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Elastomeric Polymers
Published in Kathleen Hess-Kosa, Building Materials, 2017
Although the monomers, isobutylene and isoprene, are nontoxic, they are flammable. The butyl rubber sealants and adhesives are, however, suspended in VOCs (e.g., up to 35% by weight). The VOC content varies by manufacturer; and the toxic potential of the organic components should be assessed on the basis of published information (e.g., MSDS). Nontoxic fillers (e.g., kaolin and limestone) may be as high as 70% by weight in butyl sealants. Plasticizers and other additives, however, cannot be ruled out. Flammable organic vapors emissions are likely.
A brief review of sealants for cement concrete pavement joints and cracks
Published in Road Materials and Pavement Design, 2021
Lu Lu, Deying Zhao, Jizhou Fan, Guoqiang Li
In addition to bitumen or coal-tar based sealants, polymeric sealants have played a major role over the years. The earliest polymeric sealants were triglyceride esters of long-chain fatty acids. They were considered as low-performance sealants and showed little or no chemical curing after application. They were inexpensive, had little flexibility, and tended to crack when they were subjected to moderate joint movement. Solvent-based acrylics and butyl sealants are considered medium performance sealants. Butyl rubber is prepared by the polymerisation of isobutylene. Butyl sealants are relatively low in price and adhere to a wide range of substrates. Solvent-based butyl sealant shows joint shrinkage due to solvent loss and sealant stringiness during application.
The direct, one-step process for synthesis of dimethyl ether from syngas. III. DME as a chemical feedstock
Published in Petroleum Science and Technology, 2018
Ethylene and propylene are two of the most important, high-volume chemicals in the petrochemicals and refinery industry, produced to the tune of 120 MMT/annum and 90 MMT/annum (2010 basis), respectively; nevertheless, the MTO process is not in commercial operation in United States. However, UOP (Des Plaines, Ill.) and UOP/Norsk Hydro (of Norway) are licensors of an in-house technology for methanol-to-olefins process. The technology is based on a fluidized bed reactor operation, at 450 – 500°C and achieves ∼80% C-selectivity to olefins at ∼100%, or, stoichiometric methanol conversions (Apanel and Netzer 2002). Despite the fact that the MTO process is now only on the pilot scale, the cost-effective routes to ethylene and propylene are particularly interesting. Thus, apart from uses for their respective polymeric analogs, polyethylene and polypropylene, both monomeric forms can be converted to other value-added chemicals, such as ethylene oxide, propylene oxide, and ethylene glycol. Isobutylene, the other olefin, a co-product in the MTO process, is also an important commodity, as a chemical intermediate, for further conversion into methyl tert-butyl ether (MTBE), methyl methacrylate, and isoprene (synthetic rubber). In light of the importance of the MTO process, pioneering research on a number of these DME-to-hydrocarbons processes have also been carried out at the University of Akron first and later at University of Missouri-Columbia (Sardesai 1997; Lee et al. 1995; Gogate, Lee and Kulik 1995; Lee and Sardesai 2005). A schematic of the fixed-bed reactor system for the DME-to-hydrocarbons test reactions is given in Figure 3.