Published April 1998
This review presents designs for three processes for the manufacture of 55.5 million lb/yr (25,200 t/yr) of formaldehyde. In each process, the formaldehyde is produced as 111 million lb/yr (50,400 t/yr) of 50 wt% formaldehyde aqueous solution, with a methanol content of 0.5 wt% or less. (The yield is equivalent to 150 million lb/yr [68,000 t/yr] of 37 wt% solution.) The processes are: (1) ferric molybdate catalyst, (2) silver catalyst with wet gas recycle (WGR), and (3) conventional silver catalyst.
The last PEP evaluation of formaldehyde processes was PEP Report 23A, Formaldehyde (December 1978). That report evaluated a silver-catalyzed WGR process based on BASF patents and a ferric molybdate-catalyzed process. Both produced 37 wt% formaldehyde. Since that time, formaldehyde solutions of 50 wt% or more have become the item of commerce in order to reduce shipping costs. Although the basic processes have changed very little, important improvements continue to be made. In this review, we summarize the patents that have been assigned since 1978, present SRIC's versions of the three main competing processes, and compare the economics of the processes.
Ferric molybdate-catalyzed processes are licensed by D.B. Western, Perstorp, and others. Mitsubishi Gas Chemical licenses a version of the silver-catalyzed WGR process and also licenses a conventional silver-catalyzed process. BASF also has WGR technology, but it is not readily available under license. Derivados Forestales, S.A. (Barcelona, Spain) licenses a conventional silver-catalyzed process. Various versions of the conventional silver-catalyzed process are widely used commercially, but many of these installations are based on proprietary technology. Most new facilities use a ferric molybdate-catalyzed process, but new silver-catalyzed units continue to be built. This situation leads many industry experts to feel that the economics for silver- and ferric molybdate-catalyzed processes are very close, but other experts say that the ferric molybdate process is more widely used because it is more readily available as an off-the-shelf unit from a licensing company.
Process economics are derived for the ferric molybdate-catalyzed process, and compared with the silver-catalyzed WGR process and the conventional silver-catalyzed process.