Sugars are the basic, fungible raw material to manufacture bio-based fuels and
chemicals. One of the significant challenges to economical biorefining
over the last 15 years has been creating a biomass-tosugar technology capable of
delivering industrial quantities of cellulosic-based sugars.
One method, enzymatic hydrolysis, requires biomass to be pretreated via technologies
such as the NREL dilute-acid or Metso reactors, and is being used by biorefinery
development companies like Abengoa and Iogen.
Once the raw biomass is pretreated, enzymes are added to convert or hydrolyse
the cellulose-rich biomass into sugar. Companies such as Novozymes, Genencor-
Danisco-DuPont, EdeniQ, Codexis and others have been developing enzymes to advance this enzymatic hydrolysis front-end approach.
The HCL CleanTech and BlueFire hydrolysis approaches, relying on a conventional
concentrated acid process with advanced acid recycles, have also been gaining
attention as contenders. Once a front-end process is operational, the resulting
sugars are used as the raw material for the scores of sugar conversion processes
developed by companies including LS9, Amyris, Gevo, Cobalt and Genomatica. for producing bio-based fuels and chemicals.
Countercurrent technology platform
US-based development company PureVision Technologyy has a thermochemical mechanical process that employs a modified reactor based on well established extruder technology to achieve continuous countercurrent biomass conversion. The continuous
countercurrent extruder reactor (CCER) advances solid biomass downstream while
liquids move in counter-current flow. PureVision’s biorefining innovation suite includes two synergistic inventions: biomass fractionation and biomass hydrolysis.
Biomass fractionation
The biomass fractionation technology employs the patented counter-current process to rapidly fractionate biomass into lignin, xylose liquor and a digestible solid cellulose fraction that can be converted into glucose, a raw material used to manufacture a wide variety of fuels, chemicals and consumer products.
PureVision’s approach relies on counter-flow reactors with minimal reactant use. In
the beginning, the company began generating continuous fractionation data with its
process development unit, a modified 27mm twin-screw extruder. Early work focused
on corn stover, triticale straw and wheat straw feedstocks.
The three biomass product streams, cellulose, lignin and xylose liquor, appeared
to be suitable for numerous applications in the pulp and paper industry and PureVision sought out larger partners capable of advancing lignin and pulping aspects of the technology. In spite of developing process chemistries for obtaining purified pulps and lignins from straw and woody biomass, the company was unable to attract a partner to continue minipulping or lignin applications in an era marked by dramatic changes and restructuring of the pulp and paper industry.
In September 2010, PureVision achieved a biorefining ‘breakthrough’ by rapidly converting cellulosic biomass into fermentable sugars in minutes without the use of enzymes or concentrated acids. The company is proceeding from experimental proof-of-concept to its half a tonne a day continuous reactor during the next 12 months
and expects to achieve the conversion of over 90% of the theoretical sugar yield.
Rapid Integrated Continuous Countercurrent Hydrolysis (RIC2H)
PureVision can convert raw biomass into mixed C5 and C6 sugars without the use
of enzymes or concentrated acid. To date, proof of concept experiments using
bagasse as the feedstock have shown better than 80% total mixed sugar yield, with the majority of the remaining sugars as recoverable residual saccharide solids. Ongoing studies are expected to achieve the conversion of over 90% of theoretical sugar yield with sugar concentration above 25% by weight.
PureVision estimates the technology would be able to produce concentrated sugar syrup in the range of $0.10 (€0.07) a pound, inclusive of feedstock costs of $55/tonne, in minutes, with minimal byproducts.
The RIC2H pathway provides a reasonable scale-up and rollout of economical cellulosic sugars for use in existing markets (furfural, ethanol, butanol and PLA) and leapfrogs the slow progress of enzymatic hydrolysis of cellulosics.
The RIC2H technology is now being scaled up using PureVision’s existing 50mm CCER located at its research facilities.
‘While scale-up hurdles remain, reliance on equipment from the mature and large extrusion industry reduces equipment scaling uncertainties,’ says PureVision’s
CTO Richard Wingerson.
Commercial scale-up
Because each feedstock and downstream process requires a unique CCER processing chemistry, PureVision is advancing a fourphased biorefinery project development programme. This offers a roadmap for project developers, stakeholders and project
collaborators to secure the necessary information:
Phase 1: Batch optimisation studies for target feedstocks to determine chemistry
to achieve fermentable sugars and to determine preliminary economics of the
biomass-to-sugars process.
Phase 2: Scale-up to half a tonne per day CCER using the company’s existing
small continuous pilot plant to optimise conditions to achieve fermentable
sugars and determine commercial viability.
Phase 3: Build and operate a 25 tonne per day demonstration-scale plant in cooperation with clients and stakeholders. With verified economics and
project financing, proceed to commercial-scale.
Phase 4: Build and operate commercial-scale equipment in 250 tonne per day modules.
The modular aspects of the CCER equipment allow biorefineries to expand by adding pre-assembled modules or ‘trains’ to achieve large-scale operations, such
that four 250 tonne per day CCER reactors would achieve a 1,000 tonne per
day feedstock input.
PureVision is currently involved with a number of Phase 1 and 2 studies testing a variety of cellulosic feedstocks. During 2012, the company expects to begin several additional programmes including its first Phase 3 programme, with an eye to developing the first commercial-scale 250 tonne per day CCER in 2014.
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