Octane quality

In conventional alkylation operations, 98 wt. %, sulfuric acid is used as the catalyst, although some processes use HF.The spent alkylation acid, withdrawn as 88-92% acid, is not consumed in the chemical sense, but is diluted by carbonaceous material and small amounts of water. Acid reconditioning is usually completed in a separate plant. The range in makeup acid requirement and in octane quality varies with plant design, with type of feedstock, and with alkylate product rate. A wide variety of feedstocks can be processed through alkylation plants, as both low and high boiling olefins can be alkylated. 

Compositions of lead free gasoline with octane qualities equivalent to present day gasoline are shown in Table IV. These compositions represent the sum total of the many different refinery models presented in the API report. 

Table VIII. Automobile Compression Ratio and Gasoline Octane Quality...

The most important quality parameter for gasoline is the octane quality. 

In all cases some improvement in selectivity and octane quality was obtained. Cetylamlne and CTMAB showed the best results with typical improvements of about 0.5 MON and 1.5% in selectivity throughout the range of olefin space velocities. Figure 18 shows the improvements obtained with the C33 amine. 

The cost of the acids, the relative hazards of each, the actual alkylate yield and quality all must be considered when selecting the alkylation process to use. The installed cost of the plant and operating costs also must be considered. Oost savings can be realized if octane quality is lowered. 

Alkylates are very desirable no-lead ingredients and obviously the 04 alkylate is preferred because of its substantially higher octane quality. Moreover, the manufacture of 04 alkylate requires about 15% less isobutane than 03 alkylate. 

Ether synthesis produces branched ethers like methyl t-butyl ether (MTBE) by reacting methanol (or ethanol) with branched alkenes such as isobutene. These ethers are valuable for their high octane quality and also, on account of the oxygen they contain, their ability to reduce both CO and hydrocarbon exhaust emissions. Alcohols, such as methanol, manufactured from natural gas or coal, and ethanol, produced by fermentation, are other oxygenated components in limited use. 

Fig. 7.3. Development of Research Octane Number of two grades of gasoline in Germany, with the technologies responsible for the changes. The octane quality of the original unprocessed hydrocarbon (S.R. tops) was improved and augmented by material from cracking and reforming processes, from tetra-alkyl lead addition and by alcohols which were used at times of crisis because they could be produced from internal resources.

Fig. 7.9. Effect on octane quality of adding 3 ml/US gal tetra-ethyl lead to pure alkane and alkene fuels. The Performance Number is a practical measure of the propensity of a fuel to knock and related to the research octane number, RON, by the empirical formula PN = 2800/(128-RON). Except for a few highly branched species, the TEL increases the the performance number of alkanes by a constant factor of 1.5. It is less effective in alkene...

Bioethanol is also a very attractive compound for increasing gasoline octane quality and it can be added up to 10% to gasoline (E5 is the preferred European solution while ElO is used in USA) without engine modification or also used practically pure, as E85 or ElOO, in the Flexible Fuels Vehicles. 

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. 

Antiknock Compounds—improve octane quality of gasoline... 

The practical application of a skeletal isomerization catalyst for alkenes are numerous. There is an increasing interest in conventional petroleum refining in optimizing the use of light alkenes both to increase liquid yields and at the same time improve octane quality. 

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