anurag ppt

64
SEMINAR ON BIOCHEMICAL ROUTES :ANAEROBIC DIGESTION TRANSESTERIFICATION PHOTOFERMENTATION By ANURAG CHANDRA SHEKHAR (M.TECH. FIRST YEAR ) ROLL No. 06 In The Expert Guidance Of Dr. SONAL DIXIT ASST. PROFESSOR(GUEST) DEPT. ENVIROMENTAL SCIENCE

Upload: anurag-chandrashekhar

Post on 09-Feb-2017

78 views

Category:

Engineering


1 download

TRANSCRIPT

Page 1: Anurag ppt

SEMINAR ON BIOCHEMICAL ROUTES :ANAEROBIC DIGESTION

TRANSESTERIFICATIONPHOTOFERMENTATION

By ANURAG CHANDRA SHEKHAR(M.TECH. FIRST YEAR )ROLL No. 06

In The Expert Guidance OfDr. SONAL DIXIT

ASST. PROFESSOR(GUEST)DEPT. ENVIROMENTAL SCIENCE

Page 2: Anurag ppt

Anaerobic Digestion

Anaerobic digestion is the conversion of organic material in the absence of oxygen to methane and carbon dioxide by a microbial consortia.

CXHYOZ CO2 +CH4+ anaerobic bacterial biomass

Page 3: Anurag ppt

How Do We Get Methane?

Need Methanogens:Either Hydrogen (Lithotrophic methanogens)4H2 + CO2 CH4 + 2 H2O

Acetate (acetoclastic methanogens)CH2COOH + H2O CH4 + CO2

But have a limited range of substrates can also include carbon monoxide, formate, methanol.

Page 4: Anurag ppt

The Anaerobic Digestion Microbial Consortia

The production of biogas is dependant on the successful interaction of interdependent microbial species.

The production of methane is a property of a (relatively) limited number of micro-organism species, the “methanogens”.

There is a limited number of substrates that the “methanogens” can use to produce methane.

Page 5: Anurag ppt

5

Anaerobic Digestion Process

Liquefaction

LiquefyingBacteria

Acid Production

Liquefiedsoluble organic

compounds

InsolubleCompounds

(organic,inorganic,

water)

Acid-FormingBacteria

BiogasProduction

Simpleorganic

acids

Methane-FormingBacteria

Manure

BiogasBiogas

(Methane, CO2, misc.)

Effluent

End Products

Page 6: Anurag ppt

The Stages in Anaerobic Digestion

HydrolysisLong chain polymers broken down to smaller molecules.

AcidogenesisProduction of hydrogen and volatile fatty acids.

AcetogenesisAlcohols, >C2 VFAs converted to acetate and hydrogen.

MethanogenesisHydrogen and acetate converted to methane.

Page 7: Anurag ppt

The Steps in Anaerobic Digestion

Hydrolysis

Acidogenesis

Acetogenesis

Methanogenesis

Taken from Guwy, (1996). Modified from Mosey, (1983)

Page 8: Anurag ppt

Factors Effecting the Rate of Hydrolysis

Particle size of the waste, smaller is better. Accessibility of the substrate i.e. how easy is it for the

enzymes to attack the substrate. Problems with lipids . Residence time in the reactor. Chemical structure of substrate. Negative impact of lignin and hydrocarbons, Organic content of the substrate.

Page 9: Anurag ppt

Acidogenesis

The sugars, amino acids and longer chain fatty acids are then fermented to acetate, propionate, butyrate, valerate, ethanol, lactate, hydrogen, CO2, ammonia and sulphide by the acidogenic bacteria.

The proportion of the organic products of the acidogenic bacteria is determined by the H2 concentration and pH.

Page 10: Anurag ppt

Acetogenesis

The acetogens (obligate hydrogen producing acetogenic bacteria) convert the fermentation products which the methanogens cannot use (alcohols, >C2 VFAs, aromatic compounds) to the substrates which the methanogens can utilise.

The Gibbs free energies for the conversion of ethanol, propionic and butyric to acetate and hydrogen are energetically unfavourable i.e. positive at standard free biochemical energy levels (pH 7.0, 1 atm.).

Page 11: Anurag ppt

Why are Propionic and Butyric Acids bad?

Don`t smell very nice . Wasted energy as methanogens can`t use them. Very difficult to get rid of.

CH3CH2COOH + 2H2O CH3COOH + CO2+ 3H2

Propionic acid

NOT beneficial for the microorganisms as: G0 =+ 76.1.9 KJ mol -1

Energy could be required to be put in to use the propionic acids.

Page 12: Anurag ppt

Role of Interspecies Hydrogen Transfer

The H2 partial pressure must be maintained at between 10-6-10-

4 atmospheres for sufficient energy for growth to be obtained from propionic and butyric acids.

As H2 is continually being generated it must be continually be removed for methanogenesis to occur.

The removal of H2 is achieved by conversion to methane by the hydrogen utilising methanogens.

This symbiosis is known as interspecies hydrogen transfer and is crucial to the success of the anaerobic digestion process.

Page 13: Anurag ppt

Graphical representation of the hydrogen-dependant thermodynamic favourability of acetogenic oxidations and inorganic respirations associated with the anaerobic degradation of waste organics. (1) Propionic oxidation to acetic acid, (2) butyric oxidation to acetic, (3) ethanol to acetic, (4) lactic

to acetic, (5) acetogenic respiration of bicarbonate, (6) methanogenic respiration of bicarbonate, (7) respiration of sulphate to sulphide, (8) respiration of sulphite to sulphide, (9) methanogenic

cleavage of acetic acid, (10) SRB-mediated cleavage of acetic acid. (From Harper and Pohland, 1985).

Methanogenic “Hydrogen” Niche

Page 14: Anurag ppt

The Methanogens

A group of gram –ve bacteria. Belong to the group of bacteria termed the Archaea or

archaebacteria. Are strict anaerobes they evolved billions (3.5 billion) years

ago when the earth had very low or zero levels of oxygen. Utilise simple inorganic substrates such as H2, CO2 or simple

organic substrates such as acetate, formate and methanol.

Page 15: Anurag ppt

Image source: Dr L. Hulshoff and Professor van Lier; Sub-department of Environmental Technology, Wageningen University, Netherlands

The Archaea

Scanning electron micrograph of archaea from the genus Methanosaeta. Members of the genus Methanosaeta are acetotrophic, i.e. they produce methane from acetate.

Scanning electron micrograph of a cocci-shaped archaea from the genus Methanosarcina. Members of the genus Methanosarcina can use all 3 routes to methane.

Page 16: Anurag ppt

Specific Growth Conditions

These micro-organisms have been difficult to culture in vitro as in nature they are dependant on other bacteria to provide a suitable environment for their growth.

The fermentative bacteria provide a environment with :Low redox potential (-330 mV).Extremely low in O2 .Suitable range of substrates .

Page 17: Anurag ppt

Analysing The Consortia Traditional microbiology

“petri” dish technology (some problems here) Enzymatic profiles

Molecular Biology Techniques PCR/RT PCR DGGE FISH Genomics and Proteomics Microarrays

Page 18: Anurag ppt

Limited Range of Substrates

Hydrogen (Lithotrophic methanogens)

4H2 + CO2 CH4 + 2 H2O

Very beneficial for the microorganisms as G0 =-138.9 KJ mol -1 is gained.

But only 30% of methane produced via this route.

Page 19: Anurag ppt

Cont…

Acetate (acetoclastic methanogens)

CH2COOH + H2O CH4 + CO2

Not so beneficial for the microorganisms as only G0 = - 32 KJ mol -1 is gained.

But 70% of methane produced via this route.

Page 20: Anurag ppt

Other Anaerobic Processes

Unfortunately other gases are produced as well as methane and CO2.

These include hydrogen sulphide (H2S) and ammonia (NH3). Hydrogen Sulphide is produced by a competing group of

bacteria to the methanogens called the sulphate reducing bacteria.

Page 21: Anurag ppt

What Effects the % and amount of Methane in the Biogas

Relative solubility of the gases. Is alkalinity being destroyed? Biodegradability of substrate. Chemical composition of biodegradable substrate.

– Buswell equation

Page 22: Anurag ppt

Sulphate Reducing Bacteria (SRBs)

Are a problem for methanogenesis as? Compete with methanogens for their source of energy

(hydrogen and acetate). Can become inhibitory (cellular toxin) at dissolved levels of

50 mg/l. More of the dissolved form at lower pH.

Page 23: Anurag ppt

Competitive Nature of SRBs

4H2 + SO42- H2S + 2 H2O

Very beneficial for the micro-organisms as G0 =-154 KJ mol -1 is gained.

CH2COOH + SO42- H2S + 2HCO3

-

Not so beneficial for the micro-organisms as only G0 = - 43 KJ mol -1 is gained BUT more than the methanogens

Page 24: Anurag ppt

The bacterial consortium requires a number of factors to be controlled to maintain performance. These include: Temperature pH (related to buffering capacity) Essential Nutrients Avoid toxic compounds Sufficient residence time to reproduce

Page 25: Anurag ppt

The Effect of Temperature Three temperature optima have been reported for the

anaerobic digestion process phsycrophilic (around 15oC), mesophilic (around 35oC) and thermophilic (around 55oC) temperatures.

Methanogenesis has been found to occur upto 75oC but the optimum temperature is thought to be 55-60oC.

The advantage of the higher temperature ranges is that the process will proceed at a faster rate than the lower temperature ranges as stated by the Arrhenius equation.

Page 26: Anurag ppt

The Effect of pH Different groups in the anaerobic consortia can cope with

different pH levels. Methanogens prefer pH 6-5- 7.5 Acidogens also prefer pH 6.5-7.5 BUT can cope with pH 5.2 Therefore if pH is lowered methane production will slow and

consumption of VFA reduce while VFA production continues. Spiral of Decline.

Effects methane production but also distribution of volatile fatty acids.

Page 27: Anurag ppt

Bicarbonate Alkalinity and pH

pH Scale is the log10 of the H+ concentration. Bicarbonate alkalinity is a measure of the H+ buffering

capacity of the reactor. Measured in mg/l CaCO3

If you have a alkalinity buffer then difference is between walking a tight rope and a plank when operating the digester.

If alkalinity is decreasing may be a sign of trouble before pH drops below critical level.

Page 28: Anurag ppt

Nutrient Requirements

The anaerobic consortia need nutrients to grow their cells and drive their enzymes and metabolic processes.

Can be divided up into macro and micro nutrients.

Need to be “available”

Page 29: Anurag ppt

Macro nutrients Relatively large quantities

C/N/P ratiosAlso need sulphur C N P S

500-1000:15-20: 5 : 3

Micronutrients (Trace Elements) Needed in much lower quantities (g per m3) Required for enzyme activity Ni, Fe, Co, Se, Mg etc.

Page 30: Anurag ppt

Toxic or Inhibitory Compounds Divided into two groups:

Too much of a good thingAmmoniaSulphateCa/Na/K

Should not be here at all Cleaning compoundsAntimicrobialsSolventsHeavy metals

Page 31: Anurag ppt

31

Environmental Benefits

Reduces odor from land application. Protects water resources. Reduces pathogens. Weed seed reduction. Fly control after digestion. Greenhouse gas reduction. Help in bio gas generation &

WWT.

Page 32: Anurag ppt

Conclusions The anaerobic digestion process depends on the effective

working of a complex interaction of microorganisms. It has been working successfully for 3.5 billion years. However there a wide number of ways which we can make it

not work very well. It can be breaking down and still seem to be working.

Page 33: Anurag ppt

Transesterification

Transesterification is based on the chemical reaction of triglycerides with Methanol to form methyl esters and glycerin in the presence of an alkaline catalyst .

Methanol & Catalyst are injected into Light layer from esterification and virgin oil and reacted in the Bio-Conversion Processor (BCP).

Crude Biodiesel and Crude Glycerin are separated using Centrifuge after completion of the transesterification reaction .

Crude Biodiesel and Crude Glycerin are refined using distillation columns.

Use of Ultrasonication Conversion can speed up this process significantly.

Page 34: Anurag ppt

Transesterification RXN O O || || CH2 - O - C - R1 CH3 - O - C - R1 | | O O CH2 - OH | || || | CH - O - C - R2 + 3 CH3OH => CH3 - O - C - R2 + CH - OH | (KOH) | | O O CH2 - OH | || || CH2 - O - C - R3 CH3 - O - C - R3

Triglyceride methanol mixture of fatty esters glycerin

Page 35: Anurag ppt

Triglyceride Sources

Rendered animal fats: beef tallow, lard Vegetable oils: soybean, canola, palm, etc. Chicken fat Rendered greases: yellow grease (multiple sources) Recovered materials: brown grease, soapstock, etc.

Page 36: Anurag ppt

Feedstock OilMethanol Catalyst

Raw Biodiesel

Fuel-Grade Biodiesel

Water

Wash Water

Glycerol (with methanol)

Glycerin

Transesterification

Drier

Reactor

Washer

Separator

Page 37: Anurag ppt

Standard Recipe

100 lb oil + 21.71 lb methanol

 → 100.45 lb biodiesel + 10.40 lb glycerol + 10.86 lb XS methanol

Plus 1 lb of NaOH catalyst

Page 38: Anurag ppt

Competing Reactions

Free fatty acids are a potential contaminant of oils and fats.

O || HO - C - R

Carboxylic Acid (R is a carbon chain)

O || HO - C - (CH2)7 CH=CH(CH2)7CH3

Oleic Acid

Page 39: Anurag ppt

 O

|| + KOH HO - C - (CH2)7 CH=CH(CH2)7CH3

  Oleic Acid Potassium

Hydroxide  

O ||

→ K+ -O - C - (CH2)7 CH=CH(CH2)7CH3 + H2O 

Potassium oleate (soap) Water

Fatty acids react with alkali catalyst to form soap.

Page 40: Anurag ppt

Water is also a problem

Water hydrolyzes fats to form free fatty acids, which then form soap.

O || CH2 - O - C - R1 CH3 - OH | | | O | O O | || | || || CH - O - C - R2 + H2O >>> CH3 - O - C - R2 + HO - C-R1 | | | O | O | || | || CH2 - O - C - R3 CH3 - O - C - R3

Triglyceride Water Diglyceride Fatty acid

Page 41: Anurag ppt

Soap

Soaps can gel at ambient temperature causing the the entire product mixture to form a semi-solid mass.

Soaps can cause problems with glycerol separation and washing.

Page 42: Anurag ppt

Process Issues

Feedstock requirements Reaction time Continuous vs. batch processing Processing low quality feed stocks Product quality Developing process options

Page 43: Anurag ppt

Feedstock Used in Biodiesel Production

Triglygeride or fats and oils (e.g. 100 kg soybean oil) – vegetable oils, animal fats, greases, soapstock, etc.

Primary alcohol (e.g. 10 kg methanol) – methanol or ethanol (44% more ethanol is required for reaction)

Catalyst (e.g. 0.3–1.0 kg sodium hydroxide) Neutralizer (e.g. 0.25 kg sulfuric or hydrochloric acid)

Page 44: Anurag ppt

Reaction time Transesterification reaction will proceed at ambient (70°F)

temperatures but needs 4-8 hours to reach completion. Reaction time can be shortened to 2-4 hours at 105°F and 1-2

hours at 140°F. Higher temperatures will decrease reaction times but require

pressure vessels because methanol boils at 148°F (65°C). High shear mixing and use of cosolvents have been proposed

to accelerate reaction.

Page 45: Anurag ppt

Batch vs Continuous Flow Batch is better suited to smaller plants (<1 million gallons/yr). Batch does not require 24/7 operation. Batch provides greater flexibility to tune process to feedstock

variations. Continuous allows use of high-volume separation systems

(centrifuges) which greatly increase throughput. Hybrid systems are possible.

Page 46: Anurag ppt

Hybrid Batch/Continuous Base Catalyzed Process

Ester TG

AlcoholTG

AlcoholCatalyst

Ester

Biodiesel Mixer

Glycerol Decanter

CSTR 1 CSTR 2

Glycerol

Alcohol

Alcohol Water

Water

Dryer

Wash Water

Acid

CrudeGlycerol

Page 47: Anurag ppt

Processing Lower Quality Feedstock’s

Biodiesel feedstock’s vary in the amount of free fatty acids they contain:

• Refined vegetable oils < 0.05%• Crude soybean oil 0.3-0.7%• Restaurant waste grease 2-7%• Animal fat 5-30%• Trap grease 75-100%Price decreases as FFAs increase but processing demands

increase, also.Not suitable for high FFA feeds because of soap formation.

Page 48: Anurag ppt

Preferred method for High FFA feeds: Acid catalysis followed by

base catalysis Use acid catalysis for conversion of FFAs to methyl esters,

until FFA < 0.5%.Acid esterification of FFA is fast (1 hour) but acid-

catalyzed transesterification is slow (2 days at 60°C).Water formation by FFA + methanol ==> methyl ester + water can be a problem.

Then, add additional methanol and base catalyst to transesterify the triglycerides.

Page 49: Anurag ppt

Acid Catalyzed FFA Pretreat System

Hi-FFA TG Esters

toAcid base-

process Alcohol

Acid Reactor NeutralizeSeparate

WaterMethanol recovery

Page 50: Anurag ppt

Product Quality Product quality is important – modern diesel engines are very

sensitive to fuel. It is not biodiesel until it meets ASTM D6751. Critical properties are total glycerol (completeness of reaction)

and acid value (fuel deterioration). Reaction must be >98% complete.

Page 51: Anurag ppt

Developing Process Options Schemes for accelerating the reaction

Supercritical methanolHigh shear mixingCo solvents (Biox)

Solid (heterogeneous) catalystsCatalyst reuseEasier glycerol clean-up

Page 52: Anurag ppt

Environmental Impacts of Biodiesel

Large Reductions in:CO2SOxParticulatesOdor

Slight Increase in:NOx

Page 53: Anurag ppt

Conclusions Biodiesel is an alternative fuel for diesel engines that can be

made from virtually any oil or fat feedstock. The technology choice is a function of desired capacity,

feedstock type and quality, alcohol recovery, and catalyst recovery.

Maintaining product quality is essential for the growth of the biodiesel industry.

Page 54: Anurag ppt

Photobiological This method involves using sunlight, a biological component,

catalysts and an engineered system. Specific organisms, algae and bacteria, produce hydrogen as a

byproduct of their metabolic processes. These organisms generally live in water and therefore are

biologically splitting the water into its component elements. Currently, this technology is still in the research and

development stage and the theoretical sunlight conversion efficiencies have been estimated up to 24%.

Page 55: Anurag ppt

Materials Requirements for Photobiological Hydrogen Production

Biological H2 production is expected to be one of many processes that

contribute to the ultimate supply of H2.

But it is useful to consider that in an area of less than 5,000 square miles (about 0.12 % of the U.S. land area) of bioreactor footprint in the desert southwest, photobiological processes could in principle produce enough H2 to displace all of the gasoline currently used in the U.S. (236 million vehicles).

The underlying assumptions are that H2 could be produced from water at 10

% efficiency (the maximum theoretical efficiency of an algal H2 production

system is about 13 %) and that fuel cell-powered vehicles could get 60 miles/kg of H2.

Page 56: Anurag ppt

DESCRIPTION OF THE PROCESS The photobiological production of H2 is a property of only three classes of organisms

photosynthetic bacteria, cyanobacteria, and green algae. These organisms use their photosynthetic apparatus to absorb sunlight and convert it into

chemical energy. Water (green algae and cyanobacteria) or an organic/inorganic acid (photosynthetic bacteria) is

the electron donor. This review will focus on oxygenic organisms such as green algae and some cyanobacteria, which

produce hydrogen directly from water, without an intermediary biomass accumulation stage.

This process is considered to have highest potential sunlight conversion efficiency to H 2, which as mentioned above, could be on the order of 10 to 13 %.

To accomplish this, green algae and cyanobacteria can utilize the normal components of photosynthesis to split water into O2, protons, and electrons, deriving the requisite energy from sunlight.

However, instead of using the protons and electrons to reduce CO2 and storing the energy as starch molecules (the normal function of photosynthesis), these organisms can recombine the protons and electrons and evolve H2 gas under anaerobic conditions (figure 5.1) using a reaction catalyzed by an induced hydrogenate.

Page 57: Anurag ppt
Page 58: Anurag ppt

Conti..

The enzymes responsible for H2 production are metallocatalysts that belong to the classes of [NiFe]- (in cyanobacteria) or [NiFe]- (in green algae) hydrogenases.

Although sustained and continuous photobiological H2 production has been achieved with green algae, the establishment and maintenance of culture anaerobiosis is currently a sine qua non for the process.

This requirement results from the following biological realities.

Page 59: Anurag ppt

Cont… The hydrogenase genes in green algae and in some cyanobacteria are not

expressed (the genes are not turned on) in the presence of O2, and a variable

period of anaerobiosis is required to induce gene transcription. The expression and function of the genes that catalyze the assembly of the

catalytic metallocluster of the algal [FeFe]-hydrogenases require anaerobiosis, while in most cyanobacteria, the [NiFe]-hydrogenase genes are expressed and the protein assembled in the presence of O2; in this case, the proteins are

assembled in an inactive form, but can be activated quickly when exposed to anaerobic conditions.

The activity of the catalytic metallocluster of the hydrogenases is inhibited reversibly (in cyanobacteria) or irreversibly (in green algae) by the presence of O2.

Page 60: Anurag ppt

Reactor Materials

Engineering design of full-scale photobioreactors and the balance of the facility for photobiological hydrogen production has not been considered beyond very general concepts.

Consequently, there has been little effort to identify construction material and establish boundaries for specifying materials performance and properties.

Page 61: Anurag ppt
Page 62: Anurag ppt

Major Benefits Of The Method High theoretical conversion yields. Lack of oxygen involving , which causes problem of oxygen

in activation of different biological systems. Ability to use wide spectrum of light. Ability to consume organic substrates derivable from waste

and then , for their potential to be used in association with wastewater treatment.

Page 63: Anurag ppt

ConclusionsThe photo biological hydrogen production processes are mostly operated at ambient temperature and pressure, but less energy intensive. These process are not only environment friendly, but also they lead to opening of new avenues for the utilization of renewable energy resources , which are inexhaustible. They can also use various waste material , which facilitate waste recycling.

Page 64: Anurag ppt