Benzene level

Petrochemical units generate waste waters from process operations such as vapor condensation, from cooling tower blowdown, and from stormwater runoff. Process waste waters are generated at a rate of about 15 cubic meters per hour (m /hr), based on 500,000 tpy ethylene production, and may contain biochemical oxygen demand (BOD) levels of 100 mg/1, as well as chemical oxygen demand (COD) of 1,500 to 6,000 mg/1, suspended solids of 100 to 400 mg/1, and oil and grease of 30 to 600 mg/1. Phenol levels of up to 200 mg/1 and benzene levels of up to 100 mg/1 may also be present. 

FCC gasoline contains 0.5 to 1.3 vol% benzene. Since it accounts for about 35 vol% of the gasoline pool, it is important to know what affects the cat cracker gasoline benzene levels. The benzene content in the FCC gasoline can be reduced by ... 

The benzene content of FCC gasoline is typically in the range of 0.6 vol /i to 1.3 vol%. CAAA s Simple Model requires RFC to have a maximum of 1 vol% benzene. In California, the basic requirement is also 1 vol% however, if refiners are to comply with averaging provisions, the maximum is 0.8 vol%. Operationally, the benzene content of FCC gasoline can be reduced by reducing catalyst-oil contact time and catalyst-to-oil ratio. Lower reactor temperature, lower rates of hydrogen transfer, and an octane catalyst will also reduce benzene levels. 

It should be mentioned that the predicted curve at highest benzene level in Figure 13 agrees with classical kinetics (no diffusion-control). It is not clear therefore why measured data at even higher benzene concentrations do not agree with classical kinetics. There may be some subtle chemical interactions at these high solvent levels. Duerksen(lT) fomd similar effects with styrene polymerization in benzene and had to correct kp for solvent. 

Unless the immunoassay kit is benzene sensitive, the kit may display strong biases, such as the low affinity for benzene relative to toluene, ethylbenzene, xylenes, and other aromatic compounds. This will cause an underestimation of the actual benzene levels in a sample, and since benzene is often the dominant compound in leachates due to its high solubility, a low sensitivity for benzene is undesirable. 

USEPA issued the NESHAP for benzene waste operations March 7, 1990, under the Clean Air Act. The compliance date was May 1992. It affects not only equipment leaks but also emissions of benzene in wastewater streams. Eacilities with greater than 10 tonnes/year benzene in wastewater streams are affected. They must identify wastewater streams containing greater than 10 mg/L benzene and divert them to units that will reduce benzene to acceptable levels, that is, below 10 mg/L or by 98%. This rule affected most major refineries and olefins plants. Mobil Corp. spent 10 million on a benzene recovery project at its Chalmette, LA, refinery. The refinery uses vacuum steam stripping to decrease benzene emissions by about 10 tonnes/year. One Gulf Coast petrochemical plant has also spent 10 million on a wastewater stripping facility, which reduced benzene levels from several thousand mg/L to less than 5 mg/L [70]. 

Systems containing monomer and DMF but no other diluent were discussed in the previous section, and it was noted that a maximum rate is associated with intermediate monomer-DMF compositions. Imoto (79) observed a similar effect with monomer-benzene-DMF mixtures. A shallow minimum in polymerization rate was found at a low benzene level and then a very pronounced maximum at a higher benzene content. Molecular weight increased monotonically, however, with the benzene/ DMF ratio. In these ternary systems the amount of DMF was not enough to keep the polymer in solution but considerable swelling must have occurred. Thomas, Thomas and Deichert (130) show electron photomicrographs of polymer made under these conditions. 

Polymeric cationic curable formulations containing an d -biphenylthioxanthenium salt initiator 638 have been reported to reduce the residual odor and benzene levels associated with other -phenyl cationic photoinitiator systems <2006W02006/060281 >. The mechanism of photo-acid generation from related rS -aryl thiopyranium salts... 

Reference Solution A Prepare a solution in Toluene containing 2500 ppm of benzene. If the toluene available contains benzene as the only impurity, the benzene level can be determined by gas chromatography and sufficient benzene added to bring the level to 2500 ppm. 

The effect of even higher benzene levels has been studied on a demonstration plant scale a feed of 15 wt.-% benzene and 85 wt.-% n-C5 was completely saturated at a liquid hourly space velocity of 4 h 1 and a pressure of 30 bar at a weight average bed temperature (WABT) as low as 120°C (3). 

Releases to the Environment from Facilities That Manufacture or Process Benzene 5-2 Benzene Levels in Air Samples... 

A retrospective cohort study was done in 1982-83 on 28,460 benzene workers in China, all of whom had worked in various factories for at least half a year between 1972 and 1981 however, exposure and employment duration were not necessarily limited to those years (Yin et al. 1987a). Thirty cases of leukemia (23 AML, 7 CML) with a mean latency of 11.4 years (0.8-49.5 years) were found in the benzene cohort, as opposed to 4 cases in a matched control cohort. Twenty-five of the leukemic workers had already died. Information on exposure levels was collected from company records, but there is no indication of the extent of these records with the exception of a note that three of the reported levels were based on only one measurement. Mean benzene levels to which workers with leukemia were exposed ranged from 3 to 313 ppm, with the majority falling between 16 and 157 ppm. Exposure ranges from which the means were derived were rather wide, indicating the possibility of at least occasional high exposures. Only 4 upper-level measurements were less than 10 ppm, while half of the remaining measurements were between 10 and 100 ppm, and the other half were between 100 and 2,000 ppm. The authors observed that the cumulative mortality due to leukemia was proportional to the duration of the exposure to benzene for exposure of up to 20 years and then leveled off. 

Additional evidence of benzene absorption following inhalation exposure comes from data on cigarette smokers. Benzene levels were significantly higher in the venous blood of 14 smokers (median level of... 

Following a 10-minute inhalation exposure to 2,000 ppm of benzene by pregnant mice, benzene and its metabolites were found to be present in lipid-rich tissues, such as brain and fat, and in well-perfused tissues, such as liver and kidney. Benzene was also found in the placenta and fetuses immediately following inhalation of benzene (Ghantous and Danielsson 1986). During inhalation exposure of rats to 500 ppm, benzene levels reached a steady-state concentration within 4 hours in blood (11.5 pg/mL),... 

Benzene was rapidly distributed throughout the bodies of dogs exposed via inhalation to concentrations of 800 ppm for up to 8 hours per day for 8-22 days (Schrenk et al. 1941). Fat, bone marrow, and urine contained about 20 times the concentration of benzene in blood benzene levels in muscles and organs were 1-3 times that in blood and erythrocytes contained about twice the amount of benzene found in plasma. During inhalation exposure of rats to 1,000 ppm (2 hours per/day, for 12 weeks), benzene was stored longer (and eliminated more slowly) in female and male rats with higher body fat content than in leaner animals (Sato et al. 1975). 

Popp et al. (1994) reported a mean blood benzene level in car mechanics of 3.3 pg/L. Urinary muconic acid and S-phenyl-N-acetyl cysteine (PhAC) levels increased during the work shift, and were well correlated with the blood levels and the benzene air levels, which reached a maximum of 13 mg/m3. 

Blood concentrations of benzene following inhalation exposure in mice and rats were adequately predicted. Bone marrow concentrations of benzene following subcutaneous injection in mice and inhalation exposure in rats were accurately predicted, as were blood concentrations of benzene in rats following intraperitoneal injection. For humans, the model slightly overestimated the data for benzene in expired air at the low concentration of 5 ppm. For the mid concentration of 25 ppm, excellent fit was obtained from the model for both benzene in expired air and blood benzene levels. Model agreement for expired benzene was also good at concentrations of 57 and 99 ppm. The model was also accurate in predicting the amount of phenol in the urine after a 5-hour exposure to 31.3 or 47 ppm. 

However, benzene levels in ambient air, drinking water, and at hazardous waste sites are not likely to be of concern. 

Ong et al. (1995) evaluated the various biomarkers of benzene exposure for their relationship with environmental benzene levels. Muconic acid in the urine correlated best with environmental benzene concentrations. Urinary hydroquinone levels were the most accurate biomarker of exposure for the... 

In another study, benzene levels measured in the breath of occupationally exposed workers 16 hours after exposure ended were elevated as compared to benzene levels in the breath of people not occupationally exposed to benzene (Brugnone et al. 1989). A group of coal tar distillation workers with TWA exposure to benzene between 0.2 and 4.1 ppm had measurable benzene vapor in their breath 16 hours after exposure and showed a progressive build-up of benzene in their expired air during the working week (Money and Gray 1989). 

Benzene levels in blood and expired air were determined in a population of 168 men divided into 4 groups blood donors, hospital staff, and chemical workers with and without benzene exposure (Brugnone et al. 1989). Workers with a TWA benzene exposure of 0.4 ppm had measurable blood and alveolar concentrations of benzene that were significantly different from the other 3 groups. However, blood levels would be expected to provide a more accurate assessment of internal dose and, thus, a more accurate prediction of target organ effects than other monitoring end points. In addition, baseline levels of benzene in the blood of environmentally sensitive individuals not known to have exposure to benzene... 

As discussed in Chapter 6, the primary method of analyzing benzene in body fluids and tissues is gas chromatography (GC) in conjunction with either mass spectrometry (MS), photoionization detection (PID), or flame ionization detection (FID). For detection of benzene metabolites, both GC/FID and high-performance liquid chromatography (FIPLC) with ultraviolet detection (UV) have been used. A recent article describes the development of simple and sensitive methods for determination of blood and urinary benzene levels using gas chromatography headspace method (Kok and Ong 1994). 

Breath levels of benzene have been used as a measure of exposure (Brugnone et al. 1989 Money and Gray 1989 Nomiyama and Nomiyama 1974a, 1974b Ong and Lee 1994 Pekari et al. 1992). However, the amount of benzene lost in expired air will vary not only with the dose, duration, and time from exposure, but also with the extent of metabolism in the body. Benzene levels in blood have been measured. 

Salanitro (1993) has summarized the aerobic degradation rates for BTEX in laboratory subsoil-groundwater slurries and aquifers. The data indicate that decay rates for benzene are highest (19-52% per day) for benzene concentrations less than 1 ppm when initial dissolved oxygen levels are about 8 ppm. Rates are significantly reduced (0-1.1% per day) when benzene levels are 1-2 ppm, and no degradation was observed when benzene levels were greater than 2 ppb. 

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