**2. Biomass catalytic pyrolysis and upgrading to aromatics**

Anellotech, a Pearl, NY start-up chemical company founded in 2008, has developed a feedstock flexible, in situ catalytic fast pyrolysis process to convert low-cost lignocellulosic biomass solids to a range of hydrocarbons containing valuable benzene, toluene, and xylenes (BTX). These monoaromatics are further refined to produce bio-pX which are valuable feedstocks for bio-PTA [4–13]. In situ CFP technology was originally developed by Dr. George W. Huber, Harvey Spangler Professor of Chemical Engineering at the University of Wisconsin-Madison.

Anellotech has partnered with Suntory, a global consumer beverage company. The technology has been jointly developed by IFPEN, Axen (a subsidiary of

IFPEN), and Johnson Matthey. IFPEN is tasked with scale-up, Axen for technology marketing, and Johnson Matthey for catalyst development. On May 6, 2019, Anellotech announced successful six months of operations of their Bio-TCatTM continuous process in their Silsbee, TX pilot plant. The bio-pX process yield ranged from 22 to 24%, 98% C6+ aromatics. Currently, Anellotech is seeking partners and funding to construct their first commercial CFP based bio-pX plant (500 bone-dry tonnes/day of loblolly pine and target production of 40,000 tonnes BTX and C9+ aromatics per year).

Pyrolysis is an extraordinarily complex, thermochemical reaction which can be operated in slow or fast mode to yield products ranging from solids to liquids and gas. Pyrolysis is challenged by high feedstock complexity and the multiphasic nature of this process. More than 300 compounds are found in an acidic, aqueous, unstable, and viscous heterogeneous mixture (a.k.a. pyrolysis oil) of esters, alcohols, ketones, aldehydes, and carboxylic acids [14–16]. By themselves, these oxygenates have little fuel value. However, they can be catalytically upgraded to aromatic hydrocarbons, particularly bio-pX. The upgrading catalyst must maintain stability and tolerate wide range of oxygenates [17]. CFP can convert the entire plant, not just sugars, which makes this thermochemical process advantageous to fermentation [18].

Zeolites, particularly HZMS-5, have proven to be effective catalysts for pyrolysis oil upgrading to benzene, toluene, and xylenes (BTX). Crystalline zeolites have well-defined microporous structures with pore sizes ranging from 5 to 12 Å. Zeolites are acidic materials with controllable acid site densities. CFP must operate under O2-free, optionally ambient pressure, and does not require H2 (a.k.a. hydroprocessing), but operating under H2 atmosphere might offer advantage of decreased coking (discussed later in this chapter).

Temperature is an important parameter. In CFP, a moderate temperature of approximately 450 to 550 °C is optimum to produce mainly liquids, but the heating and subsequent cooling rates must be extremely high. The biomass must be ground to a finely divided material with averaged particle sizes of less than 3 mm. The cost of the process is inversely proportional to the averaged particle size. The pyrolysis vapor must condense quickly to avoid unwanted secondary reactions such as cracking. Alkali and alkaline earth metal ions in biomass feed pose substantial challenges to the process (addressed in Pretreatment) [17, 19–33].

### **3. In situ vs. ex situ CFP**

There are two process schemes that can be employed in CFP: in situ and ex situ [32, 34]. Pyrolysis and catalytic upgrading that occur in the same zone is in situ. This "one-pot" process is lower in cost than ex situ. However, in situ CFP is sensitive biomass feed content of inorganics, and minimum catalyst/biomass ratio where 10:1 gives highest yield of aromatics [35].

Pyrolysis and catalytic vapor upgrade that occur in separate zones (two-stage) is ex situ CFP. This mode of operation affords the advantage to exclude biochar and metallic ionic impurities from the catalyst which can extend catalyst lifetime. Additionally, the temperature of pyrolysis and vapor upgrade can be independently controlled, an option not available for in situ CFP. BioBTX operates an ex situ pyrolysis process, and has developed an integrated cascading pyrolysis reactor. Their two-stage process excludes non-volatile impurities from entering catalyst pores and this provides the benefit of improved catalyst vapor contact [26].

A comparison of in situ and ex situ CFP of hybrid poplar at 700 °C was conducted in a microreactor. In situ CFP produced 5.4% olefins and 26.1% aromatics. *Catalytic Fast Pyrolysis of Lignocellulosic Biomass to Benzene, Toluene, and Xylenes DOI: http://dx.doi.org/10.5772/intechopen.99946*

While operating in an ex situ mode, up to 17.4% olefins and 18.9% aromatics were made. The carbonaceous material yields for in situ and ex situ were 31.3% and 18.6%, respectively. Temperature strongly influenced the product distribution in ex situ. A comparison of both modes of operations in a mini-plant for CFP of pinewood was conducted [36]. An analysis of ex situ economics has also been published [37].
