Study On New Type Of Low Temperature Hydrodesulfurization Catalyst For The Claus Tail Gas

Claus process has been widely used in recovery of sulfur from industrial off-gas (such as off-gas of oil refineries , depurating of natural gas and coking). Claus reaction is restricted by the thermodynamics and operating conditions, no more than 97% of the sulfur can be recovered generally, therefore,Claus tail gas requires being treated before emission.. One of the Claus tail gas treating methods is hydrogenation of sulfur dioxide to hydrogen sulfide, then H₂S generated from SO₂ hydrogenation is recycled to the Claus system. At present, CoMo/γ-Al₂O₃ catalysts are used in industry for the hydrogenation of sulfur dioxide to hydrogen sulfide. However these catalysts are costly and used at higher temperature(260～320℃). Therefore,the interest is focused on studying and improving new catalysts for hydrogenation of Claus tail gas recently.Firstly, usingγ-Al₂O₃ as support, the activity of some familiar transition-metal elements and their loading amounts for hydrogenation of Claus tail gas to H₂S were studied in the present work. Difference of the activities among these catalysts were explained via H2-TG and XRD as well. And then the metal phase of catalysts before presulfuring, before and after catalytic reaction were investigated respectively. At last, Influence of Ni/Al ratio and calcining heat on the form of existence of NiO also studied.The following conclusion was obtained through aboving experiments:(1) a series supported transition metal sulfides can be divided into four groups according to the activity: Ni,Co,Fe＞Mo,W,Cu＞Cr＞Zn, Mn.(2) Over the Ni-based catalyst prepared by impregenation method,under the condition that the concentration of SO₂/=0.5vol.%, the gas hourly space velocity per g(WHSV)= 6000ml·h^-1.g^-1, the lowest temperature that SO₂ was completely conversed was 260℃. The activity is higher than industrial CoMo/γ-Al₂O₃catalyst. And presulfuring under the 10%H₂S+N₂ atmosphere at 400℃is propitious to enhance the activity.(3) The active phase in Ni based catalyst changed as the reaction temperature and atmosphere varied. The active phase was mixture of NiS₂ and NiS when reaction occurred above 240℃. As the temperature declined, NiS transformed into NiS₂, at 240℃, only NiS₂ could be detected via XRD.(4) In A-NiO-Al₂O₃ catalysts, Ni species dispersed better, hence, the catalytic activity was higher, the lowest temperature that SO₂ was completely conversed was 220℃.(5) Adding 30vol.%H₂O to the reactor, the activity of Ni based catalyst decreased at some degree. But, the activity could be recovery when stopped providing H₂O; The catalytic activity remained constant within150h.