Catalysis over zinc-incorporated berlinite (ZnAlPO4) of the methoxycarbonylation of 1,6-hexanediamine with dimethyl carbonate to form dimethylhexane-1,6-dicarbamate

How To Get Isocyanate?

Isocyanate, a pivotal chemical intermediate to synthesize polyurethane with widespread applications in household appliances, automobiles, and construction, is predominantly produced via the phosgene process, which currently holds a paramount status in industrial isocyanate production. Nonetheless, concerns arise from the toxicity of phosgene and the corrosiveness of hydrogen chloride, posing safety hazards. The synthesis of isocyanate using nonphosgene methods represents a promising avenue for future development. This article primarily focuses on the nonphosgene approach, which involves the formation of carbamate through the reaction of nitro-amino compounds with carbon monoxide, dimethyl carbonate, and urea, among other reagents, subsequently leading to the thermal decomposition of carbamate to get isocyanate. This paper emphasizes the progress in catalyst development during the carbamate decomposition process. Single-component metal catalysts, particularly zinc, exhibit advantages such as high activity, cost-effectiveness, and compatibility with a wide range of substrates. Composite catalysts enhance isocyanate yield by introducing a second component to adjust the active metal composition. The central research direction aims to optimize catalyst adaptation to reaction conditions, including temperature, pressure, time, and solvent, to achieve high raw material conversion and product yield.

Synthesis mechanism of dimethylhexane-1,6-dicarbamate from 1,6-hexamethylenediamine, urea and methanol: A molecular scale study based on density functional theory

This work provides a molecular scale insight into non-phosgene synthesis based on the reaction of dimethylhexane-1,6-dicarbamate from 1,6-hexamethylenediamine, urea and methanol with computational electronic method. By exploring almost all possible reaction modes and comparing the effective barrier of each channel, this work analyzes the optimal reaction mechanism for both non-catalytic and self-catalytic systems. The mechanism without catalysis has a high effective free energy barrier (FEB) of 47.0 kcal mol^-1. As for self-catalytic system, after sorting out the reaction pathway network, an effective FEB of 24.6 kcal mol^-1 is confirmed which corresponds to dissociation of urea.

Effective Synthesis of m-Xylylene Dicarbamate via Carbonylation of m-Xylylene Diamine with Ethyl Carbamate over Hierarchical TS-1 Catalysts

Carbonylation of m-xylylene diamine (XDA) with ethyl carbamate to produce m-xylylene dicarbamate (XDC), which is the crucial intermediate for the production of m-xylylene diisocyanate (XDI), over the hierarchical TS-1 (HTS-1) zeolite catalyst was studied. The catalysts were characterized by Brunauer-Emmett-Teller, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and temperature-programed desorption of ammonia techniques systematically. The results showed that the high performance of HTS-1 could be attributed to the weak acidity and high V _meso/V _total ratio of the catalyst. Impacts of reaction time and reusage on the HTS-1 catalyst were also investigated. Under 6 h and 200 °C, XDA conversion could reach 100% with 88.5% XDC yield. Furthermore, partial loss of Ti active sites with Lewis acidity on the catalyst surface led to the decrease of XDC yield during recycling. Moreover, a possible reaction mechanism for the title reaction was primarily proposed.

Enhanced Performance of Zirconium-Doped Ceria Catalysts for the Methoxycarbonylation of Anilines

The methoxycarbonylation of anilines stands as an attractive method for the phosgene-free production of carbamates. Despite the high yields obtained for ceria catalysts, the reduction of the amount of side products and the prevention of catalyst deactivation still represent major hurdles in this chemistry. One advantage of ceria is the possibility of tuning its reactivity by doping its lattice with other metals. In the present work, a series of doped ceria-based materials, prepared by substitution with metals, are evaluated in the methoxycarbonylation of 2,4-diaminotoluene with dimethyl carbonate. Among all catalysts, containing Eu, Hf, La, Pr, Sm, Tb, Y or Zr, ceria promoted with 2 mol % Zr exhibited 96 % selectivity towards the desired carbamates, improving the pure CeO₂ catalyst. Density functional theory demonstrates that two descriptors are needed: 1) a geometric factor that governs the reduction of energy barriers for carbamate formation through ureas; 2) catalyst basicity as N-H bonds need to be activated. Assessment in subsequent reaction cycles revealed that the CeO₂ -ZrO₂ catalyst is more stable than bulk CeO₂ , along with the reduction of fouling processes.

The highly selective oxidation of cyclohexane to cyclohexanone and cyclohexanol over VAlPO4 berlinite by oxygen under atmospheric pressure

Background

The oxidation of cyclohexane under mild conditions occupies an important position in the chemical industry. A few soluble transition metals were widely used as homogeneous catalysts in the industrial oxidation of cyclohexane. Because heterogeneous catalysts are more manageable than homogeneous catalysts as regards separation and recycling, in our study, we hydrothermally synthesized and used pure berlinite (AlPO₄) and vanadium-incorporated berlinite (VAlPO₄) as heterogeneous catalysts in the selective oxidation of cyclohexane with molecular oxygen under atmospheric pressure. The catalysts were characterized by means of by XRD, FT-IR, XPS and SEM. Various influencing factors, such as the kind of solvents, reaction temperature, and reaction time were investigated systematically.

Results

The XRD characterization identified a berlinite structure associated with both the AlPO₄ and VAlPO₄ catalysts. The FT-IR result confirmed the incorporation of vanadium into the berlinite framework for VAlPO₄. The XPS measurement revealed that the oxygen ions in the VAlPO₄ structure possessed a higher binding energy than those in V₂O₅, and as a result, the lattice oxygen was existed on the surface of the VAlPO₄ catalyst. It was found that VAlPO₄ catalyzed the selective oxidation of cyclohexane with molecular oxygen under atmospheric pressure, while no activity was detected on using AlPO₄. Under optimum reaction conditions (i.e. a 100 mL cyclohexane, 0.1 MPa O₂, 353 K, 4 h, 5 mg VAlPO₄ and 20 mL acetic acid solvent), a selectivity of KA oil (both cyclohexanol and cyclohexanone) up to 97.2% (with almost 6.8% conversion of cyclohexane) was obtained. Based on these results, a possible mechanism for the selective oxidation of cyclohexane over VAlPO₄ was also proposed.

Conclusions

As a heterogeneous catalyst VAlPO₄ berlinite is both high active and strong stable for the selective oxidation of cyclohexane with molecular oxygen. We propose that KA oil is formed via a catalytic cycle, which involves activation of the cyclohexane by a key active intermediate species, formed from the nucleophilic addition of the lattice oxygen ion with the carbon in cyclohexane, as well as an oxygen vacancy formed at the VAlPO₄ catalyst surface.

Electronic supplementary material

The online version of this article (10.1186/s13065-018-0405-6) contains supplementary material, which is available to authorized users.

Methoxycarbonylation of 1,6-hexanediamine with dimethyl carbonate to dimethylhexane-1,6-dicarbamate over Zn/SiO2 catalyst

The activated Zn(OAc)₂ in Zn/SiO₂ catalysts facilitates the activation of DMC which leads to better catalytic performance.

Phosgene-free synthesis of hexamethylene-1,6-diisocyanate by the catalytic decomposition of dimethylhexane-1,6-dicarbamate over zinc-incorporated berlinite (ZnAlPO4)

The phosgene-free synthesis of hexamethylene-1,6-diisocyanate (HDI) by the decomposition of dimethylhexane-1,6-dicarbamate (HDU) was carried out on a self-designed fixed-bed catalytic reactor, using zinc-incorporated berlinite (ZnAlPO4) as catalyst, dioctyl phthalate (DOP) as solvent and N2 as carrier gas. Factors influencing the yield of HDI, including the Zn/Al molar ratio, HDU concentration and liquid space velocity (LHSV), were investigated. Under the optimized reaction conditions, i.e., 4.8 wt.% concentration of HDU in DOP, 100ml/min N2 flow rate, 0.09 MPa vacuum, 623K reaction temperature, 1.2h(-1) LHSV and catalyst usage 2.0 g, a 89.4% yield of HDI had been achieved over the ZnAlPO4 (molar ratio Zn/Al=0.04) catalyst. The ZnAlPO4 catalyst was found to exhibit a considerable large on-stream stability and could be repeatedly used in the decomposition of HDU to HDI, after its regeneration.