Analysis of CO2 from fermentation and other sources – where and why?

By Sam A. Rushing, President, Advanced Cryogenics Ltd.  www.CO2consultant.us
Special to The Digest

CO2 quality begins with the raw feedstock, and even the ingredients and agents which go into this feed gas or feedstock – these agents can be substances such as the natural gas or coal which is combusted for flue gas, then downstream liquefaction and purification occurs. The lion’s share of CO2 source types, are chemical by-product in nature. Then, most of which are a handful of source types, including a highly – concentrated by-product from reformer operations in oil refineries, and by-product from anhydrous ammonia operations, then an ever – important fermentation as the predominant number of plants in the United States, which is distilled ethanol from (usually) corn and grain. Then we have natural sources from mother nature’s bosom; which are wells dating back before the dawn of man.

These major sources, often, are the cleanest and easiest to recover and refine, and typically these sources are very high in raw CO2 content, in a water saturated stream. Once the water is knocked out, then the CO2 content alone can be up to or beyond 99% by volume. In some cases, as with the natural sources, impurities are a challenge, for example, there have been cases containing high levels of hydrocarbons, including methane and heavier hydrocarbons; too much sulfur content, and of course the case of benzene, which is particularly difficult. Beyond these potential problems with some natural sources, the wells can be the cheapest method of producing CO2, if they are high pressure (thus eliminating the feed compression component in the plant), and very pure, where many of these sources are extremely pure.

In the extremely pure case, little more than carbon is required for purification, plus the usual liquefaction in a CO2 plant. These chemical by-product sources are also relatively easy to purify, and often do not require additional hardware such as Lo -Cat operations for sulfur removal, or catalytic oxidation for removal of higher levels of impurities. In the end, when operating a CO2 plant, to accomplish the desired food and/or beverage grade quality, in-line (GC) gas chromatographs are used to monitor a continuous flow of quality. GC is a standard analysis measure today.

Then, other source types include titanium dioxide, and ethylene oxide are less common; and in the case of ethylene oxide, this is a bit more difficult to refine, due to chlorides in the raw stream, and requiring some more expensive metals used in the construction of the CO2 plant. The metallurgical issue requires more capital investment in an ethylene oxide by-product operation. However, food and beverage quality is fully achievable from these sources, in any event.

Next, flue gas and natural gas processing operations are found in some markets, albeit few in number, however, the common amine solvent MEA (monoethanolamine) is the basis behind recovering CO2 from a lean stream, with CO2 content down to 3% from natural gas fired cogeneration exhaust, once found in a New England plant. Then, more commonly, CO2 content in the teens or above, on a percentage basis, which is recovered and concentrated in the MEA plant. Downstream is the traditional CO2 plant, which liquefies and purifies the CO2, which is readily achieved.

In the end, an excellent quality product is available from this form of raw feedstock, and the ingredients used in producing the flue gas; that being natural gas, and even coal, in some cases; such as with the former AES cogeneration plants in Maryland and Oklahoma. Flue gas in my view, is a great untapped CO2 source; however extremely expensive to recover and produce for the markets – costing upwards of $200/ton in some cases, without subsidies. There are subsidies in some cases, which help reduce the high cost – however, still making this source uncompetitive. 45Q and IRA tax credits may help here – but they fall short of making economics work in competitive markets.

What is important, is reviewing the most common plant types found in the US and in many global markets; is to mention that food and beverage grade is well produced from these traditional source types.

QUALITY PERCEPTION

In the world of chemistry and chemical process, much can be done in term of taking a rather ‘dirty’ product (or a product which is perceived to be offensive), and turning it into something desirable. With the ‘dirty’ perception taken into context, many consumers would be less than pleased to know their product is coming from various chemical sources, like ammonia or ethylene oxide; as well as their view of waste –  related sources per se. On the other hand, some of this thinking is changing, with respect to the sources themselves, as well as the refiners, and ultimately the consumers. It is entirely feasible to turn many waste borne streams into something chemically pure, meeting all the demands surrounding the chemical, physical, odor, and taste elements laid down by organizations including the CGA, ISBT, and like organizations which set standards; as well as the gas companies. In the end, as the world requires more recycling, and reclamation of otherwise wasted raw feedstocks, particularly when chemical purity is fully achievable, and a desire to reduce emissions becomes a matter of fact on a global level; the sources for CO2 refinement will become more diverse, and ultimately reduce the carbon footprint, and become acceptable. It is interesting to see some of the major soft drink firms starting to recycle materials to produce plastic containers, where this recycling will eventually morph into raw ingredients, including CO2 supplies, which are chemically pure and strategically located. With improvement in strategic location of sources, this would impact the bottom line of both the supplier and consumer very favorably. Commercial labs test the product along the supply chain from the source to the gas company; to the customer, in many cases; all dependent upon need and set protocols.

Then, sources are known for their ease or difficulty to produce a quality product for industry; and ongoing testing and monitoring of quality is a directive in the industry today – and ethanol by-product is probably the most sought after CO2 product for refinement. From this point forward, the next steps from distribution to storage, and then the application in industry have their input on, and interpretation of quality, and testing.

ORGANIZATIONS WHICH SET THE BAR

In the US, many years ago, the USP was a simple guide as to standards, and even certain independents in the US used this very basic standard for quality at one time. On the other hand, in part, what prompted the stringent standards for quality in the beverage market, were a few cases of contamination, as I recall a few incidents in Europe; and there were additional cases elsewhere. For example, in the US, an independent producer owned and operated a CO2 plant sourced from Eastman Chemical, which was a coal gasification source; which probably was never tested properly, perhaps not required at the time. After years of operations, it was discovered the CO2 product sold from this plant contained higher than acceptable levels of hydrogen cyanide; subsequently CO2 was no longer derived from this business. Many of the cases of testing or contamination included operator misunderstandings or error as well.

Today, organizations which are relied upon include the CGA (Compressed Gas Association), the ISBT (International Association of Beverage Technologists), and EIGA (European Industrial Gas Association); among others. Within the CGA, grade ‘I’ generally defines beverage grade; then ‘H’ grade covers food applications in industry. There are other organizations and standards used for quality guidelines, by large food processors, such as Tyson Foods; which now has more meat and poultry operations combined than any other US processor. By the way, the USP grade ‘G’ corresponds to commercial use for the product.

Table indicating constituents tested, levels, and process for ISBT/beverage grade.

NET EFFECTS PRODUCED BY QUALITY AND DOWNSTREAM TESTING

The bottom line, with respect to testing and retesting product, representing redundancy, is assurance that quality and chemical purity will be met; however, other features of the CO2 will be in line, such as definitions surrounding taste and odor. For example, we don’t want our food products to taste like the feedstock or ingredients contained in the sources where CO2 is derived, do we?

As to USP grade, given the limited applications sought for the commodity, generally medical in nature, represents a great deal of work preparing, largely due to production requirements surrounding extensive monitoring and paperwork than any other grade, at least on a production level – and this segment of the market is only some 5%. Then, when thinking of beverage applications, it is well known this sector is the most highly tested of all sectors of the industry, beyond USP, even though it probably represents 20% of US demand for CO2 in the merchant market, with relatively modest growth.

Due to a history of a few accidents in sourcing, processing, and handling, representing cases of contamination, whether this be plant operator error, or feedstock contamination, for example; it is the stringently tested line of CO2 for a given product, that being soft drinks primarily; and second to this, beer production. In some markets, many of the large breweries use merchant (beverage grade) CO2 to back pressure the system, and not for actual carbonation. In the beer arena, smaller breweries use merchant CO2 to supplement their carbonation needs, more commonly, unlike some of the largest breweries – which recover their own CO2.

Once again, in the case of soft drink manufacturing, the demands for CO2 are very stringent, to the point of testing every load of product delivered to the soft drink manufacturing plants; not just what the gas manufacturer is already testing, and all the care already taken. The major beverage firms have their list of requirements and standards from quality and assurance perspectives, and further requirements for tours of new plants which produce CO2. Then, a regimen of testing occurs with many of these firms, such as quality specifications covering both limiting characteristics and specific test methodology, and of course testing every delivered load of product. These standards are supported by definitions set by the trade organizations.

For the CO2 producer and suppliers, it is critical to follow the requirements defined by the beverage customers, and the trade associations; and even work with the trade associations and beverage majors to initiate change and further acceptance of source types for the merchant CO2 market.

Even though it is often not apparent for the consumers of food and beverage products which are scrutinized rather strongly for taste, odor, and quality; it remains key to producing a viable product to serve the desired markets. This is an industry which is constantly evolving, and developing new applications; which is truly interesting.

About the author

Sam A. Rushing is president of Advanced Cryogenics, Ltd; and a chemist by background. The company serves a full menu of CO2 – related consulting services to all CO2 – related projects. Please contact the company for your next consulting task. The company is supported by a strong merchant background, and over 30 years as a consultant, working domestically and globally.

Tel: 305 852 2597; email: rushing@terranova.net; web: www.carbondioxideconsultants.com