Chemical Hydrolysis

 

Chemical hydrolysis

chemical hydrolysis scheme
Introduction:

Abundant plant biomass and waste has the potential to become a sustainable source of fuels and chemicals. Realizing this potential requires the economical conversion of recalcitrant lignocellulose into useful intermediates, such as sugars (monosaccharides). Chemical hydrolysis is an abiotical processing method for processing (contaminated/hazardous) lignocellulosic material, such as waste wood. The process consists of a grinding step, a pretreatment to free the polysaccharides and an acid hydrolysis of cellulose and hemicellulose. Several types of acids, concentrated or diluted, can be used, such as sulphurous, sulphuric, hydrocloric, hydrofluoric, phosphoric, nitric and formic acid. Sulphuric and hydrochloric acids are the most commonly used catalysts. Furfural and organic acids are formed, together with a solid residue which can be processed further by pyrolysis into bio-oil and bio-char.

Potential:

Chemical hydrolysis can be viable at small scales. It is highly feedstock flexible because, compared to biological processing there are no concerns on biota inhibitors, water content , or gasifier performance. The produced compounds (levulinic acid, formic acid, furfural and lignin) are valuable platform chemicals with a huge potential.

Aim:

The main advantage of the acid hydrolysis is that acids can penetrate lignin without any preliminary pretreatment of biomass, thus breaking down the cellulose and hemicellulose polymers to form individual sugar molecules.

Difference to BAU technology/approach:

For contaminated waste wood there are not much recycling alternatives available apart from combustion with energy and heat recovery.
Material recovery from ‘clean’ waste wood can be reuse or biological treatment .

Input stream requirements:

Waste wood, also contaminated waste wood  can be treated with this technology with the aim of material recovery.

Waste wood

Available quantity:

All types of waste enriched with cellulose and hemicellulose (wood waste, crop waste, inedible parts of the plants, sawdust, energy crops, food waste) are suitable for the process. Also mixtures of feedstocks can be treated. However, the process efficiency needs to be optimised depending on the feedstock.

Drivers for treating this stream:

For contaminated waste wood there are not much recycling alternatives available.

Potential environmental risks related to this waste stream:

Plant patogens and dangerous insects for forestry and agriculture can spread with the waste.

Economic/technical barriers to collect this stream:

No technical barriers exist; wood waste is currently collected across Europe, mainly for biogas and biofuel production. Cost of logistics could present a drawback.

Output stream:

Result of testing in project:
Out of 1 tonne of waste wood (mixed ) you get 258kg Levulinic Acid, 102 kg Formic Acid, 127 kg Furfural, 180 kg Lignin and 165 kg of residues.

Potential uses of this output stream:

Residues  are combusted and can be used to generate heat and power.
The platform chemicals that are formed, levulinic acid, formic acid, furfural and lignin, can be converted (catalytic conversion) into value-added-chemicals, biofuels or other bio-products. Several chemicals can be derived from them. From levulinic acid, for example, diphenolic acid (used in resins, paints, polymers and lubricants) and succinic acid (used in food additives) can be formed, among other compounds. 

Potential environmental risks/benefits related to this output stream:

The technology requires energy  (heat and pressure)
Biofuels  replacing fossil fuels reduce CO2 offset.

Economic barriers/drivers for market introduction of this output stream:

Monosacharides are widely used as raw materials in fermentation processes, pharmaceutical production and biopolymer production.Industrial sugars are well accepted by the market. However, purity of the components recovered will define the applicability and market value of the output streams.

Technical barriers for market introduction of this output stream:

There are no fundamental technical barriers. However, in order to obtain efficient yields, downstream processing and purification needs to be optimised for each feedstock.

Legislative barriers for market introduction of this output stream:

Legislative constraints depend on the field of application.

Pilot description:

The University of Limerick provides opportunities for companies, academic institutions and other research bodies to undertake a trials and optimisation studies with a labscale reactor for chemical hydrolysis of various waste and feedstocks.

Installation:

 


Lab scale batch system

Continuous pilot ‌

 

Capacity:
  • Reactor volume: 0,1-0,8 liter (batch lab system)
  • Throughput: 1 liter/ min (continuous pilot system)
  • Pressure Limit:  Atmosphere – 50 Bar
  • Sampling: Several Ports for In line sampling available to measure gaseous and liquid outputs, and monitoring evolution of the reaction
Scale of the equipment:

Pilot scale

Main technological barriers for market introduction:
  • Interference with many potential unwanted reactions
  • The optimal process conditions are different for cellulose and hemicellulose
  • Selectivity of the reaction is highly temperature dependent
  • Intermediates are reactive
Main economic barriers/drivers for market introduction:
  • Simplicity and cost-efficiency of sugar separation and purification from the hydrolysis liquor produced from complex and heterogeneous biomass
  • Process requires  a higher temperature to release the sugars, making the process less desirable than enzymatic digestion
Research steps:
  • Reduce energy use of the process
  • Increase the reaction rate of cellulose hydrolysis
  • Increase throughput
  • Optimise operating conditions for multiple components
  • Improve the stability of the desired products under process conditions
  • Fractionate and recover lignin
  • Search for new green solvents which facilitate a recovery of sugars
  • Reduce detioration of process equipment by acids
  • Scale-up of equipment
Economic steps:
  • Search for R&D finance dedicated to purification steps after the chemical hydrolysis.
  • Reduction of temperature required for hydrolysis.
  • Identification of cheaper, green and recoverable solvents which can substitute the harsh chemicals like H2SO4 which currently applied for chemical hydrolysis processes. 
Legislative steps:
  • Improve standatisation and grade of industrial sugars
  • Stimulating policy measures to increase uptake of sugars from chemical hydrolysis by fermentation industries
  • Registration of new patents
Other:

None

Contact details:
Organisation: TCBB at UL/NUI Galway

Department:

Leading researcher: J.J. Leahy

Phone number:

E-mail: j.j.leahy@ul.ie

 

Documentation:

Presentation: Chemical Hydrolysis Technology for organic waste streams, TCBB, University of Limerick, JJ Leahy, RENEW Technology Foresight Conference 24/04/2013

Current pilot installations available for industries at University of Limerick: Overview capacities