FIELD

This invention relates to a reforming catalyst that is tolerant of low levels of sulfur contamination in a feed for processing, and corresponding systems and methods for reforming in the presence of the reforming catalyst.

BACKGROUND

Increasing amounts of available petroleum feedstocks correspond to natural gas sources or other methane-containing sources. The increased availability of methane and/or small hydrocarbon petroleum sources can potentially have increased value if efficient methods can be identified for conversion to larger compounds.

One option for converting methane (and other small hydrocarbons) to other compounds is to reform the methane to form H2and/or CO (i.e., synthesis gas). Both steam reforming and dry reforming are known, but each type of reforming poses a variety of challenges. Some of the challenges can be related to the low tolerance of conventional reforming catalysts for sulfur contamination. For conventional reforming catalysts, even part-per-million amounts of sulfur in a reforming feed can quickly result in deactivation of the reforming activity of a reforming catalyst. Unfortunately, for many applications, performing sufficient sulfur removal on a feed to reduce the sulfur content to 0.1 vppm or less can be cost prohibitive. In order to overcome this deficiency, reforming catalysts that can avoid deactivation in the presence of part-per-million amounts of sulfur and/or that can be effectively regenerated after exposure to part-per-million amounts of sulfur are desirable.

In some environments, such as automotive engine environments, reforming of small hydrocarbons can also be beneficial for modifying the combustion properties of a fuel. Traditional engine fuels are typically processed for sulfur removal, but current specifications typically specify sulfur contents of up to 10 wppm for liquid fuels, such as gasoline or diesel, or sulfur contents up to 15 vppm for gaseous fuels, such as natural gas. As a result, conventional fuels can quickly poison a reforming catalyst, leading to loss of reforming activity. Thus, a reforming catalyst that can be effectively regenerated in an engine environment after exposure to part-per-million amounts of sulfur is also desirable for on-board reforming.

U.S. Pat. Nos. 7,901,565 and 7,901,566 describe sulfur-tolerant reforming catalysts that do not include alumina and/or that do not include bulk, unreacted, or free alumina. The sulfur-tolerant catalysts are described as being non-sulfating.

U.S. Patent Application Publications 2015/0166913 and 2017/0051708 describe vehicle powertrains that include on-board catalytic reforming. Various metal oxides, zeolitic materials, and mixtures thereof are described as potential support materials for a reforming catalyst. A specific mixture of metal oxides that is described as a catalyst support material is a mixture of aluminum oxide, lanthanum oxide, cerium oxide, and zirconium oxide.

U.S. Pat. No. 7,815,873 describes methods for reforming of a hydrocarbon fuel in a reverse flow reactor configuration. The reactor is described as being suitable for performing pressure swing reforming, such as a pressure swing reforming process as described in U.S. Pat. No. 7,491,250.

SUMMARY

In various aspects, a method for reforming a hydrocarbon-containing stream is provided. The method includes exposing a hydrocarbon-containing stream comprising 0.1 vppm of more of sulfur to a catalyst in the presence of at least one of H2O and CO2under reforming conditions to form a reformed product comprising H2. The catalyst can include 0.1 wt % to 10.0 wt % of a Group VIII metal, such as Rh, Pt, Pd, or a combination thereof, on a sulfur-tolerant support comprising bulk alumina. The catalyst is then exposed to a stream comprising 0.1 vol % or more of O2at a regeneration temperature for a regeneration time period. Optionally, the exposure of the catalyst to the stream containing O2under the regeneration conditions can be performed periodically. The molar ratio of O2delivered during the regeneration time period to sulfur exposed to the catalyst during the prior reforming time period can be, for example, 20 or more.

In some aspects, the sulfur-tolerant support can include 1.0 wt % to 80 wt % alumina and/or can include alumina with octahedral coordination. Optionally, the sulfur-tolerant support can also include at least one of silica, titania, and zirconia. In some aspects, the Group VIII metal can correspond to Rh, Pd, Pt, or a combination thereof. Optionally, the catalyst can further include a Group 11 metal. In some aspects, the catalyst can correspond to a first catalytic metal and a second catalytic metal. In such aspects, the first catalytic metal can correspond to Rh, Ni, or a combination thereof, while the second catalytic metal can correspond to Pt, Pd, or a combination thereof. In such aspects, a weight ratio of the first catalytic metal to the second catalytic metal can be 0.1 to 10.

In some aspects, the hydrocarbon-containing stream is exposed to the catalyst in a reverse flow reactor. In such aspects, the hydrocarbon-containing stream can include 5.0 wt % or more C2+hydrocarbons and/or 40 wt % or more methane. In other aspects, the hydrocarbon-containing stream can correspond to a fuel for a spark ignition engine. In such aspects, exposing the hydrocarbon-containing stream to the catalyst can further include exposing a recycle portion of an exhaust gas from combustion of at least a portion of the reformed product to the catalyst.

In various aspects, a reformer including a reforming catalyst as described above is also provided. Optionally, the reformer can correspond to a reformer in a reverse flow reforming reactor. Optionally, the reformer can correspond to an on-board reformer in fluid communication with a spark ignition engine. In such an aspect, the reformer can further include a reformer inlet in fluid communication with an engine exhaust and a reformer outlet in fluid communication with an engine fuel input.

