Oxidative cleavage of fatty acids and fatty acid derivatives is a practical way to obtain bifunctional molecules that can be used in polycondensation reactions. Diacids, hydroxyacids, and amino acids can then be used to produce polyesters or polyamides and also a large range of other products, such as lubricants and plasticizers. Ozonolysis has long been the sole industrial process for oxidative cleavage, but recently, routes using hydrogen peroxide as a clean oxidant have regained interest. Hydrogen peroxide is easier to use, but the kinetics of the catalyzed reactions are still slow. Although several catalytic systems have been described in the literature, tungsten-based catalysts are still the preferred choices. Different catalysts can trigger different mechanisms, such as a radical mechanism instead of a catalytic reaction. In addition, some side products and co-products often disregarded in the literature, such as shorted cleavage products, indicate the presence of side reactions that affect the quality of the final products. The oxidative cleavages in continuous and batch processes have significant differences, which are discussed with an illustration of our understanding of the process used by Matrica S.p.A.
Aiming to synthesize high-value renewable monomers for the preparation of renewable specialty polyamides, we designed a new protocol. Amino-esters, produced via the hydrogenation of unsaturated nitrile-esters, are alternative monomers for the production of these polymers. A high monomer yield can be obtained using a Raney ® -nickel catalyst despite the drawback of fast deactivation. The hydrogenation of 10-cyano-9-decenoate (UNE11) was tentatively reactivated by three different regeneration procedures: solvent wash, regeneration under hydrogen, and regeneration under sonication. Among these procedures, the in-pot catalyst regeneration (H 2 30 bar, 150 • C) demonstrated complete activity recovery and full recycling.Catalysts 2020, 10, 229 2 of 13 W8. The differences in these catalysts are the varied activities that they show, which are the result of different preparation methods, alloy composition, NaOH concentration, the temperature at which the alloy is added to the basic solution, the temperature and duration of alloy digestion after addition to the base, and the method used to wash the catalyst from the sodium aluminate and excess base [16]. Type W6 is the most active catalyst and has several well-known advantages, including high activity and selectivity, but its poor stability and short lifetime mean that catalyst replacement is required, which entails high costs and environmental impact. Deactivation is caused by several factors: chemical (poisoning, vapor compound formation accompanied by transport, and vapor-solid and/or solid-solid reactions), mechanical (fouling and attrition/crushing), thermal (thermal degradation), and sintering (agglomeration of metal particles) [11,17,18]. The storage solvent can also affect catalyst stability. It is known that a catalyst in the W5 form can lose its activity after about a week of storage in ethanol, due to the formation of acetaldehyde, which poisons the catalyst [19].The hydrogenation of nitriles to primary amines leads to the co-production of secondary and tertiary amines. The choice of catalyst and reaction conditions can dramatically improve selectivity and yield (about 100% primary amine) and prevent co-product formation.The synthesis of amino-ester from nitrile-esters was tested with different catalysts such as Ru and Co and Raney-nickel catalysts [20]. The aim of the present work is to study the deactivation and reactivation mechanism of Raney-nickel, as it is deactivated faster. Raney-nickel or sponge nickel is popular in chemical industry for the reduction of nitriles to amines.In nitrile hydrogenations, Raney ® -nickel deactivation is caused by chemisorption through multiple bonds and π backbonding [21].The most common procedures for exhausted (inactive) Raney ® -nickel recycling include acidic treatment (acetic acid at 20-50 • C) [22] or treatment with non-oxidizing aqueous alkaline solution (NaOH at 40-150 • C). More recently, Ping et al. proposed a regeneration method that involves coke elimination with water, from 300 • C to 450 • C, for a catalyst that...
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