Etherification isobutene

Etherification of glycerol with isobutene (2-methylpropene) is an acid-catalyzed reaction and produces five ethers two monoethers, two diethers and one triether (Fig. 10.2). The IUPAC names for the two monosubstituted ethers are 3-tertiary-butoxypropane-l,2-diol and 2-tertiary-butoxypropanc-1,3-diol, the two disubsti-... 

Some studies and patents related to the etherification reaction between glycerol and isobutene are available in the literature, which report the production of the ethers with various catalysts, such as zeolites [19], ion-exchange resins [20, 21] and some homogeneous catalysts, e.g., p-toluene sulfonic acid [21, 22] and methane sulfonic acid [22], Recent studies, however, have concentrated on the etherification of glycerol with isobutene on ion-exchange resins [8, 23]. 

The etherification reaction was studied in the temperature range 45-90 °C. The initial molar ratio of isobutene to glycerol varied between 1.5 and 4.5 [8, 23]. 

In a system of two parallel reactions (Fig. 10.4), selectivity is an important parameter to monitor. The measure of selectivity is defined here as the ratio of isobutene reacted to ethers / total amount of isobutene reacted . Glycerol is consumed only in the etherification reaction, so the selectivity is calculated with respect to isobutene. Depending on the extent of the reaction, the formation of an ether molecule consumes from one to three isobutene molecules, and oligomerization consumes from two to four isobutene molecules [8],... 

In the dimerization of isobutene, tertiary-butyl alcohol (TBA, 2-methyl-2-propanol) has a strong role in modifying the selectivity of the reaction to Cg hydrocarbons and limits further oligomerization to C12 and Ci6 hydrocarbons [34]. Also, in the etherification of glycerol with isobutene the addition of TBA has a clear effect on the selectivity and on hydrocarbon distribution. The selectivity to ethers increased and the fraction of the Cu and Ci6 hydrocarbons decreased while the concentration of TBA was increased from 0 to 2.6 mol.%. As a conclusion, the formation of C12 and C16 hydrocarbons can be prevented in two ways either TBA should be added to the reaction mixture or the reaction should be carried out at high temperatures [8]. 

A more recent raw material for plasticizer alcohols is crack-C4 as a byproduct of steamcrackers in ethene/propene production. After extraction of butadiene for use and etherification of isobutene with methanol to methyl-tertiary-butylether MTBE as an octane enhancer, a stream is left containing 1-butene, 2-butene, and butanes, so-called raffinate II. Oligomerization of the butenes yields C8 olefin mixtures ( dibutene ) as the main product and the corresponding C12 olefins as the main byproduct (tributene). They are the... 

Production of light olefins (propylene, n-butenes and isobutene) will be one of the main targets of FCC untis in the near future. These olefins can be fed to alkylation and etherification units to produce additional high octane environmentally acceptable gasoline components, or used as petrochemical feedstock. Johnson and Avidan (85) used higher amounts of ZSM-5 (10-20%) to increase the production of light olefins, mainly propylene. 

Methyl Ter Butyl Ether (MTBE), which is obtained by the action of methanol on isobutene in a C4 cut, is a compound of vital interest to refiners because of its antiknock properties, which allow it to improve the quality of commercial gasolines, and the possibility of introducing methanoHndirectly into them. It is also a valuable intermediate for petro emicals, in so far as its decomposition leads to the r eneration of the starting olefin in a high degree of purin% and because, by ensuring the virtually complete conversion of the isobutene, etherification facilitates subsequent separation operations on the residual C4 cut Hence two steps must be considered from this standpoint ... 

The etherification of isobutene in a blend in a C4 cut is carried out according to the following equilibrium reaction ... 

A newly developed isobutene recovery is based on its selective and quantitative etherification into methyl f-butyl ether (MTBE) by treatment of the C4 stream with methanol in the presence of a cation-exchange resin (e.g., Amberlyst 15), followed by catalytic splitting of the isolated ether [43-45]. MTBE was, and still is, primarily produced as a high-octane blending component for unleaded gazoline. 

The catalytically promoted liquid-phase etherification of isobutene with an excess of methanol to produce MTBE has been carried out on a commercial scale in conventional fixed-bed reactors since the 1970s isobutene conversion is on the order of 90-97%. MTBE can be subsequently separated from the inerts and excess methanol by distillation— although this is complicated by the presence of minimum boiling azeotropes between MTBE and methanol and between isobutene and methanol. Unreacted isobutene is, however, difficult to separate from n-butanes and n-butenes because of their low relative... 

Selectivity to ETBE is usually very high and the main side reactions are isobutene dimerization with formation of 2,4,4-trimethyl-l-pentene and 2,4,4-trimethyl-2-pentene (DIB), ethanol self-condensation to diethyl ether (DEE), water addition to isobutene with formation of tert-butyl alcohol (TBA) and the etherification of linear butenes, if present, to produce ethyl sec-butyl ether (ESBE). 

The reaction rate of linear olefins etherification is much lower than isobutene so ESBE presence in the product is limited to a few hundred ppm. Formation of both DIB and DEE is favored at high temperatures and at low molar ratio alcohol/ isobutene. 

Therefore, in the case of etherification reaction, it is the isobutene/alcohol molar ratio that determines the catalytically active species and thus the reaction rate, as shown in Figure 11.4 for MTBE [5]. 

Figure 3.35 shows a process flow diagram of Phillips MTBE/ETBE/TAME process. This process is often called the Phillips Etherification Process. The reaction section (1,2) which receives methanol and isobutene concentrate, contains an ion exchange resin. The isobutene concentrate may be mixed olefins from a Fluid Catalytic Cracking Unit (FCCU) or steam cracker or from the on-purpose dehydration of isobutene (Phillips STAR process). High purity MTBE (99 wt%) is removed as a bottoms product from the MTBE fractionator (3). AH of the unreacted methanol is taken overhead, sent to a methanol... 

In both cases, subsequent operations include simple distillation to separate the cuts rich in isobutene and in 2-butenes at the top and bottom respectively. A second hydro-isomerization on the fraction containing isobutene enhances the purity. This technique can also oe applied to residual CA cuts from arid extraction or etherification, in order to obtain an effluent rich in 2-butenes. 

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