Multiscale Evaluation of Catalytic Upgrading of Biomass Pyrolysis Vapors on Ni- and Ga-Modified ZSM-5

Abstract

Metal-impregnated (Ni or Ga) ZSM-5 catalysts were studied for biomass pyrolysis vapor upgrading to produce hydrocarbons using three reactors constituting a 100 000× change in the amount of catalyst used in experiments. Catalysts were screened for pyrolysis vapor phase upgrading activity in two small-scale reactors: (i) a Pyroprobe with a 10 mg catalyst in a fixed bed and (ii) a fixed-bed reactor with 500 mg of catalyst. The best performing catalysts were then validated with a larger scale fluidized-bed reactor (using ∼1 kg of catalyst) that produced measurable quantities of bio-oil for analysis and evaluation of mass balances. Despite some inherent differences across the reactor systems (such as residence time, reactor type, analytical techniques, mode of catalyst and biomass feed) there was good agreement of reaction results for production of aromatic hydrocarbons, light gases, and coke deposition. Relative to ZSM-5, Ni or Ga addition to ZSM-5 increased production of fully deoxygenated aromatic hydrocarbons and light gases. In the fluidized bed reactor, Ga/ZSM-5 slightly enhanced carbon efficiency to condensed oil, which includes oxygenates in addition to aromatic hydrocarbons, and reduced oil oxygen content compared to ZSM-5. Ni/ZSM-5, while giving the highest yield of fully deoxygenated aromatic hydrocarbons, gave lower overall carbon efficiency to oil but with the lowest oxygen content. Reaction product analysis coupled with fresh and spent catalyst characterization indicated that the improved performance of Ni/ZSM-5 is related to decreasing deactivation by coking, which keeps the active acid sites accessible for the deoxygenation and aromatization reactions that produce fully deoxygenated aromatic hydrocarbons. The addition of Ga enhances the dehydrogenation activity of the catalyst, which leads to enhanced olefin formation and higher fully deoxygenated aromatic hydrocarbon yields compared to unmodified ZSM-5. Catalyst characterization by ammonia temperature programmed desorption, surface area measurements, and postreaction temperature-programmed oxidation (TPO) also showed that the metal-modified zeolites retained a greater percentage of their initial acidity and surface area, which was consistent between the reactor scales. These results demonstrate that the trends observed with smaller (milligram to gram) catalyst reactors are applicable to larger, more industrially relevant (kg) scales to help guide catalyst research toward application.

Overview of catalytic upgrading of biomass pyrolysis vapors toward the production of fuels and high‐value chemicals

“…In situ reduction of NiO to Ni during CP was also more recently observed (Yung et al, ). Hydrogen pretreatment of Ni/ZSM‐5 catalysts with varied nickel loadings was investigated on their ability to produce aromatic hydrocarbons by upgrading of pine pyrolysis vapors.…”

Recent research progress on bio‐oil conversion into bio‐fuels and raw chemicals: a review

“…Yung et al . investigated the upgrading of biomass pyrolysis vapors over Ga/ZSM‐5 aimed at the selective production of aromatics, showing that the addition of Ga to ZSM‐5 zeolite increased its Lewis acidity, which enhanced its dehydrogenation capability.…”

Advanced biofuels production by upgrading of pyrolysis bio‐oil

“…A number of different scale reactor types have been employed—such as fluid‐bed, circulating fluid‐bed, auger, fixed‐bed, entrained flow, rotating cone, microwave, ablative, vacuum, and screw and auger kiln reactors—some of which have been recently reviewed in the literature . Likewise, catalytic pyrolysis has already been validated in several pilot plant units . Fluidized‐bed reactors are the most popular type because of their good heat/mass transfer, allowing the fast heating of the feedstock particles …”