1.2.1.6 Adsorption
There is a solid adsorbent material in adsorption which will adsorb the alcohols in
the fermenter. The extractant is usually enclosed in a packed-column contactor that
assists as both adsorber and desorber. On the other hand, the solid extractant is not
stimulated through the system causing a cyclic loading and unloading process of the
adsorbent. This solid will show a greater sorption selectivity for alcohol than water
and high distribution coefficients for sorption equilibrium resulting in a high separation factor distillation by adsorption method. To collect the excess water content,
use the variance in molecular sizes of the ethanol and water combination. In this type
of distillation, molecular sieves separate ethanol from the combination according to
the size of the sieve openings. The 4 Å diameter ethanol molecules are sequestered
from the water molecules through sieve having 3 Å in diameter, meanwhile water
molecules are characteristically of 2.5 Å in diameter and size (Kumar et al. 2010).
Dual beds of molecular sieve in majority are mandatory in typical adsorption
distillation process. The water vapor molecules fill the empty space of the molecular
sieve and are adsorbed in the column where ethanol water vapor is fed and injected
into the first bed. Once the mixture vapor stream starts to flow, water molecules are
absorbed uninterruptedly until the bed can absorb the complete mass of water
molecules, sorting out the dehydrated and anhydrous feed. If the bed is filled with
particles of water, the additional bed substituting the hydrated bed will be switched
using the robotics system or control valve to help. The bed is reformative with
certain different absorption cycles, and it can be reused. Zeolite is one of the
instances of absorbent material that makes the reusable property. Aditiya et al.
(2016) reported that activated carbon (252 mg per g) showed maximum adsorption
while bone charcoal (206 mg per g) and silicate (97 mg per g) exhibited lowermost
adsorption. Though, silicalite presents the assistance of complete desorption at low
energy consumption (1948 kcal/kg) (Qureshi et al. 2005). Certain bio-adsorbents
(based on lignocelluloses and starch) were produced to extract water from the
alcohol and water vapor mixture (Chang et al. 2006). These adsorbents are less
able to differentiate, but can be regenerated at lower temperatures.
1.2.1.7 Extraction Liquid-Liquid
An extractant should have the highest possible selectivity for alcohol in relation to
water, resulting in a greater factor of separation and a more concentrated product
stream. Also important is the equilibrium distribution coefficient, since it defines the
quantity of extractant needed to remove the desired alcohol. A typical diagram of
this type of extraction is demonstrated in Fig. 1.5.
Ideally, there should be no solubility between the extractant and the soil, but some
soil-soluble extractant is likely to be lost because the extractant has a high alcohol
affinity which should be examined carefully as it can cause problems for the
bioreactor, the products, and even the wastewater treatment plant. It should be easily
1 Downstream Processing of Biofuels
13
There is a solid adsorbent material in adsorption which will adsorb the alcohols in
the fermenter. The extractant is usually enclosed in a packed-column contactor that
assists as both adsorber and desorber. On the other hand, the solid extractant is not
stimulated through the system causing a cyclic loading and unloading process of the
adsorbent. This solid will show a greater sorption selectivity for alcohol than water
and high distribution coefficients for sorption equilibrium resulting in a high separation factor distillation by adsorption method. To collect the excess water content,
use the variance in molecular sizes of the ethanol and water combination. In this type
of distillation, molecular sieves separate ethanol from the combination according to
the size of the sieve openings. The 4 Å diameter ethanol molecules are sequestered
from the water molecules through sieve having 3 Å in diameter, meanwhile water
molecules are characteristically of 2.5 Å in diameter and size (Kumar et al. 2010).
Dual beds of molecular sieve in majority are mandatory in typical adsorption
distillation process. The water vapor molecules fill the empty space of the molecular
sieve and are adsorbed in the column where ethanol water vapor is fed and injected
into the first bed. Once the mixture vapor stream starts to flow, water molecules are
absorbed uninterruptedly until the bed can absorb the complete mass of water
molecules, sorting out the dehydrated and anhydrous feed. If the bed is filled with
particles of water, the additional bed substituting the hydrated bed will be switched
using the robotics system or control valve to help. The bed is reformative with
certain different absorption cycles, and it can be reused. Zeolite is one of the
instances of absorbent material that makes the reusable property. Aditiya et al.
(2016) reported that activated carbon (252 mg per g) showed maximum adsorption
while bone charcoal (206 mg per g) and silicate (97 mg per g) exhibited lowermost
adsorption. Though, silicalite presents the assistance of complete desorption at low
energy consumption (1948 kcal/kg) (Qureshi et al. 2005). Certain bio-adsorbents
(based on lignocelluloses and starch) were produced to extract water from the
alcohol and water vapor mixture (Chang et al. 2006). These adsorbents are less
able to differentiate, but can be regenerated at lower temperatures.
1.2.1.7 Extraction Liquid-Liquid
An extractant should have the highest possible selectivity for alcohol in relation to
water, resulting in a greater factor of separation and a more concentrated product
stream. Also important is the equilibrium distribution coefficient, since it defines the
quantity of extractant needed to remove the desired alcohol. A typical diagram of
this type of extraction is demonstrated in Fig. 1.5.
Ideally, there should be no solubility between the extractant and the soil, but some
soil-soluble extractant is likely to be lost because the extractant has a high alcohol
affinity which should be examined carefully as it can cause problems for the
bioreactor, the products, and even the wastewater treatment plant. It should be easily
1 Downstream Processing of Biofuels
13