Maintaining concentration of catalyst and reducing emission of HFC-23

Prepared by: Mishra Santosh K

Yadav Balram D

Guide: Prof-A M Patel

Introduction

We choose this project because it offers many benefits in

expanding our knowledge and prepares us to deal with tough

challenge with fluorocarbons.

Working with this kind of project will allows us to interact

with new technologies and process to decompose or to decrease

the emissions of HFC-23 gas.

PROCESS FLOW DIAGRAM

HFC-23 emission points during HCFC-22 production

The major emission point for HFC-23 in the HCFC-22 production process is the condenser vent, where it is discharged to the atmosphere after separation from the HCFC-22.

Fugitive emissions from leaking compressors, valves and flanges

HFC-23 can also be emitted when it is removed with the aqueous phases from caustic and water scrubbers used in the process.

Some HFC-23 is removed with the HCFC-22 product

Causes of catalyst maintenance problem and higher emission of HFC-23 gas:-

Improper preparation of catalyst

Not maintaining proper addition of chloroform to maintain continuous reflux in stripper column to sent back halides vapour which vaporize during chlorination in reactor.

Flooding over trays of stripper due to high flow rate or due to high feed rate in reactor.

Reason for emission of R-23 gas:-

In general the higher catalyst concentration and higher pressure will increase the amount of HFC-23

Catalyst life is one of the most important factors affecting generation of HFC-23.

Actually accepted mechanism for the stepwise fluorination of chloroform is as follows: 

SbCl5 + HF ---------- SbCl4F + HCl (1)

CHCl3 + SbCl4F -------- SbCl5 + CHCl2F (2)

CHCl2F + SbCl4F ------- SbCl5 + CHClF2 (3)

CHClF2 + SbCl4F ------- SbCl5 +CHF3 (4)

Effect of catalyst on process and Emission of HFC-23 on product & Environment

If catalyst vapour carry over in further process it will first come into

contact with chiller and choked the tubes of chiller or scale up the

tubes.

further process will stop and simultaneously result into end of

catalyst life (deactivation of catalyst life).

So loss of raw materials and energy in large amount and emission of HFC-23 will increase that is among most stable of the fluorocarbons gas and decompose slowly in the atmosphere with atmospheric life time of 200yrs.

1Kg of HFC-23 released in atmosphere would have of same effect as 11700Kg of CO2 gas within next 100yrs

EXPECTED OUTCOMEMaintaining catalyst ratio and concentration :-

Proper catalyst ratio should be maintained during preparation of catalyst in the reactor. It should be under acceptable conditions.

And to maintain proper addition of chloroform for continuous reflux in stripper column to sent back antimony halide vapour to reactor

CATALYST PREPARATION The catalyst used in the preparation of Refrigerant HFC-22

(CHClF2) is a molten, complex mixture of antimony

pentachloride (SbCl5) and antimony trichloride (SbCl3).

This mixture is prepared by chlorination of antimony trichloride in Reactor itself.

Reaction

523 SbCl Cl SbCl

MOLECULAR WT. : 228 71 299

Antimony trichloride is in powder (crystal) form, once antimony trichloride charged in to reactor, then chloroform must be fedand reactor should be line up with steam to achieve necessary temperature i.e. 88-90 °C and lineup of cooling water to Stripper column reflux condenser After that chlorination must chlorination continue till catalyst ratio achieve 85%. be done at slow rate

RATIO:35

5

SbCl SbCl

SbCl

It is necessary to remove free chlorine from reactor after chlorination; otherwise free chlorine will appear in final R-22 product, so product quality will suffer.

The Antimony Ratio of the Catalyst in the running reactor should be maintained between 80% ~ 86 %.

Table 1

Typical limits

Sb + 3

Sb + 5

Antimony Ratio

Chlorides

Organics

Fluorides

Organics free fluoride

Flow ability

5%

30%

86%

40%

25

2.8~3%

2.5~3.5%

Free flowing

6.0(max)%

25.0(min)%

80 to 86%

45%

15(min) & 35(max)%

4.8(max)%

5.5(max)%

Slightly viscous

By standard or acceptable design of condenser in stripper so as to condense the halide vapour and use of adequate cooling medium

The stripper column performs three separate functions:

Reaction of excess HF and catalyst and reaction of catalyst with organic.

Stripping catalyst from the gas stream.

Fractionating un-reacted or partially reacted compounds from the products of the reaction.

Final step after emission of HFC-23 Effluent gas:

Developing different destruction, incineration or transformation methods for HFC-23 gas for example (Thermal oxidation) and finding minor utilization of HFC-23.

Thermal oxidation is the most flexible, efficient and reliable means of destroying hazardous and toxic chemical wastes - in some cases, the only solution.

This method also presents options for recovery of energy and valuable products gas.

Types of thermal oxidizers:

1. Recuperative thermal oxidizers

2. Regenerative thermal oxidizers

 

High temperature, gas phase oxidation processes use temperatures in the range of 1,000°F to 2,000°F (650°C to 1,260°C).

The terms recuperator and regenerator refer to the type of heat exchanger used in the oxidizer system.

Regenerative thermal oxidizers:

Regenerative thermal oxidizers have much higher heat recovery efficiencies than recuperative units. Heat recovery efficiencies as high as 95% are possible.

Because of the high inlet gas temperatures created by the heat recovery, burner fuel is required only if the organic vapor concentrations in the gas stream are very low.

Regenerative Heat exchanger

Figure5.1: Regenerative Heat exchanger

FUEL PROPERTIES USED IN THERMAL OXIDIZER (LNG)

LNG is natural gas which has been converted to liquid form for ease of storage or transport. LNG takes up about 1/600th of the volume of natural gas.

Depending upon its exact composition, natural gas becomes a liquid at approximately -162°C (-259°F) at atmospheric pressure.

LNG is principally used for transporting natural gas to markets, where it is regasified and distributed as pipeline natural gas. There it is called R-LNG.

Key liquid and gas properties for LNG are:

It is a mixture of methane, ethane, propane and butane with small amounts of heavier hydrocarbons and some impurities, notably nitrogen and complex sulphur compounds, water, carbon dioxide and hydrogen supplied which may exist in the feed gas but are removed before liquefaction.

The density of LNG falls between 430 kg/m3 and 470 kg/m3. LNG is less than half the density of water; therefore, as a liquid, LNG will float if spilled on water.

In an air-fuel mixture of about 10% methane in air, the auto ignition temperature is approximately 540°C (1,000°F).

Preparation of HFC-23 for incineration.

The quantity of the HFC23 stored prior to decomposition and subsequently decomposed would be counted as a part of the project. The emission reductions to be credited are based on the ex-post measurement of the quantity of actually decomposed HFC23.

During the HFC23 thermal destruction process, hydrofluoric acid (HF) with the concentration of 40% is produced. These HF by-products will be stored in barrels

MONITORING PLAN OF THERMAL OXIDIZER

MINOR APPLICATIONS OF HFC-23 EFFLUENT GAS.

Electronics: Trifluoromethane (CHF3) is used in plasma etching of silicon oxide or nitride layers.

CHF3 is a low temperature refrigerant. It is replacing chlorodifuoromethane (R22 or CHF2Cl)

When used as a fire suppressant, the fluoroform carries the DuPont trade name, FE-13. CHF3 is recommended for this application because of its low toxicity, its low reactivity, and its high density.

HFC-23 has been used in the past as a replacement for Halogen 1301 in fire suppression systems as a total flooding gaseous fire suppression agent.

CONCLUSIONS

The default emission factor for older plants is 4%, with 3% for newer facilities, but use ofa default is no substitute for actual measurement

Also we can prolonged the catalyst life by maintaining its ratio 80-82%.

By doing above mention technique we can reduce the emission of HFC-23 from 4% to 1-2%.

THANK YOU!