Increasing the Dissolution Rate of Polystyrene Waste in Solvent-Based Recycling

Solvent-based recycling of plastic waste is a promising approach for cleaning polymer chains without breaking them. However, the time required to actually dissolve the polymer in a lab environment can take hours. Different factors play a role in polymer dissolution, including temperature, turbulence, and solvent properties. This work provides insights into bottlenecks and opportunities to increase the dissolution rate of polystyrene in solvents. The paper starts with a broad solvent screening in which the dissolution times are compared. Based on the experimental results, a multiple regression model is constructed, which shows that within several solvent properties, the viscosity of the solvent is the major contributor to the dissolution time, followed by the hydrogen, polar, and dispersion bonding (solubility) parameters. These results also indicate that cyclohexene, 2-pentanone, ethylbenzene, and methyl ethyl ketone are solvents that allow fast dissolution. Next, the dissolution kinetics of polystyrene in cyclohexene in a lab-scale reactor and a baffled reactor are investigated. The effects of temperature, particle size, impeller speed, and impeller type were studied. The results show that increased turbulence in a baffled reactor can decrease the dissolution time from 40 to 7 min compared to a lab-scale reactor, indicating the importance of a proper reactor design. The application of a first-order kinetic model confirms that dissolution in a baffled reactor is at least 5-fold faster than that in a lab-scale reactor. Finally, the dissolution kinetics of a real waste sample reveal that, in optimized conditions, full dissolution occurs after 5 min.

A Review of Biodegradable Plastics: Chemistry, Applications, Properties, and Future Research Needs

Environmental concerns over waste plastics' effect on the environment are leading to the creation of biodegradable plastics. Biodegradable plastics may serve as a promising approach to manage the issue of environmental accumulation of plastic waste in the ocean and soil. Biodegradable plastics are the type of polymers that can be degraded by microorganisms into small molecules (e.g., H2O, CO2, and CH4). However, there are misconceptions surrounding biodegradable plastics. For example, the term "biodegradable" on product labeling can be misconstrued by the public to imply that the product will degrade under any environmental conditions. Such misleading information leads to consumer encouragement of excessive consumption of certain goods and increased littering of products labeled as "biodegradable". This review not only provides a comprehensive overview of the state-of-the-art biodegradable plastics but also clarifies the definitions and various terms associated with biodegradable plastics, including oxo-degradable plastics, enzyme-mediated plastics, and biodegradation agents. Analytical techniques and standard test methods to evaluate the biodegradability of polymeric materials in alignment with international standards are summarized. The review summarizes the properties and industrial applications of previously developed biodegradable plastics and then discusses how biomass-derived monomers can create new types of biodegradable polymers by utilizing their unique chemical properties from oxygen-containing functional groups. The terminology and methodologies covered in the paper provide a perspective on directions for the design of new biodegradable polymers that possess not only advanced performance for practical applications but also environmental benefits.

Hydroformylation of pyrolysis oils to aldehydes and alcohols from polyolefin waste

Waste plastics are an abundant feedstock for the production of renewable chemicals. Pyrolysis of waste plastics produces pyrolysis oils with high concentrations of olefins (>50 weight %). The traditional petrochemical industry uses several energy-intensive steps to produce olefins from fossil feedstocks such as naphtha, natural gas, and crude oil. In this work, we demonstrate that pyrolysis oil can be used to produce aldehydes through hydroformylation, taking advantage of the olefin functionality. These aldehydes can then be reduced to mono- and dialcohols, oxidized to mono- and dicarboxylic acids, or aminated to mono- and diamines by using homogeneous and heterogeneous catalysis. This route produces high-value oxygenated chemicals from low-value postconsumer recycled polyethylene. We project that the chemicals produced by this route could lower greenhouse gas emissions ~60% compared with their production through petroleum feedstocks.

Controlling the toxicity of biomass-derived difunctional molecules as potential pharmaceutical ingredients for specific activity toward microorganisms and mammalian cells

A biomass-derived difuran compound, denoted as HAH (HMF-Acetone-HMF), synthesized by aldol-condensation of 5-hydroxyfurfural (HMF) and acetone, can be partially hydrogenated to provide an electron-rich difuran compound (PHAH) for Diels-Alder reactions with maleimide derivatives. The nitrogen (N) site in the maleimide can be substituted by imidation with amine-containing compounds to control the hydrophobicity of the maleimide moiety in adducts of furans and maleimide by Diels-Alder reaction, denoted as norcantharimides (Diels-Alder adducts). The structural effects on the toxicity of various biomass-derived small molecules synthesized in this manner to regulate biological processes, defined as low molecular weight (≤ 1000 g/mol) organic compounds, were investigated against diverse microbial and mammalian cell types. The biological toxicity increased when hydrophobic N-substitutions and C=C bonds were introduced into the molecular structure. Among the synthesized norcantharamide derivatives, some compounds demonstrated pH-dependent toxicities against specific cell types. Reaction kinetics analyses of the norcantharimides in biological conditions suggest that this pH-dependent toxicity of norcantharimides could arise from retro Diels-Alder reactions in the presence of a Brϕnsted acid that catalyzes the release of an N-substituted maleimide, which has higher toxicity against fungal cells than the toxicity of the Diels-Alder adduct. These synthetic approaches can be used to design biologically-active small molecules that exhibit selective toxicity against various cell types (e.g., fungal, cancer cells) and provide a sustainable platform for production of prodrugs that could actively or passively affect the viability of infectious cells.

Techno-Economic and life cycle assessment of standalone Single-Stream material recovery facilities in the United states

Material Recovery Facilities (MRFs) are crucial players in achieving a circular economy. MRFs receive complex waste streams and separate valuable recyclables from these mixtures. This study conducts techno-economic analysis (TEA) to estimate the net present value (NPV) and life cycle assessment (LCA) to estimate different environmental impacts of a commercial scale standalone, single-stream MRF to assess the economic feasibility and environmental impacts of recovering valuable recyclables from an MRF processing 120,000 tonnes per year (t/y). The TEA employs a discounted cash flow rate of return (DCFROR) analysis over a 20-year facility lifetime, along with a sensitivity analysis on the impact of different operating and economic parameters. Results show that the total fixed cost of building the MRF facility is $23 MM, and the operating cost is $45.48/tonne. The NPV of the MRF can vary from $3.57 MM to $60 MM, while 100-year global warming potential can range from 5.98 to 8.53 kg carbon dioxide equivalents (CO2-eq) per tonne of MSW. We have also found that MSW composition (arising from regional effects) significantly impacts costs, 100-year global warming potential, and other impact categories such as acidification potential, eutrophication potential, ecotoxicity, ozone depletion, photochemical oxidation, carcinogenic effects, and non-carcinogenic effects. Sensitivity and uncertainty analysis indicate that waste composition and market prices significantly impact the profitability of the MRF, and the waste composition mostly impacts global warming potential. Our analysis also indicates that facility capacity, fixed capital cost, and waste tipping fees are vital parameters that affect the economic viability of MRF operations.

Design of supported organocatalysts from a biomass-derived difuran compound and catalytic assessment for lactose hydrolysis

The engineered structures and active sites of enzyme catalysts give rise to high catalytic activity and selectivity toward desired reactions. We have employed a biomass-derived difuran compound to append N-substituted maleimides with amino acid (glutamic acid) substitution by Diels-Alder reaction to mimic the chemical functional groups that comprise the active site channels in enzyme catalysts. The difunctionality of the biomass-derived difuran allows production of Diels-Alder adducts by appending two amino acid moieties to form a difunctional organocatalyst. The catalytic activity of the organocatalyst can be improved by immobilizing the organocatalyst on solid supporting materials. Accordingly, the structures of these immobilized organocatalysts can be engineered to mimic enzymatic active sites and to control the interaction between reactants, products, and transition states of catalytic reactions. Lactose hydrolysis was carried out to provide an example of industrial application of this approach to design and fabricate new supported organocatalysts as artificial enzymes.

Controlled hydrogenation of a biomass-derived platform chemical formed by aldol-condensation of 5-hydroxymethyl furfural (HMF) and acetone over Ru, Pd, and Cu catalysts

We studied the hydrogenation at temperatures from 313 - 393 K of a biomass-derived platform molecule, 5-hydroxymethyl furfural (HMF)-Acetone-HMF (HAH) over Pd, Ru, and Cu based catalysts. HAH was selectively hydrogenated to produce partially-hydrogenated monomers (PHAH) over Cu and Ru catalysts and to fully-hydrogenated HAH monomers (FHAH) over the Ru catalyst. Pd based catalysts yielded a mixture of partially and fully hydrogenated monomers. Lumped reaction kinetics models were employed to quantify the kinetic behavior for hydrogenation over Ru, Cu, and Pd catalysts. The 5-step pathway exhibited over Pd and Ru catalysts consists of both series and parallel reaction steps, where HAH is both converted to fully hydrogenated products sequentially via series reactions of partially hydrogenated intermediates, as well as converted directly in parallel reactions to form the fully hydrogenated products. In contrast, the 3-step pathway over the Cu catalyst consists only of the consecutive reaction steps, where the final product was formed via series reactions of intermediate products. Additionally, reaction over the Cu catalyst did not hydrogenate the furan rings of the HAH molecule and yielded a different final product than those hydrogenation over Pd and Ru catalysts. Batch conditions are determined for each hydrogenated product that give the highest yields in both batch and plug flow reactors.

Effect of catalyst support on cobalt catalysts for ethylene oligomerization into linear olefins

Here, we show that the oligomerization activity of a carbon-supported cobalt oxide catalyst is nearly twice as high when it is supported on a less oxidized carbon support.

Design of closed-loop recycling production of a Diels-Alder polymer from a biomass-derived difuran as a functional additive for polyurethanes

Acetalization of biomass-derived 5-hydroxymethyl furfural (HMF) with pentaerythritol produced a difuran (HPH) monomer in the presence of an acid catalyst. A recyclable polymer was then synthesized by Diels-Alder reaction of bismaleimide and the HMF-derived difuran (HPH). A polyurethane, produced from the Diels-Alder polymer has a higher glass transition temperature than a polyurethane, produced from ethylene glycol. The polyurethane, containing Diels-Alder polymer also has a self-healing ability. The Diels-Alder polymer could be hydrolyzed under acidic acetate buffer at 60°C to produce the monomers for recycling. Each produced monomer was separated by solvent extraction, and the extracted monomers were recovered in different solvent fractions, such as aqueous, ethyl acetate, and acetone fractions. Techno economic analysis was used to assess the minimum selling price ($14.1 per kg) for the primary production of Diels-Alder polymer at a feed capacity of 400 tons per year. The economic viability of the primary recovery process for the most expensive recovered monomer, bismaleimide, was assessed by calculating the minimum selling price of the bismaleimide ($15.2 per kg). A circular closed-loop recycling production process for the Diels-Alder polymer was developed and this approach can produce the Diels-Alder polymer at $8.2 per kg when the feed capacity was 40 ktons per year.

Reducing Antisolvent Use in the STRAP Process by Enabling a Temperature-Controlled Polymer Dissolution and Precipitation for the Recycling of Multilayer Plastic Films

The recently reported processing strategy called solvent-targeted recovery and precipitation (STRAP) enables deconstruction of multilayer plastic packaging films into their constituent resins by selective dissolution. It uses a series of solvent washes that are guided by thermodynamic calculations of polymer solubility. In this work, the use of antisolvents in the STRAP process was reduced and solvent mixtures were considered to enable the temperature-controlled dissolution and precipitation of the target polymers in multilayer films. This was considered as a means to further improve the STRAP process and its estimated costs. Two STRAP approaches were compared based on different polymer precipitation techniques: precipitation by the addition of an antisolvent (STRAP-A) and precipitation by decreasing the solvent temperature (STRAP-B). Both approaches were able to separate the constituent polymers in a post-industrial film composed primarily of polyethylene (PE), ethylene vinyl alcohol (EVOH), and polyethylene terephthalate (PET) with near 100 % material efficiency. Technoeconomic analysis indicates that the minimum selling price (MSP) of the recycled resins with STRAP-B is 21.0 % lower than that achieved with STRAP-A. This provides evidence that thermally driven polymer precipitation is an option to reduce the use of antisolvents, making the STRAP process more economically and environmentally attractive. A third process, STRAP-C, was demonstrated with another post-industrial multilayer film of a different composition. The results demonstrate that this process can also recover polymers at similar costs to those of virgin resins, indicating that the STRAP technology is flexible and can remain economically competitive as the plastic feed complexity is increased.

New Technologies are Needed to Improve the Recycling and Upcycling of Waste Plastics

In their Editorial to the Special Issue on The Chemistry of Waste Plastics Upcycling, the Guest Editors Adam Guss, George Huber, Carol Lin, Xianzhi Meng, Hugh O'Neill, Arthur Ragauskas, Jia Wang, Yanqin Wang, and Frederik Wurm highlight some of the increasingly urgent efforts being made by chemists to address challenges related to the fate of plastics at the end of, their useful lives and the valorization of plastic waste.

Computational Approach for Rapidly Predicting Temperature-Dependent Polymer Solubilities Using Molecular-Scale Models

One promising approach to recycle multicomponent plastic waste (e. g., multilayer plastic films) is selective dissolution. Selective dissolution is a solvent-mediated process in which differences in polymer solubility in a carefully chosen solvent system are exploited to recover a target polymer. Here, a computational approach was developed that rapidly predicts temperature-dependent polymer solubilities to guide the design of solvent systems for solvent-mediated polymer recycling. Polymer conformations were obtained from molecular dynamics simulations by modeling the polymer as a short oligomer and then used as input to the conductor-like screening model for real solvents (COSMO-RS) for solubility predictions. Using polyethylene (PE) and ethylene vinyl alcohol (EVOH) as representative polymers, the effect of simulation parameters was systematically studied, and predicted solubilities were found to be in good agreement with experimental measurements. The applicability of the approach was demonstrated by identifying selective solvents for PE and EVOH dissolution from a library of 524 solvents.

Synthesis of performance-advantaged polyurethanes and polyesters from biomass-derived monomers by aldol-condensation of 5-hydroxymethyl furfural and hydrogenation

Functional polyurethanes and polyesters with tunable properties were synthesized from biomass-derived 5-hydroxymethyl furfural (HMF)-Acetone-HMF (HAH) monomers. HAH can be selectively hydrogenated over Cu and Ru catalysts to produce partially-hydrogenated (PHAH) and fully-hydrogenated (FHAH). The HAH units in these polymers improve the thermal stability and stiffness of the polymers compared to polyurethanes produced with ethylene glycol. Polyurethanes produced from PHAH provide diene binding sites for electron deficient C=C double bonds, such as in maleimide compounds, that can participate in Diels-Alder reactions. Such sites can function to create crosslinking by Diels-Alder coupling with bismaleimides and can be used to impart functionality to PHAH (giving rise to anti-microbial activity or controlled drug delivery). The symmetric triol structure of FHAH leads to energy-dissipating rubbers with branched structures. Accordingly, the properties of these biomass-derived polymers can be tuned by controlling the blending ratio of HAH-derived monomers or the degree of Diels-Alder reaction. The polyester produced from HAH can be used in packaging applications.

Ethylene oligomerization into linear olefins over cobalt oxide on carbon catalyst

Stable heterogeneous cobalt oxide on carbon catalyst for ethylene oligomerization into linear and alpha olefins.

Recycling of multilayer plastic packaging materials by solvent-targeted recovery and precipitation

Many plastic packaging materials manufactured today are composites made of distinct polymer layers (i.e., multilayer films). Billions of pounds of these multilayer films are produced annually, but manufacturing inefficiencies result in large, corresponding postindustrial waste streams. Although relatively clean (as opposed to municipal wastes) and of near-constant composition, no commercially practiced technologies exist to fully deconstruct postindustrial multilayer film wastes into pure, recyclable polymers. Here, we demonstrate a unique strategy we call solvent-targeted recovery and precipitation (STRAP) to deconstruct multilayer films into their constituent resins using a series of solvent washes that are guided by thermodynamic calculations of polymer solubility. We show that the STRAP process is able to separate three representative polymers (polyethylene, ethylene vinyl alcohol, and polyethylene terephthalate) from a commercially available multilayer film with nearly 100% material efficiency, affording recyclable resins that are cost-competitive with the corresponding virgin materials.

Chemical-Switching Strategy for Synthesis and Controlled Release of Norcantharimides from a Biomass-Derived Chemical

Catalytic strategies were developed to synthesize and release chemicals for applications in fine chemicals, such as drugs and polymers, from a biomass-derived chemical, 5-hydroxymethyl furfural (HMF). The combination of the diene and aldehyde functionalities in HMF enabled catalytic production of acetalized HMF derivatives with diol or epoxy reactants to allow reversible synthesis of norcantharimide derivatives upon Diels-Alder reaction with maleimides. Reverse-conversion of the acetal group to an aldehyde yielded mismatches of the molecular orbitals in norcantharimides to trigger retro Diels-Alder reaction at ambient temperatures and released reactants from the coupled molecules under acidic conditions. These strategies provide for the facile synthesis and controlled release of high-value chemicals.

Comparison of Two Acid Hydrotropes for Sustainable Fractionation of Birch Wood

This study reports on a comparative study of acid hydrotropic fractionation (AHF) of birch wood using maleic acid (MA) and p-toluenesulfonic acid (p-TsOH). Under the same level of delignification, lignin dissolved by MA is much less condensed with a higher content of ether aryl β-O-4 linkages. Lignin depolymerization dominated in MA hydrotropic fractionation (MAHF) and resulted in a single lower molecular weight peak, in contrast to the competitive depolymerization and repolymerization in p-TsOH AHF with a bimodal distribution. The less condensed MA-dissolved lignin facilitated catalytic conversion to monophenols. Carboxylation of residual lignin in fractionated cellulosic water-insoluble solids (WISs) enhanced enzymatic saccharification by decreasing nonproductive cellulase binding to lignin. At a low cellulase loading of 10 FPU g^-1 glucan, saccharification of WIS-M_T120 from MAHF at 120 °C was 95 % compared with 48 % for WIS-P_T85 from p-TsOH AHF at 85 °C under the same level of delignification of 63 %. Residual lignin carboxylation also facilitated nanofibrillation of WIS for producing lignin-containing cellulose nanofibrils (LCNFs) through an enhanced lignin lubrication effect, which substantially decreases fibrillation energy. LCNFs from only one pass of microfluidization of WIS-M_T120 have the same morphology as those from WIS-P_T85 after three passes. MA also has a lower solubility and higher minimal hydrotropic concentration, which facilitated acid recovery. MA is U.S. Food and Drug Administration (FDA)-approved as an indirect food additive, affording significant advantages compared with p-TsOH for biorefinery applications.

Catalytic strategy for conversion of fructose to organic dyes, polymers, and liquid fuels

We report a process to produce a versatile platform chemical from biomass-derived fructose for organic dye, polymer, and liquid fuel industries. An aldol-condensed chemical (HAH) is synthesized as a platform chemical from fructose by catalytic reactions in acetone/water solvent with non-noble metal catalysts (e.g., HCl, NaOH). Then, selective reactions (e.g., etherification, reduction, dimerization) of the functional groups, such as enone and hydroxyl groups, in the HAH molecule enable applications in organic dyes and polyether precursors. High yields of target products, such as 5-(hydroxymethyl) furfural (HMF) (85.9% from fructose) and HAH (86.3% from HMF) are achieved by sequential dehydration and aldol-condensation with a simple purification process (>99% HAH purity). The use of non-noble metal catalysts, the high yield of each reaction, and the simple purification of the target product allow for beneficial economics of the process. Techno-economic analysis indicates that the process produces HAH at minimum selling price (MSP) of $1958/ton. The MSP of HAH product allows the economic viability of applications in organic dye and polyether markets by replacing its counterparts, such as anthraquinone ($3200-$3900/ton) and bisphenol-A ($1360-$1720/ton).

Catalytic strategy for conversion of fructose to organic dyes, polymers, and liquid fuels

We report a process to produce a versatile platform chemical from biomass-derived fructose for organic dye, polymer, and liquid fuel industries. An aldol-condensed chemical (HAH) is synthesized as a platform chemical from fructose by catalytic reactions in acetone/water solvent with non-noble metal catalysts (e.g., HCl, NaOH). Then, selective reactions (e.g., etherification, reduction, dimerization) of the functional groups, such as enone and hydroxyl groups, in the HAH molecule enable applications in organic dyes and polyether precursors. High yields of target products, such as 5-(hydroxymethyl) furfural (HMF) (85.9% from fructose) and HAH (86.3% from HMF) are achieved by sequential dehydration and aldol-condensation with a simple purification process (>99% HAH purity). The use of non-noble metal catalysts, the high yield of each reaction, and the simple purification of the target product allow for beneficial economics of the process. Techno-economic analysis indicates that the process produces HAH at minimum selling price (MSP) of $1958/ton. The MSP of HAH product allows the economic viability of applications in organic dye and polyether markets by replacing its counterparts, such as anthraquinone ($3200-$3900/ton) and bisphenol-A ($1360-$1720/ton).

Solid-state NMR studies of solvent-mediated, acid-catalyzed woody biomass pre-treatment for enzymatic conversion of residual cellulose

Enzymes selectively hydrolyze the carbohydrate fractions of lignocellulosic biomass into corresponding sugars, but these processes are limited by low yields and slow catalytic turnovers. Under certain conditions, the rates and yields of enzymatic sugar production can be increased by pretreating biomass using solvents, heat and dilute acid catalysts. However, the mechanistic details underlying this behavior are not fully elucidated, and designing effective pretreatment strategies remains an empirical challenge. Herein, using a combination of solid-state and high-resolution magic-angle-spinning NMR, infrared spectroscopy and X-ray diffractometry, we show that the extent to which cellulase enzymes are able to hydrolyze solvent-pretreated biomass can be understood in terms of the ability of the solvent to break the chemical linkages between cellulose and non-cellulosic materials in the cell wall. This finding is of general significance to enzymatic biomass conversion research, and implications for designing improved biomass conversion strategies are discussed. These findings demonstrate the utility of solid-state NMR as a tool to elucidate the key chemical and physical changes that occur during the liquid-phase conversion of real biomass.

The Chemistry and Kinetics of Polyethylene Pyrolysis: A Process to Produce Fuels and Chemicals

The annual global production of plastics reached 335 million metric tons in 2016. Most waste plastics are landfilled or enter the natural environment in an uncontrolled manner. Pyrolysis can convert waste plastics, such as polyethylene (PE), to smaller hydrocarbons that can be used as fuels or chemicals. In this work, pyrolysis of PE was studied by thermogravimetric analysis (TGA) and in a fluidized-bed reactor. A kinetic model based on two parallel first-order random-scission steps was developed on the basis of the TGA results. PE was pyrolyzed in a fluidized-bed reactor over the temperature range of 500-600 °C and at residence times of 12.4-20.4 s. The yield of gas-phase products increased from 8.2 to 56.8 wt %, and the yield of liquid-phase products decreased from 81.2 to 28.5 wt % as the temperature increased from 500 to 600 °C. Detailed analysis of the gas- and liquid-phase products revealed their potential as precursors for production of fuels and chemicals. Gas-phase products included hydrogen, C₁ -C₄ paraffins, C₂ -C₄ olefins, and 1,3-butadiene. The major liquid-phase products were mono-olefins and cycloalkanes/alkadienes with smaller amounts of n-paraffins, isoparaffins, and aromatics. The carbon-number distribution of the fluidized-bed pyrolysis products suggested contributions of nonrandom reactions of random-scission fragments at low conversion.

Catalytic Production of Glucose-Galactose Syrup from Greek Yogurt Acid Whey in a Continuous-Flow Reactor

The hydrolysis of lactose in aqueous solutions and dairy waste streams was studied using Amberlyst 70 as a heterogeneous acid catalyst in a continuous-flow packed-bed reactor. The catalyst was stable during hydrolysis of an aqueous lactose feed but deactivated owing to mineral poisoning when the dairy waste Greek yogurt acid whey (GAW) was used as the feedstock. A catalyst deactivation model was developed and showed that the deactivation of the Amberlyst 70 catalyst was proportional to the amounts of cations, urea and amino acids flowing through the catalyst bed. The Amberlyst 70 catalyst was regenerable with an aqueous acid regeneration treatment. Based on the experimental data, a rigorous technoeconomic analysis was performed for the production of glucose-galactose syrup (GGS) via lactose hydrolysis of GAW using three different catalysts. This approach shows that the GGS produced from GAW could become a valuable revenue stream for Greek yogurt manufacturers.

Introduction to green chemistry and reaction engineering

George Huber, Alexei Lapkin and Yan Ning introduce the Reaction Chemistry & Engineering themed issue on green chemistry and reaction engineering.

Selective Cellulose Hydrogenolysis to Ethanol Using Ni@C Combined with Phosphoric Acid Catalysts

Ethanol is an important bulk chemical with diverse applications. Biomass-derived ethanol is traditionally produced by fermentation. Direct cellulose conversion to ethanol by chemocatalysis is particularly promising but remains a great challenge. Herein, a one-pot hydrogenolysis of cellulose into ethanol was developed by using graphene-layers-encapsulated nickel (Ni@C) catalysts with the aid of H₃ PO₄ in water. The cellulose was hydrolyzed into glucose, which was activated by forming cyclic di-ester bonds between the OH groups of H₃ PO₄ and glucose, promoting ethanol formation under the synergistic hydrogenation of Ni@C. A 69.1 % yield of ethanol (carbon mole basis) was obtained, which is comparable to the theoretical value achieved by glucose fermentation. An ethanol concentration of up to 8.9 wt % was obtained at an increased cellulose concentration. This work demonstrates a chemocatalytic approach for the high-yield production of ethanol from renewable cellulosic biomass at high concentration.

Hexane-1,2,5,6-tetrol as a Versatile and Biobased Building Block for the Synthesis of Sustainable (Chiral) Crystalline Mesoporous Polyboronates

We report on the synthesis and characterization of novel mesoporous chiral polyboronates obtained by condensation of (R,S)/(S,S)-hexane-1,2,5,6-tetrol (HT) with simple aromatic diboronic acids (e.g., 1,3-benzenediboronic acid) (BDB). HT is a cellulose-derived building block comprising two 1,2-diol structures linked by a flexible ethane bridge. It typically consists of two diastereomers one of which [(S,R)-HT] can be made chirally pure. Boronic acids are abundantly available due to their importance in Suzuki-Miyaura coupling reactions. They are generally considered nontoxic and easy to synthesize. Reactive dissolution of generally sparingly soluble HT with BDB, in only a small amount of solvent, yields the mesoporous HT/polyboronate materials by spontaneous precipitation from the reaction mixture. The 3D nature of HT/polyboronate materials results from the entanglement of individual 1D polymeric chains. The obtained BET surface areas (SAs) and pore volumes (PVs) depend strongly on HT's diastereomeric excess and the meta/para orientation of the boronic acids on the phenyl ring. This suggests a strong influence of the curvature(s) of the 1D polymeric chains on the final materials' properties. Maximum SA and PV values are respectively 90 m² g^-1 and 0.44 mL g^-1. Variably sized mesopores, spanning mainly the 5-50 nm range, are evidenced. The obtained pore volumes rival the ones of some covalent organic frameworks (COFs), yet they are obtained in a less expensive and more benign fashion. Moreover, currently no COFs have been reported with pore diameters in excess of 5 nm. In addition, chiral boron-based COFs have presently not been reported. Scanning electron microscopy reveals the presence of micrometer-sized particles, consisting of aggregates of plates, forming channels and cell-like structures. X-ray diffraction shows the crystalline nature of the material, which depends on the nature of the aromatic diboronic acids and, in the specific case of 1,4-benzenediboronic acid, also on the applied diastereomeric excess in HT.

Ethanol condensation at elevated pressure over copper on AlMgO and AlCaO porous mixed-oxide supports

The coupling of ethanol to produce C₄-compounds by Guerbet condensation at 325 °C was studied using porous mixed oxide catalysts of AlMgO and AlCaO prepared by the emulsion mediated method with and without the addition of Cu.

Investigation of the Reaction Pathways of Biomass-Derived Oxygenate Conversion into Monoalcohols in Supercritical Methanol with CuMgAl-Mixed-Metal Oxide

Reaction pathways for the conversion of cellulose into C₂ -C₆ monoalcohols by supercritical methanol depolymerization and hydrodeoxygenation (SCM-DHDO) over a CuMgAl oxide catalyst have been elucidated using a range of model compounds. SCM-DHDO of intermediate oxygenates including glycerol, methyl lactate, and 1,2-ethanediol produces similar products as those produced from the SCM-DHDO of cellulose. The pathway to C₂ -C₆ monoalcohols occurs through rapid C-C coupling reactions between methanol and diols followed by C-C scission between vicinal alcohol groups to produce two monoalcohols. Methyl-branched monoalcohols are produced through a methyl shift in a secondary diol followed by dehydration. Esters are produced by dehydrogenative coupling between an adsorbed methoxy and a primary alcohol. Both dehydrogenation to a ketone and esterification to a methyl ester are in equilibrium with the corresponding alcohol and were reversible. Dehydration of diols is the slowest observed reaction and not a main pathway to monoalcohols. SCM-DHDO of glucose, dihydroxyacetone, and cellulose all produced similar high molecular weight species indicating that condensation of intermediates can produce undesired side products.

Production of high-octane gasoline via hydrodeoxygenation of sorbitol over palladium-based bimetallic catalysts

A methodology for the synthesis of gasoline-range fuels from carbon neutral resources is introduced. Sorbitol, a sugar-based compound, was employed as a raw material because the compound is readily obtained from cellulose. Gasoline-range hydrocarbons were produced via hydrodeoxygenation (HDO) on zirconium phosphate-supported Pd-bimetallic (Pt-Pd, Ru-Pd, Ni-Pd, Fe-Pd, Co-Pd, W-Pd) catalysts. Among the tested catalysts, the bimetallic W-Pd/ZrP catalyst exhibited the highest yield of gasoline products, peaking at ∼70%. However, with the bimetallic Fe-Pd and Co-Pd catalysts, high-octane gasoline products were made (research octane number (RON) of the products was higher than 100). The Fe-Pd catalyst also showed the highest initial activity for the HDO of sorbitol. This study demonstrates that HDO in the Pd-system is a promising option to produce high-quality gasoline-range hydrocarbons from lignocellulosic biomass.

Catalytic oxidation of carbohydrates into organic acids and furan chemicals

A review on the development of new routes for the production of organic acids and furan compoundsviacatalytic oxidation reactions.