GUERRA COMERCIAL ESTADOS UNIDOS – HUAWEI (CHINA)

While a solvent may not be banned or severely restricted for global or nationwide reasons it may still be unacceptable to the people who work with it or live near a factory that handles it. This may be because of health hazards (Table 10.6) or of fire and explosion hazards (Table 10.7).

The values for ‘Odour threshold’ in Table 10.6 are subjective and give only a rough guide to whether the smell of a solvent gives any protection against harmful exposure. In many cases an individual’s

Table 10.5 Possible solvent substitution

Ethylbenzene 59 for xylenes 82 Cumene 57 for trimethylbenzenesa ₁₁₇

(isopropyl benzene)

Methyl acetate 3 for acetone 19

Cyclohexane 25 for SBP2 50

Trichloroethylene 7 for SBP2 50 Isopropanol 15 for ethanol 27 Methylcyclohexane 35 for SBP5 51 Ethyl acetate 22 for MEK 42 Butyl acetate 32 for MIBK 63 Dichloromethane 1 for n-pentane 41 Perchloroethylene 0.5 for ethylbenzene 59

a_C

Table 10.6 Odour safety factor and safe dilution of common solvents (calculated at the solvent vapour pressure at 25 °C) Odour threshold Odour safety

Solvent TLV (ppm) (ppm) factor Safe dilution

Pentanea _{600 400 1.5 1 117} Hexanea _{50 130 0.4 4 000} Heptane 400 150 0.4 150 Cyclohexane 300 25 12 433 Benzene 10 12 0.9 12 000 Toluene 100 3 33 370 Ethylbenzene 100 3 33 115 Xylenes 100 1 100 110 Methanola _{200 100 2 650} Ethanol 1000 84 12 7.5 n-Propanol 200 3 67 130 Isopropanol 400 22 18 143 n-Butanol 50 1 50 184 Isobutanol 50 2 25 320 sec-Butanol 100 3 33 230 Cyclohexanol 50 0.2 250 40 Methyl Cellosolve 5 2 2.5 3 200 Ethyl Cellosolve 5 3 1.3 1 420 Butyl Cellosolve 25 0.1 250 52 MDCa _{100 250 0.4 5 500} Chloroforma _{10 300 0.03 28 600} Carbon tetrachloridea _{75 96 0.05 28 000} EDC 10 400 0.03 9 400 1,1,1-Trichloroethanea _{350 120 2.8 460} Trichloroethylene 50 28 1.8 1 980 Perchloroethylene 50 27 1.8 500 MCB 75 0.7 110 200 Acetonea _{750 13 57 387} MEK 200 5 40 650 MIBK 50 0.7 71 190 Cyclohexanone 25 0.9 28 240 Ethera _{400 9 44 1 750} DIPEa _{250 0.2 1250 840} Dioxane 25 24 1 2 080 THFa 200 2 100 1 150 Methyl acetatea _{200 100 2 800} Ethyl acetate 400 4 100 300 Butyl acetate 150 0.4 375 107 DMF 10 2 5 310 DMAc 10 47 0.2 260 Pyridine 5 0.2 25 5 400 ACN 40 170 0.2 3 000 Furfural 10 8 1.2 81

Table 10.7 Fire hazards

ability to detect an odour gets less during the course of a day’s exposure. The values of TLV are conserva- tive as far as most individuals are concerned. Com- bining the two figures to give an ‘Odour safety factor’ is therefore very inexact but gives some guid- ance as to whether smell provides any protection to the user. It also gives an indication of whether a nuisance may be caused in the neighbourhood even when there is no health hazard. A solvent with a high odour safety factor is likely to cause complaints even when no health hazard is created.

There are some circumstances where permanent ventilation cannot be installed to remove solvent fumes and the only method to make an atmosphere fit to breathe is by providing so much ventilation air that the solvent vapours will be diluted to a safe level. This will not necessarily produce pleasant working conditions since safe dilution is based on TLV and vapour pressure. A solvent (e.g. pyridine) with a very low odour threshold may have a nasty smell at a concentration well below its TLV as the values for odour safety factor indicate.

Quite apart from the harm solvents may do at concentrations greater than their TLV they can also overcome a person inhaling them by asphyxiation. The level of concentration at which this is likely to occur is 150 000 ppm (15%). The most volatile solv- ents will produce a saturated vapour of this strength at ambient temperature.

Several of the solvents widely used in the past (benzene, chloroform, carbon tetrachloride) would no longer be considered for a new formulation, however effective they may be. A solvent with a TLV of 15 ppm or less would need to have no effective substitute before it would be chosen today for long- term future use.

While odour may not be a protection against a toxic concentration the LEL is some two or three orders of magnitude higher than the TLV and a sense of smell will usually give some safety protec- tion. It must be remembered, however, that solvent vapours are very much heavier than air and, in a poorly ventilated place such as a drain or a cellar, there may be an explosive environment at a low level and not at nose level.

If a factory has not been designed to handle flam- mable liquids, major design changes may be needed to adapt it quite apart from the obvious need for

flameproof electrical equipment. Such equipment, while not generating sparks, is also classified as not to become so hot that the autoignition point of a solvent is reached. A change of solvent (e.g. from pentane to diethylether) may require costly replace- ment of electrical plant.

Temperature Maximum temperature classification inside equipment (°C)

T1 450 T2 300 T3 200 T4 135 T5 100 T6 85

IS RECOVERY WORTH

CONSIDERING?

While it is not acceptable to allow a used solvent to escape to the environment it may be economic to burn it for its calorific value and replace it with new solvent. The cheapest solvents tend to be

Table 10.8 Calorific values of solvents, conventional fuels and wastes

Calorific value Compound (kcal/kg) Solvents Toluene 10 100 Hexane 11 570 Cyclohexane 11 130 Xylene 10 270 Methanol 5 400 Ethanol 7 100 Isopropanol 7 900 Acetone 7 400 MEK 8 100 Ethyl acetate 6 100 Fuels 35 s Gas oil 10 500 Coal 6 600 Solvent wastes

Printing ink (Typical) 6 100 Paint line wash (Typical) 8 900

hydrocarbons with high calorific values (Tables 10.8 and 10.9) similar to those of fuels. They are relatively immiscible with water which could be separated using a very low cost process.

The solvents that would be potentially worth recovering because they were more expensive also are more likely to contain chlorine and nitrogen and therefore be unattractive as fuels or to contain more oxygen in the molecule and therefore have a lower LCV.

A recovery process which needs extra equipment, labour, tank storage and management time must be justified in economic terms. In the preliminary screening stage it would be realistic to guess that a simple distillation recovery process might cost UK £100/Te of recovered solvent.

CAN THE SOLVENT BE