Acrylonitrile Process Enhancement through Waste Minimization: Effect of Reaction Conditions and Degree of Backmixing

Waste minimization in reactor design is an effective approach for pollution control, when compared to the traditional practice of the end-of-pipe treatment. Reactor degree of backmixing and operating conditions are important factors that determine the performance of chemical process, including environmental impact. For the purpose of waste minimization, two modeling methods were used for simulating the performance of the acrylonitrile production reactor, based on the ammoxidation of propylene. The effect of residence time, temperature, degree of backmixing on the steady-state propylene conversion, and production of waste were determined. The tanks-in-series model and the axial dispersion model were used to account for the degree of backmixing. The two main by-products in the acrylonitrile process are acetonitrile and hydrogen cyanide, which are both highly toxic waste. Extensive reactor backmixing reduces propylene conversion, especially at high temperature and residence time. Minimum acetonitrile production is favored by low residence time, high to moderate temperature, and no backmixing. Minimum hydrogen cyanide production is favored by low residence time, low temperature, and no backmixing. At 450 °C, the percentage of increase in the selectivity of acrylonitrile, with respect to hydrogen cyanide at plug-flow reactor conditions, as compared to a continuous stirred tank reactor, is 87.1, 74.3, 50.9, 30.4, and 12.4% at a residence time of 1, 2, 4, 6, and 8 s, respectively. The reactor degree of backmixing and operating conditions are important factors that affect the environmental friendliness of the acrylonitrile production process.

Stable and selective catalysts for propane dehydrogenation operating at thermodynamic limit

Intentional (“on-purpose”) propylene production through nonoxidative propane dehydrogenation (PDH) holds great promise for meeting the increasing global demand for propylene. For stable performance, traditional alumina-supported platinum-based catalysts require excess tin and feed dilution with hydrogen; however, this reduces per-pass propylene conversion and thus lowers catalyst productivity. We report that silica-supported platinum-tin (Pt1Sn1) nanoparticles (<2 nanometers in diameter) can operate as a PDH catalyst at thermodynamically limited conversion levels, with excellent stability and selectivity to propylene (>99%). Atomic mixing of Pt and Sn in the precursor is preserved upon reduction and during catalytic operation. The benign interaction of these nanoparticles with the silicon dioxide support does not lead to Pt-Sn segregation and formation of a tin oxide phase that can occur over traditional catalyst supports.

Effects of Desilication in NaOH/Piperidine Medium and Phosphorus Modification on the Catalytic Activity of HZSM-5 Catalyst in Methanol to Propylene Conversion

Aims & Objective: H-ZSM-5 catalysts with a Si/Al molar ratio of 200 were effectively prepared by a microwaveassisted hydrothermal technique through the existence of tetrapropyl ammonium hydroxide (TPAOH). Methods: The introduction of controllable mesopores into ZSM-5 crystals was performed efficiently via desilication derived from an alkaline NaOH/piperidine solution. Then, the acidic characteristic of the desilicated ZSM-5 specimens was improved using phosphorus modification. The catalysts were subjected to XRD, ICP-OES, BET, FE-SEM, TGA, NH3-TPD and FT-IR analysis. The catalytic activity of the synthesized zeolites in the reaction of methanol to propylene (MTP) was examined in a packed-bed reactor at 475 °C, atmospheric pressure and WHSV of 0.9 h–1. Results & Conclusion: The findings showed alkaline treatment in NaOH/piperidine solution created uniform mesoporosity with no severe damage in the crystal structure. Similarly, phosphorus modification developed the acidic features and led to the optimal catalytic efficiency in terms of maximum propylene selectivity (49.16%) and propylene/ethylene (P/E) ratio (5.97) as well as the maximum lifetime of the catalyst.

Prospects in the development of catalysts for deep oxidation of propylene

The paper presents an analysis of literature data on the catalysts employed in the industrial processes of propylene conversion to the most bulky oxygen-containing products – propylene oxide (PO), acrylonitrile (AN), acrolein and n-/isobutyric aldehydes. Main trends and prospects in their development are considered. Catalytic systems for the promising processes of their production using more inexpensive propane or alternative oxidants are also analyzed; their characteristics are estimated in terms of acceptability for future commercialization.

Photocatalytic Abatement of Volatile Organic Compounds by TiO2 Nanoparticles Doped with Either Phosphorous or Zirconium

The aim of this work is to study the activity of novel TiO2-based photocatalysts doped with either phosphorus or zirconium under a UV-Vis source. A set of mesoporous catalysts was prepared by the direct synthesis: TiO2_A and TiO2_B (titanium oxide synthesized by two different procedures), P-TiO2 and Zr-TiO2 (binary oxides with either nonmetal or metal into the TiO2 framework). Complementary characterizations (N2 physisorption at 77 K, X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) analysis, X-ray Photoelectron Spectroscopy (XPS), and (DR)UV-Vis spectroscopy) were used to investigate the physicochemical properties of the prepared catalysts. Then, the photocatalysts were tested for the oxidation of propylene and ethylene under UV-Vis light. As a result, the most promising catalyst for both the propylene and ethylene oxidation reactions was the P-TiO2 (propylene conversion = 27.8% and ethylene conversion = 13%, TOS = 3 h), thus confirming the beneficial effect of P-doping into the TiO2 framework on the photocatalytic activity.