Urethane chemicals process enters a new phase
16 May 2007
Bayer's gas phase production technology represents a significant technical breakthrough for the urethanes chemicals producer. Patrick Raleigh reports
Bayer MaterialScience's site at Dormagen, Germany is the focal point for the development of a new process technology for the production of toluene diisocyanate (TDI) — a key raw material for flexible polyurethane foams.
Since mid-2004, BMS has been operating a pilot plant for gas phase phosgenation at the Dormagen site. Despite it compact size, the plant delivers an annual capacity of 30 kilotonnes per annum (ktpa).
Gas phase production of TDI has long been a holy grail for urethane chemicals producers, who recognise its potential benefits in terms of higher productivity, plant safety and climate protection compared with conventional production routes.
The scale of the global market for flexible polyurethane foam underlines the commercial significance of this development, said Peter Vanacker, head of BMS' Polyurethanes business unit speaking at a 17 April press conference at the German site.
Flexible foams — produced by reacting TDI with a polyether polyol — represent 32% of worldwide polyurethane consumption of 10.5 million tonnes. The products are used principally in upholstered furniture, mattresses and car seats.
The starting material for TDI is naphtha, which is obtained from crude oil. Toluene obtained from naphtha, following separation of the aromatic compounds, is nitrated into dinitrotoluene (DNT) using nitric acid.
The subsequent hydrogenation of the nitro groups produces toluene diamine (TDA), which is then converted to TDI via phosgenation — a reaction step, which is conventionally carried out with TDA and phosgene in the form of very dilute solutions.
Superheated
In BMS' new gas phase phosgenation process, however, TDA and phosgene are superheated to over 300°C and then transferred in gaseous form to the reaction via a specially designed nozzle. The reactants are then condensed to liquid TDI and, in the final step, cleaned by distillation, during which the solvent and excess phosgene are recovered.
"The new technology optimises productivity," claimed Vanacker. "As a result, it is far superior to the improved conventional procedures of our competitors." The process, he said, delivers savings of around 80% on solvents and consequently uses some 40% less energy, particularly in the distillation phase.
The technology also cuts operating costs significantly, principally because of the reduced energy consumption required to process the much smaller volume of liquid during subsequent distillation, the BMS polyurethanes leader continued.
Another feature is that the feedstocks have a residence time of less than a minute in the reactor, compared with almost an hour in the conventional process. This enhances productivity and reduces the required volume of phosgene considerably, said Vanacker.
"This results in significantly increased throughput per time unit or a greater space-time yield, as our technicians say. Consequently, key plant components in gas phase phosgenation can be made much smaller than is the case with conventional plants of the same capacity. This enables us to reduce investment costs by around 20%," he explained.
Vanacker also pointed to improved selectivity of the reaction, which generates fewer by-products, increases the TDI yield and improves the safety of the process due to the big reductions in the amounts of solvent and phosgene needed. The process also makes it possible to start up and shut down the plant quickly, he said.
China first
BMS will apply the gas phase TDI production technology in all new world-scale manufacturing plants, starting with the installation of a series of reactors at its world-scale facility in Caojing, near Shanghai, China.
"We intend to start up the first TDI production plant of this size, with a capacity of 300,000 annual tonnes, at our integrated Shanghai site by the end of 2010," said Patrick Thomas, chairman of Bayer MaterialScience.
"To boost production flexibility, we will equip the gas phase phosgenation facilities in the TDI plant with several reactors of a similar scale to those in our pilot plant, but each with a greater diameter.
We intend to use part of the production capacity in Shanghai to supply the fast-growing markets in eastern Europe and the Middle East until new TDI capacities are in place in Europe."
Since mid-2004, BMS has been operating a pilot plant for gas phase phosgenation at the Dormagen site. Despite it compact size, the plant delivers an annual capacity of 30 kilotonnes per annum (ktpa).
Gas phase production of TDI has long been a holy grail for urethane chemicals producers, who recognise its potential benefits in terms of higher productivity, plant safety and climate protection compared with conventional production routes.
The scale of the global market for flexible polyurethane foam underlines the commercial significance of this development, said Peter Vanacker, head of BMS' Polyurethanes business unit speaking at a 17 April press conference at the German site.
Flexible foams — produced by reacting TDI with a polyether polyol — represent 32% of worldwide polyurethane consumption of 10.5 million tonnes. The products are used principally in upholstered furniture, mattresses and car seats.
The starting material for TDI is naphtha, which is obtained from crude oil. Toluene obtained from naphtha, following separation of the aromatic compounds, is nitrated into dinitrotoluene (DNT) using nitric acid.
The subsequent hydrogenation of the nitro groups produces toluene diamine (TDA), which is then converted to TDI via phosgenation — a reaction step, which is conventionally carried out with TDA and phosgene in the form of very dilute solutions.
Superheated
In BMS' new gas phase phosgenation process, however, TDA and phosgene are superheated to over 300°C and then transferred in gaseous form to the reaction via a specially designed nozzle. The reactants are then condensed to liquid TDI and, in the final step, cleaned by distillation, during which the solvent and excess phosgene are recovered.
"The new technology optimises productivity," claimed Vanacker. "As a result, it is far superior to the improved conventional procedures of our competitors." The process, he said, delivers savings of around 80% on solvents and consequently uses some 40% less energy, particularly in the distillation phase.
The technology also cuts operating costs significantly, principally because of the reduced energy consumption required to process the much smaller volume of liquid during subsequent distillation, the BMS polyurethanes leader continued.
Another feature is that the feedstocks have a residence time of less than a minute in the reactor, compared with almost an hour in the conventional process. This enhances productivity and reduces the required volume of phosgene considerably, said Vanacker.
"This results in significantly increased throughput per time unit or a greater space-time yield, as our technicians say. Consequently, key plant components in gas phase phosgenation can be made much smaller than is the case with conventional plants of the same capacity. This enables us to reduce investment costs by around 20%," he explained.
Vanacker also pointed to improved selectivity of the reaction, which generates fewer by-products, increases the TDI yield and improves the safety of the process due to the big reductions in the amounts of solvent and phosgene needed. The process also makes it possible to start up and shut down the plant quickly, he said.
China first
BMS will apply the gas phase TDI production technology in all new world-scale manufacturing plants, starting with the installation of a series of reactors at its world-scale facility in Caojing, near Shanghai, China.
"We intend to start up the first TDI production plant of this size, with a capacity of 300,000 annual tonnes, at our integrated Shanghai site by the end of 2010," said Patrick Thomas, chairman of Bayer MaterialScience.
"To boost production flexibility, we will equip the gas phase phosgenation facilities in the TDI plant with several reactors of a similar scale to those in our pilot plant, but each with a greater diameter.
We intend to use part of the production capacity in Shanghai to supply the fast-growing markets in eastern Europe and the Middle East until new TDI capacities are in place in Europe."
