Invented by Sam Weinberger, Justin Dwight Edwards, Julian Wolfenbarger, Srinivas R. Vuddagiri, Iraj Isaac Rahmim, CB&I Technology Inc
The CB&I Technology Inc invention works as follows
Processes for producing and separating Ethane and Ethylene are disclosed herein. An oxidative coupling (OCM), product gas consisting of ethane or ethylene, is used in some embodiments to introduce a separation unit with two separators. The separation unit separates the OCM product to produce a C2-rich, methane-rich, and nitrogen-rich effluent. Some embodiments of separation are possible with minimal or no refrigeration.Background for Process to separate hydrocarbon compounds
Technical Field
This disclosure generally refers to the selectively separating carbon compounds containing at minimum two carbon atoms from mixed gas streams provided by a chemical processing.
Description of Related Art
The modern petrochemical industry uses cracking and fractionation technology extensively to separate desired compounds from crude oil. Fractionation and cracking are very energy-intensive and produce large amounts of greenhouse gases. Refiners are under immense pressure to reduce losses and increase efficiency when producing products using existing feedstocks. They also need to find viable alternatives feedstocks that can provide affordable hydrocarbon intermediates or liquid fuels for downstream consumers.
Because of its availability and low cost, methane is an attractive feedstock for hydrocarbon intermediates or liquid fuels production. At current consumption rates, methane reserves worldwide are in the hundreds. New production stimulation technologies promise commercial viability for previously unattractive methane resources.
It is used in the production polyethylene plastics and polyvinyl chloride. The demand for ethylene and its derivatives is increasing with economic growth in both developed and developing countries. Due to the high price of crude oil and the many hydrocarbon byproducts produced in crude oil cracking, ethylene production is restricted to low volume production in high-volume commodity chemical plants. The production of ethylene from natural gas is a more affordable and abundant alternative to crude oil ethylene. Oligomerization can further convert ethylene to longer chain hydrocarbons like C6 or C8 that are useful for high-value specialty chemicals and polymer gasoline.
The conversion from methane to long chain hydrocarbons, especially alkenes like ethylene, creates a product gas that contains multiple byproducts, unreacted fuel gases, and inert component in addition to the ethylene. It is possible to economically and selectively produce methane-based alkenes and to separate them on a commercially feasible scale. This opens up a new avenue for the production of ethylene-based derivatives.
The present disclosure, as noted above, is directed at methods for generating C2 carbon compounds via OCM. These steps can be summarized as follows:
a) Combining a feedstock gas consisting of methane with an oxygen-containing gas comprising oxygen;
(b) Contacting the combined feedstock and oxygen containing gases with a catalyst, and providing an OCM product gaz consisting of ethane (C2);
(c) Compressing the OCM product gaz;
(d) Condensing at most a portion the OCM Product Gas to produce an OCM Product Gas Condensate consisting mostly of water.
(e), introducing OCM product gas condensate as a first separator.
(f), isentropically expanding, reducing the temperature a first part of the OCM product gaz;
(g) Introducing the first OCM product gaz to the first separator, and introducing the second OCM product gaz to a separate separator. The second separator operates at a lower temperature and pressure than the first separator.
(h) Removing a C2-rich effluent, and a methane/nitrogen-containing gas mixture from first separator;
(i) Inserting the methane/nitrogen-containing gas mixture to a second separator; and
(j) Removing a methane rich effluent and an nitrogen-rich effluent of the second separator.
In some embodiments of the disclosed techniques, the oxygen-containing gas is compressed oxygen with an oxygen content of approximately 21 mol% and a nitrogen contents of about 78. Mol %. The nitrogen content in the methane/nitrogen removed from the first separator could be at most 85 mol.%. Other embodiments allow the first and second separators to operate below ambient temperatures. In this case, adiabatic expansion may be used to cool at least some of the OCM products gas, methane gas, nitrogen gas or methane/nitrogen mixture. Other embodiments define the oxygen containing gaz as compressed oxygen with an oxygen content at least 90 mol% and a nitrogen concentration of no more than 10 mol%. The nitrogen in the methane/nitrogen removed from the first separator can be at most 85 mol%. Another embodiment may allow the first and second separators to operate below ambient temperatures. The compressed oxygen may be supplied by a cryogenic process, which may provide some cooling to achieve the below ambient temperature.
Methods for providing C2 carbon compounds through oxidative coupling (OCM), according to embodiments described herein, may also include the introduction of at least some of the methane rich effluent from the second separator of the feedstock gaz before combining the feedstock and oxygen containing gases. The C2-rich effluent can contain at least 90.0 mol% C2, while the methane-rich effluent could include at most 92.0 mol% methane and the nitrogen-rich effluent at most 85.0 mol% nitrogen.
In addition to the methods described herein, other methods of providing C2 carbon compounds via OCM may also include reducing the water content of the OCM product gases to less than 0.001 mole % and condensing at most a portion of the OCM products gas.
Click here to view the patent on Google Patents.