239
Hydrolysis and Fermentation Technologies for Alcohols
Step 5: In this step, starch is separated from gluten by hydrocyclones.
Separated gluten that contains proteins and is called corn gluten meal
(CGM) is used for animal feed. CGM can also be used as an organic herbicide. The last 1%–2% protein remained in the starch is further removed
by repeated washings and the high-quality starch is now called unmodified
cornstarch. While most of cornstarch is converted to corn syrups and dextrose, the cornstarch is also used for a variety of industrial and domestic
uses [20].
Step 6: This is a starch-to-sugar conversion step. The starch–water suspension
is liquefied in the presence of acid or enzymes. Enzymes help convert the
starch to dextrose that is soluble in water as an aqueous solution. If needed,
the solution is also treated with another enzyme. The process of acid and
enzymatic reactions is controlled according to the desired mixtures of sugars such as dextrose and maltose (a disaccharide) for syrup. The reaction
time is used to control the concentration of dextrose and maltose in the final
product. Once the conversion is completed, the syrup is passed through
filters, centrifuges, or ion exchange columns, and the excess water is evaporated. Syrup can be sold directly as is, crystallized into pure dextrose, or
processed further to produce high-fructose corn syrup. Across the corn wet
milling industry, about 80% of starch slurry goes to corn syrup, sugar, and
fermentation.
Step 7: In this step, corn syrup is converted to several products through a fermentation process. Dextrose (called corn sugar or grape sugar) also known
as d-glucose is easily fermentable. The process of fermentation can be carried out either in a continuous way in a series of fermenters to give higher
throughput or in a batch fermenter for about 48 h to get a better quality
product.
Step 8: The resulting broth from step 7 is distilled to recover ethanol or concentrated through membrane separation to produce other byproducts.
Carbon dioxide generated from fermenter is recaptured to produce dry ice
for sale, and nutrients still remaining in the broth after fermentation are
used as components of animal feed ingredients. These byproducts contribute significantly to the overall economics of the corn refineries. A schematic of corn refinery or wet milling corn-to-ethanol process is described
in Figure 9.3.
9.3.2 dry milling Corn-To-eThAnol ProCeSS
This process also contains eight steps, which are as follows:
Step 1: In this step, corn is received and stored in silos designed to hold grain
supply for 7–12 days of plant operation.
Step 2: The grain is inspected and screened to remove corn cobs, stalks, finer
materials, stones, and other foreign objects by a blower and screen. The
cleaned material is coarse grinded using hammer mill. The grinded material is combined with hot water to form slurry.
Hydrolysis and Fermentation Technologies for Alcohols
Step 5: In this step, starch is separated from gluten by hydrocyclones.
Separated gluten that contains proteins and is called corn gluten meal
(CGM) is used for animal feed. CGM can also be used as an organic herbicide. The last 1%–2% protein remained in the starch is further removed
by repeated washings and the high-quality starch is now called unmodified
cornstarch. While most of cornstarch is converted to corn syrups and dextrose, the cornstarch is also used for a variety of industrial and domestic
uses [20].
Step 6: This is a starch-to-sugar conversion step. The starch–water suspension
is liquefied in the presence of acid or enzymes. Enzymes help convert the
starch to dextrose that is soluble in water as an aqueous solution. If needed,
the solution is also treated with another enzyme. The process of acid and
enzymatic reactions is controlled according to the desired mixtures of sugars such as dextrose and maltose (a disaccharide) for syrup. The reaction
time is used to control the concentration of dextrose and maltose in the final
product. Once the conversion is completed, the syrup is passed through
filters, centrifuges, or ion exchange columns, and the excess water is evaporated. Syrup can be sold directly as is, crystallized into pure dextrose, or
processed further to produce high-fructose corn syrup. Across the corn wet
milling industry, about 80% of starch slurry goes to corn syrup, sugar, and
fermentation.
Step 7: In this step, corn syrup is converted to several products through a fermentation process. Dextrose (called corn sugar or grape sugar) also known
as d-glucose is easily fermentable. The process of fermentation can be carried out either in a continuous way in a series of fermenters to give higher
throughput or in a batch fermenter for about 48 h to get a better quality
product.
Step 8: The resulting broth from step 7 is distilled to recover ethanol or concentrated through membrane separation to produce other byproducts.
Carbon dioxide generated from fermenter is recaptured to produce dry ice
for sale, and nutrients still remaining in the broth after fermentation are
used as components of animal feed ingredients. These byproducts contribute significantly to the overall economics of the corn refineries. A schematic of corn refinery or wet milling corn-to-ethanol process is described
in Figure 9.3.
9.3.2 dry milling Corn-To-eThAnol ProCeSS
This process also contains eight steps, which are as follows:
Step 1: In this step, corn is received and stored in silos designed to hold grain
supply for 7–12 days of plant operation.
Step 2: The grain is inspected and screened to remove corn cobs, stalks, finer
materials, stones, and other foreign objects by a blower and screen. The
cleaned material is coarse grinded using hammer mill. The grinded material is combined with hot water to form slurry.