Training That Makes A Difference

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

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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

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What are carboxylates?

• an ester or salt of a carboxylic acid

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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 ……..

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Most important products

• Butanol (£2,400/tonne)

• Succinate (£2,600/tonne)

• Acetone (£1,800/tonne)

• Ethanol (£540/tonne)

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O

O O

CH2

OH

O

CH2

NH2

O

3-hydroxypropionic acid

1,3-propanediol

EEP

acrylamide

acrylic acidmalonic acid

poly(hydroxypropionate)

HO OH

O

HO OH

HO OH

OO

OH

O

OH

n

A Route to Acrylamides

Conventional MADBiodegradable Organic Material (Carbohydrates, Fats, Proteins)

Simple Soluble Organics

Propionic Acid Butyric Acid Long ChainVFA

H2 + CO2Acetic Acid

Acetoclastic Methanogens Hydrogenotrophic

Methanogens

CH4 + CO2

Acetic Acid

Hydrolysis

Acidogenesis

Acetogenesis

Methanogenesis

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Balance of microbial processes for stable conditions

Hydrolysis Acidogenesis Acetogenesis Methanogenesis

Net acid producer Net acid remover

Ideal pH = 5.0 Ideal pH = 7.4

Biomass

polymers

Carbohydrates

Proteins

Lipids

Sugars

Amino acids

Long chain

fatty acids

Intermediate

Products

Hydrogen /

Carbon dioxide

Acetate

Biogas

Methane /

Carbon

dioxide

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

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ABE Fermentation

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Organic Loading Rate (OLR)

OLR = Feed rate (m3/d) x Feed VS (kg/m3)

Reactor volume (m3)

Dictates flow of energy through the system

Low OLR encourages Methanogenesis

High OLR encourages Solventogenesis

Very high OLR encourage Hydrogenesis

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Hydrogenesis Solventogenesis Methanogenesis

H2 Acetone, Butanol, Ethanol CH4

HRT (d)

pH

OLR

2 -3 4 – 5 >10

5.0 5.5 6.8

12 7 3

Training That Makes A Difference

Products of anaerobic metabolism of pyruvate (Solventogenesis)

Pyruvate

LactateAcetate

Acetaldehyde

Ethanol

Formate

Acetolactate

Acetoin

Butylene glycol

Acetoacetyl CoA

Butanol

Butyrate

Oxaloacetate

Malate

Succinate

Acetyl CoA

CO2

H2

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Hydrogenesis

Glucose

2 Lactate 2 Pyruvate

2 Formate

Ethanol Acetat

e

2 Acetyl-Co

2CO2 + 2H2

C 6H12O6

CH3COCOOH

HCOOH

CH3COOHCH3CHOH

CH3CH(OH)COOHLow pH route

Ten routes

of

synthesis

from

pyruvate

(a)– (i)

Selected

based on

OLR

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Batch Production of VFAs

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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

Feedstock(type)

Pre-processing(screening, blending,

pasteurisation)

Digesters(long HRT)

Whole digestate

Dewatering

Whole Fibre

Liquor

Biogas & CHP

Existing Plant

Training That Makes A Difference

Feedstock(type)

Pre-processing(screening, blending,

pasteurisation)

Digesters(long HRT)

Whole digestate

Dewatering

Whole Fibre

Liquor

Short HRT Fermenter

(to produce VFAs)

Biogas & CHP

Thickening/Dewatering

VFA rich liquor (80,000 mg/l)

Thickened sludge

To RefineryEasy Retrofit to a VFA Factory

Feedstock(type)

Pre-processing(screening, blending,

pasteurisation)

Short HRT Fermenters

Liquor

Thickened sludge

Circular Process with HTC

HTC

Liquor Solid Product

Fuel for energy recovery or to land

Thickening/Dewatering

VFA rich liquor (80,000 mg/l)

To Refinery

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Extraction?

• POD to POR approach?

• Strong UK chemical industry

• Refineries also need to diversify

• Opportunity to move away from a petrochemical economy

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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