Polyamide Monomers Research Articles

One-Pot Biocatalytic Route from Alkanes to α,ω-Diamines by Whole-Cell Consortia of Engineered Yarrowia lipolytica and Escherichia coli.

Metabolically engineered microbial consortia can contribute as a promising production platform for the supply of polyamide monomers. To date, the biosynthesis of long-chain α,ω-diamines from n-alkanes is challenging because of the inert nature of n-alkanes and the complexity of the overall synthesis pathway. We combined an engineered Yarrowia lipolytica module with Escherichia coli modules to obtain a mixed strain microbial consortium that could catalyze an efficient biotransformation of n-alkanes into corresponding α,ω-diamines. The engineered Y. lipolytica strain was constructed (YALI10) wherein the two genes responsible for β-oxidation and the five genes responsible for the overoxidation of fatty aldehydes were deleted. This newly constructed YALI10 strain expressing transaminase (TA) could produce 0.2 mM 1,12-dodecanediamine (40.1 mg/L) from 10 mM n-dodecane. The microbial consortia comprising engineered Y. lipolytica strains for the oxidation of n-alkanes (OM) and an E. coli amination module (AM) expressing an aldehyde reductase (AHR) and transaminase (TA) improved the production of 1,12-diamine up to 1.95 mM (391 mg/L) from 10 mM n-dodecane. Finally, combining the E. coli reduction module (RM) expressing a carboxylic acid reductase (CAR) and an sfp phosphopantetheinyl transferase with OM and AM further improved the production of 1,12-diamine by catalyzing the reduction of undesired 1,12-diacids into 1,12-diols, which further undergo amination to give 1,12-diamine as the target product. This newly constructed mixed strain consortium comprising three modules in one pot gave 4.1 mM (41%; 816 mg/L) 1,12-diaminododecane from 10 mM n-dodecane. The whole-cell consortia reported herein present an elegant "greener" alternative for the biosynthesis of various α,ω-diamines (C8, C10, C12, and C14) from corresponding n-alkanes.

Highly permeable PA@GO loose nanofiltration membranes enabled by hierarchical transport channels for efficient dye removal

Graphene oxide (GO) membranes exhibit ultrafast water permeation properties, which have been employed in various membrane-based separations including nanofiltration for dye removal from textile wastewater. However, it’s still a great challenge to achieve precise control over the microstructure of GO membranes and obtain ultrathin GO membranes with exceptional separation efficiency and robust membrane structure. Herein, in-situ confined interfacial polymerization (IP) is proposed for fabricating loose polyamide (PA)@GO hybrid membranes with high permeance and dye rejection as well as robust membrane stability. A new diamine of sulfadiazine (SA) with intrinsic hydrophilic and conjugated sulfonamide groups is employed as cross-linker of GO membranes and monomer of PA in IP process, simultaneously. PA is in-situ synthesized in confined GO interlayer via IP process and intercalated into GO interlayer, which enlarges the interlayer spacing of GO membranes gradiently. The combination of hydrophilic PA nanofiltration layer on GO membrane surface and the PA intercalated GO membrane with varying interlayer spacing creates hierarchical transport channels for water molecules, which contributes to the high water permeance. Moreover, the less reactive SA monomer endows PA@GO selective layer with appropriate negative charge and loose transport channels, which contributes to both of high permeance and dye rejection due to Donnon effect and size exclusion effect. The PA@GO hybrid membrane exhibits high permeance of 75.5 L/(m2·h·bar) with TB dye rejection of 99.8 %, and exhibits low NaCl rejection of 11.6 %. Moreover, PA@GO hybrid membrane shows good fouling resistance and long-term stability as well as stable separation performance under harsh conditions. Both of high permeance and dye rejection of PA@GO hybrid membrane suggests that the integration of PA nanofiltration layer and GO membrane via in-situ confined interfacial polymerization can achieve the delicate control over the interlayer channel structure and the physicochemical properties of the membrane surface of GO membranes, which offers a promising method to break through the trade-off effect between permeability and selectivity of GO membranes.

Microfluidic preparation of thin film composite hollow fiber membrane modules for water nanofiltration: Up-scaling, reproducibility and MOF based layers

BackgroundThe commercialization of thin film composite (TFC) hollow fiber (HF) membranes remains challenging owing to issues associated with membrane manufacturing. MethodsTFC membranes were synthesized by microfluidic interfacial polymerization of polyamide (PA) on polysulfone hollow fiber (HF) membrane modules. A total of 33 HF membrane modules were prepared with different number of HFs (from 1 to 25) and different lengths (from 10 to 50 cm). They were evaluated in a nanofiltration operation in terms of water permeance and rose Bengal (RB) and MgSO4 rejections. Significant findingsAmong the 33 modules, 73% showed RB rejections higher than 95%, while 36% of the modules reached rejections above 99%. During the membrane synthesis, different parameters, such as PA monomer concentration, residence time and reaction time, were studied. As a result, the amount of monomer was reduced by ca. 80%. The versatility of microfluidics allowed incorporating hydrophilic metal-organic framework (MOF) ZIF-93 to produce HF modules with PA/MOF bilayered membranes (a continuous layer of MOF between the support and the PA film) which led to an important enhancement of the water permeance from 1.3 (bare PA membrane) to 5.3 L·m−2·h−1·bar−1 (PA/ZIF-93 HF membrane), maintaining RB rejection above 95%.

Bio-based long-chain aliphatic polyamide with intrinsic flame retardancy and great overall properties

Bio-based long-chain aliphatic polyamides show remarkable potential in pursuing high-performance, sustainable bio-plastics. However, the aliphatic structure also leads to high flammability that severely restricts their applications. Herein, we demonstrate a novel flame-retardant system to fabricate high-performance, flame-retardant bio-based long-chain aliphatic polyamide. In this system, a novel reactive nitrogen-based flame-retardant monomer, PDB, was designed and synthesized. Subsequently, the corresponding bio-based long-chain polyamide copolymer was prepared through a facile polycondensation process. The nitrogen-based groups exhibited highly efficient free-radical-capturing effect, helping the copolymer achieve a high limiting oxygen index value of 32.6%, the UL-94 V-0 rating, a 33.3% lower peak heat release rate, and inhibited the release of toxic gasses at a PDB content of 6 wt%. Furthermore, the copolymer exhibited largely maintained crystallinity, thermal stability, and mechanical properties, owing to the high reactivity of PBD with polyamide monomers. At the same time, the incorporation of PBD increased the rigidity of the copolymer, resulting in a significant increase of 16.4 °C in the glass transition temperature and lower dielectric properties. This work provides a new perspective on the preparation of bio-based long-chain aliphatic polyamide with enhanced overall properties.

Biosynthesis of aliphatic plastic monomers with amino residues in Yarrowia lipolytica.

Introduciton: The α,ω-diamines (NH2-(CH2)n-NH2) and ω -amino fatty acids (NH2-(CH2)n-COOH) have been widely used as building blocks in polymerindustries. Medium- to long-chain (C8 to C18) fatty acid monomers with amino residues are almost exclusively produced via chemical processes that generate hazardous waste and induce severe environmental problems, such as global warming and pollution. Here, we present the construction platformstrains of Yarrowia lipolytica a cheese-ripening yeast, for direct biotransformation of hydrocarbons into medium- to long-chain α,ω-diamines and ωamino fatty acids using metabolic engineering of endogenous fatty acid ω- and β-oxidation pathways and introducing heterologous ω-transaminase in Y. lipolytica. Methods: We deleted six genes encoding the acyl-CoA oxidase (ACO1-6) and four fatty aldehyde dehydrogenase genes (FALDH1-4), which catalyze fatty acid β-oxidation and downstream oxidation of fatty aldehydes in Y. lipolytica, respectively. The ω-transaminase from Chromobacterium violaceum DSM30191 was introduced into the genome of the ΔPOX ΔFALDH strain under the control of Y. lipolytica-derived EXP1 promoters. Results and Discussion: The ΔPOX ΔFALDH strains with ω-CvTA successfully accumulated the corresponding C12 αω-diamines into a shaking culture medium with dodecane or dodecanol. In addition, these strains accumulated C12 ω-amino fatty acids from dodecanoic acid. With the commercially available α,ω-diacid bioprocess, this yeast biosynthesis producing medium- and longchain α,ω-diamines and ω-amino fatty acids could complete the yeast platform technology generating all medium- and long-chain aliphatic polyamide monomers, α,ω-biofunctionalized with one or both carboxylic acid and amino residues.

Oxidation resistances of polyamide nanofiltration membranes to hydroxyl and sulfate radicals

The oxidation compatibility with polyamide membranes is an important feature of nanofiltration (NF) technology in practical water treatment processes. In this study, we systematically investigated the oxidation resistance of fully aromatic (NF90) and semi-aromatic (NF270) polyamide NF membranes to reactive oxidative species including SO4•- and HO• in terms of membrane surface properties and filtration performance. SO4•− and HO• exhibit different oxidative behaviors in NF membranes with different polyamide structures. The HO•-dominated oxidation significantly damaged the membrane integrity of NF90 and NF270, with notably varied surface morphology, hydrophilicity, and charge. Further analysis of the chemical property on membrane surfaces revealed that the SO4•−-dominated oxidation was more reactive to the N moieties (N–H or N–C) of the NF90 membrane, whereas HO• unselectively reacted with polyamides. The radicals also impact the permselectivity (water permeability and salt rejection) of the NF90 and NF270 membranes in different ways. The NF90 membrane after SO4•−-exposure exhibited higher water permeability and slightly decreased salt rejection, whereas the permselectivity of the NF270 membrane was more significantly affected by HO•-exposure. To further reveal the underlying oxidation mechanisms, polyamide monomers were selected to react with the peroxodisulfate solutions. The results demonstrated that a fully aromatic polyamide membrane was more resistant to oxidative radicals than a semi-aromatic polyamide membrane. This study will facilitate the development of novel antioxidant membranes and provide information for selecting appropriate membrane materials in specific water treatment processes.

UV aging of microplastic polymers promotes their chemical transformation and byproduct formation upon chlorination

The presence and accumulation of microplastics (MPs) in water and wastewater is a growing concern. When released to the water bodies, microplastics can be subject to surface weathering due to ultraviolet (UV) exposure. In this study, the effects of UV aging of six MP polymers from three groups (e.g., polyamide, polyester, and polyolefin) on their chlorine reactivity, chemical transformation, and formation of disinfection byproducts (DBPs) were studied. Polyamide (e.g., polyamide 6) in both virgin and UV-aged forms showed significantly higher chlorine demands than other MP polymers (915.5–947.9 versus 7.0–21.1 μmol/g MP in 24 h), and polyolefins were relatively inert to chlorine. UV aging enhanced the destructions of functional groups of polyamide and polyester upon chlorination, promoting the chlorine demands and leaching of organics by up to 1.7- and 2.4-fold, respectively. Polymer monomer and oligomers of polyamide 6 and toxic or endocrine disrupting additives (e.g., dimethyl phthalate and butyl octyl phthalate) were identified in leachates from chlorinated MP polymers by mass spectrometry. Meanwhile, up to >10-fold increases in the yields of trihalomethane, haloacetic acid, haloacetaldehyde, haloacetonitrile, and haloacetamide were observed from 30-day UV-aged MP polymers as compared to their virgin counterparts. Overall, this study reveals that UV aging can promote the reactivity and chemical transformation of MP polymers during chlorination, especially for polyamide and polyester, increase the release of polymer monomers, oligomers, and additives, and aggravate the role of MP polymers as DBP precursors.

Effective whole cell biotransformation of arginine to a four-carbon diamine putrescine using engineered Escherichia coli

The rising awareness of environmental protection has triggered bio-based materials to replace the traditional petrochemical plastics. Putrescine as 1,4-diaminobutane is an important monomer of polyamide (PA) and uses in the sustainable chemical industry. Herein, a time-effective whole cell bioconversion of L-arginine to putrescine was developed, which has applied the key enzymes (i.e., SpeA and SpeB) from the arginine decarboxylase (ADC) pathway. The synergetic collaboration of both enzymes was examined from the different combination of plasmids among 4 Escherichia coli chassis. The optimal reaction condition was at pH 9 with 1 mM pyridoxal-5′-phosphate (PLP) and 10 mM magnesium, thus 90% conversion was obtained using an all-in-one plasmid with equal protein of SpeA and SpeB in BL21(DE3). The enzymatic kinetics demonstrated the higher kcat of SpeA (1212 s−1) than that of SpeB (418 s−1), while severe inhibition of putrescine on SpeA (KI = 8.61 mM), thus it was disadvantage using the surface display of enzyme. To prevent the feedback-inhibition by product, a 2-step enzymatic reaction with cold treatment was conducted. Finally, the putrescine was achieved 17.1 g/L with the productivity of 8.56 g/L/h under 86% conversion of 50 g/L L-arginine-HCl, which is an effective approach to obtain high putrescine titer.

Model-Guided Metabolic Rewiring for Gamma-Aminobutyric Acid and Butyrolactam Biosynthesis in Corynebacterium glutamicum ATCC13032

Simple SummaryThe fermentative production of desired chemicals from renewable resources is one of the promising biosynthetic routes to replace the petrochemical-based process. Gamma-aminobutyric acid (GABA) can be synthesized from l-glutamic acid and used as a building block for the synthesis of butyrolactam and polyamide 4 (nylon 4). The genome-scale metabolic model can predict the growth ability and metabolic flux distribution by genetic disturbances, which provides a strategy to construct a microbial cell factory for GABA and butyrolactam biosynthesis. Here, we performed model-guided metabolic engineering of Corynebacterium glutamicum ATCC13032 for GABA and butyrolactam fermentation from glucose. The biosynthetic pathways of GABA and butyrolactam were constructed by overexpressing the heterologous genes using a bi-cistronic expression cassette. The genetic modifications of the metabolic network cooperatively forced the carbon flux toward GABA and butyrolactam synthesis. This study provides new insights into engineering industrial microorganisms to produce target chemicals from renewable carbon sources.Gamma-aminobutyric acid (GABA) can be used as a bioactive component in the pharmaceutical industry and a precursor for the synthesis of butyrolactam, which functions as a monomer for the synthesis of polyamide 4 (nylon 4) with improved thermal stability and high biodegradability. The bio-based fermentation production of chemicals using microbes as a cell factory provides an alternative to replace petrochemical-based processes. Here, we performed model-guided metabolic engineering of Corynebacterium glutamicum for GABA and butyrolactam fermentation. A GABA biosynthetic pathway was constructed using a bi-cistronic expression cassette containing mutant glutamate decarboxylase. An in silico simulation showed that the increase in the flux from acetyl-CoA to α-ketoglutarate and the decrease in the flux from α-ketoglutarate to succinate drove more flux toward GABA biosynthesis. The TCA cycle was reconstructed by increasing the expression of acn and icd genes and deleting the sucCD gene. Blocking GABA catabolism and rewiring the transport system of GABA further improved GABA production. An acetyl-CoA-dependent pathway for in vivo butyrolactam biosynthesis was constructed by overexpressing act-encoding ß-alanine CoA transferase. In fed-batch fermentation, the engineered strains produced 23.07 g/L of GABA with a yield of 0.52 mol/mol from glucose and 4.58 g/L of butyrolactam. The metabolic engineering strategies can be used for genetic modification of industrial strains to produce target chemicals from α-ketoglutarate as a precursor, and the engineered strains will be useful to synthesize the bio-based monomer of polyamide 4 from renewable resources.

Modification Mechanism of Polyamide Reverse Osmosis Membrane by Persulfate: Roles of Hydroxyl and Sulfate Radicals.

Oxidative modification is a facile method to improve the desalination performance of thin-film composite membranes. In this study, we comparatively investigated the modification mechanisms induced by sulfate radical (SO4• -) and hydroxyl radical (HO•) for polyamide reverse osmosis (RO) membrane. The SO4• -- and HO•-based membrane modifications were manipulated by simply adjusting the pH of the thermal-activated persulfate solution. Although both of them improved the water permeability of the RO membrane under certain conditions, the SO4• --modified membrane notably prevailed over the HO•-modified one due to higher permeability, more consistent salt rejection rates over wide pH and salinity ranges, and better stability when exposed to high doses of chlorine. The differences of the membranes modified by the two radical species probably can be related to their distinct surface properties in terms of morphology, hydrophilicity, surface charge, and chemical composition. Further identification of the transformation products of a model polyamide monomer using high-resolution mass spectrometry demonstrated that SO4• - initiated polymerization reactions and produced hydroquinone/benzoquinone and polyaromatic structures; whereas the amide group of the monomer was degraded by HO•, generating hydroxyl, carboxyl, and nitro groups. The results will enlighten effective ways for practical modification of polyamide RO membranes to improve desalination performances and the development of sustainable oxidation-combined membrane processes.

EPDM‐g‐MAH toughened bio‐based polyamide 56 to prepare thermoplastic polyamide elastomer and the performance characterization

AbstractPolyamide is an engineering plastic, which has been widely used in industry and life. Polyamide 56, as a green and environmentally friendly bio‐based product, is gradually replacing traditional petroleum‐based products. However, in terms of auto parts, communication equipment, and mechanical products, a single polyamide monomer is difficult to meet the end‐use standard. EPDM‐g‐MAH (ethylene propylene diene monomer grafted with maleic anhydride) is melt blended with bio‐based polyamide 56 (PA56) in a twin‐screw extruder to obtain polyamide elastomers with different formulations. Subsequently, its morphology and structure, thermodynamic properties, crystallinity, and mechanical properties were analyzed. The test results show that the composites containing 10% EPDM‐g‐MAH have better impact resistance and thermal properties in the range of adding 0‑20 wt% EPDM‐g‐MAH. In the fracture morphology analysis, it is found that the interface between the rubber phase and the polyamide phase fused well, and the elastomer showed the ductile fracture.

Utilization of a Wheat Sidestream for 5-Aminovalerate Production in Corynebacterium glutamicum.

Production of plastics from petroleum-based raw materials extensively contributes to global pollution and CO2 emissions. Biotechnological production of functionalized monomers can reduce the environmental impact, in particular when using industrial sidestreams as feedstocks. Corynebacterium glutamicum, which is used in the million-ton-scale amino acid production, has been engineered for sustainable production of polyamide monomers. In this study, wheat sidestream concentrate (WSC) from industrial starch production was utilized for production of l-lysine–derived bifunctional monomers using metabolically engineered C. glutamicum strains. Growth of C. glutamicum on WSC was observed and could be improved by hydrolysis of WSC. By heterologous expression of the genes xylA Xc B Cg (xylA from Xanthomonas campestris) and araBAD Ec from E. coli, xylose, and arabinose in WSC hydrolysate (WSCH), in addition to glucose, could be consumed, and production of l-lysine could be increased. WSCH-based production of cadaverine and 5-aminovalerate (5AVA) was enabled. To this end, the lysine decarboxylase gene ldcC Ec from E. coli was expressed alone or for conversion to 5AVA cascaded either with putrescine transaminase and dehydrogenase genes patDA Ec from E. coli or with putrescine oxidase gene puo Rq from Rhodococcus qingshengii and patD Ec . Deletion of the l-glutamate dehydrogenase–encoding gene gdh reduced formation of l-glutamate as a side product for strains with either of the cascades. Since the former cascade (ldcC Ec -patDA Ec ) yields l-glutamate, 5AVA production is coupled to growth by flux enforcement resulting in the highest 5AVA titer obtained with WSCH-based media.

Effect of halides on polyamide-based membrane flux and monomer degradation during chloramination

Polyamide (PA)-based membranes are widely used in reverse osmosis (RO) and nanofiltration (NF) but can react with chlorine-based disinfectants (free chlorine and chloramines) applied for biofouling control. This study examined how chloramines affected PA layer reactivity and performance when individual and mixed halides (Cl−, Br−, and I−) were present, since these reactants can form a host of different halogenating agents and reactive species. Experiments measured membrane (SWC4-LD) performance via flux, membrane surface chemistry using X-ray photoelectron spectroscopy (XPS), and PA monomer (i.e. benzanilide (BA)) reactivity, under varied halide (0 to seawater range) and pH (4–9) conditions. These experiments were also compared to other experiments that were chlorinated instead. Results indicated that flux differentials were the greatest after chlorination as compared to chloramination with or without Cl−, Br−, and/or I−, implying that chlorination was more detrimental to polyamide structural integrity. The limited role of Br− was supported by its low surface halogenation but contrasted its ability to rapidly transform the BA monomer to by-products. Mass transfer limitations within the rigid 2-D polymer structure likely drove this disparity. Subsequent addition of Cl− further lowered the membrane flux and advanced monomer transformation for all pH conditions, whereas I− did not significantly impact the membrane or monomer. As a consequence, membrane and monomer changes during chloramination were highly dependent on halide type. Such observations are intended to inform how chloramines may be used to reduce biofouling when halides are present in RO- and NF- feed waters.

Technical and Environmental Viability of a Road Bicycle Pedal Part Made of a Fully Bio-Based Composite Material.

Glass fibre is the most widely used material for reinforcing thermoplastic matrices presently and its use continues to grow. A significant disadvantage of glass fibre, however, is its impact on the environment, in particular, due to the fact that glass fibre-reinforced composite materials are difficult to recycle. Polyamide 6 is an engineering plastic frequently used as a matrix for high-mechanical performance composites. Producing polyamide monomer requires the use of a large amount of energy and can also pose harmful environmental impacts. Consequently, glass fibre-reinforced Polyamide 6 composites cannot be considered environmentally friendly. In this work, we assessed the performance of a road cycling pedal body consisting of a composite of natural Polyamide 11 reinforced with lignocellulosic fibres from stone-ground wood, as an alternative to the conventional glass fibre-reinforced Polyamide 6 composite (the most common material used for recreational purposes). We developed a 3D model of a pedal with a geometry based on a combination of two existing commercial choices and used it to perform three finite-element tests in order to assess its strength under highly demanding static and cyclic conditions. A supplementary life cycle analysis of the pedal was also performed to determine the ecological impact. Based on the results of the simulation tests, the pedal is considered to be mechanically viable and has a significantly lower environmental impact than fully synthetic composites.

Reactivity of the Polyamide Membrane Monomer with Free Chlorine: Role of Bromide.

Aromatic polyamide-based membranes are widely used for reverse osmosis (RO) and nanofiltration (NF) treatment but degrade when exposed to free chlorine (HOCl/OCl-). The reaction mechanisms with free chlorine were previously explored, but less is known about the role of bromide (Br-) in these processes. Br- may impact these reactions by reacting with HOCl to form HOBr, which then triggers other brominating agents (Br2O, Br2, BrOCl, and BrCl) to form. This study examined the reactivities of these brominating agents with a polyamide monomer model compound, benzanilide (BA), and a modified version of it, N-CH3-BA. The results indicated that all these brominating agents only attacked the aromatic ring adjacent to the amide N, rather than the amide N, different from the previously examined chlorinating agents (HOCl, OCl-, and Cl2) that attacked both sites. Orton rearrangement was not observed. Species-specific rate constants (ki, M-1 s-1) between BA and HOBr, Br2O, Br2, BrOCl, and BrCl were determined to be (5.3 ± 1.2) × 10-2, (1.2 ± 0.4) × 101, (3.7 ± 0.2) × 102, (2.2 ± 0.6) × 104, and (6.6 ± 0.9) × 104 M-1 s-1, respectively, such that kBrCl > kBrOCl > kBr2 > kBr2O > kHOBr. N-CH3-BA exhibited lower reactivity than BA. Model predictions of BA loss during chlorination with varied Br- and/or Cl- concentrations were established. These findings will ultimately enable membrane degradation and performance loss following chlorination in mixed halide solutions to be better predicted during pilot- and full-scale NF and RO treatment.

Polyamide monomers via carbonate-promoted C-H carboxylation of furfurylamine.

Inedible biomass (lignocellulose) is a largely untapped resource for polymer production because it is synthetically challenging to convert to useful monomers. Here we describe streamlined syntheses of two polyamide monomers from furfurylamine, one of very few chemicals made industrially from lignocellulose. Using carbonate-promoted C–H carboxylation, furfurylamine is converted into a furan-containing amino acid and a tetrahydrofuran-containing bicyclic lactam in two and four steps, respectively. Our syntheses avoid the use of protecting groups and multiple stoichiometric organic reagents required by previous, longer routes to these targets. This work facilitates access to furan- and tetrahydrofuran-based polyamides, which are unavailable from petrochemical feedstocks.

In English

By the density functional theory method with the exchange-correlation functional B3LYP, the basis set 6-31G(d,p) and Grimme dispersion corrections, the energy values has been calculated of intermolecular interaction between adjacent polyamide fragments, and the effect of graphene-like nanoclusters on the similar values for intermolecular complexes of polyamide fragments with graphene-like nanoclusters has been evaluated. The effect of carbon materials on the energy magnitudes of covalent bonds in the polymer matrix of polyamide has been also examined. Comparison of the energy values of intermolecular interaction between two monomers (‑86.0 kJ/mol, two hydrogen bonds) and two dimers (-302.0 kJ/mol, three hydrogen bonds) indicates that the energy of interaction between two components consists of that of hydrogen bonds and the energy contribution of dispersive forces. The energy of intermolecular interaction between two dimers with the graphene matrix (C 110 H 26 ) is approximately 40 kJ/mol higher (-346.2 kJ/mol) compared to respective value for two monomers. The less value of the interaction energy (-325.0 kJ/mol) for the nanocomposite with C 96 H 24 species is due to the insufficient size of the selected model for the graphene matrix. The analysis of the hydrogen bond lengths between the oxygen atom of carbonyl group and hydrogen one of amino group indicates that, regardless of length of linkage of the polymeric chain of polyamide (monomer and dimer) and the size of the graphene-like matrix (C 96 H 24 and C 110 H 26 ) in the nanocomposite, the hydrogen bond in composites is shorter in comparison with a those values in complexes without a carbon matrix. This indicates a greater strength of the bond, that is, the presence of a carbon matrix increases the strength of the formed nanocomposite, that explains the increase in the melting point compared with that of the original polymer. In the nanocomposite formed polyamide - a carbon matrix for all the models studied, the energy of intermolecular interaction in the nanocomposite increases significantly compared to respective value between two fragments of pure polyamide, so indicating an increase in the thermal stability of this nanocomposite what is confirmed by experimental data.

Reactivity of the Polyamide Membrane Monomer with Free Chlorine: Reaction Kinetics, Mechanisms, and the Role of Chloride.

Aromatic polyamide thin-film composite membranes are widely used in reverse osmosis (RO) and nanofiltration (NF) due to their high water permeability and selectivity. However, these membranes undergo biofouling and can degrade and eventually fail during free chlorine exposure. To better understand this effect, the reactivity of the polyamide monomer (benzanilide (BA)) with free chlorine was tested under varying pH and chloride (Cl-) conditions. The kinetic results indicated that the current existing mechanisms, especially the Orton rearrangement, were invalid. Revised reaction pathways were proposed where BA chlorination was driven by two independent pathways involving the anilide ring and amide nitrogen moieties. The ability for one moiety to be chosen over the other was highly dependent on the pH, Cl- concentration, and the resulting chlorinating agents (e.g., Cl2, HOCl, OCl-, and Cl2O) generated. Species-specific rate constants for BA with Cl2, OCl-, and HOCl equaled (7.6 ± 0.19) × 101, (1.7 ± 1.5) × 101, (2.1 ± 0.71) × 10-2 M-1 s-1, respectively. A similar value for Cl2O could not be accurately estimated under the tested conditions. The behavior of these chlorinating agents differed for each reactive site such that OCl- > HOCl for N-chlorination and Cl2 > HOCl > OCl- for anilide ring chlorination. Experiments with modified monomers indicated that substituent placement largely affected which reactive site was kinetically favorable. Overall, such findings provide a predictive model of how the polyamide monomer degrades during chlorine exposure and guidance on how chlorine-resistant polyamide membranes should be designed.

Aerated extraction columns for in situ separation of bio‐based diamines from cell suspensions

AbstractBackgroundExtraction is the method of choice for separating sensitive products. For example, it has been applied in aromatics and rare‐earth metal separation. Recently, biotechnological processes entered the field of bulk chemicals and might benefit from process intensification by in situ extraction of inhibiting products, however in the presence of cells and/or aeration. This study applies reactive extraction of the polyamide monomer hexane‐1,6‐diamine from cell‐containing medium.ResultsTo prove technical feasibility of this reactive extraction, simulation of the extraction column based on single‐drop measurements was validated at pilot‐scale. Simulated results show good accordance with experimental data with an error below 20%. The extraction column was subsequently used as a bioreactor with integrated aeration and product extraction applying a four‐phase system investigating the effect on drop distributions and holdup of the dispersed phases. Interestingly, aeration increased the holdup up to five‐fold and decreased the mean drop size of the organic extractive phase by 30%, thereby potentially improving extraction efficiency.ConclusionThe ReDrop simulation tool is capable of predicting challenging separation processes like the reactive extraction of hexane‐1,6‐diamine with D2EHPA diluted in oleyl alcohol from a biotransformation medium. The process design enabled four‐phase operation of the column with aeration, extractive organic phase and cell‐containing continuous aqueous phase. © 2018 Society of Chemical Industry

Recent advances in metabolic engineering of Corynebacterium glutamicum as a potential platform microorganism for biorefinery

AbstractThe fermentative production of platform chemicals in biorefineries is a sustainable alternative to current petroleum‐refining processes. Industrial microorganisms, such as Escherichia coli, Saccharomyces cerevisiae, and Corynebacterium glutamicum, have been engineered as microbial cell factories that are able to utilize biomass for the production of value‐added platform chemicals and polymers. Compared to E. coli and S. cerevisiae, C. glutamicum displays weak carbon catabolite repression and can co‐utilize mixed sugars as carbon sources, without any significant growth retardation. Pathways for the utilization of alternative carbon sources, such as d‐xylose and l‐arabinose from lignocellulosic biomass, lactose and galactose from whey, glycerol from biodiesel, and methanol from natural gas refineries, have been evaluated for chemical production. However, the application of C. glutamicum in biorefineries is limited because it does not secrete hydrolases for the efficient utilization of cellulose, xylan, and starch from lignocellulosic and starch biomass. To solve the limitation, C. glutamicum has been engineered for the consolidated bioprocessing of biomass by the heterologous expression of amylolytic and cellulolytic enzymes. Recently, C. glutamicum has been extensively engineered for polyamide monomer production owing to its ability to produce l‐lysine and l‐glutamate. This review summarizes recent advances in the development of C. glutamicum strains that can utilize renewable biomass resources for the production of industrially important chemicals. It highlights recent progress in metabolic engineering for the production of polyamide monomers. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd