Optimizing Process Conditions during Catalytic Fast Pyrolysis of Pine with Pt/TiO₂—Improving the Viability of a Multiple-Fixed-Bed Configuration

Abstract

Catalytic fast pyrolysis (CFP) has been identified as a promising pathway for the production of renewable fuels and co-products. However, continued technology development is needed to increase process efficiency and reduce process costs. This report builds upon previous research in which a bifunctional metal–acid Pt/TiO2 catalyst was utilized in a fixed-bed reactor operated with co-fed H2 to improve product yield and reduce coke generation compared to conventional CFP methods. Here, we report further process optimization, in which we achieved similar CFP oil carbon efficiency (>35%) and CFP oil oxygen content (<20 wt %) to our previous report while reducing catalyst and equipment costs by increasing time-on-stream between regenerations by 40–95% and decreasing required regeneration time by more than a factor of 2. These process improvements were achieved by conducting parameter sweeps to determine optimum conditions for CFP and regeneration with key variables including pyrolysis temperature, catalytic upgrading temperature, hydrogen partial pressure, and regeneration oxygen concentration. Coupled with comprehensive oil analyses, these data provide foundational insight into the deoxygenation and coking chemistries for CFP under realistic process conditions while also advancing the technology through applied engineering.

A Review of Recent Research on Catalytic Biomass Pyrolysis and Low-Pressure Hydropyrolysis

“…A shift to the right (higher C recovery) was observed using Pt/TiO 2 and increasing the H 2 partial pressure from 0.5 to 0.9 bar, along with a slight reduction in coke yield. An increased extent of deoxygenation and reduced coke yields with increasing H 2 partial pressure from 0.2 to 0.8 bar were reported in a recent study by French et al 293 using Pt/TiO 2 in an ex-situ CFHP configuration (Figure 13c). For a fixed catalyst/reaction temperature of 400 °C and H 2 partial pressure of 0.8 bar, the yields and deoxygenation performance could be further improved when increasing the pyrolysis temperature from 500 to 525 °C (Figure 13c).…”

“…294,295,305,359,392 • Increased partial pressure of H 2 (both for in-situ and exsitu catalyst contact mode). 359,293,299 • Optimizing the pyrolysis temperature (in ex-situ catalyst contact mode). 293 On the other hand, increasing the time-on-stream (both for in-situ and ex-situ catalyst contact mode) and increasing the WHSV (studied for in-situ contact mode) showed more linear trends leading to increased oxygen content in the liquid organics at an increased carbon recovery.…”

“…This allows comparison of the results obtained with various biomass types, catalysts loadings, catalyst types, and CFP configurations (in situ or ex situ). For studies in which the bio-oil yields and properties of a noncatalytic reference test were not reported, it was estimated from other works for the same type of biomass feedstock. , Some studies reported only the carbon or the oxygen content of the bio-oil. ,,,,,− In those cases, the carbon or oxygen content was calculated according to the clear negative correlation (Figure a) observed in more than 200 bio-oils reported from a range of studies ,,,,,,,,,,− including different biomass types, catalysts, catalyst contact modes, and reaction atmospheres (CFP and CFHP). For comparison, Figure b shows the slope if all oxygen would be removed selectively as H 2 O, CO, or CO 2 , and it is noted that the slope observed experimentally for the 200+ bio-oils from the 25 different studies more closely follows the dehydration pathway.…”

“…of the water-free organics in the bio-oil. The 200+ data points are from a range of studies ,,,,,,,,,,− including thermal pyrolysis, CFP, and CFHP for both woody biomass and agricultural residues. (b) Illustration of the slopes if oxygen were selectively removed via dehydration, decarboxylation, or decarbonylation, respectively.…”

“…Examples include Ru, Pd, or Pt with high hydrogenation activity that are supported on solid acids such as zeolites (see examples in Table ), tungstated zirconia, and γ-Al 2 O 3 , ,,− thereby creating bifunctional catalysts. Noble metals can also be supported on reducible oxides such as TiO 2 , ZrO 2 , and CeO 2 ,,,− or on mixed metal oxides, e.g., Pt on Fe 2 O 3 /CuO. Furthermore, instead of a single precious metal, bimetallic catalysts such as PtPd or combinations of a precious and a transition metal can be used (see (2)). Transition-metal catalysts such as Ni, Co, Mo, Cu, Fe, and their oxides, sulfides, carbides, nitrides, and phosphides were found active for atmospheric pressure HDO of biomass pyrolysis vapors and model compounds. ,,,,,− Particularly phosphides such as Ni 2 P, Co 2 P, Fe 2 P, WP, Ru x P, and MoP show good activity for HDO and direct deoxygenation .…”