Metal passivation in a heat exchange reformer
A method for reducing the interaction between carbon monoxide present in a heat exchange medium and metals on the shell side of heat exchange reformer apparatus used for reforming of hydrocarbons by treatment of the shell-side of said apparatus with an effective amount of at least one passivation compound containing at least one element selected from phosphorus, tin, antimony, arsenic, lead, bismuth, copper, germanium, silver or gold is described. Where volatile compounds are formed by the passivation compound, the method further comprises compound recovery to prevent contamination and deactivation of subsequent process steps. The method reduces side reactions, provides improved reformer tube lifetime and allows tubes to be treated in-situ without the need for process shutdown.
1. A process for reforming of hydrocarbons comprising the steps;
(i) subjecting a gaseous mixture containing at least one hydrocarbon and steam to catalytic primary reforming at an elevated temperature in heat exchange reformer apparatus by passing said mixture through tubes containing a steam reforming catalyst to form a primary reformed gas, the exterior of said tubes being heated by a carbon-monoxide-containing heat exchange medium flowing through the shell side of said apparatus, and
(ii) adding to said heat exchange medium before it enters said shell side, after the reforming step, a passivation compound to reduce the interaction between the carbon monoxide present in said heat exchange medium and metals in the shell side of said heat exchange reformer apparatus, said passivation compound containing at least one atom selected from the group consisting of phosphorus, tin, antimony, arsenic, lead, bismuth, copper, germanium, silver, and gold.
2. A process according to claim 1 wherein the passivating compound contains at least one phosphorus atom.
3. A process according to claim 1 wherein at least one augmenting compound is added with said passivation compound, said augmenting compound containing at least one atom selected from the group consisting of aluminum, gallium, chromium, indium, and titanium.
4. A process according to claim 1 wherein the amount of phosphorus, tin, antimony, arsenic, lead, bismuth, copper, germanium, silver or gold present in the heat exchange medium is between 0.1 and 1000 ppm by volume.
5. A process according to claim 3 wherein the amount of aluminum, gallium, chromium, indium or titanium present in the heat exchange medium is between 1 and 100 ppm by volume.
6. A process according to claim 1 wherein the heat exchange medium is the primary reformed gas produced by the heat exchange reformer apparatus that has been subjected to a further processing step comprising a partial oxidation step and subsequently a secondary reforming step.
7. A process according to claim 6 wherein the passivation compound and any augmenting compound is added to the heat exchange medium after the secondary reforming step.
8. A process according to claim 1 wherein when the passivation compound and any augmenting compound form volatile species under the conditions present in the shell side of the heat exchange reactor that are capable of deactivating catalysts in subsequent process steps, means to recover the volatile species are provided downstream of the heat exchange reactor to prevent contamination of subsequent processes or poisoning of catalysts in any subsequent process steps.
9. A process according to claim 1 wherein the carbon-monoxide-containing heat exchange medium is a gas mixture.
10. A process according to claim 1 wherein the at least one hydrocarbon is selected from methane or natural gas.
11. A process according to claim 1 , wherein the primary reformed gas is subjected to further processing to generate the heat exchange medium.