Benzene environmental impact

In earlier editions of the Eniyclopedia there have been articles covering the properties, manufacture, capacities, etc, of polychlorinated biphenyls (PCBs), chlorinated naphthalenes, benzene hexachloride, and chlorinated derivatives of cyclopentadiene. These materials are no longer in commercial use because of their toxicity. However, they stiU impact on the chemical industry because of residual environmental problems. Their toxicity and environmental impact are discussed (see Cm.OROCARBONSANDCm.OROHYDROCARBONS, TOXIC aromatics). 

Release limits for VOCs are set for either specific components (e.g. benzene, carbon tetrachloride), or as VOCs for organic compounds with a lower environmental impact and classed together and reported, for example, as toluene. 

Young DR, Heesen TC. 1978. DDT, PCB and chlorinated benzenes in the marine ecosystem off Southern California. In Jolley RL, Gorchev H, Hamilton DH Jr. eds. Water chlorination Environmental impact and health effects. Volume 2. Aim Arbor, MI Ann Arbor Science Publishers, Inc., 267-290. 

Another synthesis of adipic acid involves the microbial degradation of toluene to muconic acid (hexa-2,4-dienedioic acid), which undergoes catalytic hydrogenation to give adipic acid. If this process can be made economically competitive, it might produce less environmental impact than the chemical synthesis from benzene. 

Product development chemists must consider human health and environmental impact when choosing between solvents. Many solvents that have been used in the past, such as benzene and carbon tetrachloride, are now known to be harmful to the health and/or the environment. 

OSHA. 1977. Final environmental impact statement Benzene. Washington, DC U.S. Department of Labor, Occupational Safety and Health Administration. Federal Register 42 22516-22529, 27460-27464. 

Bergman and Frisch [7] disclosed in 1966 that selective oxidation of n-butane was catalyzed by the VPO catalysts, and since 1974 n-butane has been increasingly used instead of benzene as the raw material for maleic anhydride production due to lower price, high availability in many regions and low environmental impact [8]. At present more than 70 % of maleic anhydride is produced from n-butane [6]. However, productivity from n-butane is lower than in the case of benzene due to lower selectivities to maleic anhydride at higher conversions and somewhat lower feed concentrations (< 2 mol. %) used to avoid flammability of a process stream. Under typical industrial conditions (2 mol. % n-butane in air, 673-723K, and space velocities of 1100-2600 h ) the selectivities [9] for fixed-bed production of maleic anhydride from n-butane are 67-75 mol. % at 70-85 % n-butane conversion [10]. Another unique feature of the VPO catalysts is that no support is used in partial oxidation of n-butane.Many studies of n-butane oxidation on the VPO catalysts indicated that crystalline vanadyl(IV) pyrophos-... 

Polycyclic aromatic hydrocarbons (PAHs) that are made up of two or more fused benzene rings are minor components of crude oil (Figures 1 and 2), but they are by far the most important HMW compounds in terms of chronic environmental impact. Indeed, total PAH loading is used as the surrogate for the overall estimation... 

The environmental impact of the cyclohexane oxidation could also be reduced. An alternative is to start from benzene and make a selective hydrogenation to form cyclohexene. Ru-based supported catalysts working in the liquid phase and in the presence of a co-catalysts such as Zn (Asahi Chemical Industry process) are selective in the reaction, with yields up to about 60% [247], but with cyclohexane as the main by-product. Cyclohexene is hydrated in the liquid phase with an MFI zeolite as catalyst at moderate temperature (100-130 °C). This reaction is very selective (>99%). This route was primarily developed for the synthesis of adipic acid, but could be used also to reduce the number of products and separation costs in the production of cyclohexanone. 

Since 1952, the cumene process has been improved to a fairly impressive extent as its yields to acetone and phenol, based on both benzene and propene, are currently close to the stoichiometric ones. Nor are there problems in building huge plants 300 0001 yr capacity is a common size, while still having a quite reduced environmental impact. Thus, although some precautions are needed to ensure safe operations, the process is fully satisfactory in many aspects. 

Chlorinated and brominated materials are burned or thermally treated in a variety of combustion sources including hazardous and municipal waste incinerators, industrial processes, backyard trash burning, and accidental fires. Chlorinated materials are used in a wide range of applications and brominated compounds are fire retardants used in many devices including electronic circuits. Although there has been some research on the reactions of CHCs and BHCs in the past 20 years, too little is known about their reactions considering the magnitude of the environmental impact. Elementary reaction studies of gas-phase reactions of Cj and C2, CHCs, and BHCs are needed to understand their most fundamental reaction properties. Reactions of the chlorinated and brominated benzenes and phenols are important intermediate steps in the formation of PCDD/F. Recent kinetic models indicate that the gas-phase reactions may be quite important and elementary gas-phase reaction studies have been overlooked by researchers. 

Hydrodealkylation of toluene is a process where toluene is converted into benzene by reaction with hydrogen, forming Diphenyl as a byproduct. This is a well known process, which has been studied in numerous publications. The reference design and flowsheet considered in this paper are taken from Seider et al. (1999), where further details can be found. The necessary steady state simulations have been performed with a commercial process simulator, from where the results have been transferred to a software developed for this work to calculate the indicator values. The steady state simulation results are also transferred to ICAS (ICAS Documentation, 2002) to determine the environmental impact factors, the sustainability metrics and the safety factors. Table 1 shows the most important indicator-values from the base case design. A detailed calculation results document can be obtained from the corresponding author. 

The cumene process is fully satisfactory in many aspects in particular, selectiv-ities to acetone and phenol, based on both benzene and propene, are very high and the environmental impact of the process is quite minimal. 

Phenol is an important raw material for the synthesis of petrochemicals, agrochemicals, and plastics. Examples of the uses of phenol as an intermediate include the production of bisphenol A, phenolic resins, caprolactam, alkyl phenols, aniline, and other useful chemicals. Today, almost 95% of worldwide phenol production is based on the so-called cumene process which is a three-step process (the conversion of benzene and propylene to cumene using supported phosphoric acid catalysts, the conversion of cumene to cumene hydroperoxide with air, and the decomposition of hydroperoxide to phenol and acetone with sulfuric acid). The great interest in the oxidation reaction of benzene to phenol is Unked to some disadvantages of the cumene process (environmental impact, production of an explosive hydroperoxide. 

The environmental impacts associated with MA production without consideration of raw material production, fiansportation and electricity consumption are found in Table 6.3. Two potential benzene suppliers are considered, benzene can be obtained from a coke plant (Benzene Supplier-Tech 1 -Bz 1), or from a 50 % mixture of ethylene reforming and pyrolysis gasoline (Benzene Supplier-Tech 2-Bz2). For the case of butane production, two suppliers are considered, one that is a proxy model obtained from a European typical refinery (Butane Supplier-Tech -Bt ) (Butane Supplier-Tech 2-Bt2), and another one fi om a mixture of the top 20 organic chemicals. The values were retrieved from Ecoinvent-V 1.3 (2006) using SimaPro 7.1.6... 

Two different types of transportation services are assumed to be available, lorries in two different sizes (16 and 32 ton). Benzene is a chemical that is liquid at standard conditions and therefore is stored and transported as a liquid. Butane, on the other hand, is a gas at standard conditions and therefore needs to be liquefied in order to be transported and stored. In this case butane liquefaction has been considered during its production, and consequently both products are transported in liquid state, with similar environmental impacts by the same kg km. Medium voltage electricity production from different countries grid is considered. Environmental impacts associated with transportation services and electricity production are found in Table 6.4. Transportation prices were estimated from current economical trends, see Table6.5. Return rate is assumed to be 25 %. 

Results obtained appear in Fig. 6.2a, which shows the dominant SC that maximizes NPV. Production is based on benzene feedstock, which is bought from both available suppliers. Two facilities are built and MA is sold in all possible markets. Alternatively, when the objective is the minimization of the environmental impact indicator, the resulting SC (Fig. 6.2b) uses butane as feedstock and raw materials are acquired from a single supplier. This SC configuration implies a single production facility which sells MA to all four markets. Table 6.7 summarizes the numerical results corresponding to both solutions ... 

In the case of minimization of environmental impact, a negative NPV is found because of the high transportation cost associated with this solution (locations of butane suppliers are far from production facility sites and butane transportation cost is 42 % higher than in case of benzene cost). 

One alternative to reduce SC environmental impacts can be to look for new feedstock providers whose production processes are more environmental friendly. It is also important to notice that Human Health impacts are considerable high in both solutions. In the case of NPV optimization this fact is due to benzene toxic properties. It is expected that CO2 emissions trading considerations will make economically more attractive the butane based production. This aspect is analyzed in Sect. 6.4.1. 

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