Hydrogenation of Polyesters to Polyether Polyols

Value-Added Upcycling of PET to 1,4-Cyclohexanedimethanol by a Hydrogenation/Hydrogenolysis Relay Catalysis

We present an innovative process for directly transforming poly(ethylene terephthalate) (PET), a polymer extensively used in food and beverage packaging, into trans-isomer-enriched 1,4-cyclohexanedimethanol (CHDM), a key ingredient in advanced specialty polymers. Our approach leverages a dual-catalyst system featuring palladium on reduced graphene oxide (Pd/r-GO) and oxalate-gel-derived copper-zinc oxide (og-CuZn), utilizing hydrogenation/hydrogenolysis relay catalysis. This method efficiently transforms PET into polyethylene-1,4-cyclohexanedicarboxylate (PECHD), which is then converted into CHDM with an impressive overall yield of 95 % in a two-stage process. Our process effectively handles various post-consumer PET plastics, converting them into CHDM with yields between 78 % and 89 % across different substrates. Additionally, we demonstrate the applicability and scalability of this approach through a temperature-programmed three-stage relay process on a 10-gram scale, which results in purified CHDM with an isolated yield of 87 % and a notably higher trans/cis ratio of up to 4.09/1, far exceeding that of commercially available CHDM. This research not only provides a viable route for repurposing PET waste but also enhances the control of selectivity patterns in multistage relay catalysis.

Recent Advances in Environment-Friendly Polyurethanes from Polyols Recovered from the Recycling and Renewable Resources: A Review

Polyurethane (PU) is among the most universal polymers and has been extensively applied in many fields, such as construction, machinery, furniture, clothing, textile, packaging and biomedicine. Traditionally, as the main starting materials for PU, polyols deeply depend on petroleum stock. From the perspective of recycling and environmental friendliness, advanced PU synthesis, using diversified resources as feedstocks, aims to develop versatile products with excellent properties to achieve the transformation from a fossil fuel-driven energy economy to renewable and sustainable ones. This review focuses on the recent development in the synthesis and modification of PU by extracting value-added monomers for polyols from waste polymers and natural bio-based polymers, such as the recycled waste polymers: polyethylene terephthalate (PET), PU and polycarbonate (PC); the biomaterials: vegetable oil, lignin, cashew nut shell liquid and plant straw; and biomacromolecules: polysaccharides and protein. To design these advanced polyurethane formulations, it is essential to understand the structure-property relationships of PU from recycling polyols. In a word, this bottom-up path provides a material recycling approach to PU design for printing and packaging, as well as biomedical, building and wearable electronics applications.

Chemical recycling technologies for PVC waste and PVC-containing plastic waste: A review

The extensive production and consumption of plastics has resulted in significant plastic waste and plastic pollution. Polyvinyl chloride (PVC) waste has a high chlorine content and is the primary source of chlorine in the plastic waste stream, potentially generating hazardous chlorinated organic pollutants if treated improperly. This review discusses PVC synthesis, applications, and the current types and challenges of PVC waste management. Dechlorination is vital for the chemical recycling of PVC waste and PVC-containing plastic waste. We review dehydrochlorination and dechlorination mechanisms of PVC using thermal degradation and wet treatments, and summarize the recent progress in chemical treatments and dechlorination principles. This review provides readers with a comprehensive analysis of chemical recycling technologies for PVC waste and PVC-containing plastic waste to transform them into chemicals, fuels, feedstock, and value-added polymers.

Selective Hydrodeoxygenation of Esters to Unsymmetrical Ethers over a Zirconium Oxide-Supported Pt-Mo Catalyst

The catalytic hydrodeoxygenation (HDO) of carbonyl oxygen in esters using H₂ is an attractive method for synthesizing unsymmetrical ethers because water is theoretically the sole coproduct. Herein, we report a heterogeneous catalytic system for the selective HDO of esters to unsymmetrical ethers over a zirconium oxide-supported platinum-molybdenum catalyst (Pt-Mo/ZrO₂). A wide range of esters were transformed into the corresponding unsymmetrical ethers under mild reaction conditions (0.5 MPa H₂ at 100 °C). The Pt-Mo/ZrO₂ catalyst was also successfully applied to the conversion of a biomass-derived triglyceride into the corresponding triether. Physicochemical characterization and control experiments revealed that cooperative catalysis between Pt nanoparticles and neighboring molybdenum oxide species on the ZrO₂ surface plays a key role in the highly selective HDO of esters. This Pt-Mo/ZrO₂ catalyst system offers a highly efficient strategy for synthesizing unsymmetrical ethers and broadens the scope of sustainable reaction processes.

Evaluation of Manganese Catalysts for the Hydrogenative Deconstruction of Commercial and End-of-Life Polyurethane Samples

Polyurethane (PU) is a thermoset plastic that is found in everyday objects, such as mattresses and shoes, but also in more sophisticated materials, including windmills and airplanes, and as insulation materials in refrigerators and buildings. Because of extensive inter-cross linkages in PU, current recycling methods are somewhat lacking. In this work, the effective catalytic hydrogenation of PU materials is carried out by applying a catalyst based on the earth-abundant metal manganese, to give amine and polyol fractions, which represent the original monomeric composition. In particular, Mn-^Ph MACHO is found to catalytically deconstruct flexible foam, molded foams, insulation, and end-of-life materials at 1 wt.% catalyst loading by applying a reaction temperature of 180 °C, 50 bar of H₂ , and 0.9 wt.% of KOH in isopropyl alcohol. The protocol is showcased in the catalytic deconstruction of 2 g of mattress foam using only 0.13 wt.% catalyst, resulting in 90 % weight recovery and a turnover number of 905.

Catalytic Reductive Alcohol Etherifications with Carbonyl-Based Compounds or CO2 and Related Transformations for the Synthesis of Ether Derivatives

Ether derivatives have myriad applications in several areas of chemical industry and academia. Hence, the development of more effective and sustainable protocols for their production is highly desired. Among the different methodologies reported for ether synthesis, catalytic reductive alcohol etherifications with carbonyl-based moieties (aldehydes/ketones and carboxylic acid derivatives) have emerged in the last years as a potential tool. These processes constitute appealing routes for the selective production of both symmetrical and asymmetrical ethers (including O-heterocycles) with an increased molecular complexity. Likewise, ester-to-ether catalytic reductions and hydrogenative alcohol etherifications with CO2 to dialkoxymethanes and other acetals, albeit in less extent, have undergone important advances, too. In this Review, an update of the recent progresses in the area of catalytic reductive alcohol etherifications using carbonyl-based compounds and CO2 have been described with a special focus on organic synthetic applications and catalyst design. Complementarily, recent progress made in catalytic acetal/ketal-to-ether or ester-to-ether reductions and other related transformations have been also summarized.

Catalytic Hydrogenation of Polyurethanes to Base Chemicals: From Model Systems to Commercial and End-of-Life Polyurethane Materials

Polyurethane (PU) is a highly valued polymer prepared from diisocyanates and polyols, and it is used in everyday products, such as shoe soles, mattresses, and insulation materials, but also for the construction of sophisticated parts of medical devices, wind turbine blades, aircrafts, and spacecrafts, to name a few. As PU is most commonly used as a thermoset polymer composed of cross-linked structures, its recycling is complicated and inefficient, leading to increasing PU waste accumulating every year. Catalytic hydrogenation represents an atom-efficient means for the deconstruction of polyurethanes, but so far the identification of an efficient catalyst for the disassembly of real-life and end-of-life PU samples has not been demonstrated. In this work, we reveal that a commercially available catalyst, Ir- iPrMACHO, under 30 bar H2 and 150-180 °C, is a general catalyst for the effective hydrogenation of the four cornerstones of PU: flexible solid, flexible foamed, rigid solid, and rigid foamed, leading to the isolation of aromatic amines and a polyol fraction. For the first time, a variety of commercial PU materials, including examples of foams, inline skating wheels, shoe soles, and insulation materials, has been deconstructed into the two fractions. Most desirable, our reaction conditions include the use of isopropyl alcohol as a representative of a green solvent. It is speculated that a partial glycolysis at the surface of the PU particles is taking place in this solvent and reaction temperatures in the presence of catalytic amounts of base. As such a more efficient hydrogenation of the solubilized PU fragments in isopropyl alcohol becomes possible. As the isolated anilines are precursors to the original isocyanate building blocks, and methods for their conversion are well-known, the work reported in this paper provides a realistic indication of a potential circular plastic economy solution for PU. Preliminary experiments were also undertaken applying Mn- iPrMACHO for the deconstruction of a commercial flexible PU foam. Although successful, more forcing conditions were required than those when applying Ir- iPrMACHO.

Sustainable composites from biodegradable poly(butylene succinate) modified with thermoplastic starch and poly(butylene adipate-co-terephthalate): preparation and performance

A ternary blend of biodegradable polymers, namely PBS-g-GMA, thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT), was successfully fabricated attempt to achieve novel biodegradable composites with comprehensive properties.

Catalytic reductive deoxygenation of esters to ethers driven by hydrosilane activation through non-covalent interactions with a fluorinated borate salt

A fluorinated borate BArF salt catalyses the reductive deoxygenation of esters to ethers by using hydrosilanes. Experimental and theoretical studies highlight the role of noncovalent interactions in the reaction mechanism.