PROJECT DESCRIPTION
BACKGROUND
Alkoxylates are very important in the industrial world. They have many applications in every day life (detergents, pharmacy, cosmetics, textiles, painting, polyester, polyurethane etc). Alkoxylates are also important considering the volume of their production and the number of European production sites and reactors. Their production requires the handling of toxic oxides (mainly ethylene oxides and propylene oxides), and their production sites are covered by the SEVESO Directive. All the producers try to obtain the highest possible control of the chemical reactions during the production of alkoxylates. The challenge is to avoid the presence of un-reacted toxic oxides or of some of their derivatives (notably polyalkylen glycols or dioxanes) in the end products or in the discharge.
OBJECTIVES
The objective of the project was to design and construct a prototype unit for the development of an improved alkoxylation process able to synthesize a large range of optimized purified products. The improvements in the process would be directly measurable through the lower levels of impurities in the end products and in the liquid and gaseous effluents. The alkoxylation process would involve the combination, in the same reactor, of different complementary technologies. Each step would have to be optimized through the improvement of physical contact and thermal transfers between reagents. Beyond pressure and temperature controls, commonly used to follow the reaction rate, an in line infra red analyzer would be required to supply continuous information about the residual oxide content in order to minimize the risk of an oxide accumulation in the reactor. A continuous comparison with registered data was foreseen to help correct the basic flow rate of oxides predetermined by algorithms for the manufacture of given end products.
RESULTS
A new multi stage stirring system has been installed. In addition, an external circulation loop brought the reagents back to the reactor through a venturi type jet mixer which improved the liquid/gas contact. The infra red analyzer was not efficient for the monitoring of the residual oxides in the liquid phase. Therefore, it was abandoned. The process developed uses a high-pressure alcoxylation technology. The most significant improvements carried out on the pilot were the following: - Homogenization of the reaction mixture mass by: 1°) adapting the form of the reactor and installing the multi-stage stirrer. 2°) addition of a external circulation loop (possible thanks to a specific process pump- + a venturi (type jet mixer). - Fine regulation of the temperatures. - High working flexibility. - Achievement of the reaction without need of stopping the reactor (and thus without degassing, cleaning and changing the vat). Due to those improvements, the following environmental and process objectives have been achieved: • Increasing of the growing ratio. • Reduction of the gases discharged by 40 %. • Halving the liquid effluents thanks to the achievement of the synthesis in one step instead of three. • Suppression of some parasitic reactions producing toxic and volatile pollutants derived from the introduced oxides. • Diminution of the acetaldehydes and alkylic alcohol fractions. • Diminution of the starter's degradation products. • Reduction of the overstoechometry of oxides (improvement of the overstoechiometrie). Based on the results of the project, a new production plan has been build in Antwerpen (Belgium). A new multi stage stirring system has been installed. In addition, an external circulation loop brought the reagents back to the reactor through a venturi type jet mixer which improved the liquid/gas contact. The infra red analyzer was not efficient for the monitoring of the residual oxides in the liquid phase. Therefore, it was abandoned. The process developed uses a high-pressure alcoxylation technology. The most significant improvements carried out on the pilot were the following: - Homogenization of the reaction mixture mass by: 1°) adapting the form of the reactor and installing the multi-stage stirrer. 2°) addition of a external circulation loop (possible thanks to a specific process pump- + a venturi (type jet mixer). - Fine regulation of the temperatures. - High working flexibility. - Achievement of the reaction without need of stopping the reactor (and thus without degassing, cleaning and changing the vat). Due to those improvements, the following environmental and process objectives have been achieved: • Increasing of the growing ratio. • Reduction of the gases discharged by 40 %. • Halving the liquid effluents thanks to the achievement of the synthesis in one step instead of three. • Suppression of some parasitic reactions producing toxic and volatile pollutants derived from the introduced oxides. • Diminution of the acetaldehydes and alkylic alcohol fractions. • Diminution of the starter's degradation products. • Reduction of the overstoechometry of oxides (improvement of the overstoechiometrie). Based on the results of the project, a new production plan has been build in Antwerpen (Belgium).