The merits and demerits of sulfuric acid, along with my views on its future

Thread Content

The Pros and Cons of Sulfuric Acid and My Views on the Future – Some Thoughts on the Development of Catalysts for Biodiesel Esterification. Author: Ning Shoujian (Expert Member of the National Biodiesel Industry Collaboration Group, Shenyang University). 13940536479, synsj.blog.bokee.net, synsj@yahoo.com.cn. Abstract: One of the author’s views on chemical engineering technology is that simplicity is the best! Therefore, the uses and advantages/disadvantages of sulfuric acid are discussed, and it is argued that our main efforts and research should focus on how to manage it and recycle it, rather than simply rejecting or giving up on it. Keywords: sulfuric acid, biodiesel, esterification, pollution. I. Introduction The synthesis and use of sulfuric acid date back 260 years. For many years, it has played a small but important role in advancing human society thanks to its low cost and excellent properties; yet it has also been criticized for causing wastewater pollution and damaging equipment In the esterification reactions of the chemical industry, sulfuric acid plays a vital role. Its wide adaptability to the quality of raw materials and its high catalytic activity are positive aspects; however, it causes problems due to pollution generated when it mixes with wastewater, and it is also problematic as it corrodes equipment In the currently booming biodiesel industry, sulfur also plays an awkward role that is both loved and hated ； On the one hand, it plays a key role in the preparation of acidified oils and in esterification reactions; on the other hand, for the reasons mentioned above, this has given rise to many issues related to substitutes for sulfuric acid. Over the years, there have been countless research papers, reports, and patents on catalysts that can replace sulfuric acid, enough to form a small mountain of material. Yet in actual production practices, most people still opt for the traditional solution: use sulfuric acid! II. Rational Thinking 1. The three acids and two bases: This raises a question: As basic chemical raw materials with excellent properties, the three acids and two bases were once an important indicator of whether a country’s chemical industry was developed. We can imagine that without these three acids and two bases, could such an industry still be considered a chemical industry? Should sulfuric acid be continued to be used or discarded? Or abandoned after a certain period in history? Or should it be further promoted? My view is that sulfuric acid should not be abandoned or replaced; it should continue to leverage its advantages. Instead of focusing on developing solid acids to replace it, efforts should be directed toward finding ways to manage and utilize the pollutants it generates 2. Chemical building blocks and human safety: First, it is necessary to clarify one concept: at what level must humanity’s chemical building blocks reach before they stop? Just as there was an arms race during the Cold War, should there also be an end to this competition in building with chemical building blocks? My personal view is that the chemical structures created by humanity have become too complex. The development of science should follow a spiral upward pattern – that is, we should continuously discover new properties and uses for substances that have already been identified and synthesized, while also working to improve their various characteristics. Simply synthesizing new compounds poses a hidden threat to the survival and development of humanity itself! Therefore, the EU’s latest REACH regulations redefine the safety of compounds: \"A substance is considered dangerous until it is proven to be safe,\" whereas previous regulations were the exact opposite – namely, \"A substance is considered safe unless it is proven to be dangerous.\" Under such rules, it can be predicted that the production costs of newly developed compounds will **increase, as more research funds will need to be invested during the initial development phase in order to \"prove its safety\"” ； In comparison, the advantages of traditional known compounds are even more evident, as most of their properties (safety and hazards) are already known to humans; only a small additional cost is required to determine their safety and hazards in new applications, so that they can be utilized and managed accordingly! 3. Biodiesel and sulfuric acid: From the perspective of the synthesis of biodiesel, a reevaluation of it, and its use as a substitute for diesel, this is essentially the process involved ； The synthesis of fatty acid methyl esters has been around for many years, while humans have known about and used fats and oils for thousands of years ； Today’s biodiesel represents a return by humans to the use of fats and oils, but it is a return at a higher level – namely, the so-called \"spiraling upward\" mentioned earlier” ； In the process of humans using, understanding, and producing oils and fats, sulfuric acid has played a very important role. Its contributions are numerous, but the most significant and problematic one is the production of acidified oil. Soap scum must be acidified using large amounts of sulfuric acid to produce acidified oil, which in turn generates a large amount of acidic wastewater. To this day, I have not seen a single legitimate oil and fat processing plant produce acidified oil on its own; almost all such production is outsourced to individual operators or small enterprises located in remote areas. As a result, the quality of the product varies greatly, causing many problems for downstream users! Of course, the pollution caused by acidic wastewater in the local area is even greater! In fact, some oil companies have advanced wastewater treatment systems that enable them to produce acidified oil in a fairly proper manner. However, the value and profits generated by acidified oil are too low for those companies that also produce soapstock as a by-product; as a result, they are unwilling to invest in additional equipment or incur extra management costs. Solving this problem shouldn’t be difficult – the key is to take action! ? It can be seen that in the process of producing acidified oil using soap scum as raw material, it is entirely feasible to handle the acidic wastewater generated through proper wastewater treatment facilities; the key issue is that we have not done so yet! As a result, the “fault” of sulfuric acid is minimal, and when it comes to neutralizing or acidifying soap scum, sulfuric acid is the only option according to the existing processes! III. Feasibility of replacing sulfuric acid 1. The catalytic role of sulfuric acid: In the synthesis of biodiesel, the esterification reaction is the key step, and sulfuric acid can be considered the \"pioneer\" in this process; virtually all esterification reactions use sulfuric acid as a catalyst, especially when using waste oils as raw materials. This has two implications ； First, for raw materials that are not yet familiar with or have not been used before, my experimental experience suggests starting by testing sulfuric acid as a catalyst; only after success should other catalysts be tried. Given the high reactivity of sulfuric acid, if it lacks catalytic activity, then under conventional processing conditions, other catalysts are likely to be ineffective as well ； Secondly, regarding the used oil raw materials, alkaline substances are often used in the pretreatment process, and these substances are not completely removed during that stage; moreover, the raw materials contain many unknown impurities. All of these issues can basically be resolved by increasing the amount of sulfuric acid used, whereas other catalysts generally do not possess this \"impurity removal\" function! 2. Lack of alternatives: The various catalyst reports available that aim to serve as substitutes for sulfuric acid are almost all based on purified raw materials, and nearly all of these papers include a statement such as: “The raw materials were subjected to ***** pretreatment before use.” Because almost all of these catalysts face the same problem: catalyst poisoning and deactivation! Of course, sulfuric acid also becomes ineffective, making it only suitable for a one-time use; however, its extremely low price is unmatched by other catalysts ； For systems that use sulfuric acid as a catalyst, the pretreatment of the raw materials is very simple; in some cases, no pretreatment is even necessary, and only simple sedimentation and dehydration are required. For other catalysts, such pretreatment is far from sufficient! Of course, sulfuric acid catalysis has the drawback of causing the oxidation of the raw materials and resulting in a darker color. This is not a problem for used oils, but it is inappropriate to use sulfuric acid with oil raw materials such as fatty acids that have a very high purity. For such raw materials, using solid catalysts like resins for esterification allows the resulting products to reach certain standard levels without the need for distillation, thereby **reducing production costs. Of course, the price of such raw materials is also high. 3. Pollution and resources: From another perspective, what is known as pollution is actually resources that have been placed in the wrong location. Moreover, the pollution we face today has existed since the emergence of industrial civilization; in other words, pollution is the twin brother of industrial civilization. The vast majority of cases of pollution occur because companies prioritize maximizing profits over taking measures to address it, rather than because such measures cannot be implemented. Take biodiesel as an example: for feedstocks with a certain acid value, a two-step catalytic process using acids and bases is generally employed, which generates acidic waste and alkaline waste respectively. In theory, it is possible to achieve neutralization; all that is needed is to make adjustments to the process (while ensuring its normal operation) so that the amounts of these substances used are sufficient to achieve complete or near-complete neutralization, thereby completing most of the work related to pollutant treatment. However, such governance requires investment and operational costs, and it generally does not generate profits or only yields very small profits compared to the main products, making it not worth the effort; hence, companies lack the incentive to invest in and implement it, rather than it being impossible to manage. For biodiesel, glycerol by-products containing alkalis and acids are generally produced; theoretically, these by-products account for no more than 10% of the amount of raw materials used. At the current production scales of enterprises, the annual total amount generated is between 1,000 and 3,000 tons. These products are not actually pollutants, but rather a new type of resource. It’s just that the price of glycerol has temporarily dropped, leading to oversupply – this is a market issue rather than a technical one ； Of course, in my opinion, the best way to handle waste glycerin that contains acids or bases is to proceed directly to the next reaction step without neutralization, in order to obtain new glycerin derivatives that can be used as new resources and thus avoid pollution. IV. Conclusion In summary, I believe that the advantages of sulfuric acid outweigh its disadvantages; it is therefore worthwhile to actively study its new properties and better methods of use, while simultaneously taking proactive measures to address the \"pollution\" it causes ； At the same time, it is hoped that the funding provided by the technology regulatory authorities for research should not focus solely on \"innovation.\" Instead, attention should be given to exploring new properties, new applications, and new synthesis methods for existing compounds. It must be understood that such efforts are currently difficult and yield little return; there is almost no support for such practical projects. Our regulatory authorities need to change their mindset and consider the meaning and value of \"innovation\" in a realistic manner. True sustainable development should involve returning to fundamental principles rather than pursuing mere growth!