Removal of C3 lights from LPG feedstock to butane isomerization unit
Systems and methods for processing a C 3 and C 4 hydrocarbon mixture have been disclosed. The C 3 and C 4 hydrocarbon mixture is first processed in an isomerization unit to isomerize n-butane to form isobutane. The resulting effluent stream from the isomerization unit comprising primarily isobutane and C 3 hydrocarbons, collectively, is flowed into a separation unit configured to separate the effluent stream to form a C 3 stream comprising C 1 to C 3 hydrocarbons and a C 4 stream comprising primarily isobutane. The isobutane in the C 4 stream is further dehydrogenated to form isobutene, which is further flowed into an MTBE synthesis unit as a feedstock for producing MTBE.
1 . A method of processing a hydrocarbon mixture, the method comprising:
processing a first hydrocarbon mixture comprising propane, n-butane, and isobutane in an isomerization unit at a temperature of 125 to 175° C. to isomerize the n-butane to produce isobutane;
separating a mixture from the isomerization unit by a de-isobutanizer to produce and form an isomerization unit effluent comprising propane, isobutane, or combinations thereof and an unreacted n-butane stream;
separating a second hydrocarbon mixture comprising propane, n-butane, and isobutane in a second separation unit to produce an overhead stream comprising primarily propane and isobutane, collectively, and a first C4 stream comprising n-butane;
cracking the first C4 stream and/or the unreacted n-butane stream in a first steam cracking unit to produce propylene, ethylene, and benzene;
combining the overhead stream and the isomerization unit effluent to form a combined stream;
separating the combined stream to form a C3 stream comprising primarily propane and a second C4 stream comprising isobutane;
dehydrogenating the isobutane of the second C4 stream in a dehydrogenation unit to produce isobutene in a dehydrogenation unit effluent; and
reacting, in an etherification unit, the isobutene of the dehydrogenation unit effluent with an alkanol in the presence of a catalyst to produce an alkyl tert-butyl ether in a product stream.
2 . The method of claim 1 , further comprising: steam-cracking the C3 stream in a first second steam cracking unit.
3 . The method of claim 2 , wherein the steam cracking of the second C3 stream is performed at a temperature of 750 to 900° C. and a steam cracker residence time of 0.1 to 0.5 s.
4 . The method of claim 1 , wherein the isomerization unit comprises an isomerization catalyst comprising Pt/AlCl 3 /Al 2 O 3 , Pt/AlCl 3 /zeolite, Pt/SO 4 2− —ZrO 2 , SO 4 2− /ZrO 2 —Al 2 O 3 , or combinations thereof.
5 . The method of claim 1 , wherein the reaction conditions in the isomerization unit include an isomerization pressure of 20 to 30 bar.
6 . The method of claim 1 , wherein the isomerization unit effluent comprises 95 to 99.5 wt. % isobutane.
7 . The method of claim 1 , wherein the dehydrogenation unit effluent comprises 35 to 65 wt. % isobutene.
8 . The method of claim 1 , wherein the first hydrocarbon mixture and/or the second hydrocarbon mixture comprises liquefied petroleum gas.
9 . The method of claim 1 , wherein the first hydrocarbon mixture comprises 60 to 80 wt. % n-butane and 20 to 30 wt. % isobutane.
10 . The method of claim 1 , wherein the etherification unit further produces a recycle stream comprising isobutane.
11 . The method of claim 10 , further comprising: flowing the recycle stream into the dehydrogenation unit.
12 . The method of claim 1 , wherein the dehydrogenation unit comprises a dehydrogenation catalyst comprising chromia/alumina, Pt/alumina, or combinations thereof.
13 . The method of claim 1 , wherein the alkanol comprises methanol, ethanol, or combinations thereof.
14 . The method of claim 13 , wherein the alkyl tert-butyl ether comprises MTBE, ETBE, or combinations thereof.
15 . The method of claim 5 , wherein the dehydrogenation unit comprises a dehydrogenation catalyst comprising chromia/alumina, Pt/alumina, or combinations thereof.
16 . The method of claim 4 , wherein the dehydrogenation unit comprises a dehydrogenation catalyst comprising chromia/alumina, Pt/alumina, or combinations thereof.
17 . The method of claim 1 , wherein the dehydrogenation unit comprises a dehydrogenation catalyst comprising chromia/alumina, Pt/alumina, or combinations thereof.