Diphenylmethane Diisocyanates (MDI)
MDI is the largest volume industrial isocyanate produced (Fig. 2.62). Global production of MDI was 4600 thousand metric tons in 2011 and is projected to be nearly 6000 thousand metric tons in 2016 with an implied annual growth rate of about 5%. The largest volume uses for MDI are rigid foams, adhesives, sealants, coatings, elastomers, and flexible polyurethane foam. Rigid foam applications monopolize about 60% of the total MDI volume. Europe supports the largest MDI production capacity (33%) followed by the United States (25%), China (21%), and Japan (10%). It has been estimated that China's growth will encompass MDI capacity growth to about 33% of the world total by 2020, taken approximately evenly from the other regions .
MDI is produced from aniline and formaldehyde feedstocks. Aniline is produced sequentially from the nitration of benzene followed by reduction to aniline by hydrogénation (Fig. 2.63). In contrast to TDI being a minor consumer of feedstock toluene (~5%), MDI consumes more than 75% of world aniline production (Fig. 2.64) . Thus, the economics of aniline and MDI production are very tightly correlated and dependent on each other. Furthermore, since most aniline is produced and used captively by MDI producers, MDI manufacturers that are not back integrated to aniline are potentially disadvantaged from a supply and a price perspective. Potential supply constraints are theoretical since capacity consistently exceeds demand and is
FIGURE 2.63 Nitration of benzene to nitro benzene followed by hydrogenation to aniline— a fundamental feedstock for MDI production.
FIGURE 2.64 Global usage of aniline in 2010. The vast majority is used for making MDI which tethers their production and costs to each other.
projected to for the future. However, MDI manufacturers who purchase rather than make MDI may be between 5 and 10% disadvantaged in overall cost of manufacture. As a commodity chemical, the price of MDI cannot be adjusted for a particular manufacturer's cost positions, and so capital savings associated with not manufacturing aniline results in a reduced profit margin. Capacity for MDI production in 2010 was approximately 7200 thousand metric tons, while consumption was 5600 thousand metric tons representing about 78% capacity utilization.
Formaldehyde is another feedstock for MDI production. It is a very important commodity feedstock with many applications, particularly in thermoset polymers such as urea, phenol, and melamine formaldehyde resins used in many applications, particularly in wood bonding. Use in MDI manufacture only accounts for about 5% of total formaldehyde consumption and so is not a major determinant of formaldehyde pricing, but may correlate to MDI demand due to overlap in applications with other uses of formaldehyde such as construction . Made from the catalytic oxidation of methanol, Bayer and BASF produce some formaldehyde for captive production of MDI, but most formaldehyde for MDI production is purchased from companies outside of the polyurethane industry.