The Carboxylate Platform
Nigel Horan
Training That Makes A Difference Lecture Outline
• The industry – why it should innovate • What is the carboxylate platform? • Potential benefits • Retrofitting and new build • Conclusions
Training That Makes A Difference AD Industry
• Now over 185 digesters (more than water industry?) • Processing 0.72 million tonnes food waste • But producing 1.44 million tonnes digestate • And >90% recycled to land • Feedstock getting more difficult to source • Security of land route?
Training That Makes A Difference Gate Fee
Training That Makes A Difference Transport and application cost to land
We are close to a situation where the cost of digestate recycling may be greater than the gate fee!
Training That Makes A Difference A Profitable Future?
• To maintain income the industry needs to keep being innovative • The basic flow train offers huge opportunities due to the versatility of anaerobic organisms • Parallel advances in thermal technologies (HTC) extend innovative opportunities
Training That Makes A Difference What are carboxylates?
• an ester or salt of a carboxylic acid
Training That Makes A Difference Why the interest in carboxylates
• Metal salts are high-value oil-soluble, water-insoluble detergents (fracking) • Carboxylate platform provides a cheaper route for syngas (carbon monoxide, hydrogen, carbon dioxide) production from a range of waste feedstocks • And many high value chemicals ……..
Training That Makes A Difference Most important products
• Butanol (£2,400/tonne) • Succinate (£2,600/tonne) • Acetone (£1,800/tonne) • Ethanol (£540/tonne)
Training That Makes A Difference A Route to Acrylamides poly(hydroxypropionate) HO OH O O
1,3-propanediol O O OH EEP H O n
HO OH
O 3-hydroxypropionic acid
NH 2 CH2 HO OH O OH acrylamide O O CH2 O malonic acid acrylic acid
Training That Makes A Difference Conventional MAD
Biodegradable Organic Material (Carbohydrates, Fats, Proteins) Hydrolysis
Simple Soluble Organics
Acidogenesis Propionic Acid Butyric Acetic Acid Acid Long Chain VFA
Acetogenesis Acetic Acid H2 + CO2
Methanogenesis Acetoclastic Methanogens Hydrogenotrophic Methanogens
CH4 + CO2 Balance of microbial processes for stable conditions
Hydrogen / Biomass Carbon dioxide polymers Sugars Biogas Methane / Amino acids Intermediate Carbon Carbohydrates Long chain Products Proteins fatty acids dioxide Lipids Acetate
Hydrolysis Acidogenesis Acetogenesis Methanogenesis Net acid producer Net acid remover Ideal pH = 5.0 Ideal pH = 7.4
Conventional MAD at pH 7.4 is sub-optimal for acid production
Training That Makes A Difference How do we Drive Carboxylate Production • Pure culture with sterile, glucose-based media (ABE) • Mixed culture on waste with: – inhibition (iodoform at 5g/m3) – Organic loading rate control of pH
Training That Makes A Difference ABE Fermentation
Training That Makes A Difference
Organic Loading Rate (OLR)
Feed rate (m3/d) x Feed VS (kg/m3) OLR = Reactor volume (m3)
Dictates flow of energy through the system
Low OLR encourages Methanogenesis High OLR encourages Solventogenesis Very high OLR encourage Hydrogenesis
Training That Makes A Difference H2 Acetone, Butanol, Ethanol CH4
Hydrogenesis Solventogenesis Methanogenesis
HRT (d) 2 -3 4 – 5 >10 pH 5.0 5.5 6.8
OLR 12 7 3
Training That Makes A Difference Products of anaerobic metabolism of pyruvate (Solventogenesis)
Succinate
Acetyl CoA Acetate Malate Lactate
Oxaloacetate Pyruvate Ethanol Acetaldehyde
Acetoacetyl CoA Acetolactate Formate CO Acetoin 2 Butanol H Butyrate Butylene glycol 2
Training That Makes A Difference Hydrogenesis
Glucose C 6H12O6
2 Lactate 2 Pyruvate CH3COCOOH CH CH(OH)COOH 3 Low pH route
2 Acetyl-Co 2 Formate HCOOH
Ethanol Acetat 2CO2 + 2H2 eCH COOH CH3CHOH 3
Training That Makes A Difference Ten routes of synthesis from pyruvate (a)– (i)
Selected based on OLR Batch Production of VFAs
Training That Makes A Difference Continuous Culture • VFA concentrations of up to 25 kg/m3 in continuous mixed waste fermentation – and rising • Waste C:N influences yield (higher C:N better) • Low alkalinity encourages low pH
Training That Makes A Difference Existing Plant
Feedstock (type)
Pre-processing (screening, blending, pasteurisation)
Biogas & CHP Digesters (long HRT)
Whole digestate Whole Fibre
Dewatering
Liquor Easy Retrofit to a VFA Factory To Refinery
VFA rich liquor (80,000 mg/l)
Feedstock Short HRT (type) Fermenter Thickening/ (to produce VFAs) Dewatering
Pre-processing (screening, blending, Thickened sludge pasteurisation)
Biogas & CHP Digesters (long HRT)
Whole digestate Whole Fibre
Dewatering
Training That Makes A Difference Liquor Circular Process with HTC
Feedstock (type) Fuel for energy recovery or to land
Pre-processing (screening, blending, pasteurisation) Liquor Solid Product
Short HRT Fermenters HTC Thickening/Dewatering Thickened To Refinery sludge Liquor
VFA rich liquor (80,000 mg/l) Extraction?
• POD to POR approach? • Strong UK chemical industry • Refineries also need to diversify • Opportunity to move away from a petrochemical economy
Training That Makes A Difference Conclusions
• Thinking about the future will help secure the waste industry future • A lot can be achieved in the laboratory environment, but is this real? • Economic costing should drive research • What does the industry want ? • How can we involve the refineries
Training That Makes A Difference