LPG olefinicity

The major effect of ZSM-5 is to convert higher molecular weight iso-olefins into C3/C4 olefins with no discernible change in aromatics other than some dealkylation of the C9+ fraction. Most of the enhanced LPG olefinicity arises from cracking of C7+ olefins and a pore size effect is thought to be responsible for the high C3/C4 ratio compared to REHY. 

The fuel gas yield is considerably lower because of the shorter contact time. This is also expressed in a much lower fuel gas/isobutane ratio (see Figure 6). The LPG olefinicity is in the same order of magnitude as other experiments (see Figure 5). 

A shape selective zeolite cracks the low octane paraffinic components out of the gasoline boiling range, and therefore enhances the octane numbers at the expense of decreased gasoline yield. The LPG olefinic fragments can however be converted to premium gasoline components in downstream upgrading units. 

The Houdry Process, TCC and the FCC units were highly valued during World War II as a source of LPG olefins. These olefins were converted into 100 plus octane aviation jet fuel in sulfuric acid based alkylation units. The FCC naphtha which was produced in these processes was blended with the aviation gas (avgas) produced in the alkylation plant. 

Rare earth. The rare earth on zeolite level has a direct impact on catalyst stability and product selectivity. Directionally, increased rare earth levels on zeolite result in catalysts having enhanced hydrothermal stability. This results in a reduction in catalyst makeup rate. However, changes in product selectivities, especially in the LPG range, will result. Many refiners choose to compensate this loss in LPG olefinicity via the addition of ZSM-5 additive. 

Finally, zeolites may be used as functional ingredients. ZSM-5-based additives convert linear or near-linear gasoline range olefins into LPG olefins in combination with increasing the gasoline octane number. However, to maximize ZSM-5 properties, modifications with phosphorus compounds, along with convenient calcination, must be carried out. 

There is even more potential to improve gasoline yield as well as LPG olefins such as isobutene by using a catalyst that incorporates the properties of a ZSM-5 additive. This type of catalyst may also provide better conversion of light-cycle oil and residues because it has larger pores than ZSM-5. ... 

LPG recovered from natural gas is essentially free of unsaturated hydrocarbons, such as propylene and butylenes (qv). Varying quantities of these olefins may be found in refinery production, and the concentrations are a function of the refinery s process design and operation. Much of the propylene and butylene are removed in the refinery to provide raw materials for plastic and mbber production and to produce high octane gasoline components. 

About 35% of total U.S. LPG consumption is as chemical feedstock for petrochemicals and polymer iatermediates. The manufacture of polyethylene, polypropylene, and poly(vinyl chloride) requires huge volumes of ethylene (qv) and propylene which, ia the United States, are produced by thermal cracking/dehydrogenation of propane, butane, and ethane (see Olefin polymers Vinyl polymers). 

Light Olefins and LPG Recovery. Even though the normal boiling point temperature of ethylene (169.4 K) is much above 120 K, its recovery often requites much lower processing temperatures, particularly when high recoveries are needed. 

Liquefied Petroleum Gas The term liquefied petroleum gas (LPG) is applied to certain specific hydrocarbons which can be liquefied under moderate pressure at normal temperatures but are gaseous under normal atmospheric conditions. The chief constituents of LPG are propane, propylene, butane, butylene, and isobutane. LPG produced in the separation of heavier hydrocarbons from natural gas is mainly of the paraffinic (saturated) series. LPG derived from oil-refinery gas may contain varying low amounts of olefinic (unsaturated) hydrocamons. 

Liquefied petroleum gas (LPG), which is a propane-butane mixture. It is mainly used as a fuel or a chemical feedstock. Liquefied petroleum gas is evolving into an important feedstock for olefin production. It has been predicted that the world (LPG) market for chemicals will grow from 23.1 million tons consumed in 1988 to 36.0 million tons by the year 2000. ... 

Natural gas and crude oils are the main sources for hydrocarbon intermediates or secondary raw materials for the production of petrochemicals. From natural gas, ethane and LPG are recovered for use as intermediates in the production of olefins and diolefms. Important chemicals such as methanol and ammonia are also based on methane via synthesis gas. On the other hand, refinery gases from different crude oil processing schemes are important sources for olefins and LPG. Crude oil distillates and residues are precursors for olefins and aromatics via cracking and reforming processes. This chapter reviews the properties of the different hydrocarbon intermediates—paraffins, olefins, diolefms, and aromatics. Petroleum fractions and residues as mixtures of different hydrocarbon classes and hydrocarbon derivatives are discussed separately at the end of the chapter. 

Propane is a more reactive paraffin than ethane and methane. This is due to the presence of two secondary hydrogens that could be easily substituted (Chapter 6). Propane is obtained from natural gas liquids or from refinery gas streams. Liquefied petroleum gas (LPG) is a mixture of propane and butane and is mainly used as a fuel. The heating value of propane is 2,300 Btu/ft. LPG is currently an important feedstock for the production of olefins for petrochemical use. 

Chemicals directly based on propane are few, although as mentioned, propane and LPG are important feedstocks for the production of olefins. Chapter 6 discusses a new process recently developed for the dehydrogenation of propane to propylene for petrochemical use. Propylene has always been obtained as a coproduct with ethylene from steam cracking processes. Chapter 6 also discusses the production of aromatics from LPG through the Cyclar process. ... 

Butane is primarily used as a fuel gas within the LPG mixture. Like ethane and propane, the main chemical use of butane is as feedstock for steam cracking units for olefin production. Dehydrogenation of n-butane to butenes and to butadiene is an important route for the production of synthetic rubber. n-Butane is also a starting material for acetic acid and maleic anhydride production (Chapter 6). 

The most important olefins used for the production of petrochemicals are ethylene, propylene, the butylenes, and isoprene. These olefins are usually coproduced with ethylene by steam cracking ethane, LPG, liquid petroleum fractions, and residues. Olefins are characterized by their higher reactivities compared to paraffinic hydrocarbons. They can easily react with inexpensive reagents such as water, oxygen, hydrochloric acid, and chlorine to form valuable chemicals. Olefins can even add to themselves to produce important polymers such as polyethylene and polypropylene. Ethylene is the most important olefin for producing petrochemicals, and therefore, many sources have been sought for its production. The following discusses briefly, the properties of these olefmic intermediates. 

A major use of gas oil is as a fuel for diesel engines. Another important use is as a feedstock to cracking and hydrocracking units. Gases produced from these units are suitable sources for light olefins and LPG. Liquefied petroleum gas LPG may be used as a fuel, as a feedstock to... 

Cracking n-hutane is also similar to ethane and propane, hut the yield of ethylene is even lower. It has been noted that cracking either propane or butanes at nearly similar severity produced approximately equal liquid yields. Mixtures of propane and butane LPG are becoming important steam cracker feedstocks for C2-C4 olefin production. It has been forecasted that world LPG markets will grow from 114.7 million metric tons/day in 1988 to 136.9 MMtpd in the year 2000, and the largest portion of growth will be in the chemicals field. 

The overhead stream from the debutanizer or stabilizer is a mix of C, s and C4 s, usually referred to as LPG (liquefied petroleum gas). It is rich in olefins, propylene, and butylene. These light olefins play an important role in the manufacture of reformulated gasoline (RFG). Depending on the refinery s configuration, the cat cracker s LPG is used in the following areas ... 

Chemical sale, where the LPG is separated into Cj s and C4 s. The Cj s are sold as refinery or chemical grade propylene. The C l olefins are polymerized or alkylated. 

Increasing feed/catalyst mix zone temperature. Conversion and LPG yield can be increased by injecting a portion of the feed, or naphtha, at an intermediate point in the riser (see Figure 6-1). Splitting or segregation of the feed results in a high-mix zone temperature, producing more LPG and more olefins. This practice... 

LPG is a mixture of propane and n- and iso-butanes, plus small amounts of their olefinic counterparts. The main sources are natural gas wells, gas from crude oil wells and the cracking of crude oil. The requirements for commercial LPG are defined in national standards and a stenching agent is... 

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