4.03.11. PRODUCTION OF ISOCYANATES FOR POLYURETHANE PRO- DUCTION CHEMICALS AND ALLIED APPLICATION NOTE 4.03.11 PRODUCTION OF ISOCYANATES FOR POLYURETHANE PRODUCTION METHYLENE DIPHENYL DIISOCYANATE (MDI), 1,6 HEXAMETHYLENE DIISOCYANATE (HDI) Typical end products Polyurethane foam for different applications, for example, bedding, of materials can be produced to meet the needs for furniture, packaging, coatings and elastomers. specific applications. Chemical curve: R.I. for MDI at Ref. Temp. of 25˚C Application The most commonly used isocyanates for the production of PU are methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI). If color and transparency are important, an aliphatic diisocyanate such as hexamethylene diisocyanate (HDI) is used. The first step in the production of polyurethane is the synthesis of the raw materials. The diisocyanate is typically produced from basic raw materials via nitration, hydrogenation and phosgenation. The feedstock and initial processing steps depend on the Introduction desired isocyanate, but all go through a phosgenation step. Polyurethanes (PUs) are a class of versatile materials with great potential for use in different applications. For instance, for the production of MDI, benzene and They are used in the manufacture of many different nitric acid are reacted to produce nitrobenzene. After items, such as paints, liquid coatings, elastomers, a hydrogeneration step, the nitrobenzene is converted insulators, elastics, foams and integral skins. to aniline. It is then condensed with formaldehyde to produce methylene diphenyl diamine (MDA), the Polyurethanes are produced by polymerization of precursor for MDI. The MDA is fed to a phosgenation a diisocyanate with a polyol. Because a variety of reactor where it reacts with phosgene to produce the diisocyanates and a wide range of polyols can be end-product MDI. MDI is further purified by several used to produce polyurethane, a broad spectrum distillation steps to obtain pure and polymeric MDI (PM). Chemicals and Allied | Polymers and Plastics CHEMICALS AND ALLIED APPLICATION NOTE 4.03.11 PRODUCTION OF ISOCYANATES FOR POLYURETHANE PRODUCTION The products can be used to produce commercial polyurethane process. This is a crucial measurement liquid MDI and MDI prepolymers, or can be reacted point as a slight change in the raw materials can with a polyol in the presence of a catalyst to change the properties of the final PU foam. produce the polyurethane foam. The refractometer can also be used to monitor Instrumentation and installation and control the concentration at other points of the process, for example, in feed catalyst lines or solvent The K-Patents Process Refractometer recovery. PR-43-GP provides accurate and reliable refractive index measurement for different Typical measurement ranges in this application applications in the production of isocyanates and PU. are 1.3200-1.5300 for HDI and ADI applications, and 1.5200-1.7300 MDI and PM measurements in The refractometer can be installed directly in polymerization. The temperature can be up to 200 ⁰C the phosgenation reactor to monitor continuously (392 ⁰F). The K-Patents refractometer can be equipped the progress of the reaction. This helps to to safely withstand high temperatures. Automatic determine in real-time the degree of reaction and to prism wash may be required in this application. identify the point at which the reaction is completed. Appropriate equipment with hazardous and intrinsic safety approvals are available when required. The K-Patents refractometer also measures in-line the concentration of isocyanate MDI, TDI, HDI after the reaction and after the purification steps. This ensures the right concentration is always fed to the Instrumentation Description K-Patents Process Refractometer PR-43-GP is a general industrial refractometer for pipes and vessel installations. The PR-43-GP can be installed with 2, 3 and 4 inch flange and 3 inch Sandvik L coupling process connections and a variety of flow cells for pipe sizes of 1 inch and larger. User Interface Selectable multichannel MI, compact CI or a web-based WI user interface options allow the user to select the most preferred way to access and use the refractometer measurement and diagnostics data. Measurement range Refractive Index (nD) 1.3200-1.5300 or 1.5200 – 1.7300, corresponding to 0-100 % by weight. Chemicals and Allied | Polymers and Plastics.