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Extramural Research

Final Report: Polymer-Based Aqueous Biphasic Extraction Technology for Reaction Engineering of the Alkaline Paper Pulping Process

EPA 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 Amount: $350,139
RFA: Technology for a Sustainable Environment (1998)
Research Category: Pollution Prevention/Sustainable Development

Description:

Objective:

The objectives of this project were to: (1) utilize wholly aqueous systems, such as polymer-based aqueous biphasic systems (ABS), as an environmentally benign extraction media for the separation of reaction products during the pulping process; and (2) reduce chemical and energy consumption, eliminate emissions, and increase the efficiency of the pulping process.

The Kraft paper pulping process is a chemical method that produces 70 percent of the world's pulp. Though these processes are effective in the removal of lignin from the cellulose fraction of wood, they have tremendous environmental disadvantages. These processes are only 50 percent efficient in delignification of the pulp, requiring the remaining pulp to be bleached. The chemical and energy consumption of these processes is large, and they emit reduced forms of sulfur and aromatic compounds into the environment.

Summary/Accomplishments (Outputs/Outcomes):

The applicability of ABSs to the delignification and simultaneous extraction of lignocellulosic materials has been demonstrated. This work has resulted in the production of 6 refereed publications, 2 Ph.D. Theses, 40 presentations, and 2 invention disclosures that acknowledge support from this project.

We investigated the effectiveness of polymer-based ABS on the delignification of pine and mixed hardwood in conjunction with alkaline pulping solutions. Figure 1 shows the total yield of pulp recovered after samples of mixed hardwood were subjected to different pulping conditions expressed as a function of the Kappa number. The Kappa number is a measurement of lignin content remaining in the pulp after the pulping procedure. The industrial standard is to achieve the highest pulp yield and lowest Kappa number possible without compromising the quality of the cellulose fibers. In Figure 1, samples of hardwood were pulped under different conditions of time and temperature. The results were combined in the plots shown. Pulping solutions either resembled pure Kraft (i.e., no polymer was present), or contained polymer and alkaline pulping solution or an alkaline pulping solution from which the sulfide present in Kraft solutions was omitted.

Figure 1. Pulping of Mixed Southern Hardwood in the Presence of PEG 2000 With and Without Sulfide Compared to Standard Kraft Conditions

As shown in Figure 1, the yield of pulp is considerably improved compared to conditions that utilize standard Kraft pulping solutions. Comparable, if not better reduction in Kappa number, also is achieved by the inclusion of polymer. These conditions rival what can be achieved by the inclusion of both sulfide and polymer. Because sulfide is included to improve the dissolution of lignin during reaction, it may be that the PEG is achieving a similar effect. Similar results are achieved during the alkaline pulping of softwood as seen in Figure 2. Here again, greater recovery of pulp is achieved at comparable or better Kappa numbers (lignin reduction) when alkaline pulping solutions are compared with and without polymer (PEG 2000). Polymer solutions with and without sulfide included in the Kraft solution behave rather similarly, although it appears that sulfide containing solutions can go to lower Kappa numbers. Also shown in Figure 2 is data for the pulping of softwood in the presence of PEG alone. This is ineffective and demonstrates that PEG does not likely take any direct part in the reaction. Figure 2 also shows the distribution of literature data based on 'Organosolv' processes, which illustrate that the PEG-based reaction is comparable to the best 'Organosolv' practice. For both the hardwood and softwood cases, it was possible to demonstrate a considerable reduction in the consumption of alkali during the polymer enhanced Kraft pulping processes. Figure 3 is used to illustrate the softwood polymer enhanced pulping solution.

Figure 2. Alkaline Pulping of Softwood in the Presence of PEG 2000 and in Solutions With and Without Sulfide

Figure 3. Residual Alkali Fraction Following Alkaline Pulping

Analysis of the reaction kinetics of alkaline pulping, in which the presence of polymers was compared to the normal polymer free Kraft reaction conditions, revealed that the major effect of the addition of polymers occurred during the initial phase of the reaction. This was a somewhat unexpected result. It generally is accepted that the initial phase of pulping reactions is controlled by diffusion limitations, and that later stages are controlled by reaction kinetics. Our analysis has shown that for both hardwood and softwood, there was little or no effect on reaction kinetics, and that the greatest improvement in performance occurred during the initial diffusion limited stages. Analysis of wood samples by scanning electron microscopy (SEM) showed that the apparent cause of the decrease in diffusional limitations during pulping might be because of the effect of the inclusion of the phase separating polymers causing increased swelling of the wood. These results are shown in Figure 4.

Figure 4. SEM of Wood Samples Following Alkaline Pulping. Left SEM following Kraft pulping without polymer addition. Right SEM following Kraft pulping in the presence of PEG 2000, but without the inclusion of sulfide.

Examination of Figure 4 appears to show that wood samples following alkaline pulping in the presence of polymer have a more swollen fibrous structure than samples that omitted polymer during pulping. Analysis of molecular weight fractions of lignin by Size Exclusion Chromatography derived from the different processes both with and without polymer appeared to show little difference. This seems consistent with the idea that the polymer affects diffusional, rather than chemical, aspects of the pulping process.

Next, we turned our attention to the use of alternative pulping chemistry to alkaline Kraft on which to base a polymeric delignification process. In this context, we examined the use of alkaline earth catalysts, initially concentrating on lithium and magnesium sulfates in the pulping of mixed southern hardwoods. Our results with these salts showed an unexpected increase in reaction time and temperature, which increased the Kappa number. This was because of the lignin condensation on the fibers as the pH fell during the course of the reaction (see Figure 5).

Figure 5. SEM of Residual Pulp Fiber Following MgSO4-PEG ABS Pulping 180°C, 90 Minutes.

When magnesium sulfate is used as catalyst for the process, pH cannot be controlled. However, reactions may be run at pH > 12 using lithium sulfate as a catalyst, which will control the problem of lignin condensation on the fibers. Figure 6 shows the delignification selectivity of several different systems. The standard Kraft system is shown (inherently run at pH 14) compared to a magnesium sulfate/PEG pulping system and a lithium sulfate/PEG pulping system. The pH of the magnesium sulfate system is uncontrolled, resulting in lignin condensation as the reaction proceeds, and a consequently higher Kappa number. The acidic conditions also lead to more hydrolysis of the pulp. On the other hand, in the lithium sulfate system, higher pulp yields and lower Kappa numbers are attained from a comparable Kraft process.

This investigation of alternative catalysts to the alkaline Kraft process in the context of reactive extraction using aqueous polymer solutions is continuing. We hope to pursue this work both in the context of improved fiber production and as a method for the production of chemical feedstocks. We are pursuing further funding for the continuation of this work.

Figure 6. Comparison of Delignification Selectivity for Different Catalyst Systems.


Journal Articles on this Report : 17 Displayed | Download in RIS Format

Other project views: All 50 publications 18 publications in selected types All 18 journal articles

Type Citation Project Document Sources
Journal Article Cicero JA, Dorgan JR. Physical properties and fiber morphology of poly(lactic acid) obtained from continuous two-step melt spinning. Journal of Polymers and the Environment 2001;9(1):1-10.
abstract available   full text available
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  • Abstract: Springer-Abstract
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  • Journal Article Cicero JA, Dorgan JR, Garrett J, Runt J, Lin JS. Effects of molecular architecture on two-step, melt-spun poly(lactic acid) fibers. Journal of Applied Polymer Science 2002;86(11):2839-2846.
    abstract available  
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  • Abstract: Wiley-Abstract
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  • Journal Article Cicero JA, Dorgan JR, Janzen J, Garrett J, Runt J, Lin JS. Supramolecular morphology of two-step, melt-spun poly(lactic acid) fibers. Journal of Applied Polymer Science 2002;86(11):2828-2838.
    abstract available  
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  • Abstract: Wiley Online - Abstract
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  • Journal Article Cicero JA, Dorgan JR, Dec SF, Knauss DM. Phosphite stabilization effects on two-step melt-spun fibers of polylactide. Polymer Degradation and Stability 2002;78(1):95-105.
    abstract available   full text available
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  • Abstract: ScienceDIrect-Abstract
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  • Journal Article Dorgan JR, Williams JS, Lewis DN. Melt rheology of poly(lactic acid): entanglement and chain architecture effects. Journal of Rheology 1999;43(5):1141-1155.
    abstract available   full text available
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  • Abstract: AIP-Abstract
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  • Journal Article Dorgan JR, Lehermeier H, Mang M. Thermal and rheological properties of commercial-grade poly(lactic acid)s. Journal of Polymers and the Environment 2000;8(1):1-9.
    abstract available   full text available
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  • Journal Article Dorgan JR, Lehermeier HJ, Palade L-I, Cicero J. Polylactides: properties and prospects of an environmentally benign plastic from renewable resources. Macromolecular Symposia 2001;175(1):55-66.
    abstract available  
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  • Abstract: Wiley-Abstract
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  • Journal Article Dorgan JR, Janzen J, Knauss DM, Hait SB, Limoges BR, Hutchinson MH. Fundamental solution and single-chain properties of polylactides. Journal of Polymer Science Part B–Polymer Physics 2005;43(21):3100-3111.
    abstract available  
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  • Abstract: Wiley-Abstract
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  • Journal Article Guo Z, Li M, Willauer HD, Huddleston JG, April GC, Rogers RD. Evaluation of polymer-based aqueous biphasic systems as improvement for the hardwood alkaline pulping process. Industrial & Engineering Chemistry Research 2002;41(10):2535-2542.
    abstract available  
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  • Abstract: ACS - Abstract
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  • Journal Article Guo Z, Huddleston JG, Rogers RD, April GC. Reaction parameter effects on metal-salt-catalyzed aqueous biphasic pulping systems. Industrial & Engineering Chemistry Research 2003;42(2):248-253.
    abstract available  
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  • Journal Article Guo Z, April GC, Li M, Willauer HD, Huddleston JG, Rogers RD. PEG-based aqueous biphasic systems as improvement for Kraft hardwood pulping process. Chemical Engineering Communications. 2003;190(9):1155-1169.
    abstract available  
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  • Abstract: Taylor&Francis-Abstract
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  • Journal Article Lehermeier HJ, Dorgan JR, Way JD. Gas permeation properties of poly(lactic acid). Journal of Membrane Science 2001;190(2):243-251.
    abstract available   full text available
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  • Full-text: ScienceDirect-Full Text HTML
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  • Abstract: ScienceDIrect-Abstract
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  • Other: ScienceDirect-Full Text PDF
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  • Journal Article Lehermeier HJ, Dorgan JR. Melt rheology of poly(lactic acid): consequences of blending chain architectures. Polymer Engineering & Science 2001;41(12):2172-2184.
    abstract available  
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  • Abstract: WIley-Abstract
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  • Journal Article Li M, Willauer HD, Huddleston JG, Rogers RD. Temperature effects on polymer-based aqueous biphasic extraction technology in the paper pulping process. Separation Science and Technology 2001;36(5-6):835-847.
    abstract available  
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  • Abstract: Taylor&Francis-Abstract
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  • Journal Article Mierzwa M, Floudas G, Dorgan J, Knauss D, Wegner J. Local and global dynamics of polylactides: a dielectric spectroscopy study. Journal of Non-Crystalline Solids 2002;307-310:296-303.
    abstract available   full text available
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  • Journal Article Palade L-I, Lehermeier HJ, Dorgan JR. Melt rheology of high L-content poly(lactic acid). Macromolecules 2001;34(5):1384-1390.
    abstract available   full text available
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  • Journal Article Willauer HD, Huddleston JG, Li M, Rogers RD. Investigation of aqueous biphasic systems for the separation of lignins from cellulose in the paper pulping process. Journal of Chromatography B–Biomedical Sciences and Applications 2000;743(1-2):127-135.
    abstract available   full text available
    R826732 (Final)
  • Abstract from PubMed
  • Full-text: ScienceDirect-Full Text HTML
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  • Abstract: ScienceDIrect-Abstract
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  • Other: ScienceDIrect-Full Text PDF
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  • Supplemental Keywords:

    polymer-based aqueous biphasic systems, lignin, cellulose, Kraft pulping, Kappa number, pulp yield, residual alkali, cook, standard pulping solution, engineering, bio-renewables, RFA, Scientific Discipline, Waste, Sustainable Industry/Business, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Incineration/Combustion, Environmental Engineering, reaction engineering, hydrolysis, cleaner production, waste minimization, environmentally conscious manufacturing, aqueous biphasic extraction, reduced sulfur from incineration, biphasic extraction technology, alkylation reaction, polymer-based aqueous biphasic extraction technology, chemical reaction systems, Alkaline paper pulping process, innovative technology, incineration, pollution prevention, Volatile Organic Compounds (VOCs), green chemistry

    Relevant Websites:

    Robin D. Rogers Exit
    Center for Green Manufacturing Exit

    Progress and Final Reports:
    Original Abstract
    1999 Progress Report
    2000 Progress Report
    2001 Progress Report

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    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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