Yield of aromatics from naphthenics upon catalytic cracking

Abstract

Cis-e trans decalina foram submetidas à reação com catalisadores de craqueamento, para estudar a formação de aromáticos numa fração particular de produtos líquidos do processo de craqueamento catalítico fluido (FCC). Um reator batelada em leito fluidizado, CREC, foi usado a 673 e 723 K com tempos de contato entre 3 e 15 s. Cis-decalina foi muito mais reativa. Apesar de diferenças induzidas e medidas na acessibilidade dos catalisadores, seus perfis de atividade foram similares, sugerindo que restrições difusionais não prevalecem. Os produtos foram hidrocarbonetos C 1 -C 12 , enquanto o coque foi muito baixo. Reações de isomerização, craqueamento, transferência de hidrogênio, abertura/contração de anel e alquilação ocorreram, e produtos das várias reações foram observados em tempos de reação muito baixos. Naftênicos bicíclicos C 10 e aromáticos alquilsubstituídos C 7 -C 11 ou nafteno-aromáticos foram os produtos mais importantes. Um mecanismo de reação com três rotas iniciais (isomerização, abertura de anel e reações de transferência de hidrogênio) foi proposto.Cis-and trans-decalin were reacted over cracking catalysts to study the formation of aromatics in a particular fraction of the liquid products obtained in the fluid catalytic cracking process (FCC). A batch, fluidized bed CREC riser simulator reactor was used at 673 and 723 K and contact times varied from 3 to 15 s. Cis-decalin was much more reactive. Despite differences induced and measured in their accessibility indices, the catalysts led to similar activity profiles, suggesting that diffusion restrictions do not prevail. Products were C 1 -C 12 hydrocarbons while coke was very low. Isomerization, cracking, hydrogen transfer, ring opening, ring contraction and alkylation reactions occurred and products from the various reactions were observed at very short reaction times. Bicyclic C 10 naphthenics and alkyl-substituted C 7 -C 11 aromatics or naphtheno-aromatics were the most important products. A reaction mechanism with three initial routes (isomerization, ring opening and direct hydrogen transfer reactions) was proposed.

Formation of aromatics in heavy gasoline and light LCO ends in FCC

“…The cis-isomer was more reactive, as also noted previously over various FCC catalysts [18]. Different authors also observed this characteristic using different zeolites under a wide range of experimental conditions [28,29].…”

“…3 shows the yield curves of the products from the most important reactions (cracking, hydrogen transfer, isomerization and ring contraction) over all the catalysts. It can be seen that they all show a primary character, following the very early occurrence of their products, as also reported by Pujro et al [18], who used prototypes of commercial catalysts. The primary character of the products and reactions can be assigned in view of the linear relationship between yield and conversion, while a secondary character would be revealed by a zero slope at initial conversion.…”

“…Most of the products were observed at very low conversions and reaction times, thus supporting the concept that reactions such as isomerization, ring opening and hydrogen transfer are simultaneous and occur initially; moreover, reactions that would occur after them in a proposed model [18], such as cracking, ring contraction and alkylation-disproportionation would also take place immediately (Scheme 1). Other authors, who observed small concentrations of aromatics, did not consider that these hydrocarbons can be formed initially; as a consequence, only ring opening was considered a initial reaction at 450 • C [32] or, in systems were hydrogen was present, isomerization and ring contraction [28], or ring opening and contraction [29] were considered initial at 400 • C.…”

“…The unit has been described comprehensively elsewhere [18,19]. Reaction times in the experiments were from 1 to 8 s, temperature was 450 • C and catalyst to oil relationship was 1.12.…”

“…This is consistent with the wide distribution of acid strengths found in these catalysts (see Table 1). Based on the detailed product identification, reactions which were identified in the decalin conversion network over this type of catalyst were cracking, direct hydrogen transfer, isomerization, ring contraction, ring opening and alkylation-disproportionation [18].…”