Urea Synthesis Research Articles

Simulation of a reactor considering the Stamicarbon, Snamprogetti, and Toyo patents for obtaining urea

Abstract In the present work, the plug flow reactor of a urea production plant from ammonia produced from natural gas of the Camisea fields (Peru) was designed, comparatively analyzing three commercial processes currently in operation: Stamicarbon, Snamprogetti, and Toyo. ASPEN PLUS software was used as a simulation tool. To carry out the simulation and subsequent comparison of the three urea production patents, it will start from the same feed of ammonia (37,851 kmol/day) and carbon dioxide (18,989 kmol/day) for the three cases. For the design of urea synthesis reactors, reactors of the same size (2.3 m diameter and 29 m length) were designed. The results are graphs that illustrate the variation of the length of the reactor with the reaction temperature, the variation of the length of the reactor with the residence time, and the variation of the conversion with the time for each patent.

A strategy to address the challenge of electrochemical CO2 and N2 coupling to synthesis urea on two-dimensional metal borides (MBenes) by computational screening

To achieve efficient urea formation via electrocatalytic C–N coupling, we proposed a new route for synthesizing urea on 2D metal borides (MBenes) by theoretical prediction. It has been reported that inert CO2 and N2 molecules can be converted into urea via electrocatalytic C–N bond coupling, which is a promising alternative method to industrial processes. However, due to the weak adsorption of and difficulty in activating CO2 and N2 molecules, the reaction of C–N coupling is challenging to achieve. To ensure C–N bond coupling between *NN* and *CO to form *NCON intermediates, which act as the key precursor to urea formation, the utilization of sustainable energy (solar energy) can be helpful in addressing the challenge of electrochemically synthesizing urea. Furthermore, computational screening provides an effective way to gain insight into the mechanisms of the C–N coupling and protonation steps. It is also beneficial for guiding the development of the sustainable synthesis of carbon nitride chemicals via C–N coupling, and we believe it will attract full attention in the future. A new theoretical strategy was used to screen efficient catalysts for urea electrosynthesis based on coupling CO2 and N2 to generate H2NCONH2. We established the Gibbs free energy landscape and calculated the limiting potential based on the rate-determining step, and a volcano plot was constructed as a function of ΔG(*NCON) to predict MBenes for urea formation. It included the kinetic stability, CO2 and N2 adsorbability, catalytic activity, and urea synthesis selectivity. It is demonstrated that Mo2B2 and Ru2B4 are suitable urea electrosynthesis catalysts with high activity and selectivity. This work can contribute to the application of C–N coupling electrochemical reactions.

Understanding the Site‐Selective Electrocatalytic Co‐Reduction Mechanism for Green Urea Synthesis Using Copper Phthalocyanine Nanotubes

AbstractGreen synthesis of urea under ambient conditions by electrochemical co‐reduction of N2 and CO2 gases using effective electrocatalyst essentially pushes the conventional two steps (N2 + H2 = NH3 and NH3 + CO2 = CO(NH2)2) industrial process at high temperature and high pressure, to the brink. The single step electrochemical green urea synthesis process has hit a roadblock due to the lack of efficient and economically viable electrocatalyst with multiple active sites for dual reduction of N2 and CO2 gas molecules to urea. Herein, copper phthalocyanine nanotubes (CuPc NTs) having multiple active sites (such as metal center, Pyrrolic‐N3, Pyrrolic‐N2, and Pyridinic‐N1) as an efficient electrocatalyst which exhibits urea yield of 143.47 µg h–1 mg–1cat and faradaic efficiency of 12.99% at –0.6 V versus reversible hydrogen electrode by co‐reduction of N2 and CO2 are reported. Theoretical calculation suggests that Pyridinic‐N1 and Cu centers are responsible to form CN bonds for urea by co‐reduction of N2 to NN* and CO2 to *CO, respectively. This study provides the new mechanistic insight about the successful electro‐reduction of dual gases (N2 and CO2) in a single molecule as well as rational design of efficient noble metal‐free electrocatalyst for the synthesis of green urea.

Iatrogenic dehydration drives organic osmolyte production in critical COVID‐19

Fluid removal with concomitant dehydration is a common treatment strategy in acute respiratory distress syndrome (ARDS). We have previously shown that iatrogenic dehydration during treatment in the intensive care unit (ICU) is associated with a shift to organic osmolyte production in the general ICU population. In this study we investigate the development of estimated osmolality (eOSM = 2Na+2K+glucose+urea) over time in ICU, as well as the relationship between the major osmolytes and eOSM. The study includes 370 COVID‐19 patients admitted to the ICU at Uppsala University Hospital between March 13. 2020 and June 11. 2021. Complete data was available for 176 of these patients, which were used for the analysis. The results show that eOSM increases with time spent in ICU (R2 = 0.75, P<0.001), which indicates iatrogenic dehydration. Further, increasing eOSM is correlated with increasing role of urea as an osmolyte (R2 = 0.6, P<0.001), while the role of sodium and potassium are inversely correlated to eOSM. This is consistent with the aestivation response where dehydration with increased osmolality drives production of organic osmolytes through gluconeogenesis and urea synthesis. Interestingly, glucose shows a weak negative correlation to eOSM (R2 = 0.01, P<0.01), which we interpret as a sign of iatrogenic control using insulin treatment. Acute Kidney Injury with reduced kidney function is an alternative explanation for increasing urea concentration. However, although there is a correlation between urea and the GFR‐markers creatinine and cystatin‐C the effect size cannot explain more than part of the association. In conclusion, iatrogenic dehydration causes an aestivation response in critical COVID‐19 where urea plays an increasing role as an osmolyte with increasing total osmolality.

Bioactive inks suitable for 3D printing based on waterborne polyurethane urea, cellulose nanocrystals and Salvia extract

This work explores the preparation of a bioactive ink suitable for direct ink writing (DIW) 3D printing by adding extract obtained from Salvia officinalis L. during the synthesis of a waterborne polyurethane urea (WBPUU). Additionally, to guarantee a successful printing performance, cellulose nanocrystals (CNC), a well-known rheology modulator, have been added after the synthesis process. In order to predict the behaviour of the inks in DIW, the rheological properties of the inks with and without the Salvia extract and the CNC have been studied. The results showed that the incorporation of Salvia extract into the WBPUU ink resulted in a decrease of the viscosity, yield point and storage modulus, obtaining an ink that cannot maintain the shape after being printed. On the contrary, the incorporation of the CNC into the WBPUU/Salvia ink increased the aforementioned rheological parameters leading to the obtaining of pieces presenting a good shape fidelity without compromising their printability. Finally, scaffolds were prepared from the printed pieces by freeze-drying technique and were tested against Gram negative Escherichia coli and Gram positive Staphylococcus aureus. The scaffolds containing CNC and Salvia showed bactericide behaviour against both bacteria, which was not seen in the WBPUU matrix, confirming the bioactive capacity of this ink.

AuCu nanofibers for electrosynthesis of urea from carbon dioxide and nitrite

Carbon dioxide reduction reaction (CO2RR) is a promising technology for mitigating greenhouse gas emission and achieving carbon neutrality. However, coupling CO2RR with other reactions to produce high value-added chemicals remains a challenge. In this work, we report self-assembled nanofibers composed of ultrathin AuCu alloy nanowires possessing a Boerdijk-Coxeter structure with (111)-dominant facets for the electrosynthesis of urea by coupling CO2RR with nitrite reduction reaction (NO2−RR). The rich structural defects and AuCu bimetallic alloy composition provide a large number of highly catalytically active sites. The constructed AuCu nanofibers display excellent urea synthesis performance in the electrolyte solution containing 0.01 M KNO2 with continuous drumming of CO2, achieving a high urea yield rate of up to 3,889.6 μg h−1 mg−1cat. and a high faradic efficiency of 24.7% at −1.55 V (versus Ag/AgCl). This work provides a feasible method for the rational design of self-assembled bimetallic nanofibers for electrosynthesis of urea under ambient conditions.

Identifying miRNAs in the modulation of gene regulation associated with ammonia toxicity in catfish, Clarias magur (Linnaeus, 1758).

The small non-coding microRNAs play a vital role in post-transcriptional gene regulation associated with different physiological events such as metabolism, stress, etc. The freshwater catfish, Clarias magur, can grow within hyper ammonia containing stagnant water bodies and/or muddy substratum. We intended to identify organ-specific miRNAs associated with ammonia stress management. The miRNA-libraries were generated from QC passed total RNA extracted from liver, muscle, and kidney of ammonia-treated (exposed to 25mM NH4Cl for 14days) and untreated catfish. The libraries were validated using High sensitivity D1000 Screen tape. The trimmed quality-filtered reads for control and treated samples of kidney were 19,406,210; 14,904,423; for liver 15,467,727; 18,582,072; and for muscle 25,081,345; 19,782,182 respectively. Total 120 known and 150 novel differentially expressed miRNAs were identified, out of which miR-200, miR-217, miR-122, miR-133, miR-145, miR-221, miR-19, miR-138, miR-34, and miR-184 were predicted to be involved in the metabolism of nitrogen. The key miRNAs targeted several genes associated with urea synthesis like Glutaminase 2, Argininosuccinate lyase, Glutamate dehydrogenase 1, Alanine aminotransferase 2-like, Aspartate aminotransferase, cytoplasmic-like, Glutamate ionotropic receptor NMDA type subunit 2A, etc. CONCLUSIONS: This is the first report of miRNAs, which serve as a vital resource for regulating nitrogen metabolism in freshwater catfish, C. magur. The data will be resourceful for further evaluating the regulatory role of miRNAs in fishes, which grow and reproduce very well in hazardous ammonia-contaminated water bodies.

A Defect Engineered Electrocatalyst that Promotes High-Efficiency Urea Synthesis under Ambient Conditions.

Synthesizing urea from nitrate and carbon dioxide through an electrocatalysis approach under ambient conditions is extraordinarily sustainable. However, this approach still lacks electrocatalysts developed with high catalytic efficiencies, which is a key challenge. Here, we report the high-efficiency electrocatalytic synthesis of urea using indium oxyhydroxide with oxygen vacancy defects, which enables selective C-N coupling toward standout electrocatalytic urea synthesis activity. Analysis by operando synchrotron radiation-Fourier transform infrared spectroscopy showcases that *CO2NH2 protonation is the potential-determining step for the overall urea formation process. As such, defect engineering is employed to lower the energy barrier for the protonation of the *CO2NH2 intermediate to accelerate urea synthesis. Consequently, the defect-engineered catalyst delivers a high Faradaic efficiency of 51.0%. In conjunction with an in-depth study on the catalytic mechanism, this design strategy may facilitate the exploration of advanced catalysts for electrochemical urea synthesis and other sustainable applications.

Solution combustion synthesis as an alternative synthesis route for novel Ni-Mg-Al mixed-oxide catalyst for CO2 methanation

Hydrotalcite-derived catalysts are reported to be active, selective, and stable in the CO2 methanation reaction. However, the synthesis of this kind of materials requires several energetic steps, and in addition, wastewater is produced. Solution combustion synthesis (SCS) was tested as an alternative pathway for the synthesis of mixed oxide with properties similar to those of hydrotalcite-derived catalysts. Series of Ni-Mg-Al oxide matrix containing 20 wt% of nickel were prepared with two different strategies. For this purpose, the influence of the final temperature and the impact of the fuel to nitrate ratio were studied. Thus, samples were prepared at 300 and 500 °C, with a urea content of 100% (stoichiometric) or 175% (above stoichiometric). Similarities with hydrotalcite-derived oxides were found for the catalyst prepared at 500 °C and with the urea content of 100%. It is worth to note that all prepared SCS-derived samples were more active and more selective than the reference hydrotalcite-based catalyst. Materials prepared with a stoichiometric amount of urea at both 300 and 500 °C were the most active among the tested series (83% and 89% of CO2 conversion at 300 °C, respectively). Both catalysts prepared with the above stoichiometric amount of urea gave ca. 70% of the CO2 conversion at 300 °C. Furthermore, this study confirmed that the increased urea ratio and synthesis temperature led to the formation of the spinel phase. Finally, SCS-derived samples showed an overall smaller specific surface area; however, the surface basicity was higher, resulting in improved catalytic activity compared to the reference hydrotalcite-derived catalyst.

Diformylphloroglucinol derived imine based covalent organic frameworks (PHTA) as efficient organocatalyst for conversion of isocyanates to urea derivatives

New two-dimensional porous covalent organic frameworks (PHTA) with imine linkers have been synthesized and effectively utilized as metal free catalytic system for the synthesis of urea derivatives from a wide range of isocyanates under inert atmosphere. The material has been thoroughly characterized using powder XRD, HRTEM, FESEM, BET, FT-IR, XPS and a structure-activity relationship has been established. The imine based covalent organic framework owing to its highly conjugated system permits superior conduction efficiency of carriers, thereby exhibiting better performance and exceptional reusability and selectivity (> 99%) towards generation of urea derivatives from the corresponding isocyanates. At room temperature the solvent free catalytic process under nitrogen atmosphere requires short range of reaction duration (2 h) to produce high yields (84–96%) of ureaderivatives from respective isocyanates. The catalytic route of urea synthesis in presence of organocatalyst PHTA is suitably described by theoretical calculations (DFT) method. The heterogeneity and recyclability nature of the catalyst is checked for five cycles and the obtained result portrayed its good catalytic effectiveness.

A Comparison of Mesenchymal Stem Cell-derived Hepatocyte-like Cells and HepG2 Cells for Use in Drug-Induced Liver Injury Studies.

Liver cell lines obtained from hepatomas, for example, HepG2 cells, are commonly used in drug toxicity studies. However, functional hepatocyte-like cells derived from mesenchymal stem cells (MSCs) could be a better option for use in the study of drug metabolism and toxicity. Overdose of acetaminophen (APAP) and excess alcohol consumption are common causes of liver damage. The objective of the present study was to investigate the use of MSC-derived hepatocyte-like cells (MSCdH) in the assessment of drug-induced liver injury (by using APAP and ethanol), and to compare the toxic effects observed in the MSCdH with those exhibited by HepG2 cells. MSCs were isolated from umbilical cord and their functionality confirmed by their ability to differentiate into adipocytes, osteocytes and hepatocyte-like cells. It was shown that the MSCs successfully differentiated into hepatocyte-like cells, and these cells were further characterised by using various enzyme assays and by assessing albumin secretion and urea synthesis. Cytotoxicity was evaluated in the HepG2 and MSCdH after exposure to ethanol and APAP, with cell viability being determined by using the MTT assay. After exposure to ethanol and to APAP, cell viability decreased in a concentration-dependent manner for both types of hepatocytes. The respective EC50 values of ethanol-induced toxicity for HepG2 and MSCdH cells were 2.5% and 1.3% v/v (p < 0.001); for APAP-induced toxicity they were 19.1mM and 12.6mM (p < 0.001). These findings show that there is a distinct difference between the two types of hepatocytes in terms of APAP-induced and ethanol-induced liver injury.

Mimicking Native Liver Lobule Microarchitecture In Vitro with Parenchymal and Non-parenchymal Cells Using 3D Bioprinting for Drug Toxicity and Drug Screening Applications.

Bioengineering an in vitro liver model recapitulating the native liver microarchitecture consisting of parenchymal and non-parenchymal cells is crucial in achieving cellular crosstalk and hepatic metabolic functions for accurate hepatotoxicity prediction. Bioprinting holds the promise of engineering constructs with precise control over the spatial distribution of multiple cells. Two distinct tissue-specific liver extracellular matrix (ECM)-based bioinks with excellent printability and rheological attributes are formulated for supporting parenchymal and non-parenchymal cells. A physiologically relevant human vascularized liver model is bioprinted with a novel liver ECM-based bioink laden with human adipose mesenchymal stem cell-derived hepatocyte-like cells (HLCs), human umbilical vein endothelial cells (HUVECs), and human hepatic stellate cells (HHSCs) using an extrusion-based bioprinting approach and validated for hepatotoxicity assessment. The HLC/HUVEC/HHSC-laden liver model resembles native alternate cords of hepatocytes with a functional sinusoidal lumen-like network in both horizontal and vertical directions, demonstrating enhanced albumin production, urea synthesis, and cytochrome P450 (CPR) activity. Furthermore, the liver model is evaluated for drug toxicity assessment following 24 h exposure to different concentrations of (i) non-hepatotoxicants aspirin and dexamethasone, (ii) idiosyncratic hepatotoxicant trovafloxacin mesylate, and (iii) clinical hepatotoxicant acetaminophen and troglitazone. A follow-up cell viability and metabolic competence evaluation by estimating DNA concentration, lactate dehydrogenase activity, and CPR activity revealed a dose-dependent clinically relevant hepatotoxic response. These results corroborated that the developed clinically relevant vascularized liver model is affordable and would aid pharmaceutical companies in speeding up the drug development and provide a robust platform for hepatotoxicity screening.

Analysis of nucleotide insertion opposite urea and translesion synthesis across urea by DNA polymerases

Urea (Ua) is produced in DNA as the result of oxidative damage to thymine and guanine. It was previously reported that Klenow fragment (Kf) exo− incorporated dATP opposite Ua, and that DNA polymerase β was blocked by Ua. We report here the following nucleotide incorporations opposite Ua by various DNA polymerases: DNA polymerase α, dATP and dGTP (dATP > dGTP); DNA polymerase δ, dATP; DNA polymerase ζ, dATP; Kf exo−, dATP; Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4), dGTP and dATP (dGTP > dATP); and DNA polymerase η, dCTP, dGTP, dATP, and dTTP (dCTP > dGTP > dATP > dTTP). DNA polymerases β and ε were blocked by Ua. Elongation by DNA polymerases δ and ζ stopped after inserting dATP opposite Ua. Importantly, the elongation efficiency to full-length beyond Ua using DNA polymerase η and Dpo4 were almost the same as that of natural DNA.Graphical abstract

Synthesis, characterization, hydrolytic, and thermal stability of urea–formaldehyde composites based on modified montmorillonite K10

Synthesis, characterization, hydrolytic, and thermal stability of urea–formaldehyde composites based on modified montmorillonite K10

Tough Gels and Macroporous Foams Based on Chitosan through Hydrothermal Synthesis of Chitosan, Tartaric Acid, and Urea

Tough gels and foams (CHTAUR) based on chitosan were prepared by the hydrothermal reaction of a mixture of chitosan (CH), tartaric acid (TA), and urea (UR). The structure of purified CHTAUR in the solid state was analyzed by Fourier-transform infrared spectroscopy, cross-polarization magic angle spinning 13C-nuclear magnetic resonance spectroscopy, powder X-ray diffraction, and thermogravimetric analysis. CHTAUR is observed to be predominantly chitosan although a minor extent of TAUR salt is present as physical cross-links. The morphology of CHTAUR, as assessed by SEM, suggests the formation of macroporous structures with pore sizes in the range of 90 μm to 1.5 mm. X-ray CT analysis, on the other hand, suggests that the as-prepared CHTAUR foam exhibited open pores of cellular structures with a porosity of around 75% and the average pore size could be in the range of hundreds of μm to few mm. Under conditions of excess water usage, the foams turn into tough gels through water absorption. The suitability of CHTAUR for different applications was examined. Tough gels formed by using a higher extent of water were found to be suitable for compressive loading. The water absorption of the foam was around 25 g/g. A compressive strength study of foams enabled the estimation of the Young’s moduli of CHTAUR foams to be 44.28, 43.80, and 9.96 kPa for foams prepared with CH/H2O weight ratios of 1:5, 1:6, and 1:7.5, respectively. Cytotoxicity studies carried out using the NIH-3T3 cell line showed that CHTAUR, after purification through solvent extraction, supported cell growth and was not toxic to the cell growth, a feature that is also shown by CH. CHTAUR, consisting predominantly of CH, could find use as a biodegradable packaging material and also as a scaffold for tissue engineering applications.

Integrated application of multi-omics approach and biochemical assays provides insights into physiological responses to saline-alkaline stress in the gills of crucian carp (Carassius auratus)

Given the decline of freshwater resources in recent years, the accessible space for freshwater aquaculture is rapidly shrinking, and aquaculture in saline-alkaline water has become a critical approach to meet the rising demand. However, the molecular mechanism behind the adverse effects of saline-alkaline water on fish and the regulatory mechanism in fish tolerance remains unclear. Here, adult crucian carp (Carassius auratus) were exposed to 60 mmol/L NaHCO3 for 30 days. It was observed that long-term carbonate alkalinity (CA) exposure not only caused gill oxidative stress but also changed the levels of several physiological parameters associated with ammonia transport, including blood ammonia, urea nitrogen (BUN), glutamine (Gln), and glutamine synthetase (GS). According to the metabolomics study, differential metabolites (DMs) engaged in various metabolic pathways, such as glycerophospholipid metabolism, sphingolipid metabolism, and arachidonic acid metabolism. In addition, transcriptomics data showed that differentially expressed genes (DEGs) were closely related to ammonia transport, apoptosis, and immunological response. In general, comprehensive multi-omics and biochemical analysis revealed that crucian carp might adopt Rh glycoprotein as a carrier to mediate ammonia transport and increase glutamine and urea synthesis under long-term high saline-alkaline stress to mitigate the adverse effects of blocked ammonia excretion. Simultaneously, saline-alkaline stress caused the destruction of the antioxidant system and the disorder of lipid metabolism in the crucian carp gills, which induced apoptosis and immunological response. To our knowledge, this is the first study to investigate fish's molecular and metabolic mechanisms under saline-alkaline stress using integrated metabolomics, transcriptomics, and biochemical assays. Overall, the results of this study provided new insights into the molecular mechanism behind the adverse effects of saline-alkaline water on fish and the regulatory mechanism in fish tolerance.

Effect of La Doping on NiCr2O4 Properties and Catalytic Applications toward Decolorization of 4-Nitrophenol

We report the successful synthesis of urea as a fuel for low-temperature microwave combustion-based synthesis of NiCr2O4 and La-doped NiCr2O4. Synthesis parameters include the kind of precursor, fuel, and container, as well as how external heat is provided to achieve the combustion reaction. Crystal structures, morphology, surface area, solar cells, Fourier-transform infrared spectrometry, and catalytic activity were used to characterize the products. No impurities phase formed in the as-synthesized NiCr2O4 sample, confirmed by XRD. Surface area was measured with a Brunauer–Emmet–Teller adsorption isotherm. Schottky and Frenkel formation energies have been investigated. This demonstrates the time needed for full decolorization of 4-Nitrophenol (yellow color) by NiCr2O4 and La-doped NiCr2O4. The La-doped NiCr2O4 (0.03%) showed the greatest catalytic activity compared to pristine and other La-doped NiCr2O4. The decolorization occurs in 10 min. The chemical hardness and surface area of the chromites appear to be important in determining catalytic performance. For multi oxide systems, the counter-doped ions in the A and B sites may alter the metal ion-oxide bond, promoting this partial oxidation process at the interface. The results suggest multiple research subjects focusing on such materials for the future.

Coupling mechanism of N2 and CO2 to urea over artificial frustrated Lewis pairs

The simultaneous electrocatalytic conversion of N2 and CO2 into value-added urea is a top-challenging reaction. In this issue of Chem Catalysis, Zhang’s group reported a rice-like InOOH nanocrystal with the well-defined frustrated Lewis pairs (FLPs, i.e., In⋯In–OH), which promoting electrochemical C-N coupling reactions in urea production. This work provides an in-depth understanding of urea synthesis by achieving the integration of the active site.

Ammonia and the Muscle: An Emerging Point of View on Hepatic Encephalopathy.

In the last years the link between the presence of muscular alterations and hepatic encephalopathy (HE), both minimal and overt, has been deeply studied. The pathophysiological background supporting the relationship between muscle depletion, and HE is characterized by an imbalance between the capacity of muscle in ammonia metabolism and trafficking and the inability of the liver in removing ammonia through urea synthesis due to liver failure and/or the presence of porto-systemic shunts. This review will focus on the clinical burden, the physio pathological mechanisms understanding the liver muscle axis and principles of management of muscular alterations in cirrhosis.

Solvay invests in DMC Biotechnologies to advance bio-based innovation

One of the main goals of the green chemistry is to develop sustainable and less hazardous chemical processes and products. Dimethyl carbonate (DMC) is attracting attention due to the wide variety of applications and the possibility of producing it from carbon dioxide. In this work, the DMC production process via urea has been optimized. Two main sections can be distinguished: the synthesis of urea and the production of DMC. An equation based approach is used to model the system. The DMC production from renewable ammonia/methanol/CO2 presents a promising production cost, around 520 €/t. The production of urea alone has also been evaluated in this work. A sensitivity analysis is carried out showing the influence of the methanol price in the DMC cost and the ammonia price in the urea cost. A simplified sustainability index is used to evaluate the environmental performance of urea/DMC production.