Liquid mixture suitable as gasoline

Details Liquid mixture suitable as gasoline Liquid mixture suitable as gasoline

2000-03-21

2001-06-05

Medley, Margaret (Department: 1714)

Fuel and related compositions

Liquid fuels

Organic oxygen compound containing

C585S014000

Reexamination Certificate

active

06241791

ABSTRACT:

The present invention relates to a liquid mixture suitable as gasoline in compliance with the strictest regulations.
The influence of the quality of fuels on the reduction of emissions definitely plays a very important role.
In both the United States and Europe, this problem has been faced with legislative proposals (for example, in the United States, the “Clean Air Act”) and detailed studies (the so-called “Auto-Oil” Programs) which have underlined the main correlations between the composition of fuels, the types of engines and the emissions observed. The results of these correlation studies between composition and emissions have demonstrated that some characteristics of fuels for motor vehicles must be modified. From a legislative point of view, therefore, the relative composition specifications have been (or are about to be) changed, and refineries are consequently compelled to effect several process or product innovations which will enable them to produce fuels whose characteristics comply with the modified specifications.
With respect to gasoline, the most important aspects are generally the following:
the content of sulfur, benzene, aromatic hydrocarbons and olefins (mainly light olefins) should be reduced;
the volatility should also be reduced and the heavier gasoline cut should be partly removed;
oxygenated compounds, i.e. ethers (such as MTBE, but not only MTBE) or poly-branched paraffinic compounds such as for example those contained in the alkylate (iso-octane and trimethyl pentanes in general) are, on the other hand, extremely desirable (both for their high octane number and for their positive influence on the emissions).
Aromatic compounds have always been among the main components of gasoline and among the greatest contributors to the octane number. A lowering in the content of aromatics therefore causes a reduction in the quantity of gasoline produced by the refinery and a deficiency in the octane number. In addition, as aromatic compounds have a low vapour pressure, their reduction tends to increase the volatility of the gasoline. This tendential increase in volatility, in turn, causes a reduction in the content of light hydrocarbons and in particular normal-butane, which can be added to gasoline, especially during the winter months, when the vapour pressure may increase. Under these conditions, n-butane can practically only be used as GPL.
A kind of adverse cycle is therefore created as n-butane is an octane producer and increases the volume of the gasoline produced; in addition the introduction of n-butane into gasoline has a beneficial economic effect as it allows a semi-processed product either coming directly from the distillation of crude oil, for whose production it has not been necessary to invest in process plants, or generated as by-product from other process units, to be sold at the same price as gasoline. As a result, its reduction also causes direct economic damage.
From what is specified above, it is evident that the process which will produce fuels for motor vehicles, having a gradually decreasing environmental impact, requires great technological effort, as all the problems described above must be technically solved and at the same time economically acceptable.
The main oxygenated compounds which can be used are ethanol and ter-alkyl ethers.
Ethanol which generally comes from the fermentation of wheat, barley or sugarbeet, is very expensive and consequently, apart from some specific situations, its use in gasoline can be economically sustained only when tax reductions are granted. Ethanol however has particularly interesting octane characteristics, blending (RON+MON)/2=107-113, and enables the minimum oxygen content specification to be reached (when compulsory as in reformulated gasoline in the U.S.A.), using smaller concentrations of oxygenated product with respect to ethers.
Owing to its affinity towards water however, it is not mixed together with the gasoline directly in the refinery but is only added just before the last distribution network.
Moreover ethanol easily forms low-boiling azeotropic mixtures with the components of gasoline and in fact its typical vapour pressure (Rvp) varies from 17 to 22 psi.
In addition, excessively high concentrations of ethanol (up to 3.7% of oxygen by weight, about 10% of ethanol by volume) seem to cause an increase, of 4 to 8% more, in the emissions of NO
x
(G. H. Unzelman, Fuel Reformation, July/August 1995, 45): increased emissions of NO
x
can also cause increases in the emissions of atmospheric ozone.
Among the oxygenated compounds, ter-alkyl ethers have proved to be preferable; among these the most important are MTBE (methyl-ter-butylether), ETBE (ethyl-ter-butylether), TAME (ter-amyl-methylether) and TAEE (ter-amyl-ethylether). These ethers are generally obtained by the reaction in liquid phase of C
4
-C
5
iso-olefins (i.e. isobutene or some isoamylenes) with methanol (MTBE, TAME) or ethanol (ETBE, TAEE), in the presence of an ion exchange acid macromolecular resin as catalyst.
The production of these ethers, mainly MTBE, has continually increased in the last few years, so much so that MTBE has become the chemical product which has had the most rapid growth in the history of industrial chemistry.
In refineries, isobutene is normally contained in a stream generated by a Fluid Catalytic Cracking (FCC) plant, whereas in petrolchemical complexes in a stream generated by an ethylene (Steam Cracker) plant. As the quantity of isobutene contained in these charges however is not in itself sufficient to cover the 16 million tons of MTBE presently consumed every year in the world, the use of various dehydrogenation technologies of isobutane has become popular in the last 10 years. In this way it is possible to exploit the so-called field butanes, i.e. the butanes obtained by the fractionation of natural gas. Another important source for the production of MTBE is ter-butanol which is obtained together with propylene oxide by the reaction of propylene and isobutane (the latter pretreated with oxygen); the alcohol obtained is then easily dehydrated to isobutene.
Another reduction source could be the isobutanol obtained by the synthesis of methanol and higher alcohols from CO and H
2
(D. Sanfilippo, E. Micheli, I. Miracca, L. Tagliabue, Petr. Tech. Quat., Spring 1998, 87).
The use of MTBE and other ethers does not have only octane advantages: in fact the oxygen atom present in their molecule improves the combustion of gasolines. The resulting ecological advantage is considerable as the content of CO and uncombusted hydrocarbons emitted from the exhaust pipe is reduced.
In addition to oxygenated compounds, completely hydrocarbon products could also prove to be particularly convenient for the production of gasolines with a low environmental impact. Among these, the most important one is the alkylated product.
Alkylation is a refinery process which consists in the formation of highly branched paraffins with a high octane number, by the catalytic reaction of isobutane with light olefins such as propylene and butenes. Typical catalysts of this reaction are some mineral acids such as hydrofluoric acid and sulfuric acid.
The charge which is generally alkylated is the C
4
stream coming from Catalytic Cracking, as it is rich in both butenes and isobutane.
In many cases, before being “alkylated”, this charge is fed to the MTBE plant where the isobutene reacts with methanol. As far as the quality of the product is concerned, the alkylated product is ideal gasoline. Its motoristic properties are excellent: the Research octane number (RON) is very high, but above all, the Motor octane number (MON) is exceptionally high. The alkylated product, moreover, does not contain aromatic compounds, sulfur and olefins, it respects the specifications for the boiling range and has a low volatility. It therefore has all the fundamental requisites for being an ideal component for reformulated, environmentally compatible gasolines.
From an environmental point of view, both H
2
SO
4
and HF are strong acids, classified among da

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