Gasoline water tolerance

Low-temperature cooling limits are specified for each month of the year in the various states of the United States. Gasoline must meet these low-temperature limits for water tolerance before it can be marketed and sold. In addition to gasoline, water tolerance requirements also exist for jet fuel, diesel fuel, and heating oil. 

Methanol is more soluble in aromatic than paraffinic hydrocarbons. Thus varying gasoline compositions can affect fuel blends. At room temperature, the solubiUty of methanol in gasoline is very limited in the presence of water. Generally, cosolvents are added to methanol—gasoline blends to enhance water tolerance. Methanol is practically insoluble in diesel fuel. 

Methanol is not miscible with hydrocarbons and separation ensues readily in the presence of small quantities of water, particularly with reduction in temperature. On the other hand, anhydrous ethanol is completely miscible in all proportions with gasoline, although separation may be effected by water addition or by cooling. If water is already present, the water tolerance is higher for ethanol than for methanol, and can be improved by the addition of higher alcohols, such as butanol. Also benzene or acetone can be used. The wear problem is believed to be caused by formic acid attack, when methanol is used or acetic acid attack when ethanol is used. 

The butanols and their methyl and ethyl ethers have several advantages as oxygenates over methanol and ethanol in gasoline blends. Their energy contents are closer to those of gasoline the compatibility and miscibility problems with petroleum fuels are nil excessive vapor pressure and volatility problems do not occur and they are water tolerant and can be transported in gasoline blends by pipeline without danger of phase separation due to moisture absorption. Fermentation processes (Weizmann process) have been developed for simultaneous production of 1-butanol, 2-propanol, acetone, and ethanol from... 

TABLE 11.6 Water Tolerance of Alcohol-Gasoline Blends ... 

Another important issue of ethanol is its water sensitivity, which affects the water tolerance of gasoline in the case ofwater presence in ethanol-added gasoline, there is, in fact, the formation of hydrogen bonds between water and alcohol and the blend separates into two phases, with loss of octane quality. As a consequence, bioethanol requires special handling with different storage and distribution facilities for alcohol and gasoline and the blend has to be carried out just before the final use. 

Whereas gasoline and water are almost entirely immiscible, and will readily separate into two phases, a gasoline-oxygenate blend is used to dissolve water without phase separation, hence the use of the term water tolerance. Gasoline-oxygenate blends will dissolve some water but will also separate into two phases when contacted with water that is beyond the threshold concentration. Such a phenomenon is a major issue for alcohol-containing blends. 

Figure 2. Water Tolerance of Gasoline-Alcohol Blends...

Acetone is potentially useful in blends with gasoline as it can increase the oxygen content, the octane rating, and the water tolerance of the fuel (Bolt 1980 Noon 1982). Acetone can also be blended with butanol, ethanol, and water to serve as an automobile fuel (see the next section Butanol in this chapter). 

Butanol can increase the water tolerance of gasoline-ethanol blends (Bolt 1980 Noon 1982). The water tolerance of the gasoline-ethanol blends increases with the ethanol concentration and temperature. At room temperature, a 25 % ethanol blend with gasoline can tolerate about 1 % of water. If 2 % of water is present in the blend, most of the ethanol will separate from gasoline in a few seconds and settle to the bottom, which is known as phase separation. Phase separation renders the ethanol-gasoline blend unfit as an automobile fuel (Bolt 1980). Addition of butanol to the blend increases the water tolerance to prevent phase separation (Bolt 1980 Noon 1982). 

TAME has chemical and physical properties that are similar to those of MTBE and ETBE. As expected from its molecular structure, the properties of TAME are closer to gasoline than those of MTBE and ETBE. TAME is miscible with gasoline in all proportions, TAME-gasoline blends are water tolerant (the addition of water does not induce phase separation as with ethanol-gasoline blends Mueller et al., 2009) and can be distributed via pipelines in blends with gasoline, has a high octane number (blending octane number of 112, see table I-E-1), and solubility in water of 11 g liter" ... 

The eommereial HTS and LTS eatalysts require activation by careful pre-reduetion in situ and, once activated, lose aetivity very rapidly if they are exposed to air. Further, the HTS eatalyst is inactive at temperatures <300°C, while the LTS eatalyst degrades if heated to temperatures >250°C. The automotive application, because of its highly intermittent duty cycle, requires alternative water-gas shift catalysts that (1) eliminate the need to sequester the eatalyst during system shutdown (2) eliminate the need to aetivate the eatalyst in situ (3) inerease toleranee to temperature exeursions and (4) reduee the size and weight of the shift reactors. Another desirable property for an automotive WGS catalyst is tolerance to ppm levels of sulfur in the feed stream because sulfur species are present as contaminants or additives in conventional fuels (30 parts per million weight [ppmw] in future gasoline gets converted to 3 ppmv H2S in reformate). 

GTC Technology Isomerization Light naphtha Light gasoline isomerization processes using regenerable catalyst with superior tolerance to process impurities and water 7 2008... 

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