TITLE:
Process for the Utilization of Spent High Temperature Shift (HTS) Conversion Catalyst as Raw Material for the Preparation of Fresh High Temperature Shift Conversion Catalyst.
FIELD OF INVENTION:
This invention relates to a process for preparing Fresh High Temperature Shift (HTS) conversion catalyst from Spent High Temperature Shift conversion catalyst.
BACKGROUND OF THE INVENTION:
India is the second largest producer of Nitrogenous Fertilizer vis-a-vis Ammonia in the world, for which large quantities of different catalyst including High Temperature Shift (HTS) conversion catalyst is used and simultaneously huge quantities of HTS catalyst are discharged every year. In HTS catalyst, presence of chromium compound is problematic. The metal itself is costly and at the same time toxic and carcinogenic. Because of this, disposal of discharged catalyst termed as spent catalyst through SLF (Secured Land Fill) arrangement is not acceptable as the same is bound to pose acute environmental problem.

Considering the above mentioned facts, the background of the invention was to address the problem of disposal of spent catalyst by developing eco-friendyy and economically viable process for spent catalyst utilization.
OBJECTS OF THE INVENTION:
An object of this invention is to propose a process for preparing fresh high temperature shift conversion catalyst.
Another object of this invention is to propose a process for preparing fresh high temperature shift conversion catalyst from raw material which is spent high temperature shift conversion catalyst.
Further object of this invention is to propose a process for preparing fresh high temperature shift conversion catalyst from environmentally hazardous spent HTS catalyst by using a very simple method.
Still another object of this invention is to propose a process for preparing fresh high temperature shift conversion catalyst by an eco-friendly process to avoid environmental hazards.

BRIEF DESCRIPTION OF THE INVENTION:
According to this invention, a process is provided for preparing fresh high temperature shift conversion catalyst from spent high temperature shift comprising roasting the spent catalyst,
subjecting the roasted spent catalyst to the step of powdering,
dissolving the powdered spent catalyst in mineral acid,
filtering the unreacted residue,
reducing the mixed salt solution,
subjecting the mixed salt solution to the step of decantation to use in the process for
preparation of fresh HTS catalyst.
DETAILED DESCRIPTION OF THE INVENTION:
This invention relates to the development of a process to utilize 'Spen'' High Temperature Shift (HTS) catalyst as 'Raw Materia'' for the preparation of'Fresh' High Temperature Shift (HTS) Conversion Catalyst.
Before entering in details into this invention, it is worthwhile to clarify.
A. Scope and use of High Temperature Shift Catalyst.
B. The terms (a) Spent Catalyst and (b) Raw Materials

High Temperature Shift (HTS) conversion Catalyst is used in all ammonia plants,
irrespective of the 'Feed Stock' and the change of process involved producing hydrogen
by the reaction
(i) CO + H20 «-» C02 + H2 AH°298= 41.1 kJ mol"1
in presence of HTS Catalyst between the temperature range 330 °C and 500 °C. Since the
reaction (i) is highly exothermc,, the maximum operating temperature of catalyst in
converter vary from 400°C - 500°C, even goes upto 550°C depending upon the
concentration of % CO present in the feed gas though inlet to the converter feed
temperature is maintained between 330°C and 370°C. Irrespective of the brand and make
the major constituenss of HTS Catalyst are 80-90% iron oxide and 7 - 13% chromium
oxide, besides some additives as promoter which may vary from brand to brand.
Normal expected life of HTS Catalyst is 3-8 years or more depending upon the process conditions of which the catalyst operates. Calculated results from actual operating data from large capactty ammonia plants 1500 (MTPD) reveal that an increase of 0.1% CO slip from shift converter incurs a produciion loss of approximately 15-17 (MTPD) ammonia.
Therefore, in order to optimize the economics of production, it becomes necessary after a certain period of time, to discharge the catalyst before the activity of the catalyst is totally exhausted. This Discharged Catalyst is termed as Spent Catalyst.

Raw materials
As mentioned earlier, High Temperature Shift (HTS) Catalyst is basically iron oxide-chromium oxide catalyst which contains around 80-90% iron oxide, 7-13% chromium oxide and the rest are promoters. For iron oxide, basic starting material termed 'Raw materia'' is iron salts which may be sulphates, nitrates or any other compound of iron which may vary from brand to brand, process of incorporaiion of chromium oxide / promoters to iron oxide system is specific for the brand of catalyst.
Spent HTS Catalyst contains both iron oxide and chromium oxide. In spent HTS catalyst; the presence of chromium oxide is problematic. The metal itself is costly and at the same time very toxic and carcinogenic. Because of this, disposal of spent HTS catalyst through SLF (Secured Land Fill) is not acceptable as the same is bound to pose acute environmental problem.
Considering the above mentioned facts, PDIL has developed a process to address the problem of disposal of spent HTS catalys,, using the spent HTS catalyst as source of 'Raw materia'' for iron oxide, chromium oxide required for the produciion of fresh HTS catalyst. PDIL did not try methods involving direct extraction of costly metals. PDIL developed a process for leaching / extracting out the metal componenss in solution phase.

The undesirable elements present in the leached solution were removed to get desired metal salt solution in pure form. The solution in pure form was used directly in the PDIL existing process of manufacturing HTS catalyst.
The developcd process to utilizc Spent HTS Catalyst as Raw Material for the Preparation of Fresh HTS Catalyst has the following stages.
i) Roasting of spent catalyst.
ii) Powdering of roasted spent catalyst in ball mill.
iii) Dissoluiion powdered spent catalyst in mineral acid.
iv) Separation of waste residue.
v) Reduction of Fe+3 - FV2
vi) Filtration of any unreacted residue from mixed salt solution so as to get pure
mixed salt solution to be recycled back into loop of catalyst manufacture.
Roasting of spent catalyst (step-))
This step is required, since the catalyst users discharge spent catalyst from the reactors in plants, by using watcr jet to minimize time loss, required for oxidation and cooling down of bed. Roasting temperature 200-250°C and time 4 hrs. is to be maintained to get moisture content less than 1.0% in the processed spent catalyst.

Ball milling (powdering) of roasted spent catalyst (step-2)
This is required for powdering spent catalyst to desired mesh size. Powdering to specific mesh size is required for gctting maximum recovery of mctal as its salt solution in the next stage. Normally, catalyst powdered to -150 + 200 mesh size (BS) is sufficient for smooth processing of spent catalyst in the next stage. Ball milling time varies from 4-8 hrs. to get spentcatalyst powder of required mesh size.
Dissolution of powdered spent oxide in mineral acid (step-3)
Powdered spent catalyst of required mesh size is to be dissolved in mineral acid at high temperature with continuous stirring.
(i) Acid strength varies
Acid: Water ratio =1:4 to 1:8 (ii) Agitation temperature = 50 - 80°C (iii) Agitation time = 4-8hrs.
Filtration of unrcacted residue (step - 4)
Mixed salt solution thus prepared filtered, residue treated as waste and the filtrate collected in tank for reduction of oxidized metal salt solution to thc lower valence state.

Reduciion of mixed salt solution (step-5)
Reduction of oxidized mixed salt solution is effected by addition of iron turnings to the solution. The excess acid present will be sufficient to maintain the reducing condition. Reduction is done at room temperature and is completed within 12 hrs. time. Unreacted scrap iron will remain settle at the bottom.
Decantation and transfer the mixed salt solution (step-6)
Solution from the step - 5 is directly transferred to the raw material solution storage tank for the preparation of fresh HTS catalyst. The solution thus obtained has the following composition:
i) Sp gravity 1.10-1.30
ii) pH 1.0-3.0
iii) %Fe+3 0-8.0%
iv) Cr* 2.0-8.0%
v) Of2 ~1.0%
HTS catalyst prepared using above solution as raw material and subsequent addition of different other components in different stages of preparatinn has the following characteristics similar to that of standard HTS catalysss as shown in Figure I.

i) Chemical compostiion (% by wt. on dry basis)
Fe20) - 80-90
Cr203 - 7-13
LOI - <8
ii) Surface Area >90m2/g
iii) Total prove volume (tpv) : . = 0.20-0.28 cc/g
iv) CO conversion activity : 0-5 °C away from equilibrium under normal
operation conditions.
Benefits derived from the R&D work
1. Utilization of spent HTS catalyst as alternate raw material for the preparation of fresh HTS catalyst.
2. Disposal of spent HTS catalyst by eco-friendly process to avoid environmental hazards.

WE CLAIM:
1. A process for preparing fresh high temperature shift conversion catalyst from
spent high temperature shift comprising roasting the spent catalys,,
subjecting the roasted spent catalyst to the step of powderin,,
dissolving the powdered spent catalyst in mineral acid,
filtering the unreacted residue,
reducing the mixed salt solution,
subjeciing the mixed salt solution to the step of decantation to use in the process
for preparation of fresh HTS catalyst.
2. The process as claimed in claim I, wherein the said step of roasting is performed at a temperature between 200-250°C for 4 hrs.
3. The process as claimed in claim I, wherein the said roasted spent catalyst is powdered to -150 + 200 mesh size and time period varies from 4 to 8 hrs.

4. The process as claimed in claim I, wherein the powdered spent catalyst is dissolved in mineral acid at high temperature with continuoss stirring and the acid:waterratiois1:4to1:8.
5. The process as claimed in claim I, wherein the step of reduction is done at room temperature and is completed in 12 hrs time.

6. The process as claimed in claim I, wherein the solution obtained after decantation
has the following composition:
Fe+3 : 0-8.0%
Cr+3 : 2.0-8.0%
Cu'2 : ~1.0%
7. The process as claimed in claim I, wherein the said HTS catalyst has the
following composition:
Fe203: 80-90%
CrA : 7-13%
LOI : <8%