(277g) Pyrolysis, Catalytic Pyrolysis and Catalyst Characterization Using a Tandem Micro-Reactor-GC/MS

Converting various nonfood biomass feedstocks (lignocellulose, hemicellulose and cellulose) directly to biofuels or value-added specialty chemicals is of global interest. Investment in new process technologies and chemistries is increasing every year. Each new technology undergoes detailed characterization, using a variety of analytical techniques, in order to identify those with the potential to meet economic and performance goals.

Many of the new technologies are based on the thermal degradation of the biomass feedstock; however, bio-oil produced using so-called fast pyrolysis has many undesirable properties such as low heat content, high oxygen and high water content.  The quality of the bio-oil can be improved using catalysts to transform the undesirable species. Catalytic pyrolysis can be performed with zeolite catalysts, transition metal or precious metal catalysts in gaseous hydrogen, usually at elevated pressure

The overall scale of the research effort and the almost overwhelming number of different feedstocks being evaluated has precipitated a demand for a fast, reliable method to:

1)    identify the constituents formed during the pyrolysis of the feedstock,

2)    identify and quantitate the transformation products as a result of contact with the catalyst [both in-situ and ex-situ]. The effect of temperature, pressure, atmosphere, contact time, catalyst load and substrate will all influence the products formed as the sample vapors flow through the catalyst bed.

3)    evaluate the performance of the catalyst with respect to the products formed as a function of the operating conditions (e.g., temperature, pressure, atmosphere, etc.).

The Tandem micro-Reactor GC/MS system integrates these three processes into a single bench-top instrument [1-3]. This unique analytical system will be described in detail. The system consists of an upper or 1^st micro-Reactor and lower or 2^nd micro-Reactor each with independent temperature (40 – 1000 ⁰C) and reaction gas controls. The pressure of the Tandem µ-Reactor can be varied from 0.05 – 3.5 MPa. The 1st micro-Reactor can accept solid or viscous liquid samples in a batch sampling mode with catalysis occurring under different conditions in the 2^nd micro-Reactor. The 2^nd micro-Reactor is designed to allow a quick change of the catalyst bed. Batch or continuous experiments can be performed with this system to evaluate both catalyst performance and to characterize catalysis products. Provisions are also designed into the system to allow catalyst regeneration and evaluation.

In this work four examples will be presented to illustrate how the Tandem micro-Reactor – GC/MS can provide meaningful information about the feedstock being evaluated, the impact various operating parameters have on the transformation process and the characterization of a catalyst.

Fast pyrolysis with and without a catalyst

1. Analysis of Jatropha “press cake”: The press cake (0.5mg) is pyrolyzed in the 1^st µ-Reactor; the 2^nd µ-Reactor contains no catalyst – it serves as an inert transfer line to the GC inlet. The pyrogram is dominated by Hexadecadienoic acid and Octadecadienoic acid. Several other compounds are evident.
2. If the pyrolyzates formed in 1^st µ-Reactor (550°C) flow into 2^nd µ-Reactor (550°C) containing a Zeolite (ZSM-5) catalyst, only benzene, toluene, xylene and ethylbenzene are observed. This is a classic ex-situ transformation of biomass to high value fine chemicals.

Variation in transformation as a function of catalytic bed temperature

1. The transformation of ethanol to ethylene, diethylether and propylene as a function of Reactor temperature: 100 - 600ºC, (He:50 mL/min, Catalyst: 20% ZSM-5 coated on Al₂O₃) can be observed real time or at distinct temperatures. The chromatograms show that the optimum catalyst bed temperature for the ethylene transformation is between 250 – 300ºC. H₂O was strongly adsorbed below 200°C..

1. EGA-GC/MS analysis of lignin in Helium and Hydrogen at high pressures. Analysis of the lignin evolved gas analysis (EGA) thermogram done in a helium atmosphere shows that the thermal distribution is essentially independent of the reaction pressure: the reproducibility of the apex temperature (376⁰C ±0.3), the wt.% of the residual char [44.5±1.0 @1MPa, 44.2±0.3 @ 1.5MPa and 45.3±0.4 @ 2.0MPa] and the ions present in the average mass spectrum support this conclusion. When the experiments are performed in a hydrogen atmosphere their thermal distribution is much different.  A second group of compounds evolve from the lignin. The apex temperature is 640±1⁰C, the residual char wt.% is lower as the pressure increases [35.2±1.8 @1MPa, 26.3±2.5 @ 1.5MPa and 21.4±2.4 @ 2.0MPa]. Analysis of the second thermal zone using GC/MS with an analytical column (UA-5(30m x 0.25mm i.d. x 1㎛ film), confirms the presence of a wide range of aromatic hydrocarbons formed when the pyrolysis of lignin is performed in hydrogen at high pressures. 

[1]  C. Watanabe, T. Ramus, R. Meijboom, B. Freeman, A new technique for the rapid characterization of catalysts: Tandem micro-Reactor–gas chromatography/mass spectrometry, Environmental Progress & Sustainable Energy, 33 (2014) 688-692.

[2]  R.R. Freeman, A. Watanabe, C. Watanabe, N. Teramae, K. Wang, Material characterization using a Tandem micro-Reactor-GC-MS, Journal of Analytical and Applied Pyrolysis, 111 (2015) 41–46.

[3]  C. Watanabe, I. Watanabe, N. Teramae, K. Wang and R.R. Freeman, On-line analysis of catalytic products using a high pressure tandem micro-reactor GC/MS, Journal of Analytical and Applied Pyrolysis, submitted May, 2015.