Economic Benefits of Innovative Microwave Grease Processing By: Dr. Lou A. Honary President, Environmental Lubricants Manufacturing, Inc. Synopsis:
In recent years, there has been a growing interest in the production of biobased and biodegradable greases. The use of newer raw materials in these greases has introduced a different level of complexity beyond existing intricacies of grease making. However, the introduction and practice of a new patented microwave-based processing technology in 2010 helped to reduce some of those complexities. An earlier paper on the introduction of this processing technology was presented at the 23rd Annual General Meeting of the European Lubricating Grease Institute (ELGI) in 2011 (Paris, France).[1] The present paper reports on the construction and operation of an updated production scale microwave-based reactor that expands the types of products that can be manufactured using microwave technology. This paper also describes changes and improvements that were made to the equipment and compares efficiency and cost reduction benefits of the new technology and a conventional manufacturing process.[2], [3]
An Update on Manufacturing Biobased Grease Using Microwaves Introduction Typical methods for making grease include the use of a heat transfer oil that is circulated in the chambers of a jacketed vessel to heat the vessel surfaces and cook grease inside the vessel. The temperature of the heat transfer oil can be raised by using electric heating elements, heating fuels, or natural gas. Heat transfer systems also include heat exchangers that use water or a cooling fluid to help lower the temperature of the heat transfer oil and control the temperature needed for the chemical reactions to make grease. The latent heat in the oil, the vessel jacket, and transfer pipes make it difficult to reach and reliably maintain accurate temperatures. Temperature overshooting can result in overheated products, and undershooting can require additional time and adjustments to complete the grease-making process. Heat transfer oil methods are limited by the fact that product inside the vessel has to be heated by very hot metal surfaces of the vessel. There can be a temperature difference of several
hundred degrees between the walls of the vessel and the product at the center of the vessel . Products that touch the vessel walls can be exposed to temperatures far above the needed reaction temperatures. As an example, lithium greases require reaction temperatures exceeding 392⁰F (200⁰C). For the product to reach these temperatures, the heat transfer oil and the walls of the vessel could be 572⁰F (300⁰C) or higher. When vegetable oils are heated this way, the layers of oil that touch the high temperature walls of the vessel can be damaged due to overheating. The oxidation stability of the final product can be reduced as a result. Also, this method of heating requires conversion of electrical energy (when using heating elements) or chemical energy (when using fuel ) to thermal energy, then application of the thermal energy to metal surfaces, and finally, heat transfer via conduction from hot metal surfaces of the vessel to the product. Each energy conversion stage presents some energy loss and contributes to large cumulative losses. Additionally, it is necessary to use elaborate scrapers and drivers to prevent grease adherence and overcooking on the vessel walls in some types of reactors. Microwave heating eliminates the need for jacketed vessels and heat transfer media. Instead, electrical energy is converted to microwaves at high energy efficiency levels; these microwaves are applied directly to the product to heat it. Provided that microwaves can penetrate the product, they can heat it uniformly with minimal mixing or circulation and without the use of scrapers. Description of the basic process In a typical grease making process, a fatty acid, like stearic acid, is reacted with a strong base resulting in a soap and other byproducts. Bases commonly used in soap and grease manufacturing include sodium, lithium, aluminum, calcium, titanium, and barium compounds. The reaction takes place in situ in base oil, so the soap is diluted with oil and somewhat fluid. Otherwise, if soaps were manufactured on the basis of reaction stoichiometry alone, they would become too stiff to flow and handle at lower temperatures. Also, specific soaps behave differently at various temperatures. Lithium-based greases, for example, tend to be fully liquid at higher reaction temperatures in the 302 to 428°F (150 to 220⁰C) range. Lithium soaps are liquefied when they are cooked inside a
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