Hydrolysis and Fermentation Technologies for Alcohols
237
on the dimensions of effective pore opening, which include 3A, 4A, 5A, and 13x.
Commercial molecular sieves are typically available in powder, bead, granular, and
extrudate forms.
9.2.4 ByProduCTS And CoProduCTS
The nonfermentable solids in distilled mash (stillage) contain variable amounts of
proteins and fibers depending on the feedstock. The recovery of protein and other
nutrients in stillage for use as an animal feedstock is essential for making the overall
ethanol production process profitable. Corn and barley yield solid byproducts called
DDGs. The protein content of DDG typically ranges from 25% to 30% by mass and
makes an excellent feedstock for the animals. Byproducts and coproducts are very
important for corn refineries (wet milling process).
9.2.5 environmenTAl imPliCATionS
The liquid effluent generated from ethanol process may contain some harmful
chemicals and other pollutants that must be discarded properly. About 9 l of liquid effluent is generated for every liter of ethanol produced. The biological oxygen
demand (BOD) of effluent can be high and the effluent can be acidic. Both of these
factors require additional treatments before discarding the effluents to fields or water
streams.
9.3 COrn tO ethanOl PrOCess teChnOlOGies
As mentioned earlier, the conversion of corn to ethanol can be carried out as either
(1) wet milling corn ethanol (or corn refinery) technology or (2) dry milling corn
ethanol technology. We briefly describe both of these technologies in Sections 9.3.1
and 9.3.2.
9.3.1 WeT milling TeChnology For ConverSion oF Corn To eThAnol
The corn wet milling process to produce ethanol separates corn into its four basic
components: starch, germ, fiber, and protein. There are eight basic steps involved to
accomplish this corn refining and alcohol fermentation process [10].
Step 1: This step inspects the incoming corn visually and removes cob, dust,
chaff, and any other foreign unwanted materials before the next processing
step of steeping. The inspected and screened corn is then conveyed to storage silos holding up to 350,000 bushels.
Step 2: This step carries out the steeping process in which about 2,000–13,000
bushels of corn is soaked in water at 50°C–52°C for 20–48 h in a stainless
steel tank. A series of tanks are used. During this process, the kernel of corn
(Figure 9.2) absorbs water from 15% to 45% by weight and swells by more
than double its original size. The addition of 0.1% sulfur dioxide to water
suppresses the excessive bacterial growth in the warm water environment.
237
on the dimensions of effective pore opening, which include 3A, 4A, 5A, and 13x.
Commercial molecular sieves are typically available in powder, bead, granular, and
extrudate forms.
9.2.4 ByProduCTS And CoProduCTS
The nonfermentable solids in distilled mash (stillage) contain variable amounts of
proteins and fibers depending on the feedstock. The recovery of protein and other
nutrients in stillage for use as an animal feedstock is essential for making the overall
ethanol production process profitable. Corn and barley yield solid byproducts called
DDGs. The protein content of DDG typically ranges from 25% to 30% by mass and
makes an excellent feedstock for the animals. Byproducts and coproducts are very
important for corn refineries (wet milling process).
9.2.5 environmenTAl imPliCATionS
The liquid effluent generated from ethanol process may contain some harmful
chemicals and other pollutants that must be discarded properly. About 9 l of liquid effluent is generated for every liter of ethanol produced. The biological oxygen
demand (BOD) of effluent can be high and the effluent can be acidic. Both of these
factors require additional treatments before discarding the effluents to fields or water
streams.
9.3 COrn tO ethanOl PrOCess teChnOlOGies
As mentioned earlier, the conversion of corn to ethanol can be carried out as either
(1) wet milling corn ethanol (or corn refinery) technology or (2) dry milling corn
ethanol technology. We briefly describe both of these technologies in Sections 9.3.1
and 9.3.2.
9.3.1 WeT milling TeChnology For ConverSion oF Corn To eThAnol
The corn wet milling process to produce ethanol separates corn into its four basic
components: starch, germ, fiber, and protein. There are eight basic steps involved to
accomplish this corn refining and alcohol fermentation process [10].
Step 1: This step inspects the incoming corn visually and removes cob, dust,
chaff, and any other foreign unwanted materials before the next processing
step of steeping. The inspected and screened corn is then conveyed to storage silos holding up to 350,000 bushels.
Step 2: This step carries out the steeping process in which about 2,000–13,000
bushels of corn is soaked in water at 50°C–52°C for 20–48 h in a stainless
steel tank. A series of tanks are used. During this process, the kernel of corn
(Figure 9.2) absorbs water from 15% to 45% by weight and swells by more
than double its original size. The addition of 0.1% sulfur dioxide to water
suppresses the excessive bacterial growth in the warm water environment.