may be controlled within 1?2?C. Thirty-gram samples of wood chips may be loaded and liquid phase pumped through the reactor using a positive displacement pump. The process stream exits through a 100-psig back pressure valve and may be collected for analysis. Using this semibatch reactor will enable control of the flow rate, liquid residence time, and the effect of recycle on the delignification of wood in comparison to full batch processes. A series of semibatch runs will be made using the screened results from the batch study. We will examine the process variables that determine the effective and efficient separation of cellulose and lignin using PEG/salt ABS. In the longer term, we propose to examine the engineering of the process as a reactive extraction using polymer phases to remove lignins during the pulping process.
We propose to continue characterizing alternative polymer systems in the context of this separation. A range of polymers will be fully characterized in terms of their room temperature phase diagram, the partition of organic molecular model species and lignins, and the behavior of the systems at elevated temperatures. Polymers we intend to completely characterize in this context include PEG, polyethylene imine, a selection of random and block copolymers of polyethylene oxide (PEO)/polypropylene oxide, and some polymers typical of cloud point separations processing including PEO ethers, and the new environmentally friendly Triton SP series produced by Union Carbide. Promising polymer systems also will be applied to batch and semibatch pulping processes.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 50 publications||18 publications in selected types||All 18 journal articles|
||Willauer HD, Huddleston JG, Li M, Rogers RD. Aqueous biphasic systems for the separation of lignins from cellulose in the paper pulping process.. Journal Of Chromatography. 2000;743(1-2):127-135.||