New Technologies for Rendering Processing

By Annel K. Greene, PhD, Center Director
Clemson University Animal Co-Products Research and Education Center


Rendering processing has long relied on primarily thermal means of initiating separation of components. The basic procedures employed in rendering typically include size reduction, thermal cooking and pressing to separate fat and protein, and grinding. Dr. Christopher Kitchens, assistant professor of Chemical and Biomolecular Engineering and a member of the Clemson University Animal Co-Products Research and Education Center team, is working on a project entitled, “Tunable Fluids for Economic Separation of Rendered Materials for Fuels and Polymers,” in which he is studying alternative, cutting edge methods of materials separation.

Finding cost-efficient methods of further separating products can open new markets for value-added products in the energy, consumer products, and commodity chemicals areas. Typically, solvent extraction methods used for separating fat from proteins have relied on solvents such as hexane, a particularly hazardous chemical. It is volatile, flammable, and an irritant to the respiratory tract, skin, and eyes. It can affect the central and peripheral nervous system, causing a variety of symptoms including headache, nausea, blurred vision, and in higher doses, it can cause muscle weakness and numbness, and even death. It also can adversely affect a developing fetus. Hexane is commonly used in soybean oil extraction but has not had widespread use in commercial rendering due to the hazards. It also is costly, further prohibiting its use in many applications.

Recognizing that better methods of fat separation are needed, Kitchens initiated an exploratory project in which he uses a category of solvents known as “tunable solvents” or “tunable fluids” to isolate value-added fractions from rendering materials. Tunable fluids are solvents in which their properties are manipulated using pressure, temperature, or the addition of a gas such as carbon dioxide (CO2). For instance, it is known that water and fat are not miscible. In general, water only dissolves polar compounds and is unable to dissolve non-polar compounds. However, at higher temperatures and pressures, the solvent properties of water change. Near the critical temperature of water (250 degrees to 350 degrees Celsius), hydrogen bonds within the water molecule are broken, and, as a result, the properties of water are changed. Under these conditions, suddenly water and fat do mix since the water can now dissolve both polar and non-polar organic compounds.

Water under these conditions is referred to as “near critical water” or NCW. As the water heats to its critical temperature, it develops useful new properties. NCW can dissolve organic chemicals as well as salts that allow a variety of chemical reaction and separation scenarios. After a reaction or extraction, separation is simply a matter of cooling the mixture, which allows the organic compounds to come out of solution. At high temperatures, water also dissociates into natural acid and base, which can catalyze reactions. Upon reduction of the temperature, water returns to normal and acid or base neutralization is not required.

Other tunable solvents that can be created include CO2 and CO2-expanded methanol. In this scenario, methylcarbonic acid is formed from the reversible reaction between methanol and CO2 under pressure. The methylcarbonic acid can be used to catalyze specific reactions, and then acid is neutralized by simply depressurizing. This eliminates the need for acid neutralization, product purification, and salt by-product disposal. Under pressure, CO2 can exist as a liquid or supercritical fluid, where its properties enable its use as a solvent for reactions or extractions. Afterwards, simply releasing the pressure allows for the isolation of the desired products as well as capture and recycle of the CO2 solvent. In general, tunable solvents also have excellent penetrating abilities on solid matrices, making them ideal for extractions.

Kitchens has conducted previous research in which he demonstrated the use of tunable solvents in the processing of lignocellulosic biomass, synthesis and processing of nanoparticles, and as a reaction medium for homogeneous catalysis. These solvents are classified as green chemistry because they have low toxicity, are environmentally benign, and are easily recycled, generating little to no waste solvent. The simplicity of solvent recycle and product purification steps often can provide significant cost savings and energy efficiency compared to conventional industrial operations, such as distillation. Furthermore, altering the solvent composition, pressure, and temperature can provide controlled extraction and create selective fractionation conditions. Concerns of solvent or fugitive emissions and toxic residual solvent in products can be reduced or eliminated. Additionally, CO2 can act as an alternative to thermal disinfection and may eliminate unwanted microorganisms; however, the effect on microbial populations found in the rendering process is not known.

Kitchens will begin his work on separating components of meat and bone meal. His objectives are to process meat and bone meal with liquid and supercritical CO2 to separate fractions that could be used as biodiesel and specialty chemical feedstocks. These include fractionation of triglyceride, lipid, cholesterol, and fatty acid components. He will compare his methods with lipid extraction via hexane and other methods. Next, he will process meat and bone meal with CO2/methanol mixtures. Methanol increases the solvent strength and Kitchens believes it will help break the fat and protein matrix. CO2 will enhance the transport properties allowing the solvent to better penetrate and allow better extraction.

In the third phase of the study, Kitchens will use NCW to remove fat compounds and amino acids, leaving a clean protein matrix that could be used as a thermoplastic grade material. Such materials may have application for foam materials in automotive products, soil binders for agricultural applications, or for films. In the final phase, Kitchens will conduct a cost-benefit analysis for the procedure and the derived materials. He also will conduct a life cycle analysis of the proposed separation treatments to determine feasibility for industrial use in the rendering industry.

Kitchens’ projects that benefits of using tunable fluids in rendering will be to assist biodiesel production from rendered fats. In addition, rendered by-products contain a wide variety of high-value components for the specialty chemicals industry, if isolated effectively. Of course, in the industry, separation cannot focus on one single component, but must account for the entire product landscape and seek to minimize waste while enhancing efficiency. Availability of effective, low-cost separation techniques may allow renderers to seek new markets for products that are not measured in cents per pound, but several dollars per pound. The results of Kitchens’ study could lead to new partnerships for biomaterials and bioenergy and open new markets for rendered products.


ACREC Solutions – December 2010 RENDER | back