Optimizing Surfactants for Increased Corn Oil Yield

Ethanol will be used to produce bioethylene oxide as the base for oil extraction aides. This contributed article appears in the June print edition of Ethanol Producer Magazine.
By Min Wang | May 18, 2017

With its bioethylene oxide plant being commissioned this year, Croda Inc. soon will provide a range of 100 percent biobased nonionic surfactants optimized for increased corn oil yields. Surfactant is the short name of surface active agent. Soap has been made from fats and alkaline salts for millennium. An anionic surfactant, soap dominated world surfactant production before World War II. It wasn’t until between 1950 and 1960 that nonionic surfactants opened a new chapter in the detergent, food and pharmacy industries. In the 1960s, the development of steam cracking at petroleum refineries produced a low-cost ethylene suitable as an intermediate for ethylene oxide. Today, nonionic surfactants made from ethylene oxide contribute to about 45 percent of world surfactant production.

Ethylene oxide (EO) used in the U.S. is currently derived solely from petrochemical sources. In 2015, Croda Inc. invested $170 million to begin construction in New Castle, Delaware, on a bioethylene oxide plant using ethanol from biomass sources, such as corn. On schedule for completion this year, Croda soon will launch a new range of 100 percent biobased nonionic surfactants, some of which will be used as corn oil extraction aids in ethanol plants.

Net greenhouse gas emissions to the atmosphere are reduced by the use of Croda’s 100 percent biobased nonionic surfactants, when compared to their petrochemically derived counterparts. Croda’s versatile bioethylene oxide plant can accept ethanol from different sources, all of which contain only carbon sequestered from the atmosphere by photosynthesis. When considered across the whole product life cycle, products made using ethanol-derived EO have a lower carbon footprint than petrochemically derived variants. At the end of the product life cycle, when the surfactant decomposes into CO2, it returns it to the atmosphere from which it was recently drawn.

EO Process
Typical EO production starts with a stream of purified ethylene derived from a petroleum source such as oil, oil byproducts or natural gas.  Ethylene separated from an olefins stream within a refinery is the most common petrochemical source.  Regardless of source, EO producers utilize the same technology to convert ethylene using a silver catalyst.  The crude EO is then purified to a common market standard and sold as a commodity. 

For ethylene oxide produced via biomass feedstocks, the ethylene is separated from ethanol via chemical dehydration. Ethanol producers physically dehydrate ethanol using molecular sieves to remove tightly bound water molecules to produce pure ethanol—CH3CH2OH. Croda uses catalytic dehydration to produce ethylene, C2H4, plus water. The final step is the same as the conventional process, reintroducing oxygen to produce ethylene oxide—C2H4O.

Ethylene oxide is the building block to produce surfactants. Ethylene oxide forms a polyethylene glycol chain (PEG) through polymerization. The water solubility of a nonionic surfactant will be determined by how much EO is added to a substance. The correlation between the PEG chain length and hydrophilicity of a nonionic surfactant was established in 1949 by William C. Griffin of the Atlas Powder Company (now Croda). Griffin developed the HLB system (hydrophile-lipophile balance) to characterize nonionic surfactants. All nonionic surfactants consist of a hydrophilic and a lipophilic group, which are what make the molecule surface active. The hydrophilic group is usually a polyethylene glycol. The lipophilic group is usually a fatty acid or fatty alcohol. The relationship, or balance, between the hydrophilic portion of the nonionic surfactant to the lipophilic portion is called HLB. Each nonionic surfactant has a HLB value ranging on a scale of 0 to 20. The higher the HLB value, the more water soluble the nonionic surfactant is.

Corn Oil Extraction
What is the right HLB value of a nonionic surfactant for corn oil extraction in ethanol plant? Six experimental surfactants were molecularly designed to have HLB values ranging from 10 to 16. The HLB values were calculated by how many moles of ethylene oxide were added to the surfactant. Each surfactant was added at 400 ppm dosage rate to 40 milliliters of corn stillage heated to 85 Celsius (185 Fahrenheit). After centrifugation at 7,000 rpm for 3 minutes, the volume of extracted corn oil was measured as the height of clear oil layer in the centrifuge tube.

The results, shown in the accompanying chart, indicate the surfactant with an HLB of 14 provided the highest oil yield. When the surfactant with the right HLB value was added to the corn stillage, the interfacial tension between the oil droplets and continuous water phase was reduced. The oil droplets coalesce more quickly and easily to form a continuous layer and float to the top under centrifugation.
With the new facility being commissioned this year, Croda will be introducing a range of 100 percent biobased nonionic surfactants with the right HLB values to be formulated into optimized blends for increased corn oil yield.

Author: Min Wang
Applications Manager, Croda Inc.