ERT353 2014Biofuel

BIO ETHANOLWhat, Why, How, How much, ….

Biofuel : General term for fuel from bio resources

What?

Ethanol C2H5OH

Chemical production : C2H4 + H2O → CH3CH2OH

Bioethanol : Ethanol that produced through fermentation

Fermentation :?

Why?Properties are similar to fossil fuel

Flash Point : 9 CBoiling Point : 78 C

Bioethanol

FermentationGlucose ----------------yeast---------- ethanol + carbondioxide

Material Balance ?Mol equivalentDetail of fermentation

Microorganisms :Saccharomyces cerevisiae (yeast)

Zymomonas mobilis

Saccharomyces cerevisiae

Well studied, widely used commerciallyWell studied, widely used commerciallyIt growth is inhibited by ethanol (its own product)It growth is inhibited by ethanol (its own product)

The theoretical yield is 0.511 g ethanol per gr glucose consumed.

This yield can never be realized in practice since part of glucose is used for cell mass synthesis, and production of by-products such as glycerol, acetic acid, lactic acid, and succinic acid.

Zymomonas mobilis:can produce ethanol at much faster rates than S. cerevisiaehigh cell concentrations are not needed for high ethanol yieldhigh ethanol tolerance, no requirements for aeration during the fermentation processNot well studied

Sugar

Raw materials (feedstocks)

Sugar

•Sugar containing materials :

•Starch

•Cellulose

Typical Parameters of Batch Fermentation Process for Ethanol Production from Sugarcane Juice and Molasses

Starch Feedstocks :

Example

Fermentation

Theoretical Ethanol Yield

n is the number of glucose residues in the starch molecule.The amount of glucose produced from 1 kg of starch is 180n/(162n + 18). When n is 2, as in maltose, the conversion factor is 1.053.When n becomes very large, this factor approaches 1.111.

CONVERSION RATIO FROM STARCH OR CELLULOSE INTO GLUCOSE

Calculation example:

Calculate the theoritical yield of ethanol that can be produced from 10 kg of glucose

Calculate the theoritical yield of ethanol that can be produced from 10 kg of sugar cane

Calculate the theoritical yield of ethanol that can be produced from 10 kg of molasses containing 40 % of glucose

Calculate theoretical ethanol yield from 1 kg of corn which has 15 percent moisture and contains 70 percent starch on a dry basis. Assume the conversion factor is 1.111.

Determine ethanol fermentation efficiency for the corn with 70 percent starch on dry basis in laboratory. In this experiment, a mash having 30 percent total solids on dry basis and after 72 h of fermentation. Analysis of the final liquid sample by high pressure liquid chromatography (HPLC) showed an ethanol concentration of 13.1 g/L.

Example

Basis: 1 kg of mash.One kg of mash contains 300 g total solids and 700 g water.Starch content: 300 g x 0.70 = 210 g

Glucose (MW 180) production by starch hydrolysis: 210 g x 1.111 = 233.3 g

Theoretical ethanol production: 233.3 x 0.511 = 119.0 g

Total liquid: (ethanol produced + volume of remaining water)Volume of the ethanol produced: 119.0 g / 0.79 (g/mL) = 150.8 mL

Water (MW 18)consumption in starch hydrolysis: 210 g x 0.111 = 23.3 gTotal liquid volume: 700 mL – 23.3 mL + 150.8 mL = 827.5 mL

Ethanol concentration expected: 119.0 / 827.5 mL = 0.144 g/mL or 14.4 g/L.Therefore, the fermentation efficiency is: (13.1 / 14.4) x 100% = 91.0%.

Biomass Pretreatment

• High rates of hydrolysis and high yields of fermentable sugars• Minimal degradation of the carbohydrate fractions• No production of compounds that are inhibitory tomicroorganisms used in the subsequent fermentation step• Inexpensive materials of construction• Mild process conditions to reduce capital costs• Recycle of chemicals to reduce operating costs• Minimal wastes

An ideal biomass pretreatment process should meet the following requirements:

Concentrated Sulfuric Acid HydrolysisDilute Sulfuric Acid Hydrolysis

Steam ExplosionAmmonia Treatment

Lime TreatmentAlkaline Peroxide Treatment

Concentrated Phosphoric Acid FractionationEnzyme Hydrolysis

Solubilization of cellulose can be carried out at 50°C using concentrated phosphoric acid (>82 percent).

• The solubilized cellulose and hemicellulose can be separated based on the insolubility of cellulose in water. \The cellulose obtained can be hydrolyzed with enzymes at very high rates . The hemicellulose can be converted to high-value products.• Phosphoric acid and acetone can be recovered by simple processes and recycled.• Lignin can be recovered and potentially can be used to generate high-value products.

BIOGAS

Biogas is the CH4/CO2 gaseous mix evolved from digesters, including waste and sewage pits

To utilise this gas, the digesters are constructed and controlled to favour methane production and extraction

Indian ‘gobar gas’ digesterSimple oil drum batch digester

Chinese ‘dome’ for small-scale use

Accelerated rate farm digester with heating

Some organic material, e.g. lignin, and all inorganic inclusions do not digested in the process.

Example of calculation:

During anaerobic digestion, glucose is transformed into methane through a series of steps. The overall reaction is(CH2O)6 → 3CH4 + 3CO2.Calculate the percentage of methane (by both volume and mass) produced.

The temperature ranges (1) psicrophilic, about 20C,(2) mesophilic, about 35C(3) thermophilic, about 55C.

In tropical countries, the digestion is psicrophilic, with average temperature btw 20 - 30 C. (retention times at least 14 days).

In colder climates, the process is slower, the digesters is heated by using part of the biogas output.

Few digesters operate at 55C (unless the purpose is to digest material rather than produce excess biogas).

BIOGAS biochemical processes

hydrogenesis.

Insoluble biodegradable materials, e.g. cellulose, polysaccharides andfats, are broken down to soluble carbohydrates and fatty acids ( about a day at 25 C in an active digester).

acidogenesis

Acid forming bacteria produce mainly acetic and propionic acid( takes about one day at 25 C).

methanogenesis

Methane forming bacteria complete the digestion to a maximum ∼70%CH4 and minimum ∼30%CO2 with trace amounts of H2 and perhaps H2S( about 14 -20 days at 25C)

The methane forming bacteria are sensitive to pH, so conditions should be mildly acidic (pH 6.6–7.0) but not more acidic than pH 6.2.

Nitrogen should be present at 10% by mass of dry input and phosphorus at 2%.

Typical parameters for animal waste

Example -1

By using the table given, calculate the volume of a biogas digester suitable for the output of 6000 pigs, assuming a retention time of 20 days.

Vf is the flow rate of the digester fluid tr is the retention time in the digester (∼8–20 days).

The volume of the digester is

The volume of biogas is

c is the biogas yield per unit dry mass of whole input (0.24 m3/ kg) m0 is the mass of dry input

The volume of fluid in the digester is

is the density of dry matter in the fluid (∼50 kg/m3).

Energy output

Hb the heat of combustion per unit volume biogas (20MJ/m3

ANSWER

(2) Calculte the power available from the digester of example 1. (assume a burner efficiency is 0.6.

Biogas volume :

Energy output

1 J = 2.8. 10 -7 kwh