Process for producing olefins from syngas

Abstract

The present disclosure relates to an improved process for producing olefins from syngas. Raw material is treated to produce syngas comprising H.sub.2, CO and CO.sub.2. The ratio of H.sub.2 and CO in the syngas is 1:1. The syngas is contacted with at least one first catalyst to produce an intermediate stream comprising dimethyl ether (DME), and unconverted CO.sub.2, H.sub.2 and CO. The unconverted H.sub.2 and CO is recycled to a first catalyst section and a portion of the separated CO.sub.2 is recycled for producing the syngas. The remaining intermediate stream is contacted with at least one second catalyst to produce a second stream comprising olefins, H.sub.2O, methane, ethane, and propane. H.sub.2O, methane, ethane, and propane are separated to obtain the olefins. The separated methane, ethane, and propane are further recycled for producing the syngas. The CAPEX and OPEX of the improved process are reduced.

Claims

1. A process for producing olefins from syngas, said process comprising the following steps: (a) treating raw material, at a temperature in a range of 300 C. to 1000 C. and at a pressure in a range of 1 kg/cm.sup.2 to 80 kg/cm.sup.2, to produce a first stream, containing syngas comprising H.sub.2, CO and CO.sub.2, wherein a volume ratio of H.sub.2 and CO in said syngas is 1:1, wherein said raw material is at least one selected from the group consisting of coal, petcoke, biomass, natural gas and liquid fuels; (b) contacting said syngas with at least one first catalyst, at a temperature in a range of 100 C. to 400 C. and at a pressure in a range of 1 kg/cm.sup.2 to 60 kg/cm.sup.2, to produce an intermediate stream comprising dimethyl ether (DME), unconverted CO.sub.2, H.sub.2, and CO, wherein said at least one first catalyst is selected from the group consisting of chromium oxide, zinc oxide and aluminium oxide, wherein said intermediate stream is devoid of methanol; (c) separating a portion of CO.sub.2, H.sub.2, and CO from said intermediate stream and recycling the separated portion of CO.sub.2 to step (a) for producing said syngas and recycling the separated portion of H.sub.2, and CO to step (b) for producing said DME; (d) contacting said intermediate stream with at least one second catalyst, at a temperature in a range of 200 C. to 600 C. and at a pressure in a range of 0.5 kg/cm.sup.2 to 10 kg/cm.sup.2, to produce a second stream comprising olefins, H.sub.2O, methane, ethane, and propane, wherein said at least one second catalyst is ZSM-5; (e) separating H.sub.2O, methane, ethane and propane from said second stream to obtain said olefins; and (f) recycling the separated H.sub.2O, methane, ethane and propane to step (a) for producing said syngas.

2. The process as claimed in claim 1, wherein said olefins is at least one of ethylene and propylene.

3. The process as claimed in claim 1, wherein the separated portion of CO.sub.2 in step (c) and the separated H.sub.2O in step (e) are recycled to step (a), for producing said syngas by reforming at least one of: natural gas; and one of the separated methane, ethane, and propane, with CO.sub.2.

Description

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING

(1) A process for producing olefins from a gaseous mixture will now be described with the help of the accompanying drawing, in which:

(2) FIG. 1 depicts a flow-path, illustrating a conventional process for producing olefins; and

(3) FIG. 2 depicts a flow-path for producing olefins in accordance with the present disclosure.

(4) Table 1 provides a list the elements of the process of the present disclosure and their respective reference letters:

(5) TABLE-US-00001 TABLE 1 Elements Reference letters Raw material (a) Gasifier/reformer (R) First stream (Syngas) (b) DME (dimethyl ether) reactor (D) Intermediate stream (c) Separator (s) Separated portion (g) Separated CO.sub.2 (h) Separated H.sub.2 and CO (i) Reactor (O) Second stream (d) Fractionation column or divided wall (Dw) column Olefins (e) Separated stream (f)

DETAILED DESCRIPTION

(6) 2:1 ratio of H.sub.2 and CO in syngas leads to generation of an excess amount of CO.sub.2, and an excess use of H.sub.2O. Moreover, for economic viability of the methanol production process, CO.sub.2 should be minimum or nil in the feed. Therefore, it is necessary to completely separate or remove CO.sub.2. Separation of CO.sub.2 requires bigger separation units, which consume a significant amount of energy, and H.sub.2O passes through all the equipment due to which the size of the equipment increases, thereby increasing the CAPEX and OPEX of the entire process.

(7) The present disclosure, therefore, provides an improved process for producing olefins with reduced generation of CO.sub.2 and with reduced CAPEX and OPEX of the entire process.

(8) The process for producing olefins is illustrated with reference to FIG. 2. Raw material (a) is treated in a gasifier/reformer (R), typically at a temperature in the range of 300 C. to 1000 C. and at a pressure in the range of 1 kg/cm.sup.2 to 80 kg/cm.sup.2, to produce a first stream (b), i.e., syngas comprising H.sub.2, CO and CO.sub.2, wherein the ratio of H.sub.2 and CO in the syngas is 1:1.

(9) The raw material (a) can be at least one of coal, petcoke, biomass, natural gas or liquid fuels.

(10) In the process of the present disclosure, the amount of CO.sub.2 produced during the production of syngas is significantly less. Additionally, the one-step dimethyl ether (DME) process of the present disclosure can handle a significant amount of CO.sub.2 in the feed, as compared to the conventional methanol process. Therefore, separation of CO.sub.2 from syngas (b) in a separate process equipment is obviated at this stage.

(11) The first stream, i.e., syngas, (b) is directly introduced into a DME reactor (D), wherein syngas (b) is contacted with a first catalyst in the DME reactor (D), typically at a temperature in the range of 100 C. to 400 C. and at a pressure in the range of 1 kg/cm.sup.2 to 60 kg/cm.sup.2, to produce an intermediate stream (c) comprising dimethyl ether (DME) and unconverted CO.sub.2, H.sub.2 and CO. CO.sub.2, and the unconverted H.sub.2 and CO can be separated from the intermediate stream (c) with less energy requirement as CO.sub.2 concentration is relatively higher. Due to the reduced criticality of the process equipment used for separating CO.sub.2, a simpler separation process equipment can be used. The separated portion (g) is introduced into a separator (s) for separating CO.sub.2 (h), H.sub.2 and CO (i). The separated CO.sub.2 (h) can be recycled for producing syngas, and the separated H.sub.2 and CO (i) can be recycled to the DME reactor (D).

(12) The first catalyst includes, but is not limited to, copper oxide, chromium oxide, zinc oxide and aluminium oxide.

(13) One-step DME process requires H.sub.2:CO ratio of 1:1, which leads to smaller water-gas shift reaction and lower water consumption and CO.sub.2 generation. As the portion of CO.sub.2 in the syngas is lower, the one-step DME process can handle syngas without removing CO.sub.2.

(14) The intermediate stream (c) is introduced into a reactor (O) and contacted with a second catalyst in the reactor (O), typically at a temperature in the range of 200 C. to 600 C. and at a pressure in the range of 0.5 kg/cm.sup.2 to 10 kg/cm.sup.2, to produce a second stream (d) comprising olefins, H.sub.2O, unreacted DME, methane, ethane, and propane.

(15) The second catalyst includes, but is not limited to, molecular sieve catalysts.

(16) In accordance with one embodiment of the present disclosure, the second catalyst is at least one selected from the group consisting of salts, aluminophosphate (ALPO) molecular sieves, and silicoaluminophosphate (SAPO) molecular sieves, as well as substituted forms thereof.

(17) In accordance with another embodiment of the present disclosure, the second catalyst is ZSM-5.

(18) The second stream (d) is introduced into a fractionation column or a divided wall column (Dw) for separating H.sub.2O, unreacted DME, methane, ethane, and propane from the second stream (d) to obtain olefins (e) and a separated stream (f).

(19) The separated CO.sub.2, H.sub.2O, methane, ethane, and propane can be recycled into the reformer for producing syngas by at least one of dry reforming, bi-reforming, or tri-reforming, wherein syngas with higher H.sub.2 and CO is produced as compared to gasification.

(20) Dry reforming of natural gas is depicted herein below:
CH.sub.4+CO.sub.2=2CO+2H.sub.2

(21) Moreover, the amount of raw materials required for producing syngas (b) is reduced, since the separated methane, ethane and propane are utilized for producing syngas, which is significantly rich in H.sub.2. Also, the separated unreacted DME can be recycled into the DME reactor (D) for producing the intermediate stream (c).

(22) In accordance with one embodiment of the present disclosure, a portion of the separated CO.sub.2 is recycled into the reformer and a remaining portion of the separated CO.sub.2 is vented out to the atmosphere.

(23) Moreover, the amount of H.sub.2O generated in the reactor (O) can be approximately 50% less as compared to that generated conventionally during the production of olefins from syngas comprising 2:1 ratio of H.sub.2 and CO.

(24) In accordance with one embodiment of the present disclosure, the second stream (d) can be introduced into a de-methanation column (not shown in FIG. 2) for separating methane contained therein.

(25) As described herein above, syngas (b) comprising 1:1 ratio of H.sub.2 and CO is utilized for producing olefins (e). Due to 1:1 ratio of H.sub.2 and CO: the amount of raw materials required for producing syngas (b) is reduced, because the separated CO.sub.2, methane, ethane and propane are utilized for producing syngas which is significantly rich in H.sub.2; the amount of CO.sub.2 produced during the production of syngas (b) and water-gas shift reaction is significantly less, and one step DME process can accommodate CO.sub.2 in the feed, which leads to smaller and less severe CO.sub.2 separating process equipment post DME; the intermediate step of methanol production, of conventional processes, is obviated, thereby eliminating the use of a reactor for producing methanol; efficient separation of the streams by the use of a divided wall column leads to an even more reduction in energy need for separation and saving in the CAPEX of the entire process; and the amount of water being circulated from gasification to olefins is significantly reduced, which leads to reduced volume of many intermediate sections.

(26) Due to the above mentioned factors, the CAPEX is significantly reduced and the OPEX is reduced upto 30%, as compared to that of the conventional process.

(27) Technical Advances and Economical Significance

(28) The present disclosure described herein above has several technical advantages including, but not limited to, the realization of an improved process that: reduces generation of CO.sub.2 during the process for producing olefins; utilizes CO.sub.2 in olefins production; reduces energy needs for separating products; reduces energy needs for separating CO.sub.2; reduces circulation of H.sub.2O in the process with lower water-gas shift reaction; and reduces CAPEX and OPEX for producing olefins.

(29) The disclosure has been described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.

(30) The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein.

(31) The foregoing description of the specific embodiments so fully revealed the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.