Structure and Composition Changes of Nitrogen Compounds during the Catalytic Cracking Process and Their Deactivating Effect on Catalysts

The comprehensive structure and composition changes of the nitrogen compounds during the catalytic cracking processes of coker gas oil and vacuum residue are investigated using electrospray ionization combined with Fourier transform ion cyclotron resonance mass spectrometry. These experiments were conducted over different cracking materials under the reaction temperatures of 500/520 °C, the weight hourly space velocity of 18 h^–1, and the catalyst/oil ratio of 5. The results show that the diffusion resistance in the micropores of the zeolite is the key factor affecting the interaction between the nitrogen compounds and the acid sites. The basic N1 and N2 class species with double bond equivalence (DBE) values smaller than 10 can easily diffuse into the micropores of the zeolite and are preferentially adsorbed onto the acid sites. These adsorbed nitrogen compounds generally conduct condensation reactions and hydrogen transfer reactions to form coke deposited on the cracking catalysts. The basic N1 and N2 class species with DBE values larger than 10, other basic nitrogen compounds other than N1 and N2, and the non-basic nitrogen compounds seldom interact with the acid sites of the zeolite. They usually undergo side chain thermal cracking on the surface of the matrix, which can reduce their carbon numbers but cannot change their DBE values. The basic N1 class species with DBE values smaller than 10 are the main compounds that poison the cracking catalysts. In comparison to the SL-CGO catalytic cracking, the nitrogen-poisoning effect on the catalysts is much less during the SL-VR catalytic cracking process because the main poisoning compounds (the basic N1 class species with DBE values smaller than 10) are much fewer

The involvement of Pol II in milRNA production.

<p>A. Race tube assays showing the growth rates of the indicated strains in the presence or absence of QA. B. Northern blot analysis showing the levels of <i>rpb5</i>-specific siRNA in the indicated strains. C and D. qRT-PCR analysis results showing the reduction of <i>rpb5 and β-tubulin</i> level in ds<i>rpb5</i> strain in the presence of QA. The asterisks indicate <i>P</i> value<0.05. Error bars indicate S.D. E. Northern blot analysis showing the levels of <i>milR-1</i> and <i>milR-4</i> small RNAs. F. ChIP assay using c-Myc antibody showing the binding of Pol II to milR loci in the Myc-RPB6 strain. A <i>tRNA</i> and the <i>β-tubulin</i> gene was served as the negative control and positive control, respectively.</p

<i>milR-1</i> transcription is mediated by a non-conventional Pol III promoter.

<p>A. Northern blot analysis showing the levels of <i>milR-1</i> in the indicated strains. B. qRT-PCR analysis showing the reduction of <i>pri-milR-1</i> levels in the <i>mut1</i> and <i>mut2</i> strains. WT and <i>milR-1^ko</i> served as the positive and negative control, respectively. C. ChIP assays using the c-Myc antibody showing the reduced binding of Myc-RPC7 at the <i>milR-1</i> locus with the mutated TATA-like element. The asterisk indicates <i>P</i> value<0.05. Error bars indicate S.D.</p

Pol III knockdown results in the reduction of milRNA expression.

<p>A. Race tube assays showing the growth rates of the indicated strains in the presence or absence of QA. B. Northern blot analysis showing the levels of <i>rpc5</i>-specific siRNA in the indicated strains. C. qRT-PCR analysis showing the reduction of pri-milR levels when <i>rpc5</i> was silenced. rRNA level was used as the loading control for qRT-PCR. A Pol III-transcribed tRNA was served as a positive control. D. Northern blot showing the levels of <i>milR-1</i> and <i>milR-4</i> small RNAs.</p

RNA sequencing of poly(A) RNA results showing the presence/absence of Pol II transcripts in the selected milR loci.

<p>Viewing window was set as 2000 nt. The vertical line in each panel indicates the location of the indicated <i>milR</i> gene.</p

RNase Z is required for <i>milR-4</i> processing.

<p>A. A Diagram showing the predicted secondary structure of <i>pri-milR-4</i>. B. RT-PCR analysis, which used a pair of primers indicated in A, showing the presence of transcript that spanning the two alanine tRNAs and <i>milR-4</i>. C. Race tube assays showing the growth rates of the indicated strains in the presence or absence of QA. D. Northern blot analysis showing the levels of <i>rnaseZ</i>-specific siRNA in the indicated strains. E. qRT-PCR analysis showing the reduction of <i>rnaseZ</i> mRNA level in the ds<i>rnaseZ</i> strain in the presence of QA. The asterisk indicates <i>P</i> value<0.05. Error bars indicate S.D. F. Northern blot analysis showing the levels of <i>milR-4</i> milRNAs in the indicated strains in the presence or absence of QA.</p

Pol III specifically binds to milR loci.

<p>ChIP assay results showing the binding of Pol III to the milR loci. A <i>tRNA</i> and the <i>β-tubulin</i> gene was used as the negative and positive control, respectively. The asterisk indicate <i>P</i> value<0.05. Error bars indicate S.D.</p

qPCR primer sequences.

<p>qPCR primer sequences.</p

DNA sequences of <i>milR-1-4</i>.

<p>The sequences of milRNA, milRNA* and the poly T sequences are indicated. TATA-like elements are underlined with single dashed lines. Putative A-boxes and B-boxes are underlined with double and triple dashed lines, respectively. The solid triangles in the <i>milR-1</i> sequence indicate the nucleotides mutated in our promoter analysis.</p

Comparison of the number of CAZymes in <i>V. volvacea</i> genome with those in other fungi genomes [3].

<p>Enzymes: GH for glycoside hydrolase, GT for glycosyltransferase, PL for polysaccharide lyases, and CE for carbohydrate esterases. Species abbreviations and genome references: V. vol. for <i>Volvariella volvacea</i> (current paper), S. com. for <i>Schizophyllum commune</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Ohm1" target="_blank">[3]</a>, P. chr. for <i>Phanerochaete chrysosporium</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Martinez2" target="_blank">[30]</a>, P. pla. for <i>Postia placenta</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Martinez3" target="_blank">[31]</a>, C. cin. for <i>Coprinopsis cinerea</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Stajich1" target="_blank">[14]</a>, L. bio. for <i>Laccaria bicolor</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Martin1" target="_blank">[32]</a>, C. neo. for <i>Cryptococcus neoformans</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Loftus1" target="_blank">[33]</a>; U. may. for <i>Ustilago maydis</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Kmper1" target="_blank">[34]</a>, S.cer. for <i>Saccharomyces cerevisiae</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Goffeau1" target="_blank">[35]</a>, N.cra. for <i>Neurospora crassa</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Galagan1" target="_blank">[36]</a>, T. mel. for <i>Tuber melanosporum</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Martin2" target="_blank">[37]</a>, A.nig. for <i>Aspergillus niger</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Pel1" target="_blank">[38]</a>, P.ind. for <i>Piriformospora indica</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Zuccaro1" target="_blank">[39]</a>, P. chr. for <i>Penicillium chrysogenum</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-vandenBerg1" target="_blank">[40]</a>, and T.ree. for <i>Trichoderma reesei</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058780#pone.0058780-Martinez1" target="_blank">[2]</a>.</p