Source: UNIVERSITY OF MAINE submitted to NRP
TUNABLE, BIORENEWABLE THERMOPLASTICS FROM 5-HYDROXYMETHYLFURFURAL AND LIGNIN
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
AFRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
1015144
Grant No.
2018-67010-27905
Cumulative Award Amt.
$500,000.00
Proposal No.
2017-06006
Multistate No.
(N/A)
Project Start Date
Apr 1, 2018
Project End Date
Mar 31, 2022
Grant Year
2018
Program Code
[A6162]- Co-products from Biomass Feedstocks
Recipient Organization
UNIVERSITY OF MAINE
(N/A)
ORONO,ME 04469
Performing Department
Chemical & Biological Engineer
Non Technical Summary
In this project, our team will convert forest resources to high-value renewable, biodegradable plastics.Modern petroleum-derived polymer plastics have found extensive use as thermoplastic engineering materials, such as high-strength plastics used in automotive applications, advanced paper coatings, and computer parts. However, thesynthesis and disposal of thermoplastics remains environmentally challenging. Moreover, the shale gas boom is putting pressure on the markets for the appropriate starting materials, which can be obtained from crude oil but not natural gas. Consequently, biobased polymers have been targeted as replacements by utilizing biomass-derived, renewable feedstocks. An added benefit to this approach is that the final products are often degradable, leading to decreases in landfilled waste. However, only poly(lactic acid) (PLA) has yet found broad commercial success as a thermoplastic. PLA has mostly been used in the disposable packaging market because it is similar in certain respects to polystyrene and polyethylene terephthalate for plastic bags and soda bottles, respectively. It has not found broader acceptance because its chemical structure yields a low softening temperature of only 60 °C, and it is susceptible to degradation in wet environments.In this work, we will use woody biomass as a feedstock for producing polymer precursors. We will use a platform chemical approach, which mimics how plastics are produced in traditional petrochemical facilities. The cellulose fraction of woody biomass will be converted to a platform chemical called 5-hydroxymethylfurfural (a.k.a. "HMF"). The HMF will be converted to a variety of polymer precursors by combining it with portions of lignin (the "glue" that holds wood together in trees). We will then apply traditional polymerization techniques to convert these precursors into plastics and characterize the properties of the final materials.
Animal Health Component
15%
Research Effort Categories
Basic
85%
Applied
15%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
4030699200050%
4030699202050%
Knowledge Area
403 - Waste Disposal, Recycling, and Reuse;

Subject Of Investigation
0699 - Trees, forests, and forest products, general;

Field Of Science
2020 - Engineering; 2000 - Chemistry;
Goals / Objectives
We will produce biobased engineering thermoplastics from lignin and 5-hydroxymethylfurfural (HMF) in a series of steps. HMF will first be functionalized with lignin-derived phenols via the selective etherification described in our preliminary results above. The functionalized HMF will then be oxidized to the corresponding furoic acid. Finally, the furan ring will be saturated and re-arranged to a δ-lactone in a single step using a bifunctional metal/acid catalyst. The resulting functionalized delta-hexalactones (FDHLs) will be converted to polyFDHLs via ring-opening transesterification polymerization (ROTEP). The proposed work will develop an overall process from these disparate steps and elucidate how the underlying chemistry influences the final polymer properties. To achieve the overall research goal, the following objectives will be met:1.Quantify the influence of pendent group identity on the kinetics of HMF etherification and demonstrate the functionalization of HMF using lignin-derived phenols that can be extracted from lignin bio-oil2.Demonstrate the saturation and re-arrangement of the furan ring in HMF molecules functionalized with phenols3.Elucidate the nature of the active sites required for ring saturation and re-arrangement and design catalysts that are highly selective for the conversion of functionalized HMF molecules to functionalized δ-hexalactones4.Elucidate the influence of FDHL pendant groups on polymerization kinetics, thermodynamics, and catalyst activity5.Develop strategies for controlling chemical and thermal properties of the polymers by modifying FDHL pendant groups, polymer architecture, and composition6.Demonstrate integrated production of polymers starting from HMF and lignin-derived phenols7. Evaluate the influence on the overall process of HMF and phenols obtained from real biomass
Project Methods
The project will proceed in two thrusts, each performed in parallel. Thrust 1 will be directed by PI Schwartz and will focus on catalytic strategies to produce FDHLs. Thrust 2 will be directed by PI Gramlich and will focus on methodologies to polymerize FDHLs. Each PI will supervise one Ph.D. student who will complete the tasks described below.Thrust 1: Chemical Catalysis: Renewable FDHL ProductionWork in Thrust 1 will focus on industrially-relevant methods for producing a family of lignin-derived FDHLs. The availability of such molecules, which have not previously been obtained from fully renewable resources, will enable the production of biobased, degradable thermoplastics suitable for engineering applications. Because of the novelty of these molecules and the lack of published data describing their production, the work to be performed in Thrust 1 will focus on elucidating a molecular-level description of the relevant reactions and using this information to design improved catalysts that can be used to produce FDHLs with high selectivity. One major objective of this thrust is to elucidate the influence of pendant group identity on chemical reactivity during FDHL production. Additionally, ring-rearrangement reactions such as those needed to convert the five-member HMF ring to the six-member δ-lactone ring have traditionally required RhRe bimetallic, bifunctional catalysts, which are prohibitively expensive for most production targets. We have performed similar chemistry using a bifunctional metal/zeolite catalyst (vide supra), and a second major objective of this thrust is to elucidate the nature of the active sites on this catalyst and evaluate how to obtain high selectivity to the δ-lactone target product. To achieve these aims, we will use a combination of reaction kinetics studies, probe molecule studies, and temperature-programmed reaction studies. The outcome of this thrust will be the design of new catalysts that can achieve high selectivity using a variety of lignin-derived phenols. In pursuit of this outcome, the following tasks will be performed.Task 1. 1 HMF FunctionalizationTask 1.2 Oxidation of Functionalized HMFTask 1.3 Ring Saturation and Re-arrangementTask 1.4 FDHL ProductionThrust 2: Polymerization: Renewable Thermoplastic ProductionThe class of FDHL monomers serves as a platform from which to synthesize a variety of lignin-derived polyesters, and effective polymerization strategies are needed to consistently and reliably create polymers. The overall objective of this thrust is to learn how different pendent functional groups affect the polymerization of FDHLs and the final properties of the polymer. The approach in this thrust will consist of synthesizing FDHLs with pendent groups derived from lignin that have different sizes and functionality and understanding how to control the polymerization kinetics and thermodynamics for these molecules while using catalysts with varying levels of activity. This work is needed because thus far the only six membered lactones that have been investigated have only pendent alkyl groups and not the lignin-derived functionalities that we propose. Pendent groups at the δ-position affect the polymerization kinetics and thermodynamics, but a comprehensive study beyond chain length effects has not been conducted because these monomers are not commercially available. Moreover, a fundamental polymerization study such as this is required to design and optimize the monomers for polymerization and future commercial use. Additionally, the physical, chemical, and thermal properties of the polyFDHLs obtained from lignin will be investigated as a function of the pendent groups of the monomer. Polymer architecture and composition will be varied to control the final physical properties of these fully renewable polymers. The overall outcomes of this thrust will be a fundamental understanding of how to polymerize FDHLs and how these pendent groups affect polymer properties. These outcomes will be achieved through the following tasks.Task 2.1 Elucidation of fundamental polymerization parameters of FDHLsTask 2.2 Optimization of polymerization conditionsTask 2.3 Characterization of polyFDHL propertiesTask 2.4 Control material properties

Progress 04/01/18 to 03/31/22

Outputs
Target Audience:The target audiences reached during this reporting period are the academic communities in the polymer chemistry and heterogeneous catalysis fields. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?For monomer development, two different Ph.D. students have been supported on this project during the reporting period. The first student has performed the majority of the work on Objective 2, and he successfully defended his PhD during the fall semester of 2020. He is the lead author on the Polymer Chemistry. A second Ph.D. student continued working on the project. Additionally, two chemical engineering undergraduate students were suported on the project. One of the undergraduate students was included on the publication related to this objective (reported in the previous period), and the lead author of that paper was a MS student who worked on this project prior to funding by USDA. For polymer development, a Ph.D. student has been supported throughout the project. This student has performed the majority of the monomer synthesis, polymerization, and characterization. Additionally, an undergraduate chemistry major worked during the reporting period to synthesize the CXDHL. He wrote an undergraduate thesis and defended it near the middle of the project. How have the results been disseminated to communities of interest?Yes, several presentations have been given at national meetings, and three peer reviewed manuscripts were published. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? 1. We have measured the rates of HMF etherification with ethanol in BEA zeolite and developed a detailed mechanism for the reaction network, which was the subject of a publication in ACS Catalysis. We also measured the rates of etherification of HMF with butanol, cyclohexanol, phenol, and o-cresol and we have analyzed these, suggesting that they behave according to the published mechanism. We continued to study the rates of HMF etherification with ethanol and other alcohols, focusing on the reaction of HMF with o-cresol and methyl-cyclohexanol. While we observed substantial catalyst deactivation for o-cresol, which we hypothesize to be related to demethylation chemistry occurring on the acid sites of the catalyst, we did not observe such substantial deactivation for methyl-cyclohexanol. However, we did observe a decrease in selectivity, owing to an increase in the extent of unimolecular dehydration (i.e., alkene formation) vs. bimolecular dehydration (i.e., etherificaiton). 2. During this project period, we continued our study of ring hydrogenation and re-arrangement of furoic acid using Ru/TiO2, and we have identified reaction conditions that lead to high selectivity to the corresponding lactone. Partially, this depends on the appropriate pre-treatment of the catalyst to generate Brønsted acidic protons at the Ru-TiO2 interface, and reduction of thecatalyst at 200 ºC is apparently sufficient for this process. We have observed >90% selectivity to delta-hexalactone using 2-furoic acid as a model reactant. Importantly, the functionalized HMF derivatives to be used in the monomers for this project will be substituted also at the 5-position, which could lead to lower selectivity. We have evaluated 5-methyl-2-furoic acid as a reactant at equivalent reaction conditions and observed selectivity only to the 6-methyl-delta-hexalactone, indicating this catalyst system will be appropriate for lactone formation from the HMF ethers developed so far. These observations have been confirmed by repeat measurements, and the yield of 6-methyl-deltahexalactone we obtain (ca. 60%) is the highest reported in the literature to date. This work was published in the journal Polymer Chemistry. 3. We believe that H+ species are formed at the Ru/TiO2 interface by heterolytic hydrogendissociation, although it is not clear that these acidic H+ species are involved in the C-O hydrogenolysis reaction. We observed that the reaction can be catalyzed even for a Ru/C catalyst, which does not contain and protons. Moreover, the reaction to form delta-hexalactone (DHL) from furoic acid (FCA) appears to proceed in parallel with the reaction to form tetrahydrofuroic acid, indicating that DHL can be formed directly from FCA. This is in contrast to the mechanism observed for Ru alloyed with an oxophilic species (e.g., RuRe, etc.). These observations were published in the journal Polymer Chemistry. 4. Four functionalized delta-hexalactone (FDHL) monomers were produced with different pendent groups that can be derived from lignin. These were a pendent methoxy group (MDHL), phenol group (PDHL), naphthol group (NDHL), and cyclohexanolgroup (CXDHL). Catalyst activity to polymerize MDHL and PDHL were explored using acid and base catalysts diphenylphosphate (DPP) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), respectively. Both MDHL and PDHL could be polymerized byDPP, but yielded short polymer chains due to adventitious initiation from the monomer itself. This led to low molecularweight polymers (below 5 kg/mol) for both monomers. TBD catalyst could only polymerize PDHL and the polymerization of MDHL was not observed. High molecular weight poly (PDHL) was possible by varying the monomer to initiator ratio (above 30kg/mol). A base-urea catalysts system was also investigated, but neither monomer could be polymerized. We have now shown that catalyst basicity compared to the monomer basicity plays a role in catalyst activity. Polymerization kinetics of PDHL using TBD followed expected controlled polymerization rate laws until reaching equilibrium. Both the entropy and enthalpy of polymerization for MDHL and PDHL were evaluated to understand how the pendent group affects polymerization. Both had similar enthalpy of polymerization values (-10 kJ mol-1 for MDHL and -9 kJ mol-1 for PDHL), but the entropy of polymerization for PDHL (-26 J mol-1 K-1) was significantly more positive than that of MDHL(-34 J mol-1 K-1), which indicates that PDHL could reach higher monomer conversions. This work was published in the journal Polymer Chemistry. 5. The 4 FDHL monomers synthesized were designed to have varying degrees of bulkiness in their pendent groups to prevent chain rotation and thus increase the glass transition temperature of their corresponding polymers. MDHL has a glass transition temperature of -55 °C with the relatively small methoxy pendent group. The glass transition temperature for a short (5 kg/mol) polyPDHL was found to be 5 °C, which is an increase of 60 °C. Higher molecular weight polyPDHLs were synthesized, which led to an increase in the Tg of 36 °C for these polymers. Both the NDHL and CXDHL monomers have more bulky pendent groups, which we have now observed to increase the Tg of their polymers even further. This was published in Polymer Chemistry. 6 and 7. These objectives were stretch objectives that were not fully studied during the project period due to difficulty in sourcing appropriate materials.

Publications

  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Highly Selective Cross-Etherification of 5-Hydroxymethylfurfural with Ethanol. Meredith C. Allen, Alexander J. Hoffman, Tsung-wei Liu, Matthew S. Webber, David Hibbitts, and Thomas J. Schwartz. ACS Catalysis 2020 10 (12), 6771-6785. DOI: 10.1021/acscatal.0c01328
  • Type: Journal Articles Status: Published Year Published: 2022 Citation: Pathway to fully-renewable biobased polyesters derived from HMF and phenols. Jalal Tavana, Atik Faysal, Anushka Vithanage, William M. Gramlich, and Thomas J. Schwartz. Polym. Chem., 2022,13, 1215-1227. DOI: 10.1039/D1PY01441B.
  • Type: Journal Articles Status: Published Year Published: 2021 Citation: Leveraging De Donder relations for a thermodynamically rigorous analysis of reaction kinetics in liquid media. Thomas J. Schwartz and Jesse Q. Bond. J. Catal., 2021, 404, 687-705. DOI: 10.1016/j.jcat.2021.09.026.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Allen, Meredith C.; Hoffman, Alexander J.; Liu, Tsung-Wei; Hibbitts, David; Schwartz, Thomas J. Selective Etherification of HMF. ACS Virtual Session #ChemistsLive, September 2020.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Schwartz, Thomas J. Renewable, Tunable Polymers from Lignin and 5-Hydroxymethylfurfural. ACS Spring Meeting, Virtual, April 5-16, 2021.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Faysal, Atik; Schwartz, Thomas J.; Gramlich, William. Functionalized, delta-hexalactone (FDHL): Bio-based monomers to synthesize renewable polyester thermoplastics. ACS Fall Meeting, San Francisco, CA, August 23-27, 2020.
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Reaction Kinetics Analysis of Ethanol Dehydrogenation Catalyzed by MgOSiO2. Hussein T. Abdulrazzaq, Amir Rahmani Chokanlu, Brian G. Frederick, and Thomas J. Schwartz. ACS Catalysis 2020 10 (11), 6318-6331. DOI: 10.1021/acscatal.0c00811.
  • Type: Theses/Dissertations Status: Published Year Published: 2020 Citation: Jalal Tavana. Understanding Biomass Upgrading Through Hydrogenolysis Reactions: Kinetics and Mechanism. PhD Thesis.
  • Type: Theses/Dissertations Status: Published Year Published: 2022 Citation: Atik Faysal. FUNCTIONALIZED ??-HEXALACTONEs (FDHLs): BIO-DERIVABLE MONOMERS TO SYNTHESIZE RENEWABLE POLYESTER THERMOPLASTICS. PhD Thesis.


Progress 04/01/20 to 03/31/21

Outputs
Target Audience:The target audiences reached during this reporting period are the academic communities in the polymer chemistry and heterogeneous catalysis fields. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?For monomer development, two different Ph.D. students have been supported on this project during the reporting period. The first student has performed the majority of the work on Objective 2, and he successfully defended his PhD during the fall semester of 2020. He is the lead author on the paper in preparation to submit to Green Chemistry. A second Ph.D. student is now working on the project. Additionally, two chemical engineering undergraduate students were supported prior to cessation of research activities during the COVID-19 pandemic. One of the undergraduate students was included on the publication related to this objective (reported in the previous period), and the lead author of that paper was a MS student who worked on this project prior to funding by USDA. For polymer development, a Ph.D. student has been supported throughout the last year on the project. This student has performed the majority of the monomer synthesis, polymerization, and characterization. Additionally, an undergraduate chemistry major worked during the reporting period to synthesize the CXDHL. He wrote an undergraduate thesis and defended it near the beginning of this reporting period. How have the results been disseminated to communities of interest?The etherificaiton results were presented at the two virtual ACS meetings during 2020 and 2021. Results of monomer synthesis and polymerization were presented at the American Chemical Society Virtual Fall Meeting in August. Work is ongoing to submit a manuscript on the synthesis and polymerization of polyFDHLs to Green Chemistry. Work is ongoing on a second manuscript focused on the polymerization of FDHLs. What do you plan to do during the next reporting period to accomplish the goals?Since the synthesis of new FDHLs has become straightforward, we will synthesize a variety of polyFDHLs with different pendent groups that can be derived from lignin to understand how the pendent group affects glass transition temperature and polymerization behavior. Catalysts with higher basicity will be investigated to increase the rate of polymerization and control over molecular weights. Monomer produced through the catalytic methods will be used to make polymers to demonstrate the validity of the entire production pathway. The Ru/TiO2 catalyst will be fully characterized to elucidate the nature of the active sites responsible for monomer production.

Impacts
What was accomplished under these goals? Some of our research activities during this reporting period were impacted by the ongoing COVID-19 pandemic, which led us to request a no-cost extension for the project (granted during this reporting year). We had very limited access to our laboratories from mid-March 2020 until about September 2020, with sporadic access limitations throughout the rest of the reporting year. 1. We have continued to study the rates of HMF etherification with ethanol and other alcohols, focusing on the reaction of HMF with o-cresol and methyl-cyclohexanol. While we observed substantial catalyst deactivation for o-cresol, which we hypothesize to be related to demethylation chemistry occurring on the acid sites of the catalyst, we did not observe such substantial deactivation for methyl-cyclohexanol. However, we did observe a decrease in selectivity, owing to an increase in the extent of unimolecular dehydration (i.e., alkene formation) vs. bimolecular dehydration (i.e., etherificaiton). We are presently evaluating the kinetics of both reactions to tease out the distinction. 2. During this project period, we continued our study of ring hydrogenation and re-arrangement of furoic acid using Ru/TiO2, and we have identified reaction conditions that lead to high selectivity to the corresponding lactone. Partially, this depends on the appropriate pre-treatment of the catalyst to generate Brønsted acidic protons at the Ru-TiO2 interface, and reduction of thecatalyst at 200 ºC is apparently sufficient for this process. We have observed >90% selectivity to delta-hexalactone using 2-furoic acid as a model reactant. Importantly, the functionalized HMF derivatives to be used in the monomers for this project will be substituted also at the 5-position, which could lead to lower selectivity. We have evaluated 5-methyl-2-furoic acid as a reactant at equivalent reaction conditions and observed selectivity only to the 6-methyl-delta-hexalactone, indicating this catalyst system will be appropriate for lactone formation from the HMF ethers developed so far. These observations have been confirmed by repeat measurements, and the yield of 6-methyl-deltahexalactone we obtain (ca. 60%) is the highest reported in the literature to date. This work is the subject of a manuscript currently in preparation for submission to Green Chemistry. 3. Characterization of the Ru/TiO2 catalyst began shortly before the cessation of on-campus research due to the COVID-19 pandemic, and upon re-entry to the labs we did not make as much progress as hoped because of other priorities needed for student graduation. From previous work, we believe that H+ species are formed at the Ru/TiO2 interface by heterolytic hydrogendissociation. During the NCE, we will evaluate whether basic molecules can inhibit the reaction, thereby confirming the participation of H+ species. Moreover, we will evaluate the rate of hydrogenolysis as a function of Ru particle size, allowing us to confirm the reaction occurs at the Ru-TiO2 interface. 4. Four functionalized delta-hexalactone (FDHL) monomers were produced with different pendent groups that can be derived from lignin. These were a pendent methoxy group (MDHL), phenol group (PDHL), naphthol group (NDHL), and cyclohexanolgroup (CXDHL). Catalyst activity to polymerize MDHL and PDHL were explored using acid and base catalysts diphenylphosphate (DPP) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), respectively. Both MDHL and PDHL could be polymerized byDPP, but yielded short polymer chains due to adventitious initiation from the monomer itself. This led to low molecularweight polymers (below 5 kg/mol) for both monomers. TBD catalyst could only polymerize PDHL and the polymerization of MDHL was not observed. High molecular weight poly (PDHL) was possible by varying the monomer to initiator ratio (above 30kg/mol). A base-urea catalysts system was also investigated, but neither monomer could be polymerized. We have now shown that catalyst basicity compared to the monomer basicity plays a role in catalyst activity. Polymerization kinetics of PDHL using TBD followed expected controlled polymerization rate laws until reaching equilibrium. Both the entropy and enthalpy of polymerization for MDHL and PDHL were evaluated to understand how the pendent group affects polymerization. Both had similar enthalpy of polymerization values (-10 kJ mol-1 for MDHL and -9 kJ mol-1 for PDHL), but the entropy of polymerization for PDHL (-26 J mol-1 K-1) was significantly more positive than that of MDHL(-34 J mol-1 K-1), which indicates that PDHL could reach higher monomer conversions. 5. The 4 FDHL monomers synthesized were designed to have varying degrees of bulkiness in their pendent groups to prevent chain rotation and thus increase the glass transition temperature of their corresponding polymers. MDHL has a glass transition temperature of -55 °C with the relatively small methoxy pendent group. The glass transition temperature for a short (5 kg/mol) polyPDHL was found to be 5 °C, which is an increase of 60 °C. Higher molecular weight polyPDHLs were synthesized, which led to an increase in the Tg of 36 °C for these polymers. Both the NDHL and CXDHL monomers have more bulky pendent groups, which we have now observed to increase the Tg of their polymers even further. 6 and 7. These objectives will be evaluated during the NCE, if time permits.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Allen, Meredith C.; Hoffman, Alexander J.; Liu, Tsung-Wei; Hibbitts, David; Schwartz, Thomas J. Selective Etherificationof HMF. ACS Virtual Session #ChemistsLive, September 2020.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: Schwartz, Thomas J. Renewable, Tunable Polymers from Lignin and 5-Hydroxymethylfurfural. ACS Spring Meeting, Virtual, April 5-16, 2021.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Faysal, Atik; Schwartz, Thomas J.; Gramlich, William. Functionalized, delta-hexalactone (FDHL): Bio-based monomers to synthesize renewable polyester thermoplastics. ACS Fall Meeting, San Francisco, CA, August 23-27, 2020.


Progress 04/01/19 to 03/31/20

Outputs
Target Audience:The target audiences reached during this reporting period are the academic communities in the polymer chemistry and heterogeneous catalysis fields. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?For monomer development, a Ph.D. student has been supported on this project during the reporting period. This student has performed the majority of the work on Objective 2. Additionally, two chemical engineering undergraduate students have been supported through the academic year and summer, and these students have continued the data collection for Objective 1. One of the undergraduate students was included on the publication related to this objective, and the lead author was a MS student who worked on this project prior to funding by USDA. For polymer development, a Ph.D. student has been supported for the last year on the project. This student has performed the majority of the monomer synthesis, polymerization, and characterization. Additionally, an undergraduate chemistry major has worked over the summer and academic year to synthesize the CXDHL. He wrote an undergraduate thesis and defended it. How have the results been disseminated to communities of interest?The etherification of HMF was published in ACS Catalysis in 2020. The etherificaiton results were presented at the New England Catalysis Society meeting in January 2020. Results of monomer synthesis and polymerization were going to be presented at the American Chemical Society Spring National Meeting in March, but the meeting was cancelled due to the worldwide pandemic of COVID-19. Work is ongoing regarding a manuscript draft for the synthesis and polymerization of polyFDHLs. What do you plan to do during the next reporting period to accomplish the goals?Since the synthesis of new FDHLs has become straightforward, we will synthesize a variety of polyFDHLs with different pendent groups that can be derived from lignin to understand how the pendent group affects glass transition temperature and polymerization behavior. Catalysts with higher basicity will be investigated to increase the rate of polymerization and control over molecular weights. Monomer produced through the catalytic methods will be used to make polymers to demonstrate the validity of the entire production pathway.

Impacts
What was accomplished under these goals? 1. We have measured the rates of HMF etherification with ethanol in BEA zeolite and developed a detailed mechanism for the reaction network, which was the subject of our recent publication in ACS Catalysis (see products section of this report). We also measured rates of etherification of HMF with butanol, cyclohexanol, phenol, and o-cresol and we are in the process of analyzing these rates to determine if they behave according to our published mechanism. Notably, o-cresol leads to substantial catalyst deactivation, which we hypothesize to be related to demethylation chemistry occurring on the acid sites of the catalyst. We plan to continue this analysis following the full resumption of research activities after the ongoing COVID-19 pandemic. 2. During this project period, we continued our study of ring hydrogenation and re-arrangement of furoic acid using Ru/TiO2, and we have identified reaction conditions that lead to high selectivity to the corresponding lactone. Partially this depends on the appropriate pre-treatment of the catalyst to generate Brønsted acidic protons at the Ru-TiO2 interface, and reduction of the catalyst at 200 ºC is apparently sufficient for this process. We have observed >90% selectivity to delta-hexalactone using 2-furoic acid as a model reactant. Importantly, the functionalized HMF derivatives to be used in the monomers for this project will be substituted also at the 5-position, which could lead to lower selectivity. We have evaluated 5-methyl-2-furoic acid as a reactant at equivalent reaction conditions and observed selectivity only to the 6-methyl-delta-hexalactone, indicating this catalyst system will be appropriate for lactone formation from the HMF ethers developed so far. Upon resumption of normal research activities following the ongoing COVID-19 pandemic, we will evaluate this reaction using functionalized HMF. 3. Characterization of the Ru/TiO2 catalyst began shortly before the cessation of on-campus research due to the COVID-19 pandemic. From previous work, we believe that H+ species are formed at the Ru/TiO2 interface by heterolytic hydrogen dissociation. Upon re-entry to the labs, we will evaluate whether basic molecules can inhibit the reaction, thereby confirming the participation of H+ species. Moreover, we will evaluate the rate of hydrogenolysis as a function of Ru particle size, allowing us to confirm the reaction occurs at the Ru-TiO2 interface. 4. Four functionalized delta-hexalactone (FDHL) monomers were produced with different pendent groups that can be derived from lignin. These were a pendent methoxy group (MDHL), phenol group (PDHL), naphthol group (NDHL), and cyclohexanol group (CXDHL). Catalyst activity to polymerize MDHL and PDHL were explored using acid and base catalysts diphenyl phosphate (DPP) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), respectively. Both MDHL and PDHL could be polymerized by DPP, but yielded short polymer chains due to advantageous initiation from the monomer itself. This led to low molecular weight polymers (below 5 kg/mol) for both monomers. TBD catalyst could only polymerize PDHL and the polymerization of MDHL was not observed. High molecular weight poly(PDHL) was possible by varying the monomer to initiator ratio (above 30 kg/mol). A base-urea catalysts system was also investigated, but neither monomer could be polymerized. The catalyst basicity compared to the monomer basicity is hypothesized to play a role in catalyst activity. Future studies are planned to probe this hypothesis. Polymerization kinetics of PDHL using TBD followed expected controlled polymerization rate laws until reaching equilibrium. Both the entropy and enthalpy of polymerization for MDHL and PDHL were evaluated to understand how the pendent group affects polymerization. Both had similar enthalpy of polymerization values (-10 kJ mol-1 for MDHL and -9 kJ mol-1 for PDHL), but the entropy of polymerization for PDHL (-26 J mol-1 K-1) was significantly more positive than that of MDHL (-34 J mol-1 K-1), which indicates that PDHL could reach higher monomer conversions. 5. The 4 FDHL monomers synthesized were designed to have varying degrees of bulkiness in their pendent groups to prevent chain rotation and thus increase the glass transition temperature of their corresponding polymers. MDHL has a glass transition temperature of -55 °C with the relatively small methoxy pendent group. The glass transition temperature for a short (5 kg/mol) polyPDHL was found to be 5 °C, which is an increase of 60 °C. Higher molecular weight polyPDHLs were synthesized so the Tg for these polymers is expected to be somewhat higher. Both the NDHL and CXDHL monomers have more bulky pendent groups which is expected to increase the Tg of their polymers beyond polyPDHL. 6 and 7. These objectives will be evaluated in the last year of the project.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Allen, Meredith C.; Hoffman, Alexander J.; Liu, Tsung-Wei; Hibbitts, David; Schwartz, Thomas J. Selective Etherification of HMF. New England Catalysis Society, Worcester, MA, Jan 13, 2020.
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Highly Selective Cross-Etherification of 5-Hydroxymethylfurfural with Ethanol. Meredith C. Allen, Alexander J. Hoffman, Tsung-wei Liu, Matthew S. Webber, David Hibbitts, and Thomas J. Schwartz. ACS Catalysis 2020 10 (12), 6771-6785. DOI: 10.1021/acscatal.0c01328
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Reaction Kinetics Analysis of Ethanol Dehydrogenation Catalyzed by MgOSiO2. Hussein T. Abdulrazzaq, Amir Rahmani Chokanlu, Brian G. Frederick, and Thomas J. Schwartz. ACS Catalysis 2020 10 (11), 6318-6331. DOI: 10.1021/acscatal.0c00811.


Progress 04/01/18 to 03/31/19

Outputs
Target Audience:The target audiences reached during this reporting period are the academic communities in the polymer chemistry and heterogeneous catalysis fields. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?For monomer development, a Ph.D. student has been supported on this project during the reporting period. The student has performed the majority of the work on objective 2. Additionally, two undergraduate chemical engineering students have been supported through the academic year and summer, and these students are continuing data collection for objective 1. For polymer development, a Ph.D. student has been supported for the last year on the project. This student has performed the majority of the monomer synthesis and polymerization. Additionally, an undergraduate chemistry major has worked over the academic year and continuing on in the summer as a work study student to synthesize FDHLs. How have the results been disseminated to communities of interest?Preliminary findings and the overview of the project were presented to industrial and governmental representatives at a Bio-plastics Summit at the University of Maine in May 1st and 2nd. Work is ongoing regarding a manuscript draft for the synthesis and polymerization of MDHL. What do you plan to do during the next reporting period to accomplish the goals?Future work on HMF conversion will focus on analysis of reaction kinetics data currently being collected, with the objective of publishing a second paper on the kinetics of HMF etherifiation. We will also evaluate the reaction using real phenols. During the next period, we will continue to evaluate catalysts for ring saturation and re-arrangement, focusing on materials similar to Pd/TiO2. We will also begin spectroscopic and titration studies to identify the active sites on these materials, which we suspect may involve acidic protons at the Pd-TiO2interface. Future work on catalyst utilization for polymerization will focus on base-urea catalyst systems that have been reported in literature to significantly increase the rate of polymerization. New FDHLs will be synthesized with a variety of pendent groups that can be derived from lignin to understand how the pendent group affects glass transition temperature and polymerization behavior. Kinetic studies will be run with the most promising base-urea catalyst. Once a library of five FDHLs are produced, their thermodynamic behaviors during polymerization will be elucidated.

Impacts
What was accomplished under these goals? 1. We have measured the rate of HMF etherification using ethanol in ethanol/water mixtures as solvents. From these kinetics data, coupled with density functional theory calculations fromProf. David Hibbitts' group at U. Florida, we have developed a detailed reaction mechanism for the cross-etherification of HMF with ethanol, which will be submitted for publication in the near future. The reaction proceeds via a concerted transition state wherein HMF is dehydrated simultaneous to its coupling to ethanol, and the catalyst surface is highly covered by ethanol monomers and dimers. We are currently measuring the kinetics of the reaction usingn-butanol, cyclohexanol, and phenol to evaluate whether these alcohols follow the same mechanism, although they are less reactive than ethanol. 2. Preliminary experiments have been performed on the saturation and ring-rearrangement of furoic acids. Following etherification, the functionalized HMF molecules would be first oxidized using well-developed Au/TiO2chemistry to yield functionalize furoic acids. In this period, we have evaluated the use of Pd/zeolite, Pd/TiO2, and Ru/TiO2catalysts for the saturation and ring re-arrangement of these functionalized furoic acids. The Ru/TiO2catlayst is active for this reaction, although it is not very selective, as Ru is an excellent catalyst for the hydrogenation of carboxylic acids. Our recent work with Pd/TiO2suggests that this may be a suitable catalyst, and we are continuing studies with this material. 3. This objective depends on the success of objective 2 and will start to be evaluated in the next period. 4. We developed a robust synthesis scheme to produce FDHL monomers with varying pendent groups that can be derived from lignin. The scheme is modular and should enable us to create various FDHLs with pendent lignin derived groups. This scheme was used to synthesize an FDHL with a pendent phenol group (PDHL), which was compared to an FDHL with a pendent methoxy group (MDHL). The PDHL was a solid and the MDHL was a liquid so polymerization methods were developed to synthesis a poly(PDHL) using minimal solvent. PDHL could be polymerized through acid and base catalyzed methods using catalysts diphenyl phosphate (DPP) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), where the DPP catalyst was more successful due to its robustness in the presence of air. MDHL could not be polymerized by TBD, suggesting that the PDHL may be more reactive, but more studies are needed to confirm. Preliminary kinetic studies suggest that PDHL and MDHL polymerize at similar rates at room temperature, reaching equilibrium in several days using the DPP catalyst. 5. Two FHDL monomers and therefore their subsequent polymers have been synthesized. The phenolic pendent group of PDHL was selected as it is bulky and therefore should prevent chain rotation and thus increase the glass transition temperature. MDHL has a glass transition temperature of -55 °C with the relatively small methoxy pendent group. The glass transition temperature of PDHL has not been measured yet since more polymer is required first, but visible inspection suggests that PDHL has a glass transition temperature around room temperature. 6. and 7. These objectives will be evaluated in the last year of the projet.

Publications

  • Type: Conference Papers and Presentations Status: Submitted Year Published: 2018 Citation: Allen, Meredith; Martell, Spencer; Shakib, Akbar Mahdavi; Gramlich, William M.; Frederick, Brian G.; Schwartz, Thomas J. Etherification of 5-Hydroxymethylfurfural Using Zeolite Catalysts. AIChE Fall Meeting, Pittsburgh, PA, Oct 28-Nov 2, 2018.