Catalytic production of branched small alkanes from biohydrocarbons

Hydroaminoalkylation for Amine Functionalization of Vinyl-Terminated Polyethylene Enables Direct Access to Responsive Functional Materials

While functionalized polyethylenes (PEs) exhibit valuable characteristics, the constraints of existing synthetic approaches limit the variety of readily incorporated functionality. New methods to generate functionalized PEs are required to afford new applications of this common material. We report 100 % atom economic tantalum-catalyzed hydroaminoalkylation of vinyl-terminated polyethylene (VTPE) as a method to produce amine-terminated PE. VTPEs with molecular weights between 2200-16800 g/mol are successfully aminated using solvent-free conditions. Our catalytic system is efficient for the installation of both aromatic and aliphatic amines, and can be carried out on multigram scale. The associating amine functional groups afford modified material properties, as measured by water contact angle, differential scanning calorimetry (DSC) and polymer rheology. The basic amine functionality offers the opportunity to convert inert PE into stimuli-responsive materials, such that the protonation of aminated PE affords the generation of functional antibacterial PE films.

Diverse uses of valuable seafood processing industry waste for sustainability: a review

Seafoods are rich in untapped bioactive compounds that have the potential to provide novel ingredients for the development of commercial functional foods and pharmaceuticals. Unfortunately, a large portion of waste or discards is generated in commercial processing setups (50-80%), which is wasted or underutilized. These by-products are a rich source of novel and valuable biomolecules, including bioactive peptides, collagen and gelatin, oligosaccharides, fatty acids, enzymes, calcium, water-soluble minerals, vitamins, carotenoids, chitin, chitosan and biopolymers. These fish components may be used in the food, cosmetic, pharmaceutical, environmental, biomedical and other industries. Furthermore, they provide a viable source for the production of biofuels. As a result, the current review emphasizes the importance of effective by-product and discard reduction techniques that can provide practical and profitable solutions. Recognizing this, many initiatives have been initiated to effectively use them and generate income for the long-term sustainability of the environment and economic framework of the processing industry. This comprehensive review summarizes the current state of the art in the sustainable valorisation of seafood by-products for human consumption. The review can generate a better understanding of the techniques for seafood waste valorisation to accelerate the sector while providing significant benefits.

Catalytic Upcycling of Polyolefins

The large production volumes of commodity polyolefins (specifically, polyethylene, polypropylene, polystyrene, and poly(vinyl chloride)), in conjunction with their low unit values and multitude of short-term uses, have resulted in a significant and pressing waste management challenge. Only a small fraction of these polyolefins is currently mechanically recycled, with the rest being incinerated, accumulating in landfills, or leaking into the natural environment. Since polyolefins are energy-rich materials, there is considerable interest in recouping some of their chemical value while simultaneously motivating more responsible end-of-life management. An emerging strategy is catalytic depolymerization, in which a portion of the C-C bonds in the polyolefin backbone is broken with the assistance of a catalyst and, in some cases, additional small molecule reagents. When the products are small molecules or materials with higher value in their own right, or as chemical feedstocks, the process is called upcycling. This review summarizes recent progress for four major catalytic upcycling strategies: hydrogenolysis, (hydro)cracking, tandem processes involving metathesis, and selective oxidation. Key considerations include macromolecular reaction mechanisms relative to small molecule mechanisms, catalyst design for macromolecular transformations, and the effect of process conditions on product selectivity. Metrics for describing polyolefin upcycling are critically evaluated, and an outlook for future advances is described.

Catalytic Strategies for the Upcycling of Polyolefin Plastic Waste

Chemical upgrading of waste plastics is currently one of the most important methods for addressing plastic pollution. In comparison to the current methods of incineration or landfill, chemical upgrading enables the utilization of carbon and hydrogen elements in waste plastics as resources. This process strongly relies on efficient catalysts and reaction systems. Through catalyst design, waste plastics can be converted into fuels or chemicals under the optimized reaction conditions, extending their life cycles. In this review, we systematically discuss various chemical conversion methods for polyolefin waste plastics, which account for a large proportion of waste plastics. We further explore the remaining challenges and future development trends in this field, including improving product value through product engineering and shifting research perspectives to exploring the tolerance of catalysts toward impurities in practical waste plastic waste rather than using pure plastic feedstock.

Boosting Polyethylene Hydrogenolysis Performance of Ru-CeO2 Catalysts by Finely Regulating the Ru Sizes

Hydrogenolysis is an effective method for converting polyolefins into high-value chemicals. For the supported catalysts commonly used, the size of active metals is of great importance. In this study, it is discovered that the activity of CeO2 -supported Ru single atom, nanocluster, and nanoparticle catalysts shows a volcanic trend in low-density polyethylene (LDPE) hydrogenolysis. Compared with CeO2 supported Ru single atoms and nanoparticles, CeO2 -supported Ru nanoclusters possess the highest conversion efficiency, as well as the best selectivity toward liquid alkanes. Through comprehensive investigations, the metal-support interactions (MSI) and hydrogen spillover effect are revealed as the two key factors in the reaction. On the one hand, the MSI is strongly related to the Ru surface states and the more electronegative Ru centers are beneficial to the activation of CH and CC bonds. On the other hand, the hydrogen spillover capability directly affects the affinity of catalysts and active H atoms, and increasing this affinity is advantageous to the hydrogenation of alkane species. Decreasing the Ru sizes can promote the MSI, but it can also reduce the hydrogen spillover effect. Therefore, only when the two effects achieve a balance, as is the case in CeO2 -supported Ru nanoclusters, can the hydrogenolysis activity be promoted to the optimal value.

Hydrogenolysis-Isomerization of Waste Polyolefin Plastics to Multibranched Liquid Alkanes

Upcycling of waste polyolefin plastics still meets with economic and technological challenges in practice. In this work, the catalytic hydrogenolysis-isomerization of nondegradable polyolefin plastic waste to high-value gasoline, diesel, and light lubricants with highly branched chain is achieved over a bifunctional Rh/Nb₂ O₅ catalyst under relatively mild conditions. Owing to the high efficiency of metallic Rh active sites, the dehydrogenation/hydrogenation of long carbon chains of polyolefins is enhanced. With the assistance of strong Brønsted acidity of Nb₂ O₅ , the cleavage of C-C bonds, skeletal rearrangements, as well as the β-scission of alkylcarbenium ions occurs, which boosts the one-step solvent-free catalytic hydrogenolysis and isomerization of polyolefins. In addition, the preliminary economic analysis shows that this technology is economical, feasible, and has great potential in accelerating the transition to a circular plastics economy for sustainable development.

Converting Plastic Wastes to Naphtha for Closing the Plastic Loop

To solve the serious environmental problem and huge resource waste of plastic pollution, we report a tandem catalytic conversion of low-density polyethylene (LDPE) into naphtha, the key feedstock for renewable plastic production. Using β zeolite and silicalite-1-encapsulated Pt nanoparticles (Pt@S-1), a naphtha yield of 89.5% is obtained with 96.8% selectivity of C5-C9 hydrocarbons at 250 °C. The acid sites crack long-chain LDPE into olefin intermediates, which diffuse within the channels of Pt@S-1 to encounter Pt nanoparticles. The hydrogenation over confined metal matches cracking steps by selectively shipping the olefins with right size, and the rapid diffusion boosts the formation of narrow-distributed alkanes. A conceptual upgrading indicates it is suitable for closing the plastic loop, with a significant energy saving of 15% and 30% reduced greenhouse gas emissions.

Sustainably Recycling and Upcycling of Single-Use Plastic Wastes through Heterogeneous Catalysis

The huge amount of plastic waste has caused a series of environmental and economic problems. Depolymerization of these wastes and their conversion into desired chemicals have been regarded as a promising route for dealing with these issues, which strongly relies on catalysis for C-C and C-O bond cleavage and selective transformation. Here, we reviewed recent developments in catalysis systems for dealing with single-use plastics, such as polyethylene, polypropylene, and polyethylene glycol terephthalate. The recycling processes of depolymerization into original monomers and conversion into other economic-incentive chemicals were systemically discussed. Rational designs of catalysts for efficient conversion were particularly highlighted. Overall, improving the tolerance of catalysts to impurities in practical plastics, reducing the economic cost during the catalytic depolymerization process, and trying to obtain gaseous hydrogen from plastic wastes are suggested as the developing trends in this field.

Catalytic Depolymerization of Waste Polyolefins by Induction Heating: Selective Alkane/Alkene Production

Low- and high-density polyethylene (LDPE/HDPE) have been selectively depolymerized, without added H2, to C2-C20 + alkanes/alkenes via energy-efficient radio frequency induction heating, coupled with dual-functional heterogeneous Fe3O4 and Ni- or Pt-based catalysts. Fe3O4 was used to locally generate heat when exposed to magnetic fields. Initial results indicate that zeolite-based Ni catalysts are more selective to light olefins, while Ni supported on ceria catalysts are more selective to C7-C14 alkanes/alkenes. LDPE conversions up to 94% were obtained with minimal aromatic, coke, or methane formation which are typically observed with thermal heating. Two depolymerization mechanisms, a reverse Cossee-Arlman mechanism or a random cleavage process, were proposed to account for the different selectivities. The depolymerization process was also tested on commercial LDPE (grocery bags), polystyrene, and virgin HDPE using the Ni on Fe3O4 catalyst, with the LDPE resulting in similar product conversion (∼48%) and selectivity as for virgin LDPE.

Recent Progress in the Chemical Upcycling of Plastic Wastes

The massive generation of plastic wastes without satisfactory treatment has induced severe environmental problems and gained increasing attentions. In this Minireview, recent progresses in the chemical upcycling of plastic wastes by using various methods (mainly in the past three to five years) is summarized. The chemical upcycling of plastic wastes points out a "plastic-based refinery" concept, which is to use the plastic wastes as platform feedstocks to produce highly valuable monomeric or oligomeric compounds, putting the plastic wastes back into a circular economy. The different chemical methods to upcycle plastic wastes, including hydrogenolysis, photocatalysis, pyrolysis, solvolysis, and others, are introduced in each section to valorize diverse plastic feedstocks into value-added chemicals, materials, or fuels. In addition, other emerging technologies as well as the new generation of plastic thermosets are covered.

Polyethylene Hydrogenolysis at Mild Conditions over Ruthenium on Tungstated Zirconia

Plastics waste has become a major environmental threat, with polyethylene being one of the most produced and hardest to recycle plastics. Hydrogenolysis is potentially the most viable catalytic technology for recycling. Ruthenium (Ru) is one of the most active hydrogenolysis catalysts but yields too much methane. Here we introduce ruthenium supported on tungstated zirconia (Ru-WZr) for hydrogenolysis of low-density polyethylene (LDPE). We show that the Ru-WZr catalysts suppress methane formation and produce a product distribution in the diesel and wax/lubricant base-oil range unattainable by Ru-Zr and other Ru-supported catalysts. Importantly, the enhanced performance is showcased for real-world, single-use LDPE consumables. Reactivity studies combined with characterization and density functional theory calculations reveal that highly dispersed (WO x )n clusters store H as surface hydroxyls by spillover. We correlate this hydrogen storage mechanism with hydrogenation and desorption of long alkyl intermediates that would otherwise undergo further C-C scission to produce methane.

Catalytic methods for chemical recycling or upcycling of commercial polymers

Polymers (plastics) have transformed our lives by providing access to inexpensive and versatile materials with a variety of useful properties. While polymers have improved our lives in many ways, their longevity has created some unintended consequences. The extreme stability and durability of most commercial polymers, combined with the lack of equivalent degradable alternatives and ineffective collection and recycling policies, have led to an accumulation of polymers in landfills and oceans. This problem is reaching a critical threat to the environment, creating a demand for immediate action. Chemical recycling and upcycling involve the conversion of polymer materials into their original monomers, fuels or chemical precursors for value-added products. These approaches are the most promising for value-recovery of post-consumer polymer products; however, they are often cost-prohibitive in comparison to current recycling and disposal methods. Catalysts can be used to accelerate and improve product selectivity for chemical recycling and upcycling of polymers. This review aims to not only highlight and describe the tremendous efforts towards the development of improved catalysts for well-known chemical recycling processes, but also identify new promising methods for catalytic recycling or upcycling of the most abundant commercial polymers.

Mining of squalene as a value-added byproduct from DHA producing marine thraustochytrid cultivated on food waste hydrolysate

The commercial production of docosahexaenoic acid (DHA) from oleaginous microorganisms is getting more attention due to several advantages over fish oils. The processing cost became a major bottleneck for commercialization of DHA from microorganisms. The most of cost shares in the feedstock to cultivate the microorganisms and downstream processing. The cost of feedstock can be compensated with the utilization of substrate from waste stream whereas production of value-added chemicals boosts the economic viability of nutraceutical production. In the present study, the docosahexaenoic acid (DHA)-producing marine protist Aurantiochytrium sp. T66 was cultivated on post-consumption food waste hydrolysate for the mining of squalene. After 120 h of cultivation, cell dry weight was 14.7 g/L, of which 6.34 g/L (43.13%; w/w) were lipids. DHA accounted for 2.15 g/L (34.05%) of total extracted lipids or 0.15 g/g_CDW. Maximum squalene concentration and yield were 1.05 g/L and 69.31 mg/g_CDW, respectively. Hence, utilization of food waste represents an excellent low-cost strategy for cultivating marine oleaginous thraustochytrids and produce squalene as a byproduct of DHA.

Co-production of DHA and squalene by thraustochytrid from forest biomass

Omega-3 fatty acids, and specifically docosahexaenoic acid (DHA), are important and essential nutrients for human health. Thraustochytrids are recognised as commercial strains for nutraceuticals production, they are group of marine oleaginous microorganisms capable of co-synthesis of DHA and other valuable carotenoids in their cellular compartment. The present study sought to optimize DHA and squalene production by the thraustochytrid Schizochytrium limacinum SR21. The highest biomass yield (0.46 g/g_substrate) and lipid productivity (0.239 g/g_substrate) were observed with 60 g/L of glucose, following cultivation in a bioreactor, with the DHA content to be 67.76% w/w_{total lipids}. To reduce costs, cheaper feedstocks and simultaneous production of various value-added products for pharmaceutical or energy use should be attempted. To this end, we replaced pure glucose with organosolv-pretreated spruce hydrolysate and assessed the simultaneous production of DHA and squalene from S. limacinum SR21. After the 72 h of cultivation period in bioreactor, the maximum DHA content was observed to 66.72% w/w_{total lipids} that was corresponded to 10.15 g/L of DHA concentration. While the highest DHA productivity was 3.38 ± 0.27 g/L/d and squalene reached a total of 933.72 ± 6.53 mg/L (16.34 ± 1.81 mg/g_CDW). In summary, we show that the co-production of DHA and squalene makes S. limacinum SR21 appropriate strain for commercial-scale production of nutraceuticals.

Upcycling Single-Use Polyethylene into High-Quality Liquid Products

Our civilization relies on synthetic polymers for all aspects of modern life; yet, inefficient recycling and extremely slow environmental degradation of plastics are causing increasing concern about their widespread use. After a single use, many of these materials are currently treated as waste, underutilizing their inherent chemical and energy value. In this study, energy-rich polyethylene (PE) macromolecules are catalytically transformed into value-added products by hydrogenolysis using well-dispersed Pt nanoparticles (NPs) supported on SrTiO₃ perovskite nanocuboids by atomic layer deposition. Pt/SrTiO₃ completely converts PE (M _n = 8000-158,000 Da) or a single-use plastic bag (M _n = 31,000 Da) into high-quality liquid products, such as lubricants and waxes, characterized by a narrow distribution of oligomeric chains, at 170 psi H₂ and 300 °C under solvent-free conditions for reaction durations up to 96 h. The binding of PE onto the catalyst surface contributes to the number averaged molecular weight (M _n) and the narrow polydispersity (Đ) of the final liquid product. Solid-state nuclear magnetic resonance of ¹³C-enriched PE adsorption studies and density functional theory computations suggest that PE adsorption is more favorable on Pt sites than that on the SrTiO₃ support. Smaller Pt NPs with higher concentrations of undercoordinated Pt sites over-hydrogenolyzed PE to undesired light hydrocarbons.

Simultaneous production of DHA and squalene from Aurantiochytrium sp. grown on forest biomass hydrolysates

BACKGROUND

Recent evidence points to the nutritional importance of docosahexaenoic acid (DHA) in the human diet. Thraustochytrids are heterotrophic marine oleaginous microorganisms capable of synthesizing high amounts of DHA, as well as other nutraceutical compounds such as squalene, in their cellular compartment. Squalene is a natural triterpene and an important biosynthetic precursor to all human steroids. It has a wide range of applications in the cosmetic and pharmaceutical industries, with benefits that include boosting immunity and antioxidant activity. Apart from its nutritional quality, it can also be utilized for high-grade bio-jet fuel by catalytic conversion.

RESULTS

In the present study, the potential of thraustochytrid strain Aurantiochytrium sp. T66 to produce DHA and squalene was evaluated. When the strain was cultivated on organosolv-pretreated birch hydrolysate (30 g/L glucose) in flask, it resulted in 10.39 g/L of cell dry weight and 4.98 g/L of total lipids, of which 25.98% was DHA. In contrast, when the strain was grown in a bioreactor, cell dry weight, total lipid, and DHA increased to 11.24 g/L, 5.90 g/L, and 35.76%, respectively. The maximum squalene yield was 69.31 mg/gCDW (0.72 g/L) when the strain was cultivated in flask, but it increased to 88.47 mg/gCDW (1.0 g/L), when cultivation shifted to a bioreactor.

CONCLUSIONS

This is the first report demonstrating the utilization of low cost non-edible lignocellulosic feedstock to cultivate the marine oleaginous microorganism Aurantiochytrium sp. for the production of nutraceutical vital compounds. Owing to the simultaneous generation of DHA and squalene, the strain is suitable for industrial-scale production of nutraceuticals.

Selective hydrogenation of amides to alcohols in water solvent over a heterogeneous CeO2-supported Ru catalyst

CeO₂-supported Ru (Ru/CeO₂) worked as an effective and reusable heterogeneous catalyst for the selective dissociation of the C–N bond in amides, particularly primary amides, with H₂ in water solvent at low reaction temperature of 333 K.

Synthesis of Renewable Lubricant Alkanes from Biomass-Derived Platform Chemicals

The catalytic synthesis of liquid alkanes from renewable biomass has received tremendous attention in recent years. However, bio-based platform chemicals have not to date been exploited for the synthesis of highly branched lubricant alkanes, which are currently produced by hydrocracking and hydroisomerization of long-chain n-paraffins. A selective catalytic synthetic route has been developed for the production of highly branched C₂₃ alkanes as lubricant base oil components from biomass-derived furfural and acetone through a sequential four-step process, including aldol condensation of furfural with acetone to produce a C₁₃ double adduct, selective hydrogenation of the adduct to a C₁₃ ketone, followed by a second condensation of the C₁₃ ketone with furfural to generate a C₂₃ aldol adduct, and finally hydrodeoxygenation to give highly branched C₂₃ alkanes in 50.6 % overall yield from furfural. This work opens a general strategy for the synthesis of high-quality lubricant alkanes from renewable biomass.

Taxonomy, ecology and biotechnological applications of thraustochytrids: A review

Thraustochytrids were first discovered in 1934, and since the 1960's they have been increasingly studied for their beneficial and deleterious effects. This review aims to provide an enhanced understanding of these protists with a particular emphasis on their taxonomy, ecology and biotechnology applications. Over the years, thraustochytrid taxonomy has improved with the development of modern molecular techniques and new biochemical markers, resulting in the isolation and description of new strains. In the present work, the taxonomic history of thraustochytrids is reviewed, while providing an up-to-date classification of these organisms. It also describes the various biomarkers that may be taken into consideration to support taxonomic characterization of the thraustochytrids, together with a review of traditional and modern techniques for their isolation and molecular identification. The originality of this review lies in linking taxonomy and ecology of the thraustochytrids and their biotechnological applications as producers of docosahexaenoic acid (DHA), carotenoids, exopolysaccharides and other compounds of interest. The paper provides a summary of these aspects while also highlighting some of the most important recent studies in this field, which include the diversity of polyunsaturated fatty acid metabolism in thraustochytrids, some novel strategies for biomass production and recovery of compounds of interest. Furthermore, a detailed overview is provided of the direct and current applications of thraustochytrid-derived compounds in the food, fuel, cosmetic, pharmaceutical, and aquaculture industries and of some of the commercial products available. This review is intended to be a source of information and references on the thraustochytrids for both experts and those who are new to this field.

Novel squalene-producing thraustochytrids found in mangrove water

On extended screening of squalene-producing strains in Okinawa mangrove water, we identified 14 novel squalene-producing thraustochytrids from 172 unialgal clonal isolates. The novel thraustochytrids produced 13.9-7.54 mg squalene/g dry cell weight. Eight isolates were found to belong to potentially novel squalene-producing genera, forming a monophyletic cluster independent from any known thraustochytrids.

Regioselectivity and Reaction Mechanism of Ru-Catalyzed Hydrogenolysis of Squalane and Model Alkanes

The dependence of the C-C hydrogenolysis activity on reaction parameters and the structure of the substrate alkanes was investigated for Ru/CeO₂ catalyst with very small (dispersion: H/Ru=0.89) Ru particles. The substrate concentration and reaction temperature did not have a significant effect on the selectivity pattern, except that methane production was promoted at high temperatures. However, the hydrogen pressure had a marked effect on the selectivity pattern. C_tertiary -C bond dissociation, terminal C_secondary -C_primary bond dissociation, and fragmentation to form excess methane had negative reaction order with respect to hydrogen partial pressure, whereas C_secondary -C_secondary bond dissociation had an approximately zero reaction order. Therefore, a high hydrogen pressure is essential for the regioselective hydrogenolysis of C_secondary -C_secondary bonds in squalane. Ru/SiO₂ catalyst with larger Ru particles showed similar changes in the product distribution during the change in hydrogen pressure. The reaction mechanism for each type of C-C bond dissociation is proposed based on reactivity trends and DFT calculations. The proposed intermediate species for the internal C_secondary -C_secondary dissociation, terminal C_secondary -C_primary dissociation, and C_tertiary -C dissociation is alkyls, alkylidynes, and alkenes, respectively.

Potential and challenges of zeolite chemistry in the catalytic conversion of biomass

This review emphasizes the progress, potential and future challenges in zeolite catalysed biomass conversions and relates these to concepts established in existing petrochemical processes.

The production of bio-jet fuel from Botryococcus braunii liquid over a Ru/CeO2catalyst

In this study, the conversion fromBotryococcus brauniiliquid to bio-jet fuelviaa Ru/CeO₂catalyst was conducted.