Beyond Plastics-to-Plastics to Waste-to-Products: Opportunities for Closing the Carbon Cycle via Chemical Recycling

The plastic crisis is a key driver for chemical recycling (CR), with focus placed on plastics circularity via Plastics-to-Plastics. This neglects its potential in enabling circularity for a wide range of carbon-containing waste and hinders a critical discussion of its broader contributions to decarbonizing the chemical sector. To address this gap, four CR routes and their integration in the conventional waste treatment and chemical production value chains are briefly reviewed, and reasons proposed for a focus expansion to Waste-to-Products to realize opportunities for closing the carbon cycle via chemical recycling.     

Dendrimers or Nanoparticles as Supports for the Design of Efficient and Recoverable Organocatalysts?

The Jørgensen–Hayashi catalyst [(S)‐α,α‐diphenylprolinol trimethylsilyl ether] was grafted onto the surface of two different supports: phosphorus dendrimers (generations 1 to 3) and magnetic, polymer‐coated cobalt/carbon (Co/C) nanobeads. These new supported catalysts displayed high activities and selectivities in the Michael additions of a wide range of aldehydes to different nitroolefins. Moreover, the dendrimer of the third generation displayed excellent recycling abilities since it could be recovered and reused in 7 consecutive runs without loss of activity.     

Density of solutions of formaldehyde in water and alcohols

Formaldehyde is an important chemical that is mostly handled in aqueous solutions, which generally also contain methanol; furthermore, also solutions of formaldehyde in other alcohols are used. The density of these solutions is an important thermophysical property. The available models of the density of formaldehyde-containing solutions, however, all have shortcomings, such as a poor accuracy or a limited range of applicability. Therefore, in the present work, a new model of the density in systems of the type (formaldehyde + water + alcohol) was developed. The alcohols that are presently included in the new model are methanol, 1-propanol, and isoprenol; an extension to other alcohols is straightforward. The model was developed using literature data and extensive new density data measured in this work covering binary, ternary, and quarternary solutions of formaldehyde in water, methanol, 1-propanol, and isoprenol at temperatures of $283-333$ K and formaldehyde concentrations of 0.06 − 0.30 g g⁻¹.     

Digital Extraction Column: Measurement and Modeling Techniques

The digitization of extraction columns requires a profound knowledge of the present hydrodynamics/mass transport interaction as well as appropriate measurement techniques for the detection of relevant input and target values. In this article, the different techniques for droplet size distribution as well as concentration determination are presented and new methods for online evaluation are discussed. In combination with the simulation of droplet size, holdup and solute concentration distribution, an online-capable process tool for controlling and optimizing extraction columns will be obtained.     

Ketonization of Proline Residues in the Peptide Chains of Actinomycins by a 4‐Oxoproline Synthase

X‐type actinomycins (Acms) contain 4‐hydroxyproline (Acm X₀) or 4‐oxoproline (Acm X₂) in their β‐pentapeptide lactone rings, whereas their α ring contains proline. We demonstrate that these Acms are formed through asymmetric condensation of Acm half molecules (Acm halves) containing proline with 4‐hydroxyproline‐ or 4‐oxoproline‐containing Acm halves. In turn, we show—using an artificial Acm half analogue (PPL 1) with proline in its peptide chain—their conversion into the 4‐hydroxyproline‐ and 4‐oxoproline‐containing Acm halves, PPL 0 and PPL 2, in mycelial suspensions of Streptomyces antibioticus. Two responsible genes of the Acm X biosynthetic gene cluster of S. antibioticus, saacmM and saacmN, encoding a cytochrome P450 monooxygenase (Cyp) and a ferredoxin were identified. After coexpression in Escherichia coli, their gene products converted PPL 1 into PPL 0 and PPL 2 in vivo as well as in situ in permeabilized cell of the transformed E. coli strain in conjunction with the host‐encoded ferredoxin reductase in a NADH (NADPH)‐dependent manner. saAcmM has high sequence similarity to the Cyp107Z (Ema) family of Cyps, which can convert avermectin B1 into its keto derivative, 4′′‐oxoavermectin B1. Determination of the structure of saAcmM reveals high similarity to the Ema structure but with significant differences in residues decorating their active sites, which defines saAcmM and its orthologues as a distinct new family of peptidylprolineketonizing Cyp.     

Extraction of Algal Lipids and Their Analysis by HPLC and Mass Spectrometry

Algae are a promising source of biofuel but claims about their lipid content can be ambiguous because extraction methods vary and lipid quantitation often does not distinguish between particular lipid classes. Here we compared methods for the extraction of algal lipids and showed that 2-ethoxyethanol (2-EE) provides superior lipid recovery (>150–200 %) compared to other common extraction solvents such as chloroform:methanol or hexane. Extractions of wet and dry algal biomass showed that 2-EE was more effective at extracting lipids from wet rather than dried algal pellets. To analyze lipid content we used normal-phase HPLC with parallel quantitation by an evaporative light scattering detector and a mass spectrometer. Analysis of crude lipid extracts showed that all major lipid classes could be identified and quantified and revealed a surprisingly large amount of saturated hydrocarbons (HC). This HC fraction was isolated from extracts of bioreactor-grown algae and further analyzed by HPLC/MS, NMR, and GC/MS. The results showed that the sample consisted of a mixture of saturated, straight- and branched-chain HC of different chain lengths. These algal HC could represent an alternative biofuel to triacylglycerols (TAG) that could feed directly into the current petroleum infrastructure.     

Degradation of Nextel™ 610‐based oxide‐oxide ceramic composites by aluminum oxychloride decomposition products

Nextel? 610 alumina fibers and alumina‐YAG (yttrium‐aluminum garnet) matrices were used to make oxide‐oxide ceramic matrix composites (CMCs) with and without monazite (LaPO₄) fiber‐matrix interfaces. Twelve sequential aluminum oxychloride (AlOCl) infiltrations with 1 hour heat treatments at 1100°C and a final 1 hour heat treatment at 1200°C were used for matrix densification. This matrix processing sequence severely degraded CMC mechanical properties. CMC tensile strengths and interlaminar tensile (ILT) strengths were less than 10 MPa and 1 MPa, respectively. Axial fracture of Nextel? 610 fibers was observed after ILT testing, highlighting the extreme degradation of fiber strength. Extensive characterization was done to attempt to determine the responsible degradation mechanisms. Changes in Nextel? 610 fiber microstructure after CMC processing were characterized by optical microscopy, SEM, and extensively by TEM. In AlOCl degraded fibers, grain boundaries near the fiber surface were wetted with a glass that contained Y₂O₃/SiO₂ or Y₂O₃/La₂O₃/P₂O₅/SiO₂, and near‐surface pores were partially filled with Al₂O₃. This glass must also contain some Al₂O₃ and initially some chlorine. AlOCl decomposition products were predicted using the FactSage^® Thermochemical code, and were characterized by mass spectrometry. Effects of AlOCl precursors on monazite coated and uncoated Nextel? 610 fibers tow and filament strength were evaluated. A mechanism for the severe degradation of the oxide‐oxide CMCs and Nextel? 610 fibers that involves subcritical crack growth promoted by release of chlorine containing species during breakdown of intergranular glasses in an anhydrous environment is proposed.     

Selective oxidation of H2S in Claus tail-gas over SiC supported NiS2 catalyst

Very high activity and selectivity could be achieved for the direct oxidation of H₂S into elemental sulfur at low reaction temperature (40–60°C), on nickel sulfide supported SiC catalyst. The heterogeneous nature of the support surface (hydrophilic and hydrophobic areas) could explain the important role played by water to maintain a high and stable H₂S conversion level. The formation of a very active superficial nickel oxysulfide phase was proposed in order to explain the activation period necessary at reaction temperatures <60°C. Total selectivity for sulfur was attributed to the very low reaction temperature and the absence of any microporosity in the support.