Influence of drying on the extraction of different processed lignites

Abstract

Industrial extraction of montan wax from lignite requires a specific pre‐treatment of raw material concerning milling and drying aiming on particles with sufficient strength and grain size distribution. The wax or its intermediate is a basic material, for example, in foundry, asphalt, or cosmetic industry. First time, the effects of drying temperature and moisture content of lignite samples on extraction rate, extraction yield, and mechanical properties were investigated. The examination was conducted out in lab‐scale with two different mechanical pre‐treatments. The experimental conditions ranged from 85 to 135°C concerning drying temperature and 1–20% for moisture content. The kinetic analysis of analytical wax extraction was made by adopting an approach from natural material extraction by Bucić‐Kojić et al. . The extraction yield as well as the extraction rate is increasing with increasing moisture content until a constant level is reached whereas temperature of drying air showed unexpectedly no significant influence on both parameters. The mechanical properties of the solids were determined by a pressure stress test. For both investigated solids, mechanical strength increases with lowering moisture content. The solids produced with the novel pre‐treatment showed in general a favorable compression behavior than the normally used particles.Practical applications: Industrial montan wax extraction process requires hard lignite particles, which do not decay during processing and handling. The strength of lignite is highly influenced by moisture content besides other factors such as the kind of lignite, the surface mine, drying technology, milling, and processing. The strength of lignite particles increases until a maximum in solidity is reached while drying down from deposit moisture of about 50 wt%. Lignite beds with high moisture content or wide grain size distribution offer the risk of their compression. Such compressed beds are not suitable for extraction due to a lowering or even total loss of permeability for the solvent. The selection of an adequate drying procedure and moisture content of the lignite avoids such problems. But a decrease of moisture content to 1% is known to reduce extraction yield considerably, e.g., the maximal extraction yield requires a specific moisture content of lignite particles .