Trap­ping car­bon

The food and drink in­dus­try is fac­ing a scarcity of CO2. But the ex­ces­sive car­bon in the at­mos­phere can help PETER STYRING AND KATY ARM­STRONG

Down to Earth - - CONTENTS - (Styring is pro­fes­sor of chem­i­cal en­gi­neer­ing and chem­istry and Arm­strong is CO2 CHEM net­work man­ager at the Univer­sity of Sh­effield. By spe­cial ar­range­ment with The Con­ver­sa­tion)

Ex­ces­sive car­bon in the at­mos­phere can help solve Co2 scarcity in the food and drink in­dus­try

MORE PEO­PLE than ever are acutely aware that ris­ing lev­els of car­bon diox­ide (CO2) in the at­mos­phere are ac­cel­er­at­ing climate change and global warm­ing. And yet food man­u­fac­tur­ers have been is­su­ing stark warn­ings that they’ve nearly run out of the gas, which is used in many prod­ucts from beer to crum­pets. The ob­vi­ous ques­tion is: why we can’t just cap­ture the ex­cess CO2 from the at­mos­phere and use that?

It is ac­tu­ally pos­si­ble to take CO2 from the at­mos­phere us­ing a process known as di­rect air cap­ture. In­deed, there are a num­ber of com­pa­nies across the world, in­clud­ing one in Switzer­land and an­other in Canada, that can al­ready carry out this process. In the­ory, it could turn a prob­lem into a valu­able re­source, par­tic­u­larly in devel­op­ing coun­tries with lit­tle other nat­u­ral wealth.

The prob­lem is the cost. While the amount of CO2 in the air is dam­ag­ing the climate, rel­a­tively speak­ing there are so few CO2 mol­e­cules in the air that suck­ing them out is very ex­pen­sive. But there may be other so­lu­tions that could help re­duce car­bon emis­sions and pro­vide a new source of CO2 for in­dus­try.

It’s all a mat­ter of con­cen­tra­tion and en­ergy con­sump­tion. The amount of CO2 in the air (which is mostly made up of ni­tro­gen and oxy­gen) is around 400 parts per mil­lion or 0.04 per cent. If we were to rep­re­sent a sam­ple of mol­e­cules from the air as a bag of 5,000 balls, just two of them would be CO2. Pulling them out of the bag would be very dif­fi­cult.

We can cap­ture CO2 us­ing what’s known as a sor­bent material that either phys­i­cally in­ter­acts or bonds with the gas at a molec­u­lar level. To cap­ture a vi­able amount of CO2 from the air, we would need to com­press huge amounts in or­der to pass it through the sor­bent, some­thing that would re­quire a lot of en­ergy.

The ex­haust of power sta­tions is a more con­cen­trated source of CO2 (and one re­spon­si­ble for so much of our to­tal car­bon emis­sions). The Car­bon

xprize, a com­pe­ti­tion to en­cour­age the de­vel­op­ment of car­bon cap­ture and util­i­sa­tion tech­nol­ogy, has iden­ti­fied 10 fi­nal­ists that fo­cus on cap­tur­ing CO2 from power

plants rather than the at­mos­phere.

Yet while the typ­i­cal CO2 con­cen­tra­tion of around 10 per cent (600 balls out of the 5,000) in power sta­tion ex­haust is much greater than that of air, cap­tur­ing the CO2 would still be a costly way of pu­ri­fy­ing the gas us­ing cur­rent tech­nolo­gies. You also need to re­move the wa­ter vapour in the ex­haust, which would re­quire more en­ergy.

Bet­ter sources

As it be­comes more im­por­tant to re­duce the con­cen­tra­tion of CO2 in the at­mos­phere, or if you needed to pro­duce the gas in re­mote lo­ca­tions with large re­new­able en­ergy sources, di­rect air cap­ture could be­come a vi­able tech­nol­ogy. But at the moment there are CO2 sources that are more con­cen­trated and so cheaper to har­ness.

For ex­am­ple, dis­til­leries and brew­eries pro­duce the gas as a waste prod­uct with high pu­rity (over 99.5 per cent) once any wa­ter has been re­moved. Ce­ment works, steel works and other process in­dus­tries also have rel­a­tively high CO2 con­cen­tra­tions. Build­ing smaller fa­cil­i­ties that just cap­ture the CO2 from in­di­vid­ual fac­to­ries and plants would be a cheaper way to cre­ate a new source of the gas. They may also prove a good in­vest­ment at plants that need their own sup­ply of CO2 to carry out their pro­cesses.

The cur­rent CO2 short­age is mainly af­fect­ing the food and drink in­dus­try. But we’re also start­ing to see a greater push to use CO2 in other in­dus­tries as a way of cre­at­ing a mar­ket for a sub­stance that is oth­er­wise a waste prod­uct con­tribut­ing to dan­ger­ous climate change. You can now buy chem­i­cals and build­ing ma­te­ri­als that started life as CO2 mol­e­cules in­stead of fos­sil fu­els, for ex­am­ple, in­clud­ing min­eral ag­gre­gates that ac­tu­ally cap­ture more car­bon than is used to pro­duce them.

As more of these CO2 util­i­sa­tion tech­nolo­gies emerge, de­mand for the gas will in­crease and so will the need for more lo­calised pro­duc­tion. The fu­ture is about turn­ing a waste into a com­mod­ity.

TARIQUE AZIZ / CSE

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