The rapid separation and efficient recycling of catalysts after a catalytic reaction are considered important requirements along with the high catalytic performances. In this view, although heterogeneous catalysis is generally less efficient if compared to the homogeneous type, it is generally preferred since it benefits from the easy recovery of the catalyst. Recycling of heterogeneous catalysts using traditional methods of separation such as extraction, filtration, vacuum distillation, or centrifugation is tedious and time-consuming. They are uneconomic processes and, hence, they cannot be carried out in the industrial scale. For these limitations, today, the research is devoted to the development of new methods that allow a good separation and recycling of catalysts. The separation process should follow a procedure economically and technically feasible with a minimal loss of the solid catalyst. The aim of this work is to provide an overview about the current trends in the methods of separation/recycling used in the heterogeneous catalysis.

Recovery/Reuse of Heterogeneous Supported Spent Catalysts

In situ catalytic co-pyrolysis (CCP) of mixtures of lignocellulosic biomass (LB) and plastic (polypropylene (PP) and polystyrene (PS)) with spent FCC catalyst (10% w/w loading) was performed in a s...

Catalytic Co-pyrolysis of Biomass and Plastics (Polypropylene and Polystyrene) Using Spent FCC Catalyst

Hydrogen peroxide (H2O2) is a chemical which has gained wide importance in several industrial and research fields. Its mass production is mostly performed by the anthraquinone (AQ) oxidation reaction, leading to high energy consumption and significant generation of wastes. Other methods of synthesis found in the literature include the direct synthesis from oxygen and hydrogen. However, this H2O2 production process is prone to explosion hazard or undesirable by‑product generation. With the growing demand of H2O2, the development of cleaner and economically viable processes has been under intense investigation. Heterogeneous photocatalysis for H2O2 production has appeared as a promising alternative since it requires only an optical semiconductor, water, oxygen, and ideally solar light irradiation. Moreover, employing a metal-free semiconductor minimizes possible toxicity consequences and reinforces the sustainability of the process. The most studied metal‑free catalyst employed for H2O2 production is polymeric carbon nitride (CN). Several chemical and physical modifications over CN have been investigated together with the assessment of different sacrificial agents and light sources. This review shows the recent developments on CN materials design for enhancing the synthesis of H2O2, along with the proposed mechanisms of H2O2 production. Finally, the direct in situ generation of H2O2, when dealing with the photocatalytic synthesis of added-value organic compounds and water treatment, is discussed.

Recent Strategies for Hydrogen Peroxide Production by Metal-Free Carbon Nitride Photocatalysts

Sustainable management of spent fluid catalytic cracking catalyst from a circular economy approach.

Influence of dual reinforcement (nano CuO + reused spent alumina catalyst) on microstructure and mechanical properties of aluminium metal matrix composite

Solid catalytic materials play major role in oil refining industry. There are various types of catalysts which are in use but the major ones are mainly hydroprocessing catalysts, Fluid catalytic cracking catalysts and reforming catalysts. During processing, catalysts gets contaminated with impurities viz coke, sulfur, vanadium and nickel in the crude oil feed and becomes deactivated over a period of time. Diesel hydrodesulfurization catalysts typically have life cycle of 3-4 years where as FCC catalysts gets lost to atmosphere on daily basis and is offloaded fortnightly / monthly based on activity. Once catalysts completes their life cycle they will be withdrawn from the process, at this stage, catalysts are considered “spent” and the heavy metals, coke, and other poisonous elements make them as hazardous waste. As per literature Dufresne estimated that the total quantity of spent hydroprocessing catalysts generated worldwide is in the range of 150,000 to 170,000 tons per year. Therefore, with anticipated 5% annual increase in catalyst consumption, the generation of spent hydroprocessing catalysts predicted to be 200,000 tons annually. The exact figures of spent FCC catalysts are not available but considering the short life span of the catalyst and 400 FCC units operating across the world volumes assumed to be very high. Significant increase of spent hydroprocessing catalysts volumes are mainly attributed to rapid growth in the distillate hydrotreating capacity to meet the increasing demand for ultra low sulfur transportation fuels, reduced cycle times due to in increased severity operations to meet stringent fuel specifications and demand of processing sour crudes based on economic criteria. The traditional way of disposing the spent catalysts is land filling which is not environmentally friendly and occasisionally it leads to ground water contamination. Various options to reduce the generation of hazardous waste spent catalyst are using highly active catalysts, regeneration of the catalysts and reuse of the spent catalysts in other processes. The present paper will discuss about alternate ways of using spent catalyst by taking case study of hydroprocessing catalysts and thereby minimizing the waste spent catalyst in refining industry.

R. Pragya

Papers

Minimization of Waste Spent Catalyst in Refineries