Process and Apparatus for Coupling Separation and Purification of Ethyl Tert-Butyl Ether (East China University Of Science And Technology)

CATEGORY: ETBE - ETHYL TERT-BUTYL ETHER
PATENT
Process and Apparatus for Coupling Separation and Purification of Ethyl Tert-Butyl Ether (East China University Of Science And Technology)
United States Patent Application 20120289750
Inventors:
Zhang, Wuping (Shanghai, CN)
Zhou, Shanhua (Shanghai, CN)
Zhang, Wenli (Shanghai, CN)
Tian, Hengshui (Shanghai, CN)
Zhang, Hanlu (Shanghai, CN)
Zhu, Fugeng (Shanghai, CN)
Gu, Jingjun (Shanghai, CN)
Application Number:
13/515497
Publication Date:
11/15/2012
Assignee:
East China University Of Science And Technology (Shanghai, CN)
Abstract:
A process and device of coupling separation and purification to produce ethyl tert-butyl ether (ETBE) is provided, wherein ethanol containing 1 wt % to 15 wt % of water, and a mixture containing ETBE and ethanol are fed into the distillation-extraction coupling zone for separation and purification. Said distillation-extraction coupling zone is composed of a distillation column and an extraction column. Said process and device can achieve the cogeneration of ETBE and ethanol, and possesses high commercial values.
FIELD OF THE INVENTION
The present invention relates to a process and device to produce ethyl tert-butyl ether (ETBE), more particularly to a process and device of purification to produce ETBE. The purification process to produce ETBE is carried out by coupling separation.
BACKGROUND OF THE INVENTION
The growth of biofuel of using ethanol (EtOH) and the like produced by fermentation as the base has attracted more and more attention in many countries.
However, one of the key issues that constrains the energy consumption and cost to produce fuel alcohol which is currently the most important bio-based alcohol ether fuel is that, if it is intended to reduce approximately 5 wt % of azeotropic water to below 1 wt %, special separation methods have to be adopted such as azeotropic distillation, extractive distillation, adsorption and pervaporation membrane separation. Meanwhile, a small amount of denaturants (e.g. fusel alcohol, ethers, etc.) enhancing cosolubilization or solubilization has to be added to offset to some extent the disadvantage of phase separation that alcogas is likely to occur. In spite of the above fact, the price of ethanol fuel is relatively lower than gasoline because of its own inadequate capacities, and in some countries, such as China, its production cost is even higher than gasoline, in other words, the value (i.e. functions/costs) of ethanol fuel is on the low side; therefore it is necessary to find a solution.
It is already known that ETBE can be used as gasoline additive.
Generally, ETBE, used as a gasoline additive, is produced by means of etherification of isobutene contained in the fraction of ethanol and mixed C4-hydrocarbons (e.g. from steam cracking or catalytic cracking) (see U.S. Pat. No. 5,248,836A, CN 1990443A, CN1772848A and CN101195560A). It is easy to make ETBE, but many problems need to be solved when ETBE has to be separated and purified before being used as the gasoline additive.
In order to improve product functions and convenience of use, especially when ETBE can be directly added to the gasoline during blending without having to change the existing transport and distribution system, it is essential to control the ethanol content during the preparation of ETBE, when necessary, the ethanol content can be controlled below 1 wt %.
Until now, with respect to the process of separation and purification to produce ETBE, in some processes, the ethanol content entering into the debutanizer is strictly controlled, including the process to control ethanol to olefine ratio below a certain stoichiometric ratio and to conduct pretreatment (such as removing part of ethanol with water and adding a certain amount of hydrocarbons) before ethanol enters into the debutanizer (see U.S. Pat. No. 7,141,705A, U.S. Pat. No. 5,447,607A and U.S. Pat. No. 5,536,886A). In such a way, the rest of ethanol can almost completely be removed with relevant hydrocarbons from the top of the debutanizer by azeotropy. But it will become difficult to further increase the conversion of isoolefine under some circumstances, including reactive distillation which is often desired to practise; therefore it may be required to add a certain amount of ethanol at the top of the debutanizer. Consequently, it may be difficult or restricted to increase the conversion of isoolefine when the ethanol content entering into the debutanizer is strictly controlled.
On the contrary, it is difficult to control the unreacted ethanol content entering into the debutanizer if it is intended to increase the conversion of isoolefine. There are two main categories of process according to different locations of the debutanizer to take off materials:
One is that the material is taken off the bottom of the debutanizer followed by further separation (see U.S. Pat. No. 5,158,652A, U.S. Pat. No. 5,250,156A, U.S. Pat. No. 5,348,624A and U.S. Pat. No. 5,569,787A); and
The other one is that the material is taken off at the side of the debutanizer followed by further separation (see CN1127243A and U.S. Pat. No. 5,607,557A).
Though each process above-mentioned has its merits, they share the common deficiency: strict requirements on the content of some components entering into the debutanizer are posed, for example, the water content of the material stream entering into the debutanizer is required to be 1 wt % maximal, the tert-butyl alcohol content is at the most 1 wt % (see CN1127243A and U.S. Pat. No. 5,607,557A), and/or special separation methods have to be taken such as adsorptive separation, pervaporation membrane separation and azeotropic separation. Accordingly, the commercial value of the process of separation and purification to produce ETBE is decreased due to the strict operating conditions and/or the separation methods with higher energy consumption.
SUMMARY OF THE INVENTION
In view of the above-described problems, it is one intention of the present invention to provide a process and device of purification to produce ETBE with commercial value (i.e. functions/costs). The purification process to produce ETBE is carried out by coupling separation. Said ETBE comes from a mixture of ETBE and ethanol, specifically, it is from the mixture of ETBE and ethanol obtained through the reaction of ethanol and mixed C4-hydrocarbons (e.g. from steam cracking or catalytic cracking) containing isobutylene. The ETBE obtained by means of purification may contain no more than 1 wt % of ethanol. In other words, the obtained ETBE products have high functions as a gasoline additive.
Another objective of the invention is to provide a process and device of purification to produce ETBE with commercial value (i.e. functions/costs), using ethanol containing at least higher than 1 wt % up to 15 wt % of water, as the feedstock. Said purification process to produce ETBE is carried out by coupling separation. Said ethanol obtained by means of purification to produce ETBE may contain no more than 1 wt % of water, or even no more than 0.5 wt % of water. It can be used as the feed for etherification and/or used as a gasoline additive as required. In other words, the obtained ethyl tert-alkyl ether (ETAE) products can have high functions when they are used as gasoline additives, and meanwhile the costs are significantly reduced and the co-produced ethanol almost contains no azeotropic water.
Said ETBE is obtained by separation and purification of a mixture mainly containing ETBE and ethanol, specifically, it is obtained by separation and purification of a mixture mainly containing ETBE and ethanol obtained through etherification of ethanol and mixed C4-hydrocarbons (e.g. originated from steam cracking or catalytic cracking) containing isobutylene, referring to U.S. Pat. No. 5,248,836A, CN 1990443A, CN1772848A and CN101195560A for detailed information. Generally, the mixture mainly containing ETBE and ethanol obtained at the bottom or side of the debutanizer behind the reaction zone contains 5%-50 wt % of ethanol or more commonly 10%-40 wt % of ethanol, including the circumstance using the total weight of ETBE and ethanol obtained from the side of the debutanizer as the reference (see CN1127243A and U.S. Pat. No. 5,607,557A for details). Apart from that, the mixture mainly containing ETBE and ethanol may further contains a small amount of other substances such as tertiary butyl alcohol (TBA), diisobutylene, ethyl sec-butyl ether (E2BE), diethyl ether and C5-hydrocarbons, during the separation and purification of ETBE and ethanol, those substances can be seen identical with ETBE without subdivision (except that tertiary butyl alcohol is left in the ethanol after separation and purification since they have the similar boiling point).
The process of purification to produce ETBE mainly includes the following steps: feeding the mixture (obtained at the bottom or side of the debutanizer behind the reaction zone used to produce ETBE) mainly containing ETBE and ethanol as well as the ethanol containing higher than 1 wt % up to 15 wt % of water into a distillation-extraction coupling zone for coupling separation and purification, wherein the distillation-extraction coupling zone is composed of a distillation column and an extraction column. As a result, not only the in spec ETBE products can be obtained from the top of the extraction column but the ethanol almost having no azeotropic water can also be co-produced at the bottom of the distillation column.
The technical solution of the present invention is as follows:
A process of coupling separation and purification to produce ETBE comprises the following steps:
Introduce the ethanol containing higher than 1 wt % up to 15 wt % of water, preferably, the supplementary ethanol containing higher than 1 wt % up to 15 wt % of water and/or the recovered ethanol or the mixture thereof as well as the mixture mainly containing ETBE and ethanol into a distillation-extraction coupling zone, wherein the distillation-extraction coupling zone is composed of a distillation column and an extraction column.
In said distillation-extraction coupling zone, the fraction containing ethanol is collected at the bottom of the distillation column, the material collected at the top of the distillation column is fed into the extraction column and extracted by water as the extraction agent, the extract liquor containing ethanol is collected at the bottom of the extraction column and reused (e.g. reintroduced into the distillation-extraction coupling zone) after the ethanol is recovered, while the extraction raffinate containing ETBE is collected at the top of the extraction column.
A preferred technical solution of the present invention, wherein said ETBE comes from the mixture (obtained at the bottom or side of the debutanizer behind the reaction zone used to produce ETBE) mainly containing ETBE and ethanol, comprises the following steps:
Introduce the supplementary ethanol containing higher than 1 wt % up to 15 wt % of water, preferably, the supplementary ethanol containing 1.5%-45 wt % of water, more preferably, the supplementary ethanol containing 2%-10 wt % of water, most preferably, the supplementary ethanol containing 3%-10 wt % of water and/or the recovered ethanol or the mixture thereof as well as the mixture mainly containing ETBE and ethanol into a distillation-extraction coupling zone, wherein the distillation-extraction coupling zone is composed of a distillation column and an extraction column.
In said distillation-extraction coupling zone, the fraction containing ethanol is collected at the bottom of the distillation column, the material collected at the top of the distillation column is fed into the extraction column and extracted by water as the extraction agent, the extract liquor containing ethanol is collected at the bottom of the extraction column and reused (e.g. reintroduced into the distillation-extraction coupling zone) after the ethanol is recovered, while the extraction raffinate containing ETBE is collected at the top of the extraction column.
The technical solution of the device provided by the invention is as follows:
A device of coupling separation and purification to produce ETBE comprises a distillation column C1 and an extraction column C2.
The distillation column C1 is disposed with a connecting pipeline 3 to introduce distillation feed. The bottom of the distillation column is disposed with a heater E3 and a pipeline 4 to collect the fraction containing ethanol. The top of the distillation column is disposed with a condenser E2 and a condensate tank B1 to collect fractions containing ETBE, ethanol and water. The top of the distillation column is also disposed with a pipeline 5 to feed the material obtained from the top of the distillation column C1 to the extraction column C2. It further comprises a pipeline 6 used to feed extraction agent into the extraction column C2, a pipeline 7 used to collect the extract liquor containing ethanol at the bottom of the extraction column C2 and a pipeline 8 used to collect the extraction raffinate containing ETBE at the top of the extraction column C2.
In accordance with the process and device of purification to produce ETBE of the invention, the purification process to produce ETBE is carried out by coupling separation. The ETBE obtained by means of purification may contain no more than 1 wt % of ethanol and the obtained ethanol may contain no more than 1 wt % of water. According to the process and device provided by the invention, no strict restriction, such as ethanol content and/or water content and/tertiary alcohols content is posed to the mixture (obtained at the bottom or side of the debutanizer behind the reaction zone) mainly containing ETBE and ethanol. The renewable ethanol containing at least higher than 1 wt % up to 15 wt % of water and the mixture to be separated mainly containing ETBE and ethanol that are hard to be directly separated can be coupled together for coupling separation in the distillation-extraction coupling zone to achieve multiple coupling such as coupling co-production of ETBE and ethanol products. Meanwhile, ethanol feed can be provided for etherification and/or ethanol products can be provided as gasoline additive as required. The ethanol/olefine ratio can be appropriately increased or loosen for the etherification so as to increase the conversion of isobutene and/or the selectivity of etherification within a certain range. Therefore, the commercial value (i.e. functions/costs) of the invention is very high.
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